ABSTRACT GABLER, WILLIAM JOHN. the Design and Evaluation of a Chemical Protective Sock Liner

ABSTRACT

GABLER, WILLIAM JOHN. The Design and Evaluation of a Chemical Protective Sock Liner. (Under the direction of Dr. Emiel DenHartog).

Chemical, Biological, Radiological, and Nuclear (CBRN) protective clothing ensembles impose physiological and ergonomic constraints on users that limit operational duration and impact the ability to perform certain tasks. There has been a continual effort to advance CBRN ensembles by introducing novel materials, improving functional designs, and specializing equipment for end-user groups.

One such effort has been the introduction of lower burden and less protective CBRN ensembles for emergency response, law enforcement, and military users. This research describes a functional clothing design process to develop a chemically protective sock liner for use in low-level vapor protective ensembles. The desire was expressed among multiple end- user groups for a more form-fitting and comfortable sock component for extended mission use.

A novel stretch material was selected and a collaborative, iterative design process was employed, which involved continual feedback from end-users to validate improvements in the sock design and construction.

The performance of the sock liner barrier material was assessed using standardized test methods according to NFPA 1994 Class 3 requirements. Since physical wear can cause damage to components, the potential change in protective performance over time was assessed through durability studies featuring actual and simulated wear. The suitability of the liner was considered in the context of its potential operational use. Comfort evaluations indicate that new liner is preferred among end-users in terms of fit and overall comfort. This was attributed to reduced bunched material inside the footwear, an improved design pattern, an expanded sizing scheme, and increased moisture absorption of the liner material.

by William John Gabler

A dissertation submitted to the Graduate Faculty of North Carolina State University in partial fulfillment of the requirements for the degree of Doctor of Philosophy

Fiber & Polymer Science

Raleigh, North Carolina

2017

APPROVED BY:

______Dr. Emiel DenHartog Dr. R. Bryan Ormond Committee Chair

______Dr. Roger Barker Dr. Donald Thompson

DEDICATION

To my mom.

ii BIOGRAPHY

Mr. Gabler previously received a Bachelor’s degree in Chemistry from the College of

William & Mary and a Master’s in Textile Chemistry from North Carolina State University.

iii ACKNOWLEDGMENTS

This work would not be possible without the support of all the members of the Textile

Protection and Comfort Center (TPACC). I would like to thank the following people: the leadership of TPACC - Dr. R. Bryan Ormond, Shawn Deaton, Dr. Roger Barker, Dr. Donald

Thompson, and Dr. Emiel DenHartog – who guided this work from inception to completion; all my fellow students, co-workers, and staff, Ashley, Alex, Candace, Cassandra, Chandler,

Chris, Gail, Kyle, Sophie, and Tyler, who helped me with the challenges of research and graduate school; the members of CTTSO/TSWG for funding and overseeing this research and for coordinating wear trials; and Jen for her hard work and knowledgeable contributions to the design and manufacturing process.

iv TABLE OF CONTENTS

LIST OF TABLES ...... ix LIST OF FIGURES ...... x Chapter 1. Introduction ...... 1 1.1 Purpose ...... 1 1.2 Research Objectives and Dissertation Overview ...... 1 Chapter 2. Literature Review on Chemical Protective Clothing: Design and Performance Concepts 5 2.1 Dermal Exposure to Chemical Hazards ...... 5 2.1.1 The Skin Barrier ...... 6 2.1.2 Classification of Chemical Hazards ...... 8 2.2 Chemical Protective Ensembles ...... 13 2.2.1 Materials ...... 13 2.2.2 Construction and Garment Features...... 18 2.2.3 Design and Classification ...... 22 2.2.4 Operational Factors ...... 32 2.2.5 Comfort and Human Factors ...... 33 2.2.6 Low-level CPC Ensembles ...... 36 2.3 Footwear Comfort and Performance ...... 39 2.3.1 Chemical Protective Footwear ...... 41 2.4 Testing and Evaluation ...... 46 2.4.1 Material Level ...... 47 2.4.2 Ensemble Level ...... 58 2.4.3 Physical Testing ...... 60 Chapter 3. A Survey on the Use and Comfort of Chemical Protective Sock Liners ...... 63 3.1 Introduction ...... 63 3.2 User Input Survey...... 63 3.2.1 Survey ...... 63 3.2.2 Participants ...... 64

v 3.2.3 Experience and Use...... 64 3.2.4 Socks and Footwear ...... 66 3.2.5 Durability and Performance ...... 69 3.2.6 Comfort, Fit, and Design ...... 72 3.2.7 Group Discussions ...... 76 3.3 Conclusions ...... 77 Chapter 4. The Design Process and the Evaluation of Fit of a Chemical Protective Sock Liner 78 4.1 Introduction ...... 78 4.1.1 Functional Design Process ...... 78 4.1.2 Sock Liners ...... 79 4.1.3 Design Requirements ...... 80 4.2 Experimental ...... 81 4.2.1 Liner Materials, Construction, and Initial Designs ...... 81 4.2.2 Subjective Evaluation Methods ...... 83 4.3 Results ...... 86 4.3.1 Prototype Design Process ...... 86 4.3.2 Experiential Focus Groups ...... 90 4.3.3 Down-selection and Design Alterations ...... 92 4.4 Discussion ...... 93 Chapter 5. The Evaluation of the Comfort of a Chemical Protective Sock Liner ...... 95 5.1 Introduction ...... 95 5.2 Comfort Evaluations ...... 95 5.2.1 Experimental ...... 95 5.2.2 Results ...... 102 5.2.3 Discussion ...... 106 5.3 Field Evaluations ...... 106 5.3.1 Experimental ...... 106 5.3.2 Results ...... 110 5.4 Measurement of Thermal and Moisture Properties of the Liners ...... 113

vi 5.5 Discussion ...... 117 Chapter 6. The Evaluation of the Durability of a Chemical Protective Sock Liner ...... 119 6.1 Introduction ...... 119 6.2 Liner Durability and Construction ...... 119 6.3 Durability Wear Trial ...... 120 6.4 Cuff Tear Analysis ...... 121 6.5 Seam Adhesive Analysis ...... 125 6.5.1 Comfort Evaluation ...... 128 6.5.2 Field Evaluations ...... 133 6.6 Physical Testing and Microscopy to Improve SPT application ...... 133 6.6.1 Samples ...... 133 6.6.2 Microscopy ...... 134 6.6.3 Tensile Testing ...... 140 6.6.4 Abrasion Testing ...... 144 6.6.5 Discussion ...... 148 6.7 Conclusions ...... 148 Chapter 7. The Evaluation of the Protective Performance of a Chemical Protective Sock Liner 150 7.1 Introduction ...... 150 7.2 Wear Durability and Chemical Permeation Resistance ...... 150 7.2.1 Conditioning Protocol ...... 152 7.2.2 Permeation Test Procedures ...... 154 7.2.3 Results ...... 161 7.3 Discussion ...... 164 Chapter 8. Summary and Future Research ...... 167 8.1 Summary ...... 167 8.2 Future Research ...... 170 8.2.1 Material and Seam Durability ...... 170 8.2.2 Quantifying Protection ...... 172 REFERENCES ...... 174

vii APPENDICES ...... 184 Appendix A. Surveys Used in End-User Evaluations ...... 185 Appendix B. Additional User Evaluation Data...... 195 Appendix C. Images...... 200

viii LIST OF TABLES

Table 1. Overview of Research Propositions and Test Methods ...... 4 Table 2. Thickness and Basis weight of some representative CPC materials ...... 17 Table 3. EPA/OSHA Protective Ensemble Levels 37, 38 ...... 23 Table 4. NFPA Protective Ensemble Classes (table style adapted from 41) ...... 26 Table 5. Example NFPA certified ensembles ...... 27 Table 6. Three currently fielded military CPC ensembles50,52,53 ...... 31 Table 7. Comparison between the IFS and prototype liner material thickness and mass of assemble liners ...... 82 Table 8. Volume measurements of the A, B, and IFS liners ...... 89 Table 9. Summary of liner preference ratings ...... 91 Table 10. Comfort Trial Participant Sizing...... 99 Table 11. Example Participant Schedule ...... 100 Table 12. Comfort Evaluation Session Task Protocol ...... 101 Table 13. Mean Response Values - All Footwear Types ...... 103 Table 14. Group 1 User Information ...... 108 Table 15. Group 2 User Information ...... 110 Table 16. Comparative Questionnaire Data for Group 2 (NY) ...... 112 Table 17. The dry thermal resistance of the liners in two different footwear configurations as measured by an instrumented manikin foot ...... 114 Table 18. GATS results of the two CPC liners and the base sock used in the comfort evaluations ...... 115 Table 19. Overview of Participants ...... 151 Table 20. Summary of preference data for each footwear and comfort property ...... 199

ix LIST OF FIGURES

Figure 1. Project Flow Chart ...... 3 Figure 2. Example dose-response curves for effects and lethality13 ...... 10 Figure 3. Response zones in a release event13 ...... 12 Figure 4. Illustrated example cross sections (not to scale) of a composite barrier (left) 24 and a textile/film laminate (right) ...... 15 Figure 5. Example seam types: a) serged seam b) bound seam c) seam with tape seal on one side d) seam with tape seal on both sides19 ...... 19 Figure 6. Three YKK brand chemical protective zippers. The left two are used in hazmat suits and the right is used in splash suits.33 ...... 20 Figure 7. Bayonet glove interface featured on a Trellchem® Class 2 ensemble35 ...... 21 Figure 8. Elastic face mask seal on an NFPA Class 3 ensemble hood36 ...... 22 Figure 9. Hierarchy of Chemical Barrier Performance (copied from Stull19) ...... 25 Figure 10. ISO 16602 Protective Clothing Types48 ...... 29 Figure 11. LION Apparel Commando Stretch Under Garment76 ...... 39 Figure 12. A chemical protective boot ...... 42 Figure 13. Molded butyl rubber overboot 82 ...... 44 Figure 14. Inner and outer legging sleeve of a pant leg interfacing with a detachable bootie83 ...... 45 Figure 15. Integrated Footwear System84 ...... 46 Figure 16. ASTM F 903 Pressure Testing Apparatus88 ...... 49 Figure 17. Example of an open-loop ASTM permeation set-up ...... 54 Figure 18. Representative theoretical permeation curve labeled with common metrics ...... 56 Figure 19. Number of times per year the liners are worn in training...... 65 Figure 20. Number of times per year the liners are worn in operation...... 65 Figure 21. The typical duration of wear of the liners...... 66 Figure 22. Footwear worn by end-users with the CPC liners ...... 67 Figure 23. Type of socks worn with the CPC liners ...... 68 Figure 24. Reported change in footwear size with wearing a CPC liner ...... 68 Figure 25. User observations of deterioration of the IFS...... 69 Figure 26. User impression of the durability of the IFS ...... 70 Figure 27. User impression of protection of the IFS ...... 70 Figure 28. User impression of suitability of the IFS ...... 71 Figure 29. Self-reported blister occurrence while wearing the IFS ...... 72 Figure 30. Location of blisters while wearing the IFS...... 73 Figure 31. User impression of the fits of the IFS ...... 73 Figure 32. User impression of the comfort of the IFS ...... 74 Figure 33. User impression of the donning/doffing ease of the IFS ...... 74 Figure 34. Reported issues while wearing the IFS ...... 75 Figure 35. Most commonly reported location for irritation in the IFS ...... 75 Figure 36. Three examples of waterproof sock liners...... 80 Figure 37. The current IFS (left) and the prototype liner without the oversock (right) ...... 83

x Figure 38. Experiential Focus Group questionnaire used for each pair of liners ...... 84 Figure 39. Six candidate designs developed by LION ...... 87 Figure 40. Styles A (on left in each picture) and B (on right in each picture) with arrows indicating the direction of the material stretch ...... 88 Figure 41 . Alterations made to liner B pattern following the experiential focus groups...... 93 Figure 42. Footwear used in comfort evaluations, from left to right: low profile (Salomon® XA Pro MID); combat (Bellville® Combat); firefighter (LION® Commander) ...... 97 Figure 43. Stretch liner and black oversock...... 98 Figure 44. The frequency of liner preference - all properties combined ...... 105 Figure 45. Tingly HazProof® Boot ...... 109 Figure 46. Average absorption behavior of the (A) base layer sock, (B) IFS, and (C) stretch liner ...... 116 Figure 47. Separation of membrane from cuff ...... 121 Figure 48. From top to bottom: 1) Control 3-thread over-edge high thread density seam 2) 3- thread over-edge low thread density seam 3) 2-thread over-edge high thread density seam 123 Figure 49. Cuff sample mounted in tensile testing instrument showing laminate tearing .... 124 Figure 50. Average laminate seam breaking strength for the three seam styles (error bars equal to 1 standard deviation) ...... 125 Figure 51. Prominent seam lift on the heel ...... 126 Figure 52. Typical minor seam lifting on the heel ...... 127 Figure 53. An adhesive irregularity, excess adhesive that made a lump under the seam tape ...... 127 Figure 54. Occurrence of lifting by footwear and conditioning level (#of steps) ...... 128 Figure 55. Multiple view points of the liner during the comfort evaluations ...... 129 Figure 56. Method of categorizing instance of adhesive damage ...... 129 Figure 57. Progression of SPT lifting occurrences (maximum rating observed on each liner) during the three comfort evaluation sessions ...... 130 Figure 58. Suter pressure test apparatus with a sock liner mounted (image provided by LION Apparel) ...... 132 Figure 59. Sample configurations prepared by LION, meant to represent the ankle seam, the toe seam, and the center of the heel seam ...... 134 Figure 60. Field evaluation sample example images (25x) showing incomplete contact between the barrier film and the seam adhesive ...... 136 Figure 61. Sample A (top) and B (bottom) example images (25x) ...... 137 Figure 62. SEM of the surface of the stretch membrane ...... 139 Figure 63. SEM of the adhesive layer ...... 140 Figure 64. A mounted tensile test sample, before and after testing...... 142 Figure 65. Mean values of the failure load (load required to separate SPT). Each error bar is constructed using 1 standard deviation from the mean...... 143 Figure 66. Wyzenbeek abrasion tester: sample strips are mounted then pressed against an oscillating drum that is covered in an abradant material ...... 145 Figure 67. Phase 3 Abrasion sample that showed the most SPT removal (left to right: 0 cycles; 5,000 cycles; 10,000 cycles) ...... 146

xi Figure 68. "Heel" samples in A after 10,000 cycles ...... 146 Figure 69. Toe sample from Phase 3 abraded for 10,000 cycles ...... 147 Figure 70. SPT edge lifting after 10,000 cycles on an unworn field evaluation heel sample147 Figure 71. Footwear used in durability study (from left to right: Low Profile, Combat, and Fire Fighter) ...... 152 Figure 72. Components supplied to participants during durability study ...... 153 Figure 73. Permeation Test Cell ...... 156 Figure 74. NCSU Chemical Permeation Resistance Test Apparatus with loaded cells ...... 157 Figure 75. Sampling locations for permeation test samples ...... 160 Figure 76. Seam sample mounted in the permeation cell ...... 161 Figure 77. Permeation results grouped by challenge chemical and conditioning level (y-axis redacted to protect sensitive information)...... 162 Figure 78. Permeation results grouped by conditioning level and footwear type (y-axis redacted to protect sensitive information)...... 163 Figure 79. Permeation results grouped by sample location (y-axis redacted to protect sensitive information) ...... 164

xii Chapter 1. Introduction 1.1 Purpose

Chemical, Biological, Radiological, and Nuclear (CBRN) protective clothing ensembles impose physiological and ergonomic constraints, which limit end-users’ operational duration and their ability to perform certain tasks. There has been a continual effort to advance

CBRN ensembles by improving material properties, creating functional designs, and specializing equipment for different end-user groups.

One such approach has been the introduction of lower burden and less protective ensembles for emergency response, law enforcement, and military users in situations involving the release of CBRN agents. The desire has been expressed among end-user groups for more ergonomic and comfortable ensembles for extended mission capabilities, increased mobility, and improved dexterity in footwear and gloves. This research focuses on the potential benefits and drawbacks of designing and evaluating form-fitting CPC constructed with stretchable barrier membranes in particular. In conjunction with comfort, the protection of CBRN equipment must also be considered. The methods of evaluating the suitability, durability, protection, and useable lifetime of redesigned CPC must be considered too.

1.2 Research Objectives and Dissertation Overview

The overall goal of this research was to develop a new chemically protective sock liner for use in low-level vapor protective ensembles. A flow chart of the research process is presented in Figure 1. A novel stretch material was selected and an iterative design process was employed that was informed by continual subjective feedback from end-users to validate improvements in comfort and construction. The suitability of the liner was considered in the

1 context of its intended operational use through a collaborative design process with end-users.

The protective performance of the liner barrier material was assessed using standardized test methods according to NFPA 1994 Class 3 requirements. The potential change in protective performance due to physical wear was assessed through durability studies featuring actual and simulated wear.

The second chapter provides a review of concepts and methods used for the evaluation of chemical protective clothing. The third chapter presents the results of a survey of end-users on the use and comfort of chemical protective footwear. The fourth chapter presented the development process and the assessment of fit factors of the liner. The fifth chapter presents the subjective evaluation of the liner in comparison with another liner and discusses factors that contribute to the comfort of different footwear materials and designs. The sixth chapter presents simulated and realistic durability testing methods used to evaluate and improve the liner. The seventh chapter presents methods of evaluating the chemical protective properties of the liner and discusses the concepts and potential improvements in methods of defining CPC protection. The final chapter suggests potential future research questions. An overview of the research propositions and research methods is presented in Table 1.

Figure 1. Project Flow Chart

3 Table 1. Overview of Research Propositions and Test Methods

Theory Questions Test Method/Data Chapter in Dissertation There is a Comfort- - What opportunities exist to alter the comfort-protection Survey of End-users 2,3 Protection Balance. balance for chemical protective footwear? Survey of market and standard - What methods exist to measure footwear comfort and fit? requirements Observation Methods for studying and - How can collaborative design processes and field evaluations- Survey of End-users - 3,4,5 evaluating comfort, function, be used to study design and identify design shortcomings? - Subjective Evaluation Studies and performance of clothing - Field Trials lead to the findings that - Can fit and sizing be improved through the use of stretch - Subjective Evaluation Studies - 4 support the development of materials? - Field Trials new materials and concepts - Quantitative Fit Assessments of for clothing systems. Novel Designs materials and construction - Can more form fitting footwear components improve - Subjective Evaluation Studies - 5 techniques have been comfort? developed over time that - Does moisture play a role in perceived footwear comfort? - Subjective Evaluation Studies - 5 incrementally improve the - Quantitative Laboratory Tests comfort and functionality of clothing. There is a Protection - Does this particular stretch sock liner has sufficient protection Durability Study 6,7 Hierarchy. Degree of for NFPA 1994 Class 3 ensembles? Permeation Testing protection is influenced by - How can seams, which are a weak point in CPC design, be - Tensile, Microscopy, and Abrasion- 6 many factors and is evaluated and improved through laboratory test methods? Durability Study changeable. - Do pass/fail requirements of test standards provide Literature review 2,6,7,8 meaningful information in determining useable lifetime or Topic of future study effective protection levels?

4 Chapter 2. Literature Review on Chemical Protective Clothing: Design and Performance Concepts 2.1 Dermal Exposure to Chemical Hazards

Inhalation and ingestion are often considered to be the most hazardous pathway for chemical exposure due to the high surface area of the lungs and the potentially rapid delivery to the blood stream and internal organs.1 Assuming adequate protection of the nose, mouth, and eyes, the skin becomes the next route of entry for chemical hazards. Even in instances of acceptable respiratory exposure risk, dangerous skin exposures are possible.2 Low-volatility chemicals can persist on surfaces and lead to contact exposure. Engineered solutions to protect against chemical exposure such as ventilation and fume hoods can still leave individuals susceptible to dermal exposure. As an example, a 1997 study of synthetic leather workers revealed that work conditions where the air concentrations of dimethylformide (DMF) were kept below threshold limit values (TLV) could still result in instances of skin contact with liquid and vapor DMF, resulting in significant DMF uptake and subsequent liver disease.3 Of the 3 million non-fatal workplace injuries and illnesses reported in 2014, skin diseases or disorders occurred at an incidence rate of 2.6 per 10,000 full-time workers, a higher incidence rate than respiratory injuries.4

Beyond occupational risks, large scale release of chemical hazards from industrial accidents, terrorist attacks, and on the battlefield are of considerable concern. In 1999 the

Environmental Protection Agency estimated that over 850,000 facilities manufacture, store, or use hazardous substances and many more shipments of hazardous materials occur annually.5

Under federal codes, facilities storing greater than 10,000 pounds of a hazardous chemical or

5 above a certain threshold quantity of among 140 select hazardous chemicals are required to submit risk management plans to the EPA and estimates of population-at-risk due to worst- case scenario release. A 2012 review of the EPA records indicate there were over 12,000 such facilities in the United States, with over 2,500 of those facilities claiming their worst-case scenarios could affect more than 10,000 people in the surrounding area.6 In addition to accidental release, the risk of intentional attacks by terrorist groups (as seen in the 1994 and

1995 Japanese sarin attacks) and military groups (recent examples of sarin and chlorine attacks in Syria) continue to be a threat. These high profile incidents, along with the Ebola outbreak in West Africa in 2014, has intensified the need for military, law enforcement, and first responder groups to train and prepare for emergency response situations that involve the use of chemical and biological protective equipment. Chemical protective clothing (CPC) is important to industrial workers, law enforcement, first responders, and military personnel for preventing hazardous dermal exposures.

2.1.1 The Skin Barrier

Dermal exposure occurs when a chemical enters the outermost layer of the skin: the layer of sebum lipids, sweat, moisture and corneocytes at the surface of the stratum corneum.7

Depending on molecular size and solubility characteristics, the chemical can then travel through the skin contaminant layer by four paths: 1) between the cells through extracellular lipids in the epidermis, 2) through cell membranes, 3) through hair follicles, sweat glands, and sebaceous glands, or 4) through openings in broken skin and cuts.8 Localized effects on the skin cells and glands are possible. Chemical that reaches cells below the stratum corneum or

6 all the way to the bloodstream is considered bioavailable and can travel through the blood stream to other organs, leading to potential systemic effects.8

The overall rate of transfer through the skin is described using Fick’s Law for diffusive mass transport. The steady-state flux, Jss (mass/area/time), is related to the concentration difference of the chemical across the skin, ΔC; the thickness or path length of diffusion, L; the average effective diffusion coefficient, D; and a partition coefficient, K, which represents the ability of the chemical to partition from the contaminant layer or “vehicle” into the skin.1

퐷퐾 퐽 = ∆퐶 푠푠 퐿

The terms (DK/L) may be combined for a chemical to define a skin permeability coefficient, P. If P is presented as a constant it implies the skin is a homogenous diffusion barrier and independent of permeant concentration, which is a useful though sometimes inaccurate assumption.9 Skin permeability can be studied in vitro using a diffusion cell in which chemical is applied to one side of biopsied skin and collected on the other side using a liquid similar to blood serum. Such studies can characterize mechanisms affecting diffusion through skin as well as predict in vivo absorption.9 Physiochemical properties of chemicals, notably the molecular weight, water solubility, and octanol/water coefficients, can be used to predict or correlate with the D and K coefficients.10,11 Studies have shown that the composition of the vehicle (whether the challenge chemical is neat, an aqueous solution, or some other solvent mixture) can affect the input rate significantly. The permeability of these complex chemical mixtures can be explained by including more physicochemical parameters into

7 quantitative structure-permeability relationship models.12 In vivo studies involve subjecting live test animals to skin exposures then observing physiological symptoms and chemical metabolites in the urine and blood.1

There is great variability associated with dermal absorption rates due to chemical properties and differences in physiology, biochemistry, and skin composition depending on body location and environmental conditions.1 In general, regions with the thinnest skin (e.g. inguinal and axillary) are more susceptible to absorption than regions with the thickest skin

(e.g. back, abdomen, and palm of the hand).1 Not all chemical to which an individual is exposed enters the contaminant skin layer or results in absorption. Limited diffusivity and concentration, the location or duration of the exposure, hydrolysis, evaporation, and intervention steps taken by the victim can all reduce absorption significantly. These concepts of skin exposure are important in the context of assessing protective clothing performance.

2.1.2 Classification of Chemical Hazards

A full description of a chemical hazard includes information on the physiological classification, toxicity, chemical and physical properties, and the way in which the chemical is encountered. All of these factors influence the possible extent and likelihood of exposure and the resulting impact of exposure.13

Chemical warfare agents (CWAs) and toxic industrial chemicals (TICs) are chemicals that are known (or sometimes intentionally designed) to be highly toxic and effective hazards.

CWAs are classified traditionally according to the physiological system which they target. The categories include: choking agents, blood agents, riot control agents, vesicant (blister) agents, nerve agents, and psychochemical agents.

8 Specific effects can be acute (exhibited within the following hours of an exposure) or long term (such as a resulting risk of chronic or delayed health complications, e.g. cancers).

The impact can also be differentiated by the degree of effective damage: whether the agent exposure is lethal, incapacitating, or damaging (causing illness).13 In addition to absorption through skin, local dermal effects can include nervous system reactions such as dermatitis and itching, skin blistering, and corrosive effects to the skin, typically by strong acids and bases.

Severe, large area skin damage, as with thermal burns, can be lethal.

Toxicity is defined according to Haber’s Law, which states that the total mass (dose) of material in the body determines the likelihood of a resulting effect.13 Different chemicals have different doses required for an effect. In general, as long as chemical is present, the body will absorb it at a certain rate that eventually can build up a toxic dose. Exceptions exist for chemicals which can be metabolically detoxified and for patients that may be more susceptible to effects (e.g. elderly, children, and those with allergic sensitivity). The exposure dosage for a dermal exposure is the product of the concentration and time for which a liquid or vapor is present at the skin. This principle may be represented using a dose-response curve, where an effective dose (mg of chemical or mg per kg of body weight) or exposure dosage (product of concentration and time, Ct) is plotted against the probability of a response. Toxicity values are expressed using an abbreviation of the effect (L for lethal, I for incapacitating, E for effective) and the dose definition (D for mg/kg, C for inhalation concentration, and Ct for vapor or gas dosage), followed by a subscript denoting the fraction of population exhibiting the effect (see

Figure 2).13 As stated previously, these values are exposure site dependent.

Figure 2. Example dose-response curves for effects and lethality13

For the purposes of distinguishing types of CPC, exposure scenarios often differentiate along a physical description of the hazard. This may include submerged, vapor, gas, splash, droplet, and residual contact. These exposures can be augmented by increasing the concentration, time, or pressure of the exposure. The physical properties of the chemical affect the severity of the hazard and exposure route.

On the battlefield especially, chemical threats may be deployed in a way that optimizes the exposure hazard. A general distinction is made between volatile and persistent chemicals.

Persistency is a function of the boiling point, vapor pressure, and density of a chemical. Lower boiling point, high vapor pressure, and low vapor density chemicals will disperse more quickly and thus reduce the potential exposure duration. However, they have the ability to expose larger areas and can travel downwind. For instance, though chlorine is a gas at room temperature, it is stored in large quantities as a pressurized liquid in tanks, which can release

10 large volumes of gas. Further, gaseous chlorine has a higher density than air, which causes it to accumulate in low lying or wind covered areas – a property notable to its use in the first instance of modern chemical warfare in 1915 when German troops released over 5,000 cylinders of chlorine across a 4-mile stretch of road, sending the toxic gas downwind where it flooded the Allies’ trenches and killed 1,100 soldiers.14

Low-volatility liquids, unless dispersed as a vapor or mist, will be confined to a smaller area. However, that liquid will exist at a higher concentration and persist, leading to potential contaminations by contact.15 Atmospheric activity can affect persistence of a vapor greatly.

Chemicals released in conditions just below their boiling point or as saturated vapors can form high concentration vapors and mists (small airborne droplets) that have high mobility.13

Highly reactive chemicals additionally can damage equipment and protective clothing, compromising protection and operational capabilities. Similarly, chemicals with high solubility in certain media are able to contaminate equipment and protective clothing items and will be more difficult to subsequently decontaminate.13

Models are used to classify Chemical, Biological, Radiological and Nuclear (CBRN) incidents to inform operational responses by emergency and tactical groups. The most common conceptual model identifies “response zones” that indicate the relative hazard of regions around a chemical release (Figure 3). The “hot zone” is the location of release and surrounding area where hazmat operations require the highest level of protection and where atmospheric levels are considered above those Immediately Dangerous to Life and Health (IDLH).16 The

“warm zone” or “protective action zone” are the perimeter around the hot zone, which contain a hazard at levels below IDLH. This area is actively evacuated and may contain rescue or

11 tactical operations. The “cold zone” contains safe atmospheric conditions where operations such as medical response or decontamination occur.13

IDLH values are defined as concentrations in air. The NIOSH website states the following about the use of these values: “The purpose of establishing an IDLH value is (1) to ensure that the worker can escape from a given contaminated environment in the event of failure of the respiratory protection equipment and (2) is considered a maximum level above which only a highly reliable breathing apparatus providing maximum worker protection is permitted.”17 Based on the primacy of respiratory protection and considering that dermal exposure limits or dermal dosage effects are not defined for many chemicals, IDLH hazard classifications are generally used to determine dermal protection as well.

Figure 3. Response zones in a release event13

12 The hazard classifications discussed above help inform protection priorities and issues related to protection when considering the design and evaluation of personal protective equipment.

2.2 Chemical Protective Ensembles

2.2.1 Materials

Chemical protective clothing must create a barrier between the chemical (as a particle, liquid, vapor, or gas) and the skin. This can be achieved by the incorporation of a barrier that impedes the chemical, an absorbent material that captures the chemical, or a reactive material that destroys the chemical.

There are two general modes of transport by which a chemical may pass through a barrier: penetration and permeation.18 Penetration involves the bulk flow of a substance through openings and pores (i.e. the substance remains unchanged in form as it moves). The rate of penetration relies on physical properties of the substance, the size of the openings, and the pressure across the material. In permeation the substance must dissolve into the barrier material (i.e. each molecule must separate from its bulk and dissolve into the material). The molecule then diffuses through the material through random motion and desorbs from the back surface of the barrier. The rate of this process is governed by the concentration of the permeating substance and the affinity of the substance for the barrier material.18

Conventional textiles are porous, meaning gases and liquid can pass through the openings between fibers and thus do not provide substantial chemical protection. However, they are often incorporated into CPC materials; nonwoven and knit fabrics are used as supporting substrates for coatings and films, while woven materials often serve as durable

13 outer layer materials.19 Tightly woven fabrics and those treated with repellent finishes can cause liquid chemical to run off, reducing absorption and penetration. Some nonwoven construction techniques are capable of creating barrier textiles, most notably flashspun polyethylene (tradename Tyvek ®), which creates a dense network of 0.5-10 μm fibers capable of preventing liquid and particulate penetration. It has high strength, durability, and chemical stability and can be sewn like conventional fabric.20

Polymer films in the form of extruded films, laminates, coatings, and molded products are the most common barriers in modern CPC.19 Elastomeric films that can be formed through molding or applied as coatings are commonly used for flexible components such as footwear, gloves, facemasks, and seals. Example materials include butyl rubber, polyvinyl chloride, natural rubber, polychloroprene, fluoropolymer elastomers, silicone, EPDM, and nitrile rubber. Mechanically weak polymers are combined with textile supports. Each material may have chemical incompatibilities. For that reason, chemical protective clothing items are available that made from nearly all of these materials and must be selected specifically for the chemical being encountered.21

Extruded film materials are commonly used in ensemble materials, as part of composite film laminates or bound to a fabric with adhesive. The polymers used include polyethylene, polypropylene, polyesters, polyvinyl chloride, polyvinylidene chloride, and fluoropolymers such as fluorinated ethylene propylene and perfluoroalkokxy alkane. Laminate films consist of layers of different polymers to achieve the combined chemical resistance and physical properties of each material. Commercial laminates are used in the majority of broad-protection

CPC ensembles. Some commercial examples include Dupont Tychem® products,

14 Silvershield® consisting of ethyelene vinyl alcohol (EVOH) and polyethylene22 used in gloves, and Saranex®, a coextruded barrier film of polyethylene and polyvinylidene chloride.23

Saranex® is available bonded to nonwoven substrates as part of disposable chemical splash suits from multiple manufacturers. An illustrated cross section of a broad protection composite barrier and a fabric laminate are presented in Figure 4.

Figure 4. Illustrated example cross sections (not to scale) of a composite barrier (left) 24 and a textile/film laminate (right)

Semi-permeable films are materials with microscopic pores or open molecular structures, which limit the transport of liquids and vapors while allowing some compounds, typically the smallest molecules, to pass through.13 These are the barriers used in moisture vapor-permeable materials commonly found in lower level CPC ensembles and commercial rain wear, which allow moisture vapor through the material to lessen thermal burden on the wearer. These materials are typically still capable of stopping aerosol and liquid penetration.

15 There are a number of polymers that can exhibit moisture vapor transport, and their chemical permeation resistance has been shown to vary depending on their microstructure, the extent of hydration, and temperature.25,26 A popular example of such materials are the expanded polytetrafluorethylene (ePTFE) membranes manufactured by W.L. Gore.27

Sorptive and reactive materials seek to reduce the physiological impact of clothing by allowing air flow through the material but filtering out chemical hazards before they reach the skin. Activated carbon is the most common adsorbent for chemical protection. It is relatively inexpensive and an effective adsorbent. The surface area of carbon used in CBRN respiratory canister filters is typically 1000 square meters per gram of carbon.13 Carbon has been incorporated into clothing by various means: foam impregnated with powered activated carbon, carbonized fabric, and beads of carbon laminated to clothing layers.13 Lower molecular mass chemicals are not as effectively sorbed as higher molecular weight compounds and at some point the carbon reaches a sorptive capacity.28 High wind speeds and high humidity reduce the ability of a carbon layer to capture vapors. The liquid and particulate protection of a carbon suit depends on the repellency of the face fabric. Reactive materials can be incorporated into a material layer to remove a chemical hazard by binding with or breaking down the agent.13 Various chemistries have shown potential to decompose chemical and biological hazards, however none are known to be used in commercial CPC at the moment.13,29

High surface area electrospun nonwovens have also been investigated as potential barrier materials due to their light weight and filtration efficiency, and derivatized forms have also been proposed for use as self-detoxifying chemical protective fabrics.30,31

16 An overview of the range of thicknesses, basis weights, and characteristics of a selection of common CPC materials is provided in the Table 2 along with a typical cotton t- shirt material for comparison. The elastomers are the highest density materials, while laminate films are generally thinner and lighter. The carbon sorptive material is thicker and heavier, however comfort properties such as flexibility, drape, and air permeability (not represented on the table) may be preferable. The meaning of the certifications is discussed in the next section.

Table 2. Thickness and Basis weight of some representative CPC materials

Material Thickness, Basis Weight, Textile Certification or oz/sq.yrd.** Support intended use mil* Bulk film stock from FEP film 1 - none manufacturer EVOH laminate barrier 3 2.5 none EN 374-1– ABC exam gloves, ASTM D Nitrile glove 3 to 5 3 none 6978 Suit fabric with inner and 17 6 NFPA 1994 Class 3 fluoropolymer laminate outer knit Knit t-shirt 28 7 N/A (for comparison) Butyl glove 32 41 none EN 374 Multilayer laminate suit nonwoven 44 11.5 NFPA 1991 material layer Carbon Sorptive woven face Military CWA 48 17.5 Material knit backing ensemble knit lining, Neoprene glove 52 27 EN 374-1- ACJKL pebble grip NFPA 1991 chemical Visor 84 - none and flash fire certified Visor/suit seam NFPA 1991 chemical 144 - yes interface and flash fire certified *1 mil = 1/1000 in = 0.0245 mm - measured with Ames BG1110 gauge, 1 in.2 circular foot, and 8.6 oz. load ** rounded to nearest 0.5 oz/yrd2 (dash means not measured)

17 2.2.2 Construction and Garment Features

Beyond the material’s ability to protect, the integrity of the ensemble also depends on design and construction. The type and location of seams, the type and location of closures, the designs of the interfaces, and other factors can all impact the level of protection afforded by an ensemble or component. Seams and interfaces could exist between the garment materials and with the gloves, footwear, visor, facemask, closures, and between different layers.

Ensembles can may be constructed with welded seams or they may be sewn like conventional clothing. There are different stitch options available depending on the desired geometry of the seam and the construction of the fabrics being joined (see Figure 5 for some examples). Surged seams are used when the edges of the material must be contained to prevent unraveling, such as a knit. Lapped seams (not shown), where the two edges of the material are overlapped then sewn, are another common seam that are strong and low profile. Since sewing introduces holes in the barrier, the seam must then be sealed using a heat-sealing or curing adhesive. An additional strip of chemical resistant material, called seam tape, may be used to cover the seam.32

Figure 5. Example seam types: a) serged seam b) bound seam c) seam with tape seal on one side d) seam with tape seal on both sides19

Interfaces are locations between two components of the ensemble that are not sewn together. To obstruct the opening, they require an overlap of material, a closure system (such as a zipper or hook-and-loop closure), or a specialized seal. Fully encapsulating ensembles typically have only one zippered opening for entry into the ensemble and an exhaust valve to release air generated by a pressurized breathing air supply. Lower level ensembles may have interfaces at the cuffs, the ankles, the waist, the chest, the neck, and around the facemask.

Zipper closures consist of two tracks of metal or plastic teeth that interlock as a slider brings them together. Some zippers are capable of maintaining an air or pressure seal. These

19 feature a rubber surface on each track that are forced together as the teeth are closed (Figure

6).

Figure 6. Three YKK brand chemical protective zippers. The left two are used in hazmat suits and the right is used in splash suits.33

Hook-and-loop closures are typically used as part of protective flaps covering zippered interfaces on the chest and neck. They may provide some improved splash protection over a closure, but do not prevent the passage of vapors and gases. Adhesive closures may be used in place of hook-and-loop closures for an improved seal in single-use garments. Once the ensemble is donned the closure is glued shut. After use, the ensemble is sheared for removal.

It is common practice to use additional removable adhesive tape over interfaces for added protection; however, the newest editions of NFPA standards prohibit the use of additional tape to pass performance tests during certification.34

Geometrically complex interfaces feature specialized closures. Removable gloves on high-level protective ensembles often feature a “bayonet” interface where two plastic pieces containing O-rings lock together (see Figure 7). Some ensembles have a glove sewn directly

20 onto the cuff. The interface around the neck or face mask often feature a circular, flat rubber seal designed to fit tightly against the face seal of the respirator (see Figure 8). These interfaces are used in low level ensembles, which do provide some vapor protection. Less protective interfaces feature an elastic cinch or drawstring to tighten the material overlap. Simple overlapping material at the waist or flaps and cuffs around gloves and footwear may help cover skin and divert liquid flow to prevent liquid from entering inside the ensemble.

Figure 7. Bayonet glove interface featured on a Trellchem® Class 2 ensemble35

Figure 8. Elastic face mask seal on an NFPA Class 3 ensemble hood36

2.2.3 Design and Classification

Chemical protective clothing ensembles may be broadly classified using four criteria:

1) descriptions of the physical characteristics and components of the ensemble 2) descriptions of the hazards for which the ensemble is appropriate/intended, 3) performance based definitions of the protection afforded by the ensemble; and/or 4) the associated work function for the ensemble in situations involving hazardous materials. The U.S. Environmental

Protection Agency (EPA), the National Fire Protection Association (NFPA), and the

International Standards Organization (ISO), among others, have suggested classifications of

CPC for occupational and emergency use.

The U.S. Environmental Protection Agency (EPA) along with the Occupational Safety and Health Administration (OSHA) define four “levels” for equipment used in hazardous waste operations and emergency response.37 The levels, intended to aid in the selection of

22 appropriate protective equipment, use relative hazard designations and define the components that each equipment ensemble should include (Table 2).

Table 3. EPA/OSHA Protective Ensemble Levels 37, 38

PROTECTION HAZARD DEFINITION REQUIRED EQUIPMENT LEVEL (OPTIONAL EQUIPMENT EXCLUDED) Level A Greatest skin, respiratory, and eye hazard. - Positive pressure self-contained Protection required due to either: breathing apparatus (SCBA) or - high concentration gas, vapor, or particulate supplied air respirator - high potential for splash, immersion, or - Totally-encapsulating chemical exposure to high skin hazard protective suit - operations are conducted in confined, - Inner and outer chemical resistant poorly ventilated space gloves - Chemical resistant boots

Level B Highest respiratory hazard but lesser skin - Positive pressure self-contained hazard. Protection required due to: breathing apparatus (SCBA) or - oxygen deficient environment supplied air respirator - atmospheric concentrations identified above - Hooded chemical resistant IDLH levels clothing - incompletely identified vapors or gases that - Inner and outer chemical resistant are not suspected to be harmful through skin gloves exposure - Chemical resistant boots

Level C Lesser respiratory hazard. Protection due to : - Full-face or half mask air - identified atmospheric concentrations for purifying respirator which air purifying respirators are - Hooded chemical resistant appropriate (below IDLH levels) clothing - atmosphere, liquid splashes, or direct - Inner and outer chemical resistant contact will not be harmful through skin gloves exposure

Level D Nuisance contamination hazard - Coveralls - no known hazard in the atmosphere - Chemical resistant boots - work precludes splashes, immersion or inhalation of any chemical

All of the levels have “optional, as appropriate” equipment recommendations, which consist of hard hat, face shield, chemically resistant boot covers, and additional under-layers

23 such as long underwear or coveralls. The required equipment descriptions are imprecise. For instance, the document does not define “totally-encapsulating” nor “chemical resistant.” The

Level C ensemble requires hooded chemical resistant clothing event though the defined hazards are stated to not be harmful through skin exposure. Clearly, decisions on the suitability of a protective ensemble require an assessment of the situational risks and information specific to the site, user activities, and properties of an ensemble. Unlike respiratory protective equipment, clothing ensembles are not regulated and enforced by a government agency, so the levels are only guidelines.

The National Fire Protection Association (NFPA) currently has three standards used for the industry certification of five categories of chemical protective ensembles that address needs of emergency responders:

 NFPA 1991-16 Standard on Vapor-Protective Ensembles for Hazardous

Materials Emergencies and CBRN Terrorism Incidents34

 NFPA 1992-12 Standard on Liquid Splash-Protective Ensembles and Clothing

for Hazardous Materials Emergencies39

 NFPA 1994-12 Standard on Protective Ensembles for First Responders to

CBRN Terrorism Incidents40

These standards, unlike the EPA levels, emphasize performance requirements for each ensemble “Class” based on standardized test methods. Performance based tests help determine a more detailed “hierarchy of protection” that can aid in differentiating ensembles and selecting the proper equipment (see Figure 9).19

Figure 9. Hierarchy of Chemical Barrier Performance (copied from Stull19)

Test methods help define the ensemble’s protection based on concepts of integrity. For instance, the most protective ensembles as defined by NFPA 1991 ensembles are said to provide “gas tight” and “liquid tight” integrity, as demonstrated by test methods applied to the entire ensemble. The chemical protective material integrity is determined by both physical testing (e.g. abrasion, tear strength, flexing, etc.) and chemical permeation resistance against

24 chemicals. A summary of the requirements for the five ensemble types is given in Table 4.

25 Table 4. NFPA Protective Ensemble Classes (table style adapted from 41)

Property NFPA 199134 NFPA 199239 NFPA 1994 Class 2 NFPA 1994 Class 3 NFPA 1994 Class 4 40

Threat Fully-encapsulating chemical Full body Incidents involving Incidents involving Incident involving Definition protective suit (wearer’s torso, protection against concentrations at or concentrations below biological hazards or and head, arms, legs, hand, feet, liquids which pose above IDLH, full IDLH, full body radiological particulate Ensemble and respiratory equipment) a dermal hazard. body protection for protection for use hazards with Features with chemical resistant use with Self- with an air-purifying concentrations below footwear, gloves, and visor to contained breathing respirator (APR) or IDLH, for use air-purifying protect against release of apparatus (SCBA) powered air-purifying respirator (APR) or hazardous materials and respirator (PAPR) powered air-purifying CBRN terrorism incidents. respirator (PAPR)

Ensemble Man-in-Simulant-Test N/A Man-in-Simulant- Man-in-Simulant- Particulate inward leakage integrity PPDFi≥488 PPDFsys≥1071 and Test PPDFi≥ 360 Test PPDFi ≥120 test: No visible leakage ASTM F 1052 gas-tight PPDFsys ≥361 PPDFsys≥76 integrity

Liquid tight ASTM F 1359 No leakage ASTM F 1359 No ASTM F 1359 No ASTM F 1359 No N/A integrity leakage leakage after 20min leakage after 4min

Permeation ASTM F 739 against 24 N/A TOP 8-2-501 against TOP 8-2-501 against N/A 2 resistance of chemicals at 100 g/m and 2 CWAs and 1TIC at 2 CWAs and 1 TIC at materials TOP 8-2-501 against 2 CWAs 10 g/m2 closed top 10 g/m2 open top and and seams of at 10 g/m2 and 4 TICs at 350 4 TICs at 40 ppm ensemble ppm and bootie

Penetration closures only ASTM F 903 ASTM F 903 >1h ASTM F 1671 >1h ASTM F 1671 >1h ASTM F 1671 >1h Viral resistance of >1h against 15 chemicals against 7 chemicals Viral Penetration Viral Penetration Penetration Resistance materials Resistance Resistance and seams

Table 5. Example NFPA certified ensembles

NFPA 1991 NFPA 1992 NFPA 1994 Class 2 NFPA 1994 Class 3 Kappler Zytron 50042 Dupont CPF343 Ansell Trellchem ACT35 LION ERS44

The NFPA classifications are more detailed than the EPA levels. Additional physical and ergonomic performance criteria are in the standards including test such as burst strength, tear resistance, closure strength, cut resistance, glove dexterity, abrasion resistance, puncture resistance, and footwear slip resistance. It is important to note too that the NFPA standards committees work on a constant revision cycle, often introducing significant changes in new editions. The 5th edition of NFPA 1991, released in 2016 included revised permeation testing requirements and for the 4th edition of NFPA 1994, to be released in 2016, the addition of a new ensemble class along with optional “ruggedized” certification options, which feature additional durability requirements are being discussed.

In promotional documents, manufacturers of NFPA 1994 Class 2 and 3 ensembles emphasize ensemble use by law enforcement and first responder groups and suggest use for tactical applications, emergency response, rescue, and hazardous material mitigation situations. At the time of writing, there are at least nine Class 2 ensembles (some of which are dual certified to NFPA 1992) from the manufacturers Blauer45, LION44, Saint-Gobain46,

Kappler42, Ansell35, and Dupont43 while there are three commercially advertised Class 3 ensembles: the Blauer XRT, Lion ERS, and LION Commando suits.

More commonly encountered in the occupational and industrial protective clothing industry are international and European performance standards ISO 16602:2007 Protective clothing for protection against chemicals -- Classification, labelling and performance requirements and EN 943 Protective clothing against dangerous solid, liquid and gaseous chemicals, including liquid and solid aerosols. These standards define “types” with a similar hierarchy of protection to the NFPA classes, but use EN and ISO test methods and performance

criteria, which differ slightly from the NFPA requirements (see Figure 10). Another European standard, EN 374 Protective gloves against chemicals and micro-organisms, is commonly used to define the performance of industrial gloves in the United States.47

Figure 10. ISO 16602 Protective Clothing Types48

Military systems are primarily designed for protection against militarized chemical warfare agents and thus are defined based on operational needs of specific groups within the military. The use of self-contained or supplied air breathing apparatuses does not align with

the duration and mobility required of many military operations. Chemical protective ensembles designed for military use air-purifying respirators and are designed to be compatible with standard uniform and equipment.

Three examples of currently fielded non-encapsulating ensembles include the JSLIST,

AP-PPE, and UIPE 1 (Table 6). JSLIST is a carbon impregnated ensemble with lighter weight, greater durability, and less heat stress than previous generation Battle Dress Overgarment

(BDO) ensembles.49 It is a two piece ensemble with a 50-50 nylon-cotton rip stop outer layer and a liner consisting of a nonwoven laminated to activated carbon spheres and knit backing.50

It is said to provide protection against CWAs for 24 hours and last up to 45 days of wear if not contaminated.51 The AP-PPE was developed for special operations forces and utilizes a selectively-permeable membrane, which has certain advantages over carbon suits such as increased liquid protection and thinner material.52 The UIPE, the newest of the three ensembles, attempts to reduce thermal burden and bulk by placing a stretchable protective membrane next to the skin, underneath conventional uniform garments. A two piece ensemble covers the torso, arms, and lower body while a sock liner is worn under combat footwear. A deployable hood, mask, gloves, and overboots are worn over the uniform garment.53

Table 6. Three currently fielded military CPC ensembles50,52,53

Joint Service Lightweight All Purpose- Uniform Integrated Protection Integrated Suit Technology Personal Protective Ensemble Ensemble Increment 1 (UIPE 1) (JSLIST) (AP-PPE) (under garment barrier layer)

Military operations occasionally include hazardous materials duties as well. In June

2007, during Operation Iraqi Freedom, several thousand five-gallon containers of nitric acid were discovered in Fallujah, Iraq.54 A hazmat remediation mission, dubbed Operation

Dragon’s Den, took place over several days and included a fire suppression operation, containment to neutralize a large spill, and the over-packing and removal of several hundred intact containers. Personnel were equipped with “Level B” ensembles and SCBAs. Two marines were injured – one when acid infiltrated a cut in an overboot and a second when acid infiltrated the zippered area of his suit. In 2014 it was reported that at least 17 American service

members were exposed to chemical warfare agents while encountering remnants of Iraq’s inactive CWA arsenal.55 The soldiers, sometimes unaware of the presence of agent, manually came into contact with agent while moving contaminated shells or were exposed to hazardous vapors after remotely detonating IEDs and abandoned shell piles. It is not clear if any exposures occurred due to shortcomings of protective equipment. The military also maintains large stores of toxic industrial chemicals, notably fuels, which regularly require the use of conventional chemical protective clothing by military personnel.

2.2.4 Operational Factors

Respirators and some ensembles are assigned protection factors (PFs) based upon laboratory test methods that define the reduction in exposure an item of CPC provides.

However, biological monitoring studies of CPC have shown lower protection factors occur in use than expected.56 This inconsistency is often attributed to operational factors: anything related to the user, task, and environment (UTE) that may affect the performance of CPC.57

These factors cannot always be predicted but can often be investigated by observing CPC in use. For example, ensemble level tests and wear protocols such as the Man-In-Simulant-Test may be able to identify the impact of movements, improper donning, or poor fit which affect the interfaces of an ensemble. Real-life environmental damage of different materials can inform bench level testing requirements for abrasion, puncture, and tear resistance. Other examples include doffing procedures that could result in self-contamination and decontamination/wash procedures that could leave residual chemical in the suit material or degrade the material performance over time.58 There are no standardized methods for

implementing UTE studies, but they are an important tool to identify potential operational pitfalls or inform new performance standards, test methods, or operational tactics.

2.2.5 Comfort and Human Factors

Clothing comfort is equally important to protective properties because discomfort and physical limitations can seriously degrade a user’s ability to perform their required tasks.

Comfort and ergonomics are a matter of physiology, anatomy, psychology, and perception.59,60

Physiological comfort is related to a human’s ability to maintain body temperature and perform biological functions. Metabolic activity causes the body to generate heat. This heat is dissipated through conductive, convective, and evaporative heat transfer (sweat evaporation) between the skin and the surrounding environment.61 Clothing alters that transfer by creating a different environment between the skin and the clothing exterior, typically by reducing air, heat, and moisture transfer. In warm conditions or during intense activity, clothing can cause the accumulation of liquid sweat next to the skin, the sensation of heat, and increased skin and core body temperature, causing discomfort and potential heat illness.60 Heat stress can be managed in occupational settings by following industrial hygiene guidelines, which limit metabolic work rates and recommend work/rest times based on environmental conditions and clothing properties.61

Testing approaches and theoretical models exist that relate physical properties of fabrics and garment designs to comfort or physiological impacts in different climates and work rates.60 The models are confirmed using human wear trials and measurements taken with instrumented manikins, which simulate the heat transfer dynamics of a human form. The relevant fabric properties are typically the air permeability, moisture permeability, and dry and

evaporative heat transfer rates.60 Based on such studies the NFPA has established minimum requirements for the total heat loss (THL), as measured on a sweating hot plate, of materials used in some protective clothing ensembles. For instance suit materials used in NFPA 1994

Class 3 and Class 4 ensembles are required to have a THL of at least 200 W/m2 and 450 W/m2, respectively.40

Anatomical and ergonomic impacts of clothing involve reduced mechanical or sensory capabilities of the end-user. These impacts can be assessed by comparing a user’s ability to perform tasks with and without the clothing.32,60,62,63 For instance a glove may cause a measurable reduction in grip strength or increase the time needed to perform a task64; a facemask or hood may reduce visual and auditory acuity65; bulky footwear may reduce speed or increase the occurrence of trips66; a poor fitting garment may reduce the flexibility of the user as measured using a goniometer and heavy/stiff/bulky material may increase the metabolic work rate required by the end-user.32 The heat stress and bulkiness of protective clothing has been shown to impair the performance of medical personnel performing lifesaving tasks.67

Tactile discomfort from abrasive textures, heat, moisture, or pressure on parts of the body can have physical and psychological impacts.57,60 Pressure and skin abrasion can result in skin damage or musculoskeletal injuries. Blisters especially can be painful, restricting function and increasing susceptibility to chemical absorption through broken skin. Knowledge of biomechanics and anthropometrics is necessary for designing the proper fit and function of clothing items.68

Finally, there is an important psychological component to protective clothing.

Irritation, discomfort, and altered perception from clothing can result in reduced mental

concentration and human error that lead to safety risks or the improper use of protective equipment. Psychological factors may be heightened by the stress associated with chemical exposure risks, which may further degrade task performance.49 Equally important are the end- users’ impressions and expectations about clothing aesthetics and function based on previous experiences and the current social or physical environment. These perceptual “stored modifiers” may impact their desire to wear or purchase an item and can influence whether an end-user has confidence in a clothing item.59 Additional “fashion factors” are relevant to protective apparel such as outward perception, identity, tradition, and a sense of innovation and functionality.69

Studies of human factors often require the subjective measurement of comfort and discomfort, which requires psychological experimental techniques. The following necessary elements for a psychological measurement have been identified: commonly recognized attributes; language that describes those attributes; a scale to associate with the attributes; and, if possible, a means of relating the psychological scale to a physical measurement.70

For clothing, many common attributes and sensory phenomena have been identified that are universally identified by subjects in comfort research studies. To perform data analysis, these “sensory descriptors” must be associated with numerical values. One common approach involves rating scales in which the subject must assign an intensity to an attribute on a scale of

1-to-5 or 1-to-10 or -5 to +5. An example of this approach is presented in ISO 10551:1995

Ergonomics of the thermal environment- Assessment of the influence of the thermal environment using subjective judgement scales.71 Numerical intervals between two descriptive end-points, for instance, at 1 the item is “not at all X” and at 5 “very X” may be used or itemized

scales may be used, where each interval is given a description. The scaling may be comparative, when a reference point is provided, or non-comparative, when the specimen/sensation must be evaluated on its own. A variation on the rating scales is a semantic differential scale, where two opposite descriptors are used as the scale end-points.72 It is often, but not always, assumed that the intervals between the assigned numerical points are equal and the data can be analyzed using parametric statistical methods.73

Another approach involves paired comparison or ranking, where subjects are asked to directly compare a set of specimens and rank them for each attribute. Rank order data forces a discrimination, which may make a differentiation in the data more likely. However, this data does not provide a magnitude of difference and the resulting ordinal data can only be analyzed using non-parametric statistical methods.73

Wear trials and laboratory techniques generally use more than one of the subjective measures above. The trial must also be designed in a manner that encourages the attribute of interest to be perceived. This may require surveying the subjects at multiple points during a trial or in dynamic thermal and moisture conditions.73

2.2.6 Low-level CPC Ensembles

As discussed in previous sections, there is a general tradeoff between protection of CPC and the user’s thermal comfort, mobility, and dexterity. Apart from finding material advances that can improve both protection and ergonomics, there is the appealing option of lowering the protective requirements of ensembles and materials to increase the performance of end-users and reduce the risk of heat strain. Low-level CPC ensembles may have a limited scope of use to fulfill the needs of specialized duties or introduce an added benefit to end-users. Benefits

may include: decreased cost, increased moisture permeability, increased flexibility/mobility, reduced bulk/weight, or features aiding in maintenance, durability, decontamination, interoperability, procurement, design, fit, and customization.

One associated risk of low-level CPC is the situation where an end-user employs an ensemble that does not perform to their expectation. The challenge of low-level CPC ensembles requires additional steps for clarifying and validating fitness for use, which may include:

1) Validate the improvement: if the sacrifice in protection does not provide a clear

physiological or operational improvement then it may not be worth the risk.

2) Standards development: new standardized performance criteria and test methods

may have to be created to ensure targeted product performance and the practical

relevance of the testing.

3) Specify and optimize design tradeoffs: industry and end-users must be educated on

ensemble differences and the system may be targeted to specific user groups.

One instance of a novel approach has been the introduction of next-to-skin protective clothing. Such a suit is made possible by the use of a thin, stretchable protective material. The suit has the advantage of modular layering, whereby additional protective layers (fire or physical protection) need not be incorporated with the barrier material. A more form-fitting design reduces bulk, which could also equate to less thermal burden.74

Such a suit could serve both specialist and broad application for personnel who would not be performing typical hazardous materials tasks and may require extended operational duration. For instance SWAT, explosive ordinance disposal (EOD), secret service, and air crew

that rely on outer layer fabric features, would be able don the protective layer underneath their primary uniforms. It could also help fill the need of equipping a larger number of military, civilian, law enforcement, and first responder personnel in the instance of a CBRN terrorism incident. 74,75

Donning before a mission reduces flexibility regarding protection and thermal burden; however, the design may still allow different protective postures as the gloves, mask, and hood can be deployed separately. Such an ensemble could provide complete dermal protection from liquid splashes.

Two instances of a stretch barrier ensemble include the military’s UIPE 1 and LION

Apparel’s NFPA 1994 Class 3 certified Commando ensemble (Figure 11). In 2012 a $129 million contract was awarded by the U.S. Army Contracting Command for the procurement of

UIPE 1 garments. A project to develop a second generation UIPE with a similar protection concept is currently underway under direction of the Joint Project Manager for Protection

(JPM-P).

Figure 11. LION Apparel Commando Stretch Under Garment76

2.3 Footwear Comfort and Performance

The importance of footwear in emergency responder and military applications has been discussed by many researchers. Footwear is the primary point of contact between the user and their environment. A review of design issues associated with military footwear suggests the following factors are important to understanding footwear performance: fit, orthotic support, physiological maintenance, task performance, donning and doffing, affordability, and durability.57 Specific suggestions from the author include reducing shear between the foot and

inner boot that can lead to blisters or the sensation of slipping, managing the accumulation of moisture, and properly applying pressure to the foot to avoid nerve pain, altered articulation of the foot, and limited blood-flow.

Studies of footwear comfort have used both subjective and physical measurements.

Several studies have correlated subjective evaluations of footwear preference using thermal and moisture sensation scales with the measurement of microclimates inside footwear, skin temperatures, total sweat rates, and peripheral blood-flow measurements.77,78 However, the repeatability of subjective footwear comfort measurements has been questioned and the use of comparison controls within studies is encouraged.79 Wide variation in anthropometrics and foot sensitivity have been measured, with the implication that the orthopedic influence of footwear design can be highly individualized.68 A compelling suggestion though has been put forth that short-term assessments of footwear comfort by subjects are related to long-term comfort and possibly even the rate of injury occurrence with a specific pair of footwear, meaning that subjective preference of footwear in a wear trial can have significant long-term implications.68 Quantitative assessment of the gait of firefighters have been used to identify the impact of different PPE configurations on user mobility, fatigue, and the potential for trips and slips.66

Protective footwear often includes multiple layers of fabrics and membranes, which limit moisture and heat transfer. One study comparing the impact of different waterproofing laminates in military style leather boots using an instrumented manikin foot form did identify measureable heat loss from the sweating foot in all footwear configurations. However, the materials’ moisture vapor transmission rates were much lower than a foot’s typical sweating

rate. Additionally, there was no significant difference between the boots with full water- resistant laminates and the control boot containing only partial inclusion of a laminate film – indicating that the moisture and heat transfer resistance was largely due to the leather and textile components of the footwear. This and similar studies suggest that moisture management and comfort within rubber, laminate, and highly insulated footwear may best be influenced by the moisture properties of the inner socks and liner materials.80

2.3.1 Chemical Protective Footwear

The feet and hands are a primary means of interacting with the environment and the most likely parts of the body to be exposed in a situation containing hazardous materials. The possibility of spills, chemical deposited on surfaces or in surface water, and physical hazards such as rough terrain, debris, unstable surfaces, and falling objects necessitates proper footwear. Poor quality or ill-fitting footwear can lead to slips and falls or severe physical discomfort, reducing the wearer’s mobility and endurance.

Four approaches to chemical protection of the feet and lower legs are common19:

 Boots – Footwear that provides a chemical barrier and physical protection to

the foot and lower leg.

 Overboots – Footwear worn over conventional footwear that provides

additional chemical and physical protection.

 Boot Covers – Similar to overboots, but made of a lighter weight material; often

intended for single-use.

 Booties or sock liners – A component of the chemical protective garment, worn

inside conventional footwear, similar to a sock; either attached to the garment

or a separate item. Separable booties are referred to as “sock liners” in this

research.

The ensemble classifications discussed in the previous section largely specify the use of a chemical protective boot. Additionally, any ensemble that requires vapor or air-tight integrity would, by necessity, have attached booties. Thus two layers of chemical protective material surround the feet in most ensembles. The protective boots may require thick layers of material to incorporate chemical protective properties with physical protection (e.g. toe impact protection, puncture-resistances, etc.), and they must be sized to accommodate the extra material of the bootie. This often leads to bulky, loose-fitting, and heavy footwear in the highest protection level ensembles (Figure 12).

Figure 12. A chemical protective boot

Overboots and bootcovers have the advantage of use with conventional footwear. They are common when the CPC is intended to be worn temporarily or quickly donned, for instance, if end-users must frequently enter and leave a contained area or as part of portable, deployable ensembles for military. Both overboots and bootcovers tend to be sized in ranges (i.e. small, medium, large) and with a loose fit to fit over a variety of footwear, adding bulk to an ensemble.

Since they surround the entire shoe, including sole, they are more susceptible to physical damage from the environment. A common overboot is the Alternative Footwear Solution

(AFS), a compounded butyl rubber boot worn over normal combat footwear by the US Navy,

US Army, US Marine Corps, US Coast Guard, and US Air Force.81 These and similar commercially available products are colloquially referred to as “Mickey Mouse” boots for their resemblance to the cartoon character’s oversized feet (Figure 13).

Figure 13. Molded butyl rubber overboot 82

Booties, similarly, can be worn with conventional footwear; however, they must be donned at the start of the operation under the footwear. Booties have the disadvantage of not preventing the outer footwear from being contaminated. Attached booties are typically made using the same material as the ensemble suit and are matched in size to the ensemble. Detached booties, which may be referred to as “socks” or “liners”, may be procured in different sizes from their related ensemble, allowing more custom fit. A detached bootie is either tucked under the leg of the ensemble or the ensemble has an inner sleeve and outer sleeve (“shell” in Figure

14); neither is considered a vapor-tight interface; however, this style of bootie is used in nominally vapor protective ensembles such as NFPA 1994 Class 3 ensembles. The shell sleeve prevents liquid splashes from entering into the bootie, while the inner sleeve adds an extra layer of material to increase the coverage of the interface.

Figure 14. Inner and outer legging sleeve of a pant leg interfacing with a detachable bootie83

All of the military ensembles discussed in the previous section currently utilize a sock liner called the Integrated Footwear System (IFS), which is made of a selectively permeable barrier material laminated to an exterior and interior textile material with an attached aramid cuff (Figure 15).84

Figure 15. Integrated Footwear System84

The NFPA 1994 Class 3 ensemble footwear are allowed to be configured out of multiple components such as a bootie and overboot. However, the bootie material must be tested in the same manner as an ensemble material, which includes abrasion preconditioning followed by permeation testing and viral penetration testing.40 The outer boot is subjected to more rigorous abrasion testing.

2.4 Testing and Evaluation

CPC testing is sometimes described in terms of a hierarchy of the scale of evaluation tests.13 Material level testing is generally the lowest level and highest volume test performed because of the control, reproducibility, lower cost, and screening function of swatch tests.

Standard material tests include permeation and penetration testing. Component and full system tests, while more costly and complex, provide more realistic assessment of equipment. A testing and evaluation paradigm for CPC ensembles must consider the benefits and shortcomings of each level of testing. CPC testing is additionally complex because

performance of a product or material may be specific to the chemical challenge and its concentration. Thus there is a distinction between tests of a material/ensemble’s chemical properties and physical properties.

2.4.1 Material Level

Material level chemical testing identifies the barrier performance and chemical compatibility of CPC materials by exposing the material to a chemical challenge and observing or measuring the passage of chemical through the material. The general categories of testing are penetration testing (which includes run-off testing, hydrostatic pressure testing, and some immersion testing) and permeation testing. Both testing approaches use a challenge battery to represent different classes of chemicals.85

Penetration testing is generally qualitative, meaning the backside of the material is monitored for the chemical penetrating the material, but the amount of chemical is not quantified. Rather, the time or pressure required to cause a failure is determined. Thus, although some materials may follow a quantifiable pressure-flow dependence listed in the equation below, penetration testing for CPC is used primarily as a qualitative investigation of chemical compatibility. A material is observed to either pass or fail the test, and observations are gathered on changes due to the chemical exposure such as appearance, weight, volume, and physical stability (for instance puncture resistance).86 In general, more porous materials and those with poor chemical compatibility will show lower penetration resistance. Challenge chemicals with lower surface tension, lower viscosity, high solubility, and corrosive effects will present higher penetration challenges.86

Bulk flow of vapors and liquids through openings and pores is understood to occur due to a pressure gradient according to Darcy’s Law (though the relation may not stand for all materials tested in penetration tests). The flux, J, through a material’s thickness or flow path, l, is related to a pressure difference, 푝표 − 푝푙, by the viscosity of the fluid, 휇, and a coefficient referred to as permeability, 푘:

푘 (푝 − 푝 ) 퐽 = 표 푙 휇 ∗ 푙

The coefficient will have different units depending on the units of flow. More detailed models of pressure-flux relation exist depending on the nature of the penetrating substance and the diameter and shape of the pores. Additional factors such as pressure dependence, tortuosity, surface energy, and inertial effects are used to explain the relation further.87 Porous flow is capable of exhibiting orders of magnitude greater fluxes than permeation.18 In the absence of a pressure gradient, bulk flow of liquids can also occur by intermolecular attraction forces between a liquid and a material’s surface, as seen in capillary flow.

The primary test method for CPC is ASTM F 903, which is a one-sided hydrostatic pressure test. Samples are mounted in a cell with a reservoir of challenge chemical that can be pressurized on the face of the material and a transparent cover on the back of the material

(Figure 16). The cell is pressurized (2 psig for NFPA 1992 materials) generally up to 1 hour and the backface is observed by the test operator until the time at which droplets of liquid appear or discoloration of a contact paper occurs.88

Figure 16. ASTM F 903 Pressure Testing Apparatus88

Permeation testing is a quantitative test to identify the rate of permeation (mass flux) through a material or the amount of chemical that permeates in a given time. The membrane is mounted in a cell with challenge chemical introduced to the face, while the chamber at the backface or “downstream” of the membrane is analyzed for permeating chemical. The permeating chemical can either desorb as a vapor/gas into an airstream, dissolve into a liquid collection medium, or transfer to a solid collection medium to be analyzed.

A theoretical description of permeation through a polymer film is provided by the solution-diffusion model.18 For a homogenous non-porous polymer film the mass transport of

a chemical consists of three steps, which involves sorption of the chemical on the face, diffusion through the membrane due to random molecular motion, and then desorption from the other side. This is characterized by a coefficient also referred to as permeability, P, an empirical expression of the ease of transport of the chemical through the film, which is a product of the average diffusion coefficient, D, and, solubility/partition coefficient, S:

푃 = 퐷̅ ∗ 푆̅

Fick’s first law, which describes the diffusion step, states that:

훿퐶 퐽 = −퐷 훿푥 where the flux, J, is the mass flow rate per unit area, C is the concentration of the diffusing substance, x is the unit length normal to the direction of diffusion, and D is a diffusion coefficient for a given substance with units of length2 x time-1.89 Integrating across the thickness of the film (푙) and assuming the concentrations of the chemical at the face (Co) and backface (Cl) of the membrane are kept constant, the flux will reach a steady state value such that:

퐶 − 퐶 퐽 = 퐷̅ 표 푙 푠푠 푙

and

푙 푃 ≡ 퐽 ∗ 푠푠 푑푟푖푣푖푛푔 푓표푟푐푒 푔푟푎푑푖푒푛푡

and 푆 acts as a conversion between the external and internal driving force gradient

The driving force gradient is the concentration difference of the chemical on the exterior of the membrane, which may be defined in a number units including the concentration in liquid, molar concentration, or partial pressure.90 Solubility is the relationship between concentration in the polymer (Co) and the exterior concentration. It is related to the free energy of mixing for the solvent-polymer pair and has been described by various models.91–93 It can be studied directly using immersion and sorption studies.94,95

The simplest model for solubility is Henry’s Law, which states that the concentration of permeant in the dissolving substance is directly proportional to the concentration at the surface. This has been shown to apply generally for polymers above their glass transition temperatures interacting with gases above their critical temperatures or organic vapors at low concentrations.96 However, liquids and condensable vapors can achieve much higher sorption concentrations due to plasticization effects on the polymer and non-ideal vapor activity, resulting in higher solubility/permeability.96,97 Meanwhile polymers below their glass transition temperatures feature limited chain movement and slower relaxation times, which tend to limit the solubility and permeability of permeants at higher concentrations.96

The simplest description of diffusion assumes a constant diffusivity for a given polymer-permeant pair, which is independent of concentration. Diffusion is slower for larger molecules.98 However, the diffusion coefficient of vapors and strongly sorbing molecules can be concentration dependent due to plasticization effects, which can lead to changes in free- volume, microstructure, and the transition temperatures of the polymer.96

Diffusivity and permeability has been shown to be highly temperature dependent and can be described using an Arrhenius relationship99:

ln(푃) = ln(푃표) − 퐸푃/(푅푇)

ln(퐷) = ln(퐷표) − 퐸퐷/(푅푇) where Po and Do are pre-exponential factors and Ep and Ed are activation energies. Higher activation energies result in lower permeability and diffusivity. Breaks in the Arrhenius fit are often observed at the glass transition points of polymers.100,101

The dynamics of permeation can become quite complex in a real-life scenario involving multilayer barriers being exposed to multiple chemicals in variable environmental conditions.

This makes it difficult to predict the performance of CPC in use; however, models based on

Fickian diffusion can be applied to inform research into the permeation properties of CPC materials.

Permeation test methods begin by flooding the sample surface with challenge chemical or introducing a flow of vapor or gas. Two different configurations for CPC testing are differential/open loop where the permeant is constantly removed from the downstream surface or integral/closed loop where the permeant accumulates in a fixed collection volume. They are presumed to provide identical results unless the concentration of permeant in an integral test reaches a high enough concentration to reduce the concentration gradient across the sample

(see Fick’s First Law). Many different permeation test methods have been developed for

CPC.102

Two common standardized methods are ASTM F 739 Standard Test Method for

Permeation of Liquids and Gases through Protective Clothing Materials under Conditions of

Continuous Contact 103 - which has been in used by industry for over 35 years and is referenced in NFPA 1991- and a United States military Test Operating Procedure (TOP) 8-5-201 which

appears in a modified form in NFPA 1994 and in NFPA 1991 for warfare agent testing.104 The methods differ in several specifications including cell design, testing conditions, and applicable collection techniques.

The F 739 standard uses a cell with a vertically oriented sample, a flooded surface, and allows the use of liquid collection media, which should only be used with non-porous materials. It allows both open and closed loop testing. The TOP 8-5-201 method uses a cell with a horizontally oriented sample and removable screw top. This allows the application of smaller volumes or drop-wise application of challenge; however, it is limited to use with air flow collection because of the construction and flow patterns inside the cell. The standard contains a procedural logic whereby samples are first tested for air permeability pressure testing. If a material shows air permeability above a certain level, the specimens are tested in a differential pressure “convective flow” configuration where the air flow travels through the fabric. This allows testing of air-penetrable samples, such are carbon-sorptive materials used in military ensembles. If the air permeability is below the threshold it is tested in an open loop test configuration, with an air collection flow through the lower half of the cell.

Figure 17. Example of an open-loop ASTM permeation set-up

Many metrics have been used to characterize the permeation resistance of protective clothing (see Figure 18). These include: 1) the time to reach a detectible permeation rate, breakthrough time (BT) 2) the time to reach a predetermined permeation rate, standardized breakthrough time (sBT) 3) the equilibrium permeation rate steady-state permeation (SSPR)

4) the total amount of permeant at a given time after exposure cumulative permeation (CP), and 5) lag time (LT), the intercept of the cumulative permeation slope with the time axis. The most common flux units for CPC are μg/cm2/min. Not all material/chemical combinations reach a steady-state rate within a reasonable test duration, making SSPR and LT less common metrics. Meanwhile, not all test methods are capable of accurately determining sBT and CP.

Differences in analytical methods can greatly influence the determination of all the permeation metrics above.105

Historically, sBT, SSPR, and CP have been the metrics in test standards. Many chemical equipment manufacturers publish chemical compatibility tables for their products, which list sBT values for a variety of chemicals. Sometimes the sBT and SSPR are binned into ranges to categorize the materials as “excellent”, “good”, or “not-recommend” for use against a certain chemical.21 The ASTM sBT of 0.1 μg/cm2/min is meant to be a realistic threshold for detection methods for the relative comparison of materials, not a meaningful toxicological mark.103 However, it has become the most persistent means of evaluating CPC materials side by side.

NFPA 1994 Class 2 and 3 garments are tested using a modified TOP 8-2-501 method.

Each class is tested against a different challenge concentration based on the NIOSH standard used to evaluate CBRN certified respirators, but uses the same failure limit of a cumulative amount of 6.0 μg/cm2 of permeant during a 60 minute test .106,107

Figure 18. Representative theoretical permeation curve labeled with common metrics

There are many examples of research on the evaluation of chemical protective clothing and related fields that adopt theoretical aspects of diffusion to address practical research questions or to improve on the methodology of implementing the permeation tests themselves.

Methods of implementing and interpreting permeation tests have been reported upon widely in ASTM technical papers and industrial hygiene journals over the past several decades.108,109

Studies often attempt to extract basic solubility and diffusivity data from experimental measurements to make broader judgements on chemical/material compatibility. Rivin, et al. 95 performed permeation and immersion sorption experiments on four classes of elastomeric materials against four chemical warfare agent simulants to study if their diffusivity and solubility properties correlated with performance against actual warfare agents. That research

resulted in their own proposed operating procedure for performing permeation tests and recommendations for suitable respirator materials.110 The immersion approach to testing sorption has been investigated for the evaluation of elastomeric materials used in CPC gloves and chemical agent resistant coatings. 111–113 One researcher developed a predictive model, based on the free energy of mixing of several chemicals with butyl rubber and Viton, that was able to fit transient permeation data.114

Bromwich115 applied temperature relationship models to the measurement of permeation through supplied-air respirator hoses to predict potential occupational exposure levels. Significant research on the impact of the collection flow and applied analytical solutions to the modeling of continuous and intermittent exposure of CPC materials was also performed.102 To address issues with the removal efficiency of low volatility analytes, permeation tests have been performed using liquid collection and FTIR-ATR. 102,116 The measurement of reactive compounds has been addressed by using derivitized samplers to directly measure the performance of protective materials, for example for the measurement of exposure levels of chemical coating applicators in the automobile industry.117

Chao 118,119 has performed permeation testing following ASTM F739 procedures to characterize protective glove materials and high-density polyethylene geomembranes. He calculated diffusion and solubility coefficients from experimental data that offered good fit using a solution to diffusion equations. Gao 58 collected permeation data on commercial CPC materials subjected to multiple exposure and decontamination cycles as a measure of physical degradation use. However, no model or underlying explanations for the results were suggested.

The influence of hydration state on the permeability of protective clothing materials has also

been investigated, with the finding that the permeability of some hydrophilic polymeric materials can be influence by environmental humidity.26

Fickian mass transfer dynamics have been applied to the study of contamination and decontamination contact hazards on materials and surfaces by modeling transfer rates. 120–122

Researchers have also applied physics based models of permeation testing cells to explain the observed and theoretical differences in permeated mass as a result of test conditions and analyte vapor pressure.123 An improved method for sampling low vapor pressure challenge chemicals, specifically the chemical warfare agent, VX, by the use of solid adsorbent pads placed in direct contact with the back face of the barrier material was proposed and validated.124

Recent research on experimental methods involved a differential test methodology for real-time measurement of permeation using flame ionization detection and a novel cell design intended to maximize analyte collection efficiency.125,126 Significant similarities in experimental approaches exist in the food and packaging industries, which study the permeation of organic flavor compounds through high barrier films.127–129

Aside from pressure penetration testing of NFPA 1991 closures and seams and the requirements for closure flaps in NFPA 1994 ensembles, there are no other standardized tests below the ensemble level specific to chemical resistance of interfaces and closures.

2.4.2 Ensemble Level

Ensemble tests are performed on complete CPC garments. A collection of screening tests can be performed on ensembles and components using apparatuses designed to asses a specific property of integrity. More complex test are intended to quantify or differentiate

systemic protection by incorporating the effects of body movement, operational factors, and garment design. They may be performed using live subjects or with the aid of manikins.

Liquid integrity is determined using ASTM F1359 Standard Test Method for Liquid

Penetration Resistance of Protective Clothing or Protective Ensembles under a Shower Spray

While on a Mannequin, a shower test where the ensemble is mounted on a manikin and sprayed with water. Points of inward leakage are identified visually. Ensembles are tested for different durations depending on the level of intended protection. Gloves and footwear are subject to a liquid tight integrity test for both NFPA 1992 and NFPA 1994 ensembles following a methodology similar to ASTM D5151 Standard Test Method for Detection of Holes in Medical

Gloves, which requires these components be filled with a surfactant-treated water and observed after 1 hour for leakage.

NFPA 1991 vapor protective suits and totally encapsulating suits can be tested for air- tight integrity using ASTM F1052 Pressure Testing of Vapor-Protective Ensembles, where the suit is inflated and the pressure inside the suit is monitored for change. Non-encapsulating suits cannot be tested in this manner.

The quantitative means of testing vapor integrity is with the Man-In-Simulant Test

(MIST).40 The MIST consists of exposing human test subjects in CPC ensembles to a chemical simulant vapor- methyl salicylate- in controlled environmental conditions. The subjects don passive adsorbent samplers in predetermined locations on the skin underneath the ensemble.

The mass of simulant captured by each sampler during the test correlates to an exposure (Ct = product of concentration and time) that can be related to local and total body systemic exposure

limits of vesicant chemical warfare agents.41 The exposure values are weighted to reflect local sensitivities through a process called the Body Region Hazard Analysis (BRHA).

Lower protective NFPA Class 3 ensembles are tested against the same concentration as higher level ensembles but are allowed lower protection factors. Since the lower level ensembles are designed for lower concentrations, this implies that the test is independent of challenge concentration and primarily a challenge of the closures and interfaces – especially for air-impenetrable materials, which would not be expected to allow the simulant to permeate through the material within the test duration. An important related phenomenon to vapor protective testing is the bellows effect, where air may be pumped in and out of openings of a garment as a result of the motion of the user. The effect has been shown to be greatest for loosely fitting garments made of air-impenetrable materials.13

The lowest protection ensemble level property is particulate integrity. Particulate testing is performed in the same manner as the MIST, where a live subject enters a generated aerosol atmosphere, however the aerosol particles are a less mobile and intrusive challenge than a vapor. The extent of penetration is determined by visual assessment or quantitatively by measuring the deposition of fluorescent particles at various locations on the subject’s skin and undergarments.

2.4.3 Physical Testing

Physical testing is used as part of performance requirements and as preconditioning to some chemical test methods for CPC garment materials and components. A partial list of the physical requirements for materials used in NFPA standards includes130:

 Burst strength – ASTM D751 Standard Methods for Testing Coated Fabrics

 Breaking strength of seams and closures – tensile test in ASTM D751 Standard

Methods for Testing Coated Fabrics

 Puncture propagation tear resistance – ASTM D2582 Standard Test Method for

Puncture-Propagation Tear Resistance of Plastic Film and Thin Sheeting

 Garment abrasion preconditioning for chemical resistance test – ASTM D4157

Standard Test Method for Abrasion Resistance of Textile Fabrics (Oscillatory

Cylinder Method, “Wyzenbeek” machine).

 Garment flex fatigue preconditioning for chemical resistance test – ASTM F392

Standard Test Method for Flex Durability of Flexible Barrier Materials

(“Gelbo Flex” machine)

 Cold temperature performance – ASTM D1043 Standard Test method for

Stiffness of Plastics as Function of Temperature by Means of a Torsion Test

 Glove cut and puncture resistance

 Footwear Whole Shoe Flex- FIA 1209

 Footwear cover abrasion resistance – ASTM D3884 Standard Guide for

Abrasion Resistance of Textile Fabrics (rotary platform standard)

 Footwear traction, puncture, and bending resistance

 Overall ensemble fit and function – ASTM F1154 Standard Practice for

Qualitatively Evaluating the Comfort, Fit, Function, and Integrity of Chemical

Protective Ensembles

The performance criteria for these test methods have been chosen by the standards committees by collecting data on currently available commercial materials and selecting

conservative values for the highest level protection ensembles. Lower level performance values are chosen on the relative risk and expectations for garment durability and to ensure that the values do not preclude certain designs or materials that may be necessary to meet other ensemble requirements.130

Chapter 3. A Survey on the Use and Comfort of Chemical Protective Sock Liners 3.1 Introduction

Current users of low-level chemical protective clothing were interviewed and asked to respond to a survey on the design of the current Integrated Footwear System (IFS). The feedback was used to identify shortcomings in current equipment, identify relevant factors for the evaluation of CPC footwear, and inform the selection of candidate materials and designs for a redesigned sock liner.

Studies of chemical protective footwear in particular are typically focused on material level evaluations to judge potential use against specific challenge chemicals. 131,132 This survey of comfort and ergonomic issues, and the comfort evaluations presented in the following chapter, seek to contribute to the body of literature related to the comfort and ergonomics of chemical protective footwear.

3.2 User Input Survey

3.2.1 Survey

The survey featured open ended and multiple choice questions to collect information on the participants experience and use patterns with the IFS, including their typical duration of wear and adjoining equipment use. Non-forced, ordinal scale rating questions were used to assess participants’ attitudes on the comfort, fit, design, and durability of the current IFS.

Participants were asked to rate the level to which they agreed with various statements regarding the liner. Finally, participants were asked to respond about the type of discomfort caused by their liners and footwear. The modes and overall distributions of the responses were examined.

3.2.2 Participants

The following users participated in the survey: Sixteen (16) members of a federal law enforcement (FED) group; Six (6) members of a military (DOD) unit; and Fourteen (14) members of a state law enforcement (SLE) group. A total of thirty-five (35) individuals responded to the questionnaire.

Multiple pairs of the current IFS were provided for users to don during the feedback session. A copy of the surveys provided to end-users is in Appendix A.

The DOD members are current users of the IFS sock liner as part of the Army’s UIPE ensemble. The State and Federal members are current users of the LION MT-94® suit, which contains an integrated sock liner similar in material and construction to the IFS. Responses and discussion points are summarized below. While some differences did exist in use patterns and overall impression of the liner, the responses across the three groups were consistent and similar issues were brought up in all three group discussions.

3.2.3 Experience and Use

Nearly all of the frequency and duration ranges were reported, indicating that the liner is used in a variety of different ways by end-user groups. The most common response was to use the liner 6-10 times a year or less and for fewer than 2 hours (Figure 19-Figure 21). One user did report wearing the liner in training over 50 times a year. He reported wearing it with no additional sock, no blister incidence and no signs of deterioration.

Times per Year Worn in Training 12

8 4 3 6 2

Responses 4 6 6 4 2 4 1 1 1 0 0-2 3-5 6-10 11-50 >50

Figure 19. Number of times per year the liners are worn in training.

Times per Year Worn in Operation

15 11

10 Responses 4 5 2 1 5 1 3 3 1 0 1 0 0-2 3-5 6-10 11-50 >50

Figure 20. Number of times per year the liners are worn in operation.

Typical Duration of Wear 16 14 12 10 8 6 8 6 Responses 1 4 4 7 5 2 3 1 0 0 to 2 2 to 5 5 to 8 8 to 12 Hours

Figure 21. The typical duration of wear of the liners.

3.2.4 Socks and Footwear

The use of footwear and socks is reported in Figure 22-Figure 24.

A majority (30/35) of members reported wearing a sock under the sock liner, but no users reported wearing a sock over. There were differences in the footwear and socks worn by each group:

FED users reported wearing Tingley® Hazproof boots (9/12), Merrell hiking shoes

(3/12), and Globe boots (2/12). The group also reported more use of “hiking socks.” Some indicated that these were wool and some indicated that they were synthetic.

DOD reported wearing a light ¾ height hiking boot of their own choice (6/6) and occasionally combat boots (2/6). In the group discussion they reported that taller boots do not interface well with their ensemble. DOD primarily reported wearing “athletic socks” or “cotton socks.”

SLE reported wearing leather duty boots (14/14), mentioning brands such as Oakley,

Danner, and 5.11 and reported occasionally wearing rubber over-boots (5/14). SLE largely reported wearing cotton “tube socks” or “athletic socks”.

Footwear 20 18 16 14 12 14 10 8 Responses 6 6 4 9 2 2 5 2 2 2 0 Duty Boot Light Hiker Tingley Boot Globe Rubber Overboot

Figure 22. Footwear worn by end-users with the CPC liners

Additional Socks Worn 16 14 12 10 9 8 4 1

Responses 6 4 1 3 2 1 6 2 3 3 3 0 0 No socks Boot Sock Athletic Sock Tube Sock Sock over

Figure 23. Type of socks worn with the CPC liners

Change Size When Wearing the Liner 25

20 7

15 5

10 Responses

5 11 4 1 3 3 0 No Increase 1 size Increase 1/2 size

Figure 24. Reported change in footwear size with wearing a CPC liner

3.2.5 Durability and Performance

The users’ impressions of durability and protection were positive, though a large number reported being “unable to judge” such attributes Figure 25-Figure 28.

Have you observed any visible deterioration? 35 32 30 25 20 15 Responses 10 5 0 0 Yes No

Figure 25. User observations of deterioration of the IFS

"The IFS has excellent durability." 20 18

10 9 Responses 5 4 2 0 0 0 Strongly Disagree Neither Agree Strongly Unable to Disagree agree judge

Figure 26. User impression of the durability of the IFS

"The IFS provides excellent protection." 20 18

15 14

10 Responses 5 2 0 0 0 0 Strongly Disagree Neither Agree Strongly Unable to Disagree agree Judge

Figure 27. User impression of protection of the IFS

"The IFS meets the needs of my job" 20 16 15 11

10 Responses 5 3 2 1 0 0 Strongly Disagree Neither Agree Strongly Unable to Disagree agree Judge

Figure 28. User impression of suitability of the IFS

3.2.6 Comfort, Fit, and Design

Responses regarding comfort were less positive (Figure 29-Figure 35). One-third

(11/33) of the users reported sore skin or blisters while wearing the current IFS liner. A large portion (13/33) of those who did not experience sore skin were in the FED group. The most widely reported source of discomfort was from bunching of the materials, especially in the toes. This was reported to be aggravated by sweat pooling inside the liner.

Have you experienced any blisters or skin sores? 30 25

20 9 15 2

Responses 10 5 13 5 4 0 2 Yes No

Figure 29. Self-reported blister occurrence while wearing the IFS

Indicate where the blisters or sore skin occurs. 10 9

8 7

6 4 4

2 1

0 Toes Heel Ball of foot Top of foot

Figure 30. Location of blisters while wearing the IFS

"The IFS fits well." 14 13 12 10 8 8 7

6 Responses 4 2 2 1 0 Strongly Disagree Neither Agree Strongly agree Disagree

Figure 31. User impression of the fits of the IFS

"The IFS is comfortable." 14 12 11 10 10 8 6

6 Responses 4 3 2 1 0 Strongly Disagree Neither Agree Strongly agree Disagree

Figure 32. User impression of the comfort of the IFS

"The IFS is easy to put on and take off." 25 20 20

10 Responses 5 6 5 0 0 0 Strongly Disagree Neither Agree Strongly agree Disagree

Figure 33. User impression of the donning/doffing ease of the IFS

"Have you experienced any of the following issues?" 30 25 25

13 Responses 10 9 9 8 4 5 3 3 1 0 Bunching Excessive Irritation Selecting Excessive Selecting Hindered Issues with None of sweating the proper heat the propermovement the the above boot size size inferace

Figure 34. Reported issues while wearing the IFS

Figure 35. Most commonly reported location for irritation in the IFS

3.2.7 Group Discussions

These additional issues and suggestions were brought up in each of the response groups:

 Excess material bunches in the boot

 Sensation of slipping

 Sweat pools in the sock and boot – contributes to the foot sliding inside the liner

and the liner sliding inside the boot (contributes to toe pain)

 Locations of the seams cause the most discomfort

 Size ranges are too broad and design is too baggy

 Smallest size of IFS liner is too large for smallest females (FED group)

 Cuff slides down. Possible to add hook-and-loop attachment or grip lining.

All of the groups reported that the liners were considered single use items in exposure situations, though liners were reused for training. One user suggested this type of liner could be used as an under-bootie in Level A suits, as a protective layer for decontamination procedures. The DOD group expressed an interest in a liner designed with less durability if it was able to increase comfort. The SLE group expressed a desire to maintain durability. When the possibility of an oversock was mentioned to compress excessive material, a group member suggested that adding items to an ensemble increases the complexity and thus the chances of improper use. The FED group and DOD group expressed a strong interest in the addition of a grippy texture to prevent the foot from sliding inside the shoe. The SLE group disagreed with this addition if it were to make it more difficult to don and doff the liner. This is likely a result of the primary footwear of each group. The SLE group wears duty boots, which fit tightly

around the ankle and are less likely to have the liners slide down, while the FED group reported wearing looser firefighter or rubber chemical protective boots.

3.3 Conclusions

In summary, end-users of the current IFS liner and similar CPC sock liners wear such liners with a range of footwear options. This represents a unique need in contrast to industrial workers, who may only wear conventional CPC footwear. The footwear liners are mostly viewed as single use items in operational use; however, they can be used many times a year in training activities. End-users consistently viewed current options as durable and protective; however, there were significant negative attitudes towards the fit and comfort of their footwear liners. Bunching, irritation, sweat accumulation, and difficulty in sizing were the most common complaints. The issue of excess material appears to be related to some of the other responses.

The end of the toe was the most commonly reported area of discomfort. The collaborative nature of the survey helped develop additional design requirements and focus areas for the prototype liner.

Chapter 4. The Design Process and the Evaluation of Fit of a Chemical Protective Sock Liner 4.1 Introduction

A chemical protective sock liner was designed and compared to the current Integrated

Footwear System (IFS) for differences in fit and ergonomics. The new liner was designed using a stretch material to address issues in fit and sizing. Multiple candidate designs were compared and an experiential wear trial was performed with two prototypes to down select a design.

4.1.1 Functional Design Process

The functional design process for clothing has been defined by Watson as a process featuring the following 7 steps133: 1) A design request is made and a problem or need is identified. 2) The design situation is explored. In this step, factors that contribute to the problem are identified, users are interviewed, literature is surveyed, and a definition of the problem is formulated. 3) The problem structure is perceived. This is a data gathering step, where measurements of the activities, movements, impacts, or other factors are made to inform the specifications. 4) The specifications are described. In this step, suggested resolutions are described to address the issues. 5) In step five, the design criteria are established. This step may involve additional tools for making design decisions, such as formulating an interaction matrix between conflicting designs, identifying design priorities, and identifying the necessary specifications. 6) The prototype is developed and initial testing is conducted to ensure design criteria are met. 7) Finally, the prototype undergoes design evaluation. This stage involves objective and subjective data gathering of the prototype performance through wear trials.

This functional design process is scalable; it can be used broadly for the design of entire clothing systems, or it can be applied to incremental changes in clothing components. It is essentially a mixed methods research approach that explicitly addresses the complexity of incorporating human factors into design research: the user is central to the initial step and throughout the process. A typical research question formulated from this process may be in the following format: How does a particular design change affect the functionality or user acceptance of a clothing item?

In this research, the problem of footwear comfort in chemical protective clothing ensembles was stated by end-users in the Chapter 3 survey. The Chapter 2 literature review and Chapter 3 survey provide context for the project structure. This chapter provides the design criteria and the suggestion that the use of a stretch material can address the design issues, namely fit and sizing issues.

4.1.2 Sock Liners

There are several commercial and patented products with a similar design to the current

IFS. Laminates are incorporated into footwear to impart waterproofness. Attached liners are typically sewn into the footwear, between the outer and a cushioned interior material. Separate waterproof sock products (not intended to provide chemical protection) also exist for military and outdoor use, most of which are Gore-Tex® branded products, as seen in Figure 36. Several of the liners specify the use of stretchable materials.

The sizing and fit of a sock liner influence the amount of excess material around the foot and may impact the flexibility of the user’s foot and ankle. In the previous section, based on end-user survey responses, excess material and inhibited motion contribute to the overall

comfort of a sock liner and may be correlated with injury occurrence such as blistering. Thus, the goal of the design of the new liner is to utilize a material and design that can minimize the excess material around the foot and inside the footwear.

Gore-Tex® military Rocky ® Gore-Tex ® Klim® Gore-Tex ® waterproof boot-liners waterproof socks, with stretch sock liners, for upper panels. motorcyclists, with stretch back panel. Figure 36. Three examples of waterproof sock liners

4.1.3 Design Requirements

A separable design is required to allow users to wear the liner with a variety of footwear, and a chemical protective material is required to meet the protection requirements.

Additional design requirements included making a sock liner that has end-user preference over the current IFS, was available in sizes to fit the 5th to 95th percentile of participants, that has minimal problematic interaction with current end-user footwear and equipment, and that has a useable lifetime of 48 hours while maintaining NFPA 1994 Class 3 protection requirements.

4.2 Experimental

4.2.1 Liner Materials, Construction, and Initial Designs

The control liner is the current Integrated Footwear System (IFS). The liner is constructed from Gore® Chempak® barrier film with a Nomex® knit face and backing fabric.

The liner is available in S, M, L, and XL sizes. An image of a properly sized and donned IFS is shown in Figure 37. The liner is symmetrically constructed from a single piece of fabric joined by three seams. One seam runs down the rear midline length of the liner and terminates at the heel. Another seam runs down the front midline of the liner and terminates at a T-seam with the third seam, which runs horizontally across the front of the toes. The seams have an adhesive barrier seam tape laminated to the exterior of the seams.

The candidate fabric, Gore® Chempak Stretch®, was chosen because of its stretchability and because it has been previously shown to meet NFPA 1994 Class 3 protection requirements. It consists of a barrier film laminated to a thin, extensible knit backing and no face fabric. In its resting form, the film is pleated in one direction. Upon extension perpendicular to the pleats, the film flattens, the knit extends, and the width of the material can increase by approximately 100%.

The design process for the prototype liners involved an initial set of 6 candidate designs, two down-select phases, and a subsequent iterative modification process through the course of multiple wear trials and field evaluations. All prototypes were constructed by LION

Apparel, INC. of Dayton, Ohio. The stretch liner seams have an adhesive barrier seam tape laminated to the exterior of the sewn seams.

A comparison of the IFS and the prototype liner material thickness and liner mass is presented in Table 7. The prototype stretch material is thicker than the IFS in its unstretched form, and upon extension they become similar in thickness. However, the finished seams on a prototype liner are significantly thicker than the IFS. The Chempak Stretch® liners do not feature a textile face fabric. To ensure the protective performance of the material, all prototype liners were paired with a thin black polypropylene sock (Catawba Sox, style 8119) to wear as an oversock for all end-user evaluations.

The oversock material would increase the total material thickness slightly over the IFS.

This impacts the total mass of the liner – resulting in an extra 28 grams (~1 oz.) per pair. A side-by-side image of the IFS and the final stretch liner design is presented in Figure 37.

Table 7. Comparison between the IFS and prototype liner material thickness and mass of assemble liners

Property IFS Prototype Un-stretched Stretched – 100% extended 17 Material Thickness, mil 38 17

Un-stretched Seam thickness, mil 64 80

Oversock thickness, mil N/A 58

Liner Size Size XL Size 11 Size 12 Size 13 Liner mass, g 56 53 53 53 Oversock, g N/A 17 Total, g 56 70 70 70

Figure 37. The current IFS (left) and the prototype liner without the oversock (right)

4.2.2 Subjective Evaluation Methods

The following subjective evaluation was focused on gathering information on the sizing of the liners and comparative impressions on two prototype sock liner designs. A set of experiential focus groups were planned to present the prototype liners to four end-user groups for evaluation regarding sizing, fit, and usability. The following users participated: seven (7) members of a federal law enforcement (FED) group; ten (10) members of a homeland security group (DHS); and ten (10) members of two additional military groups (DOD).

Two (2) pairs of each liner were manufactured in whole sizes from men’s 6 to 14, providing a total of thirty-six (36) pairs. The sock information labels were placed on the rear of the sock, sewn into the cuff seam.

In the focus groups, participants were split into two groups. One half was asked to try on style A first and the other half was asked to try on style B first. Both groups were instructed to try on up to 5 sizes of each liner: their stated shoe size plus 2 sizes up and 2 sizes down from their stated shoe size. Participants were instructed to don each liner pair over their normal socks, followed by the black oversock and their own footwear, then asked to do a minimum of the following activity: walk the length of the room, jump, squat down, and perform any additional activity that would help them judge the comfort of the liners. After donning each pair they were instructed to fill out a half page questionnaire, seen in Figure 38. A cover sheet was also provided to each participant to collect information on their shoe size, the type of footwear they were wearing, and a description of their activities.

Figure 38. Experiential Focus Group questionnaire used for each pair of liners

For each style and in each size, participants were asked to assign a rating from 1 to 5 for multiple fit and comfort attributes (length, width, fit in toes, fit in heel, fit around calf, ease of donning/doffing, material bunching, and slippage). The rating was associated with a range from loose to tight or from unacceptable to ideal, depending on the attribute. The data was normalized based on the respondent’s shoe size, such that users with different shoe sizes could be compared directly. As an example a participant with a size 10 shoe trying on liner A size

10 would be grouped with a participant with a size 12 shoe trying on liner A size 12. In both examples that data would be referred to as liner A0, style A in the participants shoe size. If the liner worn was a size up from their reported shoe size it would be reported as A+1.

Matched Pairs analysis was performed on the data to identify differences between style

A and B and determine if the responses for each attribute reflect a statistically significant preferences between A and B or only variation associated with sampling. The significance level was set to 0.05. Determination of preferences and central tendencies were performed using the non-parametric Wilcoxon Sign-Rank Test, mean, and mode analysis. The non- parametric test, which represents the overall positive or negative difference between responses of the participants’ ranking of each attribute of the two styles, was used because the data could not be assumed to be normally distributed. Data was also evaluated to assess the impact of sizing and to see what size range was comfortable for users. Data was processed using

Microsoft Excel® and JMP Pro 12 by SAS®. All testing plans involving data collection from human subjects were reviewed and approved by the NC State University Institutional Review

Board for Ethics review.

4.3 Results

4.3.1 Prototype Design Process

The first design goals, based on the user input survey, were to decrease bunching, irritation, and sizing issues. It was hypothesized that an extensible material such as the Gore®

Chempak Stretch® would reduce material bunching and address sizing range issues. The source of irritation was reported by end-users to be both due to the excessive material in the liner and the placement of the seams. A series of six candidate designs were formulated with differences in the seam placement and orientation of the fabric. These designs are shown in

Figure 39.

Figure 39. Six candidate designs developed by LION

The designs were assessed by project members based on the properties of ease of manufacture, cost, and expected comfort and fit. The following assessments were made on the six designs:

1. Approved. Seam movement predicted to improve comfort.

2. Concern about the stretch being affected by the seam placement on top of foot.

3. Manufacturing concern about the seam wrapping around.

4. Difficult to manufacture seam around heel.

5. Difficult to manufacture seam around toe.

6. Approved. Single piece construction easier to manufacture.

From the six designs, two were chosen for prototypes. Style 1 was chosen to offer a design with no seam at the end of the toe; it was named Style B in future focus groups. Style 6 was chosen for its simple patterning, cut from a single piece of fabric. It was altered slightly to remove the seam that traveled under the entire length of the foot. This was named Style A in future focus groups. Style A and B are pictured from two angles in Figure 40.

Figure 40. Styles A (on left in each picture) and B (on right in each picture) with arrows indicating the direction of the material stretch

The internal volume of the two styles and the IFS were measured by filling the liners with a lightweight granular material and a higher density liquid. The liners were weighed and the volume was calculated based on the density of the filler material. The results and images

are presented in Table 8. The results indicate both stretch liners have a significantly lower volume but can increase volume when the material stretches. Both stretch liners have less excess material and that their shape can adjust to fit different volumes. Liner style B appears to retain a more natural foot shape when the material stretches.

Table 8. Volume measurements of the A, B, and IFS liners

Volume (mL) as measured with the Liner- low and high density medium Image Size (low/high, average of 3 measurements)

A-12 2400/3270

B-12 2079/2927

IFS-M 4238/4360

4.3.2 Experiential Focus Groups

With the data from all three session grouped together, no statistically significant differences were found between the ratings of each attribute, neither with the data grouped across all sizes nor when the data was separated by the normalized size (-2, -1, 0, +1, +2).

However, when the data was considered within each user group some attributes did appear to be significant.

Within the FED group the responses for ease of donning was significantly more favorable for B than for A (p = 0.03, n =27). The FED group reported a more optimal fit (closer to 3) overall in the heel for style B versus A (p = 0.03, n =27) indicating style A was tighter fitting overall. However on increasing in size of the liner, style B was generally reported to be looser in the heel. Style B was also reported by the FED group more favorably in regards to slippage inside the shoe versus A (p = 0.04, n =27).

Contradictory results were seen in the fit of the length. The DHS group reported a more optimal length for style A versus B (p= 0.05, n =33), conversely the FED group reported for style A versus B (p = 0.09, n = 27).

The two additional DOD groups were the smallest of the groups and they did not fill out their surveys for the entire size range, providing limited data to measure significance.

However in the final question to compare the styles, the majority stated a preference for style

Participants were asked to list their top 3 preferred liners in order. That data for all respondents in the three user groups is tallied in Table 9. Liner B accounts for a majority of the responses and liner B0 was the most commonly listed liner.

Table 9. Summary of liner preference ratings

RANKING 1ST 2ND 3RD SUM OCCURRENCE B-1 1 2 1 4 B0 4 2 3 9 B1 3 4 1 8 B2 1 3 0 4

A-1 1 0 1 2 A0 1 1 2 4 A1 3 1 2 6 A2 0 1 2 3

Discussion Groups

Comments provided by the end-users suggested the following:

 Style B was listed more often among the preferred styles, though it was more likely to be describing as bunching  Style A appears to fit more snuggly than style B  The black oversock had positive comments  Favorable responses were reported for both Style A and B across three whole sizes (0, +1, and +2 from the users’ original shoe size) indicating range sizes could be used. However a majority of users were not able to don liners sized two whole sizes down from their typical footwear size, indicating restrictions with the current design.  Both styles were improvements over the original IFS

Overall, the data provides some indication that attributes of liner B were more desirable than liner A. The preference can be explained by the design difference between A and B. Figure

40 (page 88) indicates the direction of stretch at multiple points on both liners. The material exhibits unidirectional stretch, though it is important to note that the seams do not stretch at all

and flexibility decreases near the seams. Liner B has a more flexible cuff and a more flexibility at the end of the toe, likely accommodating a wider range of foot sizes and shapes.

4.3.3 Down-selection and Design Alterations

As a result of these focus groups, liner B was down-selected for further exploration, with alterations to the design. The top of the side panel was widened at the ankle to make the opening more flexible. This was done to address the heel getting stuck in the ankle of the sock during donning. The ankle was also made slightly higher based on the height of the combat footwear calf. Meanwhile the curvature of the size seam was made more pronounced with the intent of removing excessive material between the side seam and the heel and reducing bunching inside the footwear (see Figure 41).

Figure 41 . Alterations made to liner B pattern following the experiential focus groups

4.4 Discussion

The initial results from the design process, subjective evaluation, and quantitative assessment indicate that the use of stretch material was able to both reduce the amount of bunched material in the footwear and expand the size ranges of the liners. Further analysis could be focused on quantifying the extent of this improvement. Examples include applying digital scanning technology to measure the surface areas of the designs or studying the relationship between the patterning and orientation of the fabric and the potential changes in volume as the liner is stretched. This could be combined with anthropometric data on foot sizes

and shapes to optimize the design. A full factor sizing study could be performed, where participants don a wide range of liner sizes in combination with quantitative fit evaluations to validate the sizing scales and inform procurement procedures.

The third survey was a comfort evaluation directly comparing the prototype sock liner and the currently available Integrated Footwear System (IFS) liner. The fourth survey was a field evaluation of the prototype sock liner to collect feedback regarding its integration with a variety of end-user ensembles and operational activities. The third and fourth survey will be discussed in the next chapter.

Chapter 5. The Evaluation of the Comfort of a Chemical Protective Sock Liner 5.1 Introduction

The new liner design was assessed in a comfort wear trial to see if the improved fit afforded by the use of a stretch material resulted in improved comfort and user acceptance.

Comfort attributes were measured through subjective data gathered through a wear trial and survey. The findings regarding fit, thermal, and moisture comfort were analyzed in regard to what could be measured quantitatively through material level tests. The operational fitness of the liner was assessed by providing prototype liners to end-users for field evaluations.

5.2 Comfort Evaluations

5.2.1 Experimental

An evaluation was performed to determine comfort, ergonomics, fit, and functional differences between the prototype liner system made with a stretch material and the current

Integrated Footwear System (IFS). HazMat certified firefighters attended three separate evaluation sessions. Each session, a different footwear type was worn: low-profile athletic shoe, combat boot, or firefighter boot. In each session the participants repeated the same task sequence twice, once with the prototype liner and once with the IFS liner. A set of structured tasks was developed to reflect the challenges placed on footwear worn during first responder and military operational tasks and to simulate a range of motions. Participants responded to two questionnaires: one on the comfort properties of each liner worn and a direct comparison survey of the two liner systems.

Subjective data was gathered through the use of surveys and interviews with prospective end-users of the product. Written prompts, visual prompts, and observations of the users interacting with the product were used to collect qualitative information and opinions from participants. Quantitative evaluations of comfort properties and end-users attitudes were gathered using ranking surveys and 5-point interval scale surveys where participants were asked to assess the magnitude of a property or their level of agreement with a statement. All surveys were non-forced preference, meaning the participants could choose a neutral,

“neither”, or an “unable to judge” option if they wished. Determination of preferences and central tendencies were performed using the non-parametric Wilcoxon Sign-Rank Test, mean, and mode analysis. Data was processed using Microsoft Excel® and JMP Pro 12 by SAS®.

All testing plans involving data collection from human subjects were reviewed and approved by the NC State University Institutional Review Board.

Participants and Materials

Three footwear types were used during the comfort and durability evaluations to represent different end-user groups (Figure 42). A common cotton athletic sock was worn under the liners (UnderArmour®). The footwear types are: LION® Commander (12” FR boot with hard toe and side zip); Belleville ® Combat Boot (8” leather boot); and Salomon XA PRO

Mid (ankle-height athletic shoe commonly used by end-users).

Figure 42. Footwear used in comfort evaluations, from left to right: low profile (Salomon® XA Pro MID); combat (Bellville® Combat); firefighter (LION® Commander)

The low-profile options is representative of law-enforcement, military, and some first responder applications. The combat boot is representative of law-enforcement and military users. The firefighter boot is representative of fire and emergency response users.

All reported number of steps taken by participants in wear trials were measured using pedometers (Fibit Zip® by Fitbit, Inc.). Environmental conditions reported during wear trials were monitored using Kestrel® 5000 series Weather and Environmental Meters.

Fourteen pairs of each liner were procured from LION. The IFS liner only comes in range sizes (S, M, L, XL) while the prototype liners are sized along standard whole-number shoe sizes. Once again, the stretch liners were worn with the black polypropylene oversock

(see Figure 43).

Figure 43. Stretch liner and black oversock

Twelve firefighters (11 Male, 1 Female) (shoe size range men’s 8 – 13) from the City of Raleigh or Wake County fire departments were recruited, with a preference towards those with experience with HazMat response and chemical protective clothing. All participants were supplied with paperwork for informed consent and signed photograph release forms. Each participant was assigned to one pair of stretch and IFS liners. Each session, shoes were provided that best fit their reported shoe size. One extra liner pair (identified as “P5”) was worn by a test coordinator in three sessions, though subjective feedback was not gathered. The P2 position was not filled due to no subject with the correct shoe size being available.

Table 10. Comfort Trial Participant Sizing

Participant Shoe Size Stretch Size IFS Size ID P1 8 8 S P2* 8 8 S P3 9 9 M P4 9.5 9 M P5** 10 10 M P6 10.5 10 M P7 11 11 L P8 11.5 11 L P9 11.5 11 L P10 12 11 L P11 12 12 L P12 12.5 12 L P13 12.5 13 XL P14 13 13 XL *No subject was assigned this pair of liners **This pair of liners worn by test coordinator for only durability assessments

th rd Six sessions were held between July 14 and 23 , 2015. Participants attended three sessions each. Each session consisted of two identical rounds of activities, performed while wearing the same footwear type but different liner types. An example participant schedule is scene in Table 11. Footwear and liner order was randomized to reduce systematic bias from the day and order of the sessions. Participants were not informed which liner was the prototype and were asked to consider each liner on its own before making direct comparisons. The liners were referred to as “stretch” and “non-stretch”. Participants wore breathable athletic attire of their choice. An electronic pedometer (Fibit Zip® by Fitbit, Inc.) worn on each participant’s waist tracked the total number of steps taken during the sessions. Clean athletic socks were

provided at the start of each round. Following wear, both sides of the liners were submerged in water, wiped with a wet cloth, turned inside-out, and allowed to dry overnight.

Table 11. Example Participant Schedule

Wear Trial Conditions

The session protocol can be seen in Table 12. The walking portion took place along a mostly shaded 1.25 mile course over a variety of terrain. Tasks were conducted under a covered exterior breezeway. Images of the tasks can be seen in Appendix C. Average environmental conditions were 25.5 ± 5°C, 68.2 ± 20%RH for Round 1 and 26.5 ± 5°C, 67.1 ± 20%RH. The average condition change within a session from Round 1 to Round 2 was + 1.3 °C and - 1.3

%RH. One exception was the final session (July 23rd) where precipitation began as the participants were starting the task portion of Round 2. The humidity increased sharply. Some surfaces became slippery and the barrel roll task was removed and replaced with an extended zig-zag course. The duration of the session was not affected. The questionnaires were filled out during a 20 minute rest session in a climate controlled room.

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Table 12. Comfort Evaluation Session Task Protocol

On average, the participants took 3,387 ± 500 steps during each round. Thus, each

3387×3 stretch liner in a pair, worn for 3 sessions, was subjected to = 5,080 steps in total. 2

Questionnaires and Assessments

After each round, participants were asked to rate the liner they had just worn on a 5 point scale for the following 11 comfort and ergonomic properties:

 Ease of donning  Impression of durability  Ease of doffing  Material bunching  Fit at the end of toes  Sensation of heat  Fit on top of toes  Sensation of slipping inside the footwear  Fit in heel  Overall comfort  Fit around calf

The responses were converted to numerical values from 1 to 5 (5 being the most favorable). At the end of the sessions the participants were given a Comparative Questionnaire

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and asked to select their preference between the two liners for those same properties. The complete questionnaire is provided in Appendix A.

Visual assessments and photographs of each stretch liner were taken before and after every session from multiple angles and during the cleaning step to monitor the durability liners.

These results are reported in the next chapter on the durability study of the liner.

5.2.2 Results

The comfort property responses for the two liner types were converted to numerical values and compared using the Wilcoxon signed-rank test (α < 0.05). Interval scaled subjective data of this nature has been evaluated using continuous data statistical analysis with assumptions of normality73, so for comparison the Student’s paired t-test (α=0.05) was also used to investigate differences in central tendencies of the responses. The two tests gave similar results of significance. The influence of footwear type and the order in which the liner were worn were also investigated.

The mean responses are summarized in Table 13. The stretch liner had higher mean responses (more favorable) than the IFS for all properties in all footwear types except for the ease of donning and doffing. These differences were found to be significant for the following properties:

 Fit at end of toes  Sensation of heat  Fit on top of toes  Sensation of slipping  Fit around calf  Overall comfort  Material bunching

The largest difference in means was found for the sensation of slipping inside the footwear. This property was emphasized as a downside of the IFS by all the focus groups

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initially surveyed for this project and thus is an important improvement. Also, according to the paired t-test, the mean values for “overall comfort” and “sensation of heat” were significantly lower (less favorable) during the sessions in which the firefighter boot was worn compared to each of the other footwear types indicating an influence of footwear type. This is supported by the comments provided by the participants as well. The firefighter boots are loosely fitting, more insulated, and stiffer.

Statistical analysis comparing values based on the order in which the liners were worn within a session showed no significant influence on responses.

Table 13. Mean Response Values - All Footwear Types

Property Non-Stretch Stretch

Ease of donning 4.4 4.4 Ease of doffing 4.4 4.4

Fit at end of toes 3.3 3.9** Fit on top of toes 3.4 4.0* Fit in heel 3.7 4.0 Fit around calf 3.5 4.0** Impression of durability 3.8 3.9

Material bunching 3.2 3.7* Sensation of heat 3.0 3.4** Sensation of slipping 3.4 4.2** Overall comfort 3.6 4.1** **Significance in paired-t test and Wilcoxon signed-rank test; * Significance in paired-t test only

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Comparative Questionnaire

The comparative questionnaire, filled out at the end of each session, prompted subjects to choose which liner they preferred for each of the 11 comfort and ergonomic properties. They were also allowed to select “no preference”. The comparative questionnaire results show a consistent preference for the stretch liner. The stretch liner was chosen more often as the preferred option for all comfort properties in each footwear type with the following exceptions:

 Donning/doffing ease  Fit around calf  Impression of durability o “No preference” was more likely to be chosen  Sensation of heat in the firefighter boot o The non-stretch liner was more likely to be preferred Those properties – don/doff, calf fit, and impression of durability – that had a high frequency of “no preference” responses are less associated with comfort and less distinguishable features of the liners. Both liners had favorable responses regarding donning and doffing and many participants stated they were not able to judge the durability of the liners.

A summary of all the responses are presented in Figure 44. All of the response data is listed in tables in Appendix B. Two of the participants did not properly fill out the comparative questionnaire while wearing the low-profile footwear; their data was not included, therefore

22 fewer statements of preference are present in the low-profile data.

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Preferred Liner – All Properties Combined

No Preference Non-Stretch Stretch 70 62 60 58 52 50 42 39 41 40

30 28 28 24

Number of Responses of Number 20

0 Combat Fire Fighter Low Profile

Figure 44. The frequency of liner preference - all properties combined

Written Responses

In the written responses and discussions, individual comments on fit and comfort varied widely by footwear and liner. Both liners were reported to cause bunching and slippage and both liners were also reported at some point as comfortable. Some opinions were shared consistently by participants. These included:

 Shoe size and footwear type was a significant influencing factor- tight fitting footwear was more likely to affect the comfort of the liners  The cuff on both liners was not high enough for the fire-fighter boot and caused the liners to slide down  Most participants saw the black oversock in the prototype system as an inconvenience and said they would be inclined to discard it

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5.2.3 Discussion

The stretch prototype presents an improvement in comfort and fit over the current IFS.

It was preferred by the majority of participants for all comfort properties investigated, except for ease of donning and doffing, which was not significantly different. The prototype liner was reported to have significantly less noticeable sensation of slipping inside the footwear – a property highlighted as desirable by previous feedback groups. Footwear type appears to be an influencing factor on perceived comfort of the liners. Low-profile, more tightly fitting shoe increased differentiation between liners and caused the prototype liner to be preferred more often, thus the prototype may present more benefit to users who wear such footwear. The more favorable responses for the stretch liner indicate that the use of a stretch fabric and redesigned pattern may have reduced pressure inside the footwear cause by excessive material and seam placement. The overall results indicate higher use acceptance.

5.3 Field Evaluations

The prototype liner was provided to two user groups to evaluate in training activities.

Twenty pairs of liners were manufactured by LION for each group in unisex sizes 10, 11, 12, and 13 (5 pairs of each size). The users were asked to wear the liners during typical training activities using their own equipment, footwear, and athletic socks, then provided with a questionnaire to collect their impression of the liner’s comfort properties. These questionnaires were identical to the ones used in the previous comfort evaluations with slight alterations to the initial general questions about footwear (See Appendix A). The following user groups participated: a state law enforcement group (Group 1) and a fire/rescue group (Group 2).

5.3.1 Experimental

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Group 1 Participants and Activities

Thirteen (13) participants (12 males, 1 female) wore the stretch liner and provided feedback on the questionnaires. The participants wore the liners for 2 to 4 hours in the afternoon at a shooting range during activities that consisted of walking, kneeling, and firing weapons. The terrain consisted of concrete and rocky sand. The weather conditions were mostly sunny. The self-reported shoe size, footwear type, sock type, liner size worn, and duration of wear for each participant is presented in Table 14. Five (5) users elected to wear the liner without socks underneath. The footwear of the participants was most comparable to the combat boot used in the comfort evaluations and the “duty boot” described by the SLE group in the initial user input study.

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Table 14. Group 1 User Information

Footwear Shoe Size Time worn User Liner Size (as described by Socks (men’s) (hours) user) 1 5 10 Work Boot none 4 2 9 10 Oakley boot athletic 4 3 10 10 Boot dress sock 2 4 10.5 11 Danner boot athletic 4 5 10.5 11 5.11 boot none 2 6 10.5 11 Salomon boot none 3 7 11 11 Salomon boot wool hiking 4 8 11 11 Bates boot none 3 9 11.5 12 Boot athletic 2 10 12 12 5.11 boot athletic 2 11 12 12 Salomon low cut athletic 3.5 12 12 12 Danner boot athletic 4 13 14 13 Oakley boot none 3

Group 2 Participants and Activities

Eleven (11) participants (all male) wore the stretch liner and provided feedback on the questionnaires. Donning began at 10:30 a.m. The participants wore the liners for 45 minutes during a simulated exercise, which included operating a decontamination line on other participants and dummies. The participants wore powered air purifying respirators and Dupont

Tychem® CPF 3 ensembles which had been modified by cutting off the attached booties to accommodate the prototype liners. All participants wore Tingly HazProof® boots, which are

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oversized, rubber, steel-toe boots certified to NFPA 1991. The footwear was most comparable to the firefighter boot used in the comfort evaluations, however the fit appeared to be very loose. Donning, doffing, and the exercises took place on concrete surfaces. The concrete became wet during the activity. Conditions were sunny and moderate temperature.

The self-reported shoe size, footwear type, sock type, liner size they wore, and duration of wear for each participant is presented in Table 15. All the users wore normal socks underneath the liners.

Figure 45. Tingly HazProof® Boot

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Table 15. Group 2 User Information

User Shoe Size Liner Footwear Socks Time worn (men) Size Under (minutes) 1 9 10 Tingly HazProof® wool 45 2 10 10 Tingly HazProof® athletic 45 3 10 10 Tingly HazProof® athletic 45 4 10.5 10 Tingly HazProof® athletic 45 5 10.5 10 Tingly HazProof® athletic 45 6 10.5 11 Tingly HazProof® athletic 45 7 10.5 11 Tingly HazProof® athletic 45 8 11 11 Tingly HazProof® athletic 45 9 13 13 Tingly HazProof® athletic 45 10 14 13 Tingly HazProof® athletic 45

5.3.2 Results

The results of the field evaluation questionnaires showed similar means and variance to the results of the comfort evaluations. Due to the small number of participants there was no statistically significant difference in the responses between Group 1 and 2 results nor with the comfort evaluation results. However, the results were consistently positive in nature towards the IFS and some important observations were made by the end-users.

The lowest group 1 rating was for the fit at the end of the toes and material bunching.

Three participants responded that the material bunching was “very noticeable” or “excessive”

(scores of 2 and 1). One of those participants also rated fit at end of toes, fit in heel, and overall

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comfort with less than a 3 score. The other two respondents provided neutral or positive responses.

The group 1 participants were also asked for additional comments on the liner. These comments were collected:

Positive: “more comfortable than other liners,” “forgot I was wearing them,” “comfortable,” and “comfortable, not sticking”

Negative: “bunching under toes and at end of toes,” “had to remove my boot insert,” “a little tight,” “hotspots on end of toe,” “excessive bunching, discomfort around toes,” and “bunching at toes, should make designated left and right”

Three group 1 participants were familiar with the current IFS. Two of those participants said they preferred the stretch prototype and one participant said he had no preference. Three participants also responded to the question about additional CPC issues. All three said their biggest problem with current CPC was excessive bulk and heat.

The lowest group 2 rating was for the fit at the end of the toes and material bunching.

Two participants stated a neutral opinion of the overall comfort and one participant gave the liner all very low scores, however, that participant still selected the stretch liner as preferred over other liner types in the comparison survey. He did not leave any comments. It is possible he misinterpreted the rating system. All other participants had positive ratings of the overall comfort. The “material bunching” was the lowest rated attribute, with three unfavorable responses and two neutral responses.

The group 2 participants were also asked for additional comments on the liner. Five comments were collected. Three participants stated the liner was too short for his boot style or slid down during the activities:

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1. “Liner slipped below boot cuff” 2. “Boot rubbed back of calf, elastic cuff too loose” 3. “Socks too short” 4. “Bunching on top of foot” 5. “Bunching in heel”

One participant also responded to the question about additional CPC issues. He said that the Tingly HazProof® boots were too “bulky”. Eight group 2 (8) participants filled out the comparative questionnaire. None of them were familiar with the IFS so they were asked to compare the liner to their current HazMat booties. Only 6 stated an overall preference, and they were all for the stretch liner. Those responses are summarized in Table 16.

Table 16. Comparative Questionnaire Data for Group 2 (NY)

Stretch Neither Current Liner Ease of donning 7 1 0 Ease of doffing 7 1 0 Fit at end of Toes 7 1 0 Fit on top of toes 7 1 0 Fit in heel 6 2 0 Fit around calf 8 0 0 Impression of Durability 6 2 0 Material bunching 7 0 1 Sensation of heat 4 4 0 Sensation of slipping 8 0 0 Overall comfort 7 1 0 Preference 6 0 0 Total 74 13 1

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Field Evaluation Discussion

The survey results were consistent with the comfort evaluation in which users expressed an overall positive impression of the liner across all attributes with only a few users who expressed negative impressions of fit and comfort.

One important observation was that participants in both field evaluations performed their donning and doffing on rough outdoor terrain such as asphalt and concrete. This highlights the importance of the durability of the bootie material. Even it is meant to be worn inside a more protective boot, it may become damaged during the donning and decontamination process.

The other insight was that there are operational limitations to the separable bootie design, especially when interfacing with certain footwear styles. Several users from the NY group specifically complained that the liner was not tall enough and slid down inside their boots. These larger footwear are also sized to accommodate excessive material from high-level

CPC ensembles. This may actually make the form-fitting sock liner less comfortable if it is used as a drop in replacement by some user groups who have selected footwear based on the more bulky liners.

5.4 Measurement of Thermal and Moisture Properties of the Liners

In the comfort evaluation, differences were reported regarding the overall comfort, thermal comfort and sensation of slipping of the liners. To investigate this further, measurements of the thermal and moisture properties of the liners were performed.

The thermal properties of the liners were measured on a thermal sweating foot instrument (Thermetrics/Measurement Systems Northwest, Seattle, WA). In that test, an

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instrumented foot form was dressed in the same configuration used in the comfort evaluations.

Four configurations were used: the IFS and stretch liners with firefighter boot or combat boot.

The instrumented foot was maintained at a temperature of 35 °C and the power (W) required to maintain the temperature in an environment of 15°C / 50% RH with a 0.4 m/s wind speed was measured. The resulting steady-state power is an indication of the thermal resistance of the system. Those results are presented in Table 17.

Table 17. The dry thermal resistance of the liners in two different footwear configurations as measured by an instrumented manikin foot

Rct (m2*K/W)

IFS Stretch FF Boot 0.2972 0.2913 Combat Boot 0.2185 0.2185

As expected, the two liners were not significantly different in terms of the thermal resistance of the footwear configurations. The two liners are similar in thickness and are much thinner in relation to the sock and footwear upper materials. Thus, they should not contribute greatly to the overall thermal resistance around the foot. The difference in evaporative resistance of the membranes was similarly expected to be negligible since they are both fluoropolymer based membranes. Again, the footwear materials are much thicker and thus should contribute more to the overall thermal evaporative resistance. Instead of analyzing the liner in a sweating foot configuration, testing was performed on the Gravimetric Absorbency

Testing System (GATS) (TPACC, Raleigh, NC) to investigate the possible contribution of

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moisture absorption effects. The GATS test indicates the lateral wicking ability of the fabric, or the ability of the sample to take up liquid spontaneously in the direction perpendicular to its plane. Demand wettability is measured by placing material swatches on a porous wetting plate and measuring the amount of water drawn from a connected water-filled reservoir.

Table 18. GATS results of the two CPC liners and the base sock used in the comfort evaluations

----- Sample Identification ----- Absorption Properties Base Sock IFS Stretch

Wd: Dry Weight (g) 3.074 1.252 1.336 Ww: Wet Weight (g) 8.759 2.074 2.996 V: Water Displaced (g) 6.212 1.707 2.475 T: Absorption Time (min) 8.891 4.197 3.523 C: Absorbent Capacity (g)a 5.685 0.822 1.660 Q: Absorbency Rate (g/min)b 0.161 0.255 0.430 Em: Evaporated Mass (g) 0.527 0.885 0.815 c Ep: Evaporation (%) 8.574 51.795 32.619

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Figure 46. Average absorption behavior of the (A) base layer sock, (B) IFS, and (C) stretch liner

The GATS testing revealed that the overall uptake demand curve of the two liners is similar in shape, but that the stretch sock has twice the absorptive capacity as the current IFS material, likely due to its knit backing (Table 18 and Figure 46). The base layer sock used in all the wear trials, however, reached an absorption capacity more than 5 times greater than the

IFS in the test period.

It has been proposed that that the humidity and moisture properties of boot liners influence the perception of thermal comfort80 and that skin hydration is an influencing factor in blister formation.134 As context to the GATS data, a research study on the regional sweating rates of feet found an average estimated discharge rate of 27.6 mL/h per foot, across all their participants during rest and exercise.135 A separate study on sweating foot measurements taken

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with different configurations of leather boots found that footwear with waterproof laminates similar to those used in this study lost only approximately half of the moisture produced by the foot to evaporation.136 Thus, typical sweating rates would quickly surpass the uptake wettability of both CB liners and the base layer sock as well, eventually. However, the combination of a highly absorbent base layer sock with a more absorbent liner would be able to delay the accumulation of moisture next to the skin for a longer period than if combined with a less absorbent liner, which may be detectable with a repeated GATS measurement where both materials are stacked with the sock material on the wetting plate. This finding supports a previous study on the effect of absorbent liners on the comfort of rubber firefighter boots.80

Thus, in the absence of differences in the thermal measurements, the most prominent factor that may explain some of the perceived differences in comfort of the two liners, in addition to the changes in fit, are the differences in moisture properties.

An additional factor for the reported perceived difference in thermal comfort may be heat generated due to friction inside the footwear. End-users reported less of a sensation of slipping inside the shoe while wearing the stretch liner. It is possible that fictional heating between the IFS and footwear inner material caused overall or localized heating. This could be measured by taking surface temperature or thermal imaging measurements of the materials following abrasion testing.

5.5 Discussion

A chemical protective sock liner was designed using a stretch material as a direct replacement to the current Integrated Footwear System (IFS). A set of candidate designs were developed based on specific issues identified by end-users. An iterative design process was

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used to further refine the design regarding fit, comfort, and operational suitability. Over the course of three rounds of user evaluations, the prototype liner was worn by over 50 end-users with hazardous materials experience in military, law enforcement, or first response roles. The prototype liner was consistently identified by a majority of end-users as an improvement over previous liner design. The primary factor appears to be the stretch material used. This stretch was able to reduce the amount of bunched material inside the footwear, which lead to more favorable impressions of the fit and overall comfort of the liners. It may have also contributed to a sense of novelty and innovation of the product among end-users.

Additional design evaluation methods could be explored to further define the improvement in the comfort and ergonomics of the prototype liner, for instance studies of changes in gait or flexibility of the lower extremities as a result of which liner is worn and physiological aspects of comfort such as measurements of skin temperature or sweat loss during wear trials. The influence of moisture was identified as a potential comfort factor.

Design approaches could be explored to incorporate even more absorptive materials in the liner to delay the sensation of sweat accumulation.

During the experiential focus group and subsequent wear trials, some issues regarding the durability of the liner were encountered, such as tearing of the membrane at the seam with the cuff and issues with the adhesion of the seam tape adhesive. Steps taken to address this issue are discussed in the next chapter on the durability of the liner.

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Chapter 6. The Evaluation of the Durability of a Chemical Protective Sock Liner 6.1 Introduction

A study was carried out to determine the impact of realistic wear conditioning on the protective properties of a chemical protective sock liner system. The primary objectives of the study were to identify and address issues in the design and construction of the sock, ensure the performance of the system according to standardized performance criteria, and investigate the impact of the duration of wear and the accompanying footwear on the integrity of the liner.

Test methods to evaluate durability of CPC components were identified and explored, then the suitability of candidate material and prototype liner was evaluated.

There were three general tasks:

1) Perform realistic wear conditioning on the prototype liner using representative

footwear types then perform permeation resistance testing on worn samples

2) Identifying causal relations for damage to the liner seams and material and address

means of improving the construction

3) Perform testing on seam adhesive and form recommendations

6.2 Liner Durability and Construction

Additional durability study, beyond the NFPA 1994 Class 3 testing requirements, were deemed necessary because the stretch material does not have a textile face, and thus may be more susceptible to physical damage. Reasons for damage could include stresses from laundering, stresses inside the shoe during wear, stresses during donning and doffing, and abrasion from the ground when the liner is been worn without footwear during donning and

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doffing. Further, the quality of seam bonds in chemical protective clothing and waterproof laminates have been discussed previously in literature as a weak point.137,138 Methods of assessing the quality of bonded or laminated seams have included microscopy, hydrostatic pressure testing, tensile tear strength, and tensile strength.137,139,140

6.3 Durability Wear Trial

The liners and materials in the wear trial are the same as those used in the previous chapter. The control liner is the current Integrated Footwear System (IFS). The liner is constructed from Gore® Chempak® barrier film with a Nomex® knit face and backing fabric.

The prototype liner is the liner constructed out of Gore® Chempak® Stretch in the design referred to as “style B”. All prototypes were constructed by LION Apparel, INC. of Dayton,

Ohio. All wear of the prototype liner was performed with a cotton athletic sock next to skin and a thin black polypropylene sock over the liner (Catawba Sox, style 8119).

The prototype liner was constructed such that all sewn seams on the body of the sock were sealed with a seam tape on the exterior. The seam tape was adhered to the barrier material using an adhesive layer, which was referred to as the seam pretreatment (SPT).

To validate the durability of the prototype system, liners were subjected to a conditioning protocol designed to replicate actual wear, before being tested for chemical permeation resistance. This durability study was based on the required useable lifetime of 48 hours for the liner. Based on the assumption that an 8-hour work day may consist of 10,000 steps, it was determined that a pair of liners should be able to withstand 60,000 steps (or 30,000 steps on each liner) and be able to withstand up to 6 launderings, 1 for each use periods.

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Human subjects were recruited to don the liners and walk on treadmills for a predetermined number of steps. All testing plans involving human subjects were reviewed and approved by the NC State University Institutional Review Board.

6.4 Cuff Tear Analysis

During the initial design process it was observed on a large fraction of the samples that the liner membrane material had torn and separated from the cuff (Figure 47) during the experiential wear trials.

Figure 47. Separation of membrane from cuff

In the image it can be seen that the membrane has torn and separated from the cuff but the backing knit fabric was still attached to the cuff. The support knit for the membrane stretches in both direction and is laminated to the membrane by use of an adhesive. The membrane only stretches in the direction parallel to the cuff seam so that the cuff can widen

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during doffing. However, during donning, a force is also applied perpendicular to the cuff seam as the sock is pulled on. The cuff may also be pulled on by the upper cuff of the footwear while the wearer is walking. In this situation the support knit is able to stretch but the membrane is not. The membrane solely is being stressed and the force is localized at the material between the holes that are introduced through the membrane by the sewing needle and thread. These holes act in the same way as perforations in a piece of paper meant to be torn. The membrane, which is stiffer than the knit, first tears at these points along the seam.

Based on initial inspection it appeared that additional adding additional stress to the torn liner cuff caused the knit to stretch more until it began to delaminate from the membrane, which could lead to failure of the protective performance of the liner.

It was hypothesized that a seam that reduces the number of holes in the membrane

(lower stitch density) would reduce tearing of the membrane. An alternate idea was to laminate some of the seam tape at the edge of the membrane before sewing the cuff, to reinforce the membrane; however, this was dismissed due to the additional cost.

The cuff was initially constructed with a 3-thread over-edge surge seam (“3/H”) with a high thread density to prevent fraying of the knit lining material. Two candidate seams were chosen that would reduce the number of holes introduced into the membrane: an identical 3- thread over-edge seam with a lower stitch density (“3/L”) and a 2-thread over-edge seam with similar stitch density (“2/H”) (see Figure 48).

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Figure 48. From top to bottom: 1) Control 3-thread over-edge high thread density seam 2) 3- thread over-edge low thread density seam 3) 2-thread over-edge high thread density seam

Test samples of all three stitches were prepared using 6” swatches of the stretch material attached to the standard cuff. Seam styles were compared for membrane failure load using a modified Grab Test performed in a MTS 5 Q-Tester with 250 lb load cell, 2” gauge length, and 1” face plates in constant rate of elongation mode (12 in/min) on 3” by 3” samples cut from the swatches.

Five replicates were tested for each seam. An image of a mounted sample shortly after the point of failure is presented in Figure 49. It was visually verified that the point at which was the membrane begins tearing was associated with the peak load on the resulting stress- strain curves.

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Figure 49. Cuff sample mounted in tensile testing instrument showing laminate tearing

The average peak loads for the three sample types is presented in Figure 50. Both candidate seams (2/H and 3/L) provided a significant increase in strength over the current seam

(3/H) according to a Student’s T-test analysis (α=0.05). However, the two candidate seams are not significantly different from each other. Either new seam option was predicted to reduce the occurrence of tears in the prototype liner. It is not clear if the effect of seam type and stitch density is additive; however, it was decided to use a combined 2-thread over-edge seam with a decreased seam thread density. Following the alteration, no cuff tears were subsequently observed in the durability study, comfort evaluations, or field evaluations.

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Figure 50. Average laminate seam breaking strength for the three seam styles (error bars equal to 1 standard deviation)

6.5 Seam Adhesive Analysis

Following the first wear durability analysis multiple liners showed visual signs of damage to the seam pretreatment used to laminate the protective seam tape. This damage was determined to be a cosmetic issue if the seam tape was not removed all the way to the seam.

However, it was judged to be a perceptual issue that would be unacceptable to end-users. From then on, all liners worn in subsequent evaluations were closely inspected for signs of damage.

An initial rating system was used on the comfort evaluation liners to group damage into three categories:

1. Adhesive irregularity – the seam pretreatment used between the seam tape and the liner material was observed to lift or appeared irregular (Figure 53) 2. Minor tape lifting – the corner or edge of white seam tape was visually separated from the membrane and could be felt by running a finger over the edge, but not enough to be able to grab (Figure 52) 3. Prominent tape lifting – the corner or edge of the seam tape was lifted to the extent that it could be grabbed, showing about 1/8th of an inch of lifted tape or more. (Figure 51)

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Figure 51. Prominent seam lift on the heel

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Figure 52. Typical minor seam lifting on the heel

Figure 53. An adhesive irregularity, excess adhesive that made a lump under the seam tape

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The samples from the durability evaluation were inspected and the occurrence of damage was categorized according to footwear type (Figure 54). There is no trend in the data, except that all footwear types cause seam adhesive lifting. Based on these observations, changes were made to the production guidelines of the liners meant to increase the amount of adhesive and add additional quality control steps.

10 9 8 7 6 5 4

3 Number Number Liners of 2 1 0 Low-profile Combat Fire Fighter Low-profile Combat Fire Fighter 5,000 Steps 5,000 Steps 5,000 steps 30,000 Steps 30,000 Steps 30,000 steps Prominent Minor No Lifting

Figure 54. Occurrence of lifting by footwear and conditioning level (#of steps)

6.5.1 Comfort Evaluation

During the comfort evaluation 26 liners were worn and subjected to three launderings.

These liners were visually inspected for signs of damage before and after each wear (Figure

55). A new method of categorizing damage to the seam pretreatment (SPT) and seam tape was devised by assigning categories of wear a number from 1-5 (Figure 55).

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Figure 55. Multiple view points of the liner during the comfort evaluations

Figure 56. Method of categorizing instance of adhesive damage

The progression of SPT lifting is presented in Figure 57. By the third wear, all of the liners showed some amount of SPT damage. Many of the samples showed “fraying” where the adhesive around the edges of the seam tape lifted into strands. Fraying was not observed in the previous lot of samples, indicating that the SPT was not improved.

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Figure 57. Progression of SPT lifting occurrences (maximum rating observed on each liner) during the three comfort evaluation sessions

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A hydrostatic pressure test was used on the comfort evaluation samples to further characterize the seam lifting. The Suter pressure tester is a hydrostatic pressure test apparatus

(Figure 58). It features a mount onto which the sample is placed face town. The chamber below the sample is pressurized with water and the backface of the sample is observed for signs of liquid penetration. All pressure testing was performed by LION. The following settings were used: 3 psi of water pressure for 2 minutes using 4” nozzle on four areas of the liner. The operation is similar in nature to the ASTM F903 test described previously, however the testing performed here was not performed according to the standard test method or to meet standard performance requirements. The test was only as a diagnostic test for quality control purposes.

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Figure 58. Suter pressure test apparatus with a sock liner mounted (image provided by LION Apparel)

Twenty-four samples were tested with the hydrostatic pressure test. The failures were defined by their location (leg, heel, top of foot, or toe area) and the sample type (seam or membrane failure). Eighteen liners failed in a total of 29 locations. Three liners failed in 3 locations, 5 failed in 2 locations, 10 failed in 1 location, and 6 passed. Three of the failures were observed through the membrane failures and 26 were observed around the seam. The locations consisted of 2 leg, 11 heel, 3 top of foot, 13 toe area failures. The pressure failure locations were cross referenced with the observed locations of SPT lifting and did not relate to

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each other in a majority of situations. Of the 3 fabric failures, only 1 location was visible: a clear pinhole located on the top of a toe.

6.5.2 Field Evaluations

Another change in the SPT application process was made before samples were manufactured for the field evaluations. However, of the 48 liners worn by the two field evaluation groups, 36 liners were identified with SPT lifting with 19 instances judged to be large, continuous sections of lifting (>3 based on the categories above). All of the samples worn during field evaluations were worn for only one session, all of shorter duration than the previous wear trials. This indicated that SPT application was not improved.

6.6 Physical Testing and Microscopy to Improve SPT application

Two new SPT application techniques were developed by varying the process conditions and were compared with previous sock samples to assess improvements in SPT adhesion.

Samples were inspected visually using microscopy and compared using two benchtop physical testing methods: tensile testing and abrasion.

6.6.1 Samples

The new SPT samples are referred to as “A” and “B”. Samples were prepared by LION in three configurations meant to replicate locations on the sock. The waves on the images in

Figure 59 represent the alignment of the pleats in the stretch material.

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“Ankle” “Toe” “Heel”

Figure 59. Sample configurations prepared by LION, meant to represent the ankle seam, the

toe seam, and the center of the heel seam

Samples were also prepared from socks manufactured previously in the project: unworn samples from the durability study manufactured in March 2015 and unworn samples from the field evaluations manufactured between August and October 2015 (these samples showed the highest occurrence of SPT lifting in the previous section). Specimens were cut from three locations on the sock: the vertical seam of the ankle, the seam on side of the toe, and the seam on the center of the heel. These locations were selected both because of previously observed

SPT lifting and because flat samples could be prepared. It should be noted that the samples prepared from socks were less uniform and often not completely symmetrical compared to the

A and B samples.

6.6.2 Microscopy

Visual observations were performed using a Bausch & Lomb Monozoom-7 Zoom

Microscope at magnifications between 15x and 25x. As a reference scale in the images below, the pleats are approximately 1 mm wide (9-10 ridges per centimeter). Cross section samples

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were prepared by cutting thin slices of material. Observations were taken on the ankle seam and toe seam of 5 samples from each lot. This is not an exhaustive look at the SPT application, however some trends were identified.

Figure 60 shows a view of a cross section of unworn field evaluation samples. These samples consistently showed instances of the SPT “bridging” across sections of the pleated stretch fabric. This incomplete contact between the SPT and the material could increase the occurrence of SPT lifting: as the material is stretched differences in the extensibility of the membrane and adhesive could place stress the interface between the adhesive and membrane and increase the occurrence of separation. No bridging was observed in any of the A or B samples (Figure 61).

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~1mm

Figure 60. Field evaluation sample example images (25x) showing incomplete contact between the barrier film and the seam adhesive

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Figure 61. Sample A (top) and B (bottom) example images (25x)

Scanning Electron Micrograms were captured using a Phenom G1 desktop SEM.

Samples were prepared with a Quorom SC7620 mini-sputter coater with gold/palladium

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coating. This approach was taken to see if additional detail on the surface of the membrane could identify other indications of damage. Figure 62 shows the smooth surface of the membrane material. It is not known what the particulates are on the surface. Figure 63 shows the interface between the adhesive layer and a portion of the membrane. The magnification achieved with the SEM was determined to be greater than necessary to observe the adhesive for purposes of identifying damage.

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Figure 62. SEM of the surface of the stretch membrane

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Figure 63. SEM of the adhesive layer

6.6.3 Tensile Testing

Tensile testing was performed using a MTS Q-Test 5 tensile testing instrument, using a modified ASTM D5034 Grab Test method. The settings were: 80 psi grip pressure, 1”x 3”

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grip plates, 2” gage length, a 250-lb load cell, extension rate of 12 inches/minutes. Samples dimensions were 3” x 3.” Seven samples were tested from each lot.

The ankle samples were subjected to tensile testing because of the observed phenomenon that the SPT tends to lift off this portion of the sock when stretched. The stress was applied perpendicular to the seam. The stress at which the SPT was seen to begin lifting was recorded - this was identified both by recording the load value as lifting occurred and by an inflection in the stress-strain curve. The SPT tended to "pop" off in part or completely, meaning the inflection was also the peak load of the sample. All samples were tested to destruction.

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Figure 64. A mounted tensile test sample, before and after testing.

The results were compared using Student’s T-test with a 0.05 significance level.

Samples A, B, and samples prepared from the comfort evaluations (“Phase 2”) all had statistically significant higher mean failure loads than the samples from the field evaluations

(“Phase 3”) (p>0.03). However, no statistical difference was discernable between A, B, and

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Phase 2 comfort evaluation samples. Interestingly, samples from Phase 2 also performed well, indicating an unintentional reduction in SPT adhesion occurred during preparation of the field evaluation samples (Figure 65).

Figure 65. Mean values of the failure load (load required to separate SPT). Each error bar is

constructed using 1 standard deviation from the mean.

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6.6.4 Abrasion Testing

A Wyzenbeek abrasion instrument, using an ASTM D4157 Oscillatory Cylinder

Method, was used to abrade SPT samples. In the method the samples are cut into strips that are mounted and pressed down against a cylindrical drum, which is covered with an abradant and oscillates back and forth at 90 cycles/minute. The following settings were used: standard

Cotton Duck #10 fabric abradant and 4 lbf Head Pressure (highest). The test is generally used for less extensible fabrics, otherwise the oscillating motion will make the samples stretch and cause the tension bars to bounce and hit the frame, which is undesirable. For this reason a 2 lbf specimen tension (second to lowest setting) was used. Samples were abraded for 10,000 cycles and inspected at 0; 1,000; 5,000; and 10,000. Specimen dimensions were approximately 2” x

9”. Four samples were tested for each lot.

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Figure 66. Wyzenbeek abrasion tester: sample strips are mounted then pressed against an oscillating drum that is covered in an abradant material

None of the samples showed prominent lifting of the SPT. Some SPT around the edges of the white seam tape was removed off the pleats on heel samples (Figure 67), however the

SPT was not observed to lift all the way as in the tensile testing. The toe style samples displayed very little observable changes from abrasion. Microscopic observations of the samples before and after revealed no clear changes (Figure 70). The majority of Phase 3 samples worn in the field evaluations showed some SPT lifting and were worn for far fewer than 10,000 steps. This implies that this abrasion method does not replicate walking completely and that stretching is a necessary step in the separation of SPT from them membrane.

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Figure 67. Phase 3 Abrasion sample that showed the most SPT removal (left to right: 0 cycles; 5,000 cycles; 10,000 cycles)

Figure 68. "Heel" samples in A after 10,000 cycles

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Figure 69. Toe sample from Phase 3 abraded for 10,000 cycles

Figure 70. SPT edge lifting after 10,000 cycles on an unworn field evaluation heel sample

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6.6.5 Discussion

The testing results suggest that both new SPT techniques (samples A and B) provide better adhesion than the samples prepared for the field evaluations, however no distinction can be made between the two new techniques. Tensile testing results show a higher load is required to cause SPT separation in the new samples. Abrasion observations suggest that stretching of the material is required to cause the SPT to lift. Microscopy observations suggest that the manner in which the SPT is applied may result in the SPT “bridging” across the pleats resulting in incomplete contact between the SPT and material, increasing the occurrence of SPT lifting.

The benchtop physical testing methods did not replicate the process of lifting as it occurs during actual wear. However tension testing does appear to be able to differentiate the quality of SPT adhesion to an extent. Based on the inability of the abrasion test to cause SPT lifting, stretching of the membrane is a necessary part of the SPT lifting process. Visual observations of the SPT may also help monitor differences in how the SPT has been applied to the membrane. The new SPT A and B are improvements over previous samples.

6.7 Conclusions

Microscopic methods were helpful in diagnosing issues with the application of the SPT adhesive. Tensile testing was found to be a means of comparing construction techniques in the liner such as cuff seam stitch style and adhesive application settings. The changes to the design made on the findings of these tests resulted in improved durability of the liner. Benchtop abrasion methods were not found to be capable of reproducing wear patterns identified during actual wear; however, they revealed information on the mechanism of damage to the seam adhesive. A more rapid or non-destructive means of monitoring the adhesive application would

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be useful for quality control purposes in the future. Additional research could be performed to provide more information on the relationship between the amount of wear and the protective performance of the liners.

Useful information could be attained by quantifying the stresses placed on footwear during use to better categorize the performance of the liners and other potential footwear materials. One approach to abrasion testing could be the use of multiple abrasives. Existing and candidate materials could be exposed to a progressive abrasive challenge in the oscillating abrasion testers, for instance advancing from a cotton woven to a nylon material to a wire mesh to sand paper. The materials could be tested after each abrasive test with liquid or air penetration testing to detect the presence of punctures. Candidate materials could then be ranked based on their performance.

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Chapter 7. The Evaluation of the Protective Performance of a Chemical Protective Sock Liner 7.1 Introduction

The conventional approaches to quantifying protective performance of CPC were discussed in Section 2.2. To characterize the useable lifetime of the liner, permeation testing was combined with a durability wear trial using actual wear.

Alternative testing approaches have been developed in the past to test CPC components. These have included immersion and exposure tests for gloves141,142, air hoses115, and zippers.143 Whole footwear test methods exist for heat resistance, flame resistance, overall liquid integrity, and electrical insulation. The chemical protection of an inner layer such as a sock liner, however, depends mainly on its interface with the pant leg and whether the material withstands the wear associated with use.

7.2 Wear Durability and Chemical Permeation Resistance

To validate the durability and protection of the prototype system, liners were subjected to a conditioning protocol designed to replicate actual wear before being tested for chemical permeation resistance. Participants were recruited from the university student population.

Sixteen participants were recruited in total (2 female, 14 male) between the ages of 18 and 21.

Participants were selected based on their shoe size (between men’s 9.5 and 13). During the recruitment process candidates were asked to don the liner and footwear then asked if the sizing felt appropriate. They were assigned to a pair of footwear, given a participant number (P1-P16) then scheduled for seven sessions over the course of 4 weeks. Five participants were assigned to each footwear type (Figure 71). One participant (P15) was not able to complete the study

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because of scheduling conflicts and was replaced after 2 sessions with a different participant

(P16) who completed the remaining 5 sessions. The participants’ shoe sizes and liners are presented in Table 19.

Table 19. Overview of Participants

Participant Footwear Liner ID #’s Shoe Type Liner Size ID #’s Size (5,000 / 30,000 steps) P1 Low Profile 9.5 10 L1R1 / L6R6 P2 Low Profile 10 11 L2R2 / L7R7 P3 Low Profile 10.5 11 L3R3 / L8R8 P4 Low Profile 12 12 L4R4 / L9R9 P5 Low Profile 13 13 L5R5 / L10R10 P6 Combat 9.5 10 L11R11 / L16R16 P7 Combat 10 11 L12R12 / L17R17 P8 Combat 12 11 L13R13 / L18R18 P9 Combat 11.5 12 L14R14 / L19R19 P10 Combat 11.5 13 L15R15 / L20R20 P11 Fire Fighter 10 L21R21 / L26R26 10 P12 Fire Fighter 10.5 11 L22R22 / L27R27 P13 Fire Fighter 11 11 L23R23 / L28R28 P14 Fire Fighter 11 12 L24R24 / L29R29 P15/P16 Fire Fighter 12.5 /12.5 13 L25R25 / L30R30

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Figure 71. Footwear used in durability study (from left to right: Low Profile, Combat, and Fire Fighter)

7.2.1 Conditioning Protocol

Each liner was coded. Table 19 shows how the codes were distributed over the different participants, the footwear, the conditioning level, and which foot it was to be worn on (left or right). Participants were instructed to wear breathable athletic attire of their choice. They were provided with clean athletic socks, the footwear, and the liner system. The same protocol was followed for all the sessions. On arrival, participants were asked to don the liner system and their assigned footwear. Donning and doffing took place in rooms with linoleum tiled floor.

Three treadmills were contained in a climate controlled room with conditions set to maintain approximately 20 °C and 50% RH. Participants were equipped with a wireless pedometer to attach to their waistband to monitor their steps. Participants were then asked to walk on a treadmill at a rate in which they could accomplish 10,000 steps (5,000 steps on each foot) within 2 hours, or approximately 3 miles per hour, however participants were allowed to alter the treadmill speed to their individual needs.

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Laundering was performed according to the directions of the manufacturer after each session. After wear, liners were submerged in warm (~105 °F) water, inverted, submerged again, wiped with a wet cloth to remove any debris, then towel dried and allowed to hang-dry overnight. All the athletic socks and oversocks were laundered after each session using conventional detergent and washing machine and dryer cycles on low heat.

After the first session, the first pairs of liners were removed for testing. The second pairs of liners were then used for the following 6 sessions. It took most participants 1.5 hours to complete their steps in a session and under 3 weeks to complete all 7 sessions.

Figure 72. Components supplied to participants during durability study

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7.2.2 Permeation Test Procedures

Chemical permeation resistance testing was performed on worn liner samples according to the NFPA 1994-2012 performance criteria for Class 3 ensemble garment materials. Testing was performed against three of the five standard test chemicals: acrylonitrile and ammonia are applied as gaseous challenges while dimethyl sulfate is applied as liquid droplets to the surface of the samples (10 g/m2).

The method of implementing the permeation tests as well as the collection, extraction, and analysis techniques were developed in previous work. The details are provided below.

Chemicals and Analytical Instrumentation

The chemicals used in this study include 99.99% carbon disulfide, 99.5% GC ResolvTM acetone, 99.9% OptimaTM acetonitrile, 99%+ acrylonitrile and dimethyl sulfate from Acros;

1,000 mg/L ammonium Certipret standards from Spex; Type 1 18 MΩ*cm deionized water from a Siemens Purelab ® Ultra Analytic purification system.

Certified standards of the challenge gases in pressurized cylinders were obtained from

Speciality Gases of America (40 ppm ammonia in an air balance) and Praxair (acrylonitrile

(40.99 ppm) in air balance).

The following collection media and sample preparation tools were used: SKC Inc 226-

115 Porapak Q sorbent tubes, 226-10-6 Treated Silica Gel sorbent tubes, 226-01 Anansorb

CSC sorbent tubes; Analytical syringes from Hamilton and SGE in 10-µL, 100-µL, and 1000-

µL volumes were used as well as Eppendorf Repeater ® Combtip pipettes; and Branson 1510 sonicator was used for some sample extractions. All standards were made in Class A volumetric flasks.

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The analytical instruments used include: Dionex ICS-2000 in Cation Mode using a

CS12a 2mm x 250mm column with guard column, CSRS-300 2mm suppressor, DS6 Heated

Conductivity Cell, and EGC III MSA Eluent Generator Cartridge, and 25-µL sample loop; and an Agilent 1260 Infinity Liquid Chromatography instrument with a Diode Array Detector and

Agilent Poroshell 120 EC-C18 2.7µm, 3.0mm x 100mm.

Testing Apparatus

Six stainless steel test cells were used, with designs in compliance with the NFPA 1994-

2012 standard (Aerospace Tooling and Machining, Salt lake City, Utah). They consisted of two compression plates using 5 Viton O-rings to compress the sample, seal the compression plates, and seal the screw top. The fabric sample sits between the two middle compression plates facing upwards. An image of the unassembled cell can be seen in Figure 73.

The cells are contained in an acrylic box inside a fume hood. The collection flow is produced by a pressure-regulated hydrocarbon free air source (Parker Balston HPZA-3500

Zero Air Generator), which supplies air to a humidity generator (Humisys by InstruQuest,

Inc.). The generator has programmable humidification settings and records data for the duration of the test. It is easily capable of maintaining temperature and humidity within the desired range of ±0.5 °C and ±5 %RH for the test conditions tested. A manifold splits the humidified air flow to four separate air lines, each regulated by calibrated mass flow controllers

(MKS, Inc.) that are capable of delivering up to 2 L/min to the lower half of each test cell.

Sorbent tubes were connected directly to the outlets of the cells using 1/4” or 3/8” inner diameter elbow connectors with stainless steel nuts and plastic ferrules to match the tube

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diameter. The upper half of the cells are attached in series to the pressurized challenge chemical cylinders or an air source and are set using a calibrated rotometer.

Figure 73. Permeation Test Cell

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Figure 74. NCSU Chemical Permeation Resistance Test Apparatus with loaded cells

All permeation results are reported in relative units to obscure values that may reveal performance properties of an export controlled material.

The test procedure is the same for all chemicals. First samples are mounted into their cells and tested for cell integrity according to the NFPA 1994 standard. The cells are placed into the test apparatus and the collection (lower) half of the cells are connected to the humidified air lines. The sorbent collection tubes are opened and attached to the outlets of the cells. The humidity and temperature are monitored to ensure conditions do not change. The test begins when the challenge chemical is applied, either by initiating flow from the cylinders

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or application of liquid dimethyl sulfate. The test continues for 60 minutes, at which point the collection tubes are removed and the challenge flow is terminated. Collection tubes are then opened and the sorbent is transferred to glass vials. The extraction solvent is added to the glass vials and samples are sonicated for 30 minutes. All samples are filtered upon transfer for analysis.

Collection and Analytical Methods

NIOSH method 6016 was followed for the collection of ammonia using 150/50 mg

SKC 226-10-6 Silica Gel treated with Sulfuric Acid sorbent tubes and 10 mL of deionized water as the desorption solution. Analysis was performed with a Dionex ICS-2000 with CS12a column, CSRS-300 suppressor, DS6 Conductivity Cell, and MSA Eluent Generator Cartridge.

The method used a 5 µL injection loop, 0.25 mL/min flow, 20mM eluent concentration and 15 mA suppressor current. The retention time was 5.5 minutes with an LOD and LOQ of 0.02 and

0.08 µg/mL. The method requires 15 minutes to elute the sulfate and sulfite. Ammonia exhibits a quadratic response on suppressed IC.

For dimethyl sulfate, 150/50 mg 226-115 Porapak Q sorbent tubes were used for collection followed by extraction with 3 mL of acetone. An Agilent 6890N Gas

Chromatograph with 5875C Mass Spectrometry Detector with a Restek RTX-1701 280°C 30m x 250µm x 0.25µm column was used for DMS and acrylonitrile. A 10-1 split was used with an injection temperature of 160°C and the following oven program: 50°C hold 3 min, ramp

50°C /min to 200°C. The highest sensitivity was seen using selected ion mode for 45, 66, 95,

96, and 125 m/z. The retention time was 4.9 min with an LOD and LOQ of 0.19 and 0.64

µg/mL.

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For acrylonitrile, SKC 400/200 mg 226-01 Anasorb CSC sorbent tubes were used for collection followed by extraction with 4 mL of carbon disulfide with 2% acetone. For analysis a 20-1 split was used with an injector temperature of 250°C and following oven program: 35°C hold 2 min, ramp 25°C /min to 200°C. Due to an overlap with the carbon disulfide peak higher sensitivity was achieved using selected ion mode for 26, 38, 50, 51, 52, 53 m/z. The retention time was 2.4 minutes with an LOD and LOQ of 0.29 and 0.97 µg/mL.

Sample Preparation

Three samples (3” x 3”) were removed from each liner for permeation testing from three of four places: one from the toe seam located on the top of the liner, one from the ball of the foot, and one from the front of the ankle or from the heel, depending on which area showed more signs of visual damage (Figure 75). A total of 180 samples were removed and 162 were tested, representing 3 samples for each location, in each footwear, in each condition, for each chemical.

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Figure 75. Sampling locations for permeation test samples

To pass the cell-integrity test in the NFPA permeation protocol, stretch fabric samples were mounted onto the sample support plate using a TEC 820 Medium Duty Hot Melt Glue

Gun with TEC Bond LM44 Low Melt polyethylene glue. The adhesive was applied to the compression plate at the edge of the circular opening. The material was placed facedown onto the compression plate and compressed in the cell. This sealing mechanism introduces slight variation in the exposed surface area of the samples because it is difficult to control the area covered by the adhesive. Additional variation is present due to the flexibility and irregular shape of the samples cut from curved portions of the liner such as the toe and heel, which are not completely flat. A seam sample mounted in the test cell is shown in Figure 76.

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Figure 76. Seam sample mounted in the permeation cell

7.2.3 Results

All 162 of the permeation samples tested satisfied the NFPA 1994 Class 3 requirements, as the cumulative permeation results were below the specification in a 1 hour test, indicating the materials is able to perform after 30,000 steps of wear and cleaning. These data are presented below (see Figure 77-Figure 79) as scatter plots with fenced quantile box plots (vertical line inside box = median value, box ends = 25th and 75th percentile, top whisker ends = (75th percentile + 1.5*interquantile range)). Samples below the detection limit of the

2 analytical method were reported as 0 μg/cm (the result for 75% of the samples tested). Twenty- five percent of the samples showed a small amount of the cumulative permeation but were still below the NFPA 1994 Class 3 requirement.

According to Wilcoxon Rank Sum Tests, no population difference is distinguishable (p

= 0.95, z ≤ 1.65) for the cumulative permeation results between samples from different number

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of steps, footwear type, or sample location. The distribution of results is likely the result of inherent sample and test procedure variation.

Figure 77. Permeation results grouped by challenge chemical and conditioning level (y-axis redacted to protect sensitive information)

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Figure 78. Permeation results grouped by conditioning level and footwear type (y-axis redacted to protect sensitive information)

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Figure 79. Permeation results grouped by sample location (y-axis redacted to protect sensitive information)

7.3 Discussion

A chemical protective sock liner was designed using a stretch material as a direct replacement to the current Integrated Footwear System (IFS). The liner was subjected to a durability wear trial to replicate the effects of wear. Each liner was subjected to a total of

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30,000 steps and 6 launderings then sampled and tested against a chemical permeation resistance test standard. All of the sampled locations performed within NFPA 1994 Class 3 permeation resistance performance criteria.

One fundamental issue that arose in this testing was the discrepancy between the permeation tests performed on the durability evaluation samples, where none of the seam samples showed significant permeation, and the hydrostatic pressure test failures on the comfort evaluation samples. According to the NFPA performance hierarchy, liquid penetration protection is less protective than vapor permeation protection. NFPA 1994 Class 3 ensembles are considered vapor protective, even though the design requirements do not exclude non- encapsulating ensembles with open interfaces between separable booties, jackets, hoods, and gloves.

One explanation for the hydrostatic pressure failures is that the hydrostatic pressure testing was performed at a high pressure (3 psi), which may have itself caused damage to the seams. Additionally, different settings were used for the application of the seam adhesive for those liners. The comfort evaluation samples did appear to have less durable SPT.

Every use condition cannot be predicted; however, the liners are not designed to be used in a situation of complete immersion in liquid, and the outer footwear requirements for

NFPA Class 3 ensembles provides additional chemical and physical protection requirements.

However, the gap between the two material testing approaches highlights the importance of system level performance requirements and the potential usefulness of more component level test methods. An initial investigation could involve performing permeation testing on a sample

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with an intentionally introduced pinhole – both under a positive pressure and negative pressure evaluation.

A related investigation could be performed on the distribution of permeation data.

Within the 60 minute test duration a majority (75%) of samples did not show measurable amounts of permeation. To get a more complete picture of the distribution pattern of the permeation test, the test duration would need to be extended so that all of the samples showed detectable amounts of permeation. The distribution of a large number of tests could reveal information about the uniformity of the material being tested or about the repeatability of the test methodology and possible shortcomings.

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Chapter 8. Summary and Future Research 8.1 Summary

A more comfortable sock liner was developed for CPC end-users. The sock is constructed with a stretch material designed to reduce the amount of material bunching inside footwear. The design process included end-user feedback to evaluated user approval and compatibility with current operational factors. Results indicate that the prototype is preferred over the current Integrated Footwear System (IFS) liner both overall and in regards to fit and comfort properties. A full size range was employed to allow improved sizing options for end- users. Wear trials and bench-level physical and chemical testing were used to ensure product performance. Physical testing suggests that the product will be durable and protective across multiple wears.

The development of the liner provided the opportunity to investigate the test methods available for evaluating clothing performance and assessing human factors. The sock was studied in terms of chemical protection, design, durability, comfort, and physiology. Several findings were made regarding the usefulness of testing and research approaches for evaluating

CPC designs broadly.

A user-centric functional design approach involving surveys and wear trials yielded the primary problem statement of this research, established design criteria, and validated the improvements in fit and comfort. An end-user survey (Chapter 3) revealed several issues with current CPC footwear. The bulk and excess material used in some common CPC sock liners cause discomfort and sizing issues. End-users from several organizations expressed the desire for a liner that is adaptable to multiple types of footwear, has improved sizing options, and that

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removes pressure from the end of the toes. To address this issue, the question was posed of whether the fit of the liner could be improved by the use of a stretch material (Chapter 4). The prototypes were evaluated primarily based on their patterns, volumes, and observations on their ability to change shape in response to foot movements. The use of stretch materials was able to reduce the volume of the liners without sacrificing the sizing ranges of the liner. A sizing study revealed that more form fitting prototype liners could be designed that still were able to be donned across 3 whole footwear sizes. The direction of stretch could also be utilized to allow for a designs that removed a seam from the end of the toes and reduced the amount of material used. The design was altered incrementally through end-user feedback and observations.

The next research task was to assess the impact of the new design on comfort. The comfort evaluation and field assessments (Chapter 5) demonstrated that subjective evaluations are essential to support the development of new concepts for clothing systems. The new stretch liner was rated more favorably for multiple comfort attributes. The form fitting design was likely responsible for improved comfort attributes related to fit. The material itself appears to have provided additional comfort attributes related to thermal comfort and a reduced sensation of slipping. Incorporating even more absorbent materials, which can delay the sensation of wetness and slip, may be desirable for comfort, as long as they are not too bulky. The stretch material may have also been identified by the end-users as a novel item, which may have contributed to a positive impression.

Design specifications for CPC footwear primarily focus on durability and protection, and there is a lack of quantitative methods to evaluate fit, pressure, and comfort inside

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footwear. In this research, subjective data from human subjects was used to validate the comfort of the new liners. This research presents an example for how comfort evaluations and user-task-environment (UTE) studies could be incorporated into standards or used to devise ensemble specifications. One focus of future improvements for CPC footwear design could be moisture management, for which there are reliable methods of measurement.

To evaluate durability (Chapter 6) the following approaches were used: abrasion testing, tensile testing, microscopy, qualitative observational ratings, laundering procedures and human wear trials. Observed failures in this liner were not material failure, but rather stress or catastrophic failure of the seams. The failure was identified to be depending on tensile stresses perpendicular to the seams. Tensile testing was applied to monitor and compare changes in the seam application process. This lead to an improvement in seam durability, as validated by wear trials. Testing and microscopy were found to be quick and insightful methods for evaluating the quality of seam lamination. These methods could be applied as a quality control measure to compare lamination process conditions or to monitor the quality of production samples. Ultimately, the use of human wear trial participants was necessary to identify durability shortcomings of the liner construction and evaluate the useable lifetime of the product.

There are opportunities in the current technology and design space to improve the ergonomic and performance properties of CPC both by introducing new materials and by defining new CPC clothing ensemble categories. Inventive construction techniques such as garments constructed with a stretchable and absorbent material designed to be worn underneath

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current uniforms are one such solution, with the potential to reduce thermal comfort, increase ergonomics, and integrate with existing ensembles for additive properties and convenience.

8.2 Future Research

Future research could be performed to broaden the scope and applicability of this work.

First, a similar design and testing approach is also applicable to the development of other protective clothing items. Though the human user is central to the design process, wear trials are expensive and time consuming. A primary goal involves the development of research tools that can either supplement, correlate with, or predict findings from human wear trials. There are three broad areas of potential additional research: First, additional ways of providing quantitative measures of fit and comfort for clothing components. Second, more research is needed to address the potential impact of membrane and seam damage on the protective performance of CPC to make better estimations of the service life of CPC ensembles. Third, connecting material level and ensemble level methods of quantifying protection and providing data to help fill in the design-performance space could inform opportunities for improving either comfort or performance of non-encapsulating CPC ensembles.

8.2.1 Material and Seam Durability

One goal could be to categorize the modes of failure and the impact on performance for ensemble barrier materials commonly used in NFPA 1994 Class 3 and Class 2 ensembles.

Specifically there is an interest in setting new preconditioning requirements for materials to create subclasses, which differentiate between more rugged materials and more comfort optimized materials in CPC. This would include an initial categorization of ensemble material types, for instance membranes with and without textile face fabrics. Next the modes of material

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damage imposed by current preconditioning methods should be categorized and described according to their expected effect on membrane performance. The transport properties of a homogenous membrane depend essentially on two factors: the permeability of a given chemical challenge and the barrier thickness. Physical test methods are expected only to impact the thickness of the barrier. An initial list of failure modes and their effect on barrier thickness include:

1) Tensile – stretching, thinning of membrane, separation from textile

2) Flexing – localized creasing, thinning of material

3) Abrasion (low hardness abradant) – thinning of membrane, removal of textile

material. (high hardness abradant) –thinning of membrane, potentially localized

puncture of membrane, removal of textile

4) Puncture – puncture of membrane

An initial theoretical approach would be to consider how damage to a membrane resulting in variation in membrane thickness may change cumulative permeation amounts. For instance a damaging event occurs to a polymer film sample with the effective result of the removal of X% of the barrier material volume but with a thickness change of less than 100% at any one point (does not puncture the membrane). This change in thickness could occur as 1) uniform (the top X% of the barrier is removed) 2) unevenly distributed (the removal occurs as a normal distribution across a patchwork of regions) or 3) localized (narrow distribution resulting in large removal from localized regions). This can be modeled using a simulation of the diffusion equation and has been applied before to predict changes in a transient permeation

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curve.144 These theoretical values could be compared with an experimental method of monitoring thinning or membrane damage.

Another persistent issue across CPC manufacturing industry has been issues associated with seam sealing and adhesive bonding technology. It may be interesting to develop a more relational understanding of the transport of chemical through pinholes and pathways formed from seam failures in CPC. New chemistry or construction methods for laminated and bonded seams that can either increase the durability or decrease the thickness of seams could significantly improve the durability and comfort of CPC ensembles and components.

8.2.2 Quantifying Protection

Another related area of interest is the methods of testing the protective performance of materials, components, and ensembles and quantifying the protection in a meaningful way.

Current material and system level tests do not give good indication of what routes of transport into the clothing system would contribute most to exposure.

One strain of research is improving methods of testing closures and component interfaces, which are often considered the weak link in ensembles. One possibility is scaling the permeation test apparatus to a larger cell diameter and applying it to closures to allow a quantitative differentiation of different closure, valve and seam designs or to be able to perform pressure penetration testing or shower testing on suit components such as mask interfaces and valves without testing the entire ensemble.

Current permeation testing methods only enable relative comparisons between materials. Permeation studies that use alternative sampling methods that may predict the transfer of permeated chemical from fabric to skin, or novel skin sampling methods for wear

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trial evaluation of chemical protective clothing, may help inform the meaning of current pass/fail requirements for permeation tests.

The current shower test, viral penetration test, and permeation test due to their performance requirements or the method in which the test is performed effectively exclude air- penetrable materials from being used. It would important to consider the potential benefits of including air-permeable materials and how the standard would have to be changed to accommodate them.

Bench-level tests cannot be expected to represent every exposure situation. The evaluation of components – separable portions of the ensemble such as gloves, sock liners, hoods, interfaces, and closures– could be improved with the use of new testing approaches and integrated models to more clearly define suitability and compare performance. Alternative methods of defining protection levels of components and ensembles can aid in the product development process and allow more informed decisions in the steps of material and design selection. An overarching research goal is to contribute to the broader question of what improvements can be made in the comparative and predictive capability of the CPC testing paradigm.

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APPENDICES

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Appendix A. Surveys Used in End-User Evaluations

A.1 Initial user input survey

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A.2 Comfort and Field evaluation survey

Liner Assessment Questionnaire Participant ID: ______Date: ______Session #______Footwear (circle): Fire / Combat / Low-profile Shoe size worn today: ______

First Liner Post-Task Questionnaire (circle): Stretch / Non-Stretch Please indicated your impression of the following properties about how the liner felt during the task sequence.

Unacceptable Poor Neutral Good Excellent

Ease of [N/A] [ ]------[ ]------[ ]------[ ]------Donning --[ ]

Ease of [N/A] [ ]------[ ]------[ ]------[ ]------Doffing --[ ]

Fit at end [N/A] [ ]------[ ]------[ ]------[ ]------of Toes --[ ]

Fit on top [N/A] [ ]------[ ]------[ ]------[ ]------of Toes --[ ]

[N/A] [ ]------[ ]------[ ]------[ ]------Fit in Heel --[ ]

Fit [N/A] [ ]------[ ]------[ ]------[ ]------Around --[ ] Calf

Impression [N/A] [ ]------[ ]------[ ]------[ ]------of --[ ] Durability

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Excessive Very noticeable Somewhat noticeable

Minimal Non-existent

Material [N/A] [ ]------[ ]------[ ]------[ ]------Bunching --[ ]

Sensation [N/A] [ ]------[ ]------[ ]------[ ]------of Heat --[ ]

Sensation of Slipping [N/A] [ ]------[ ]------[ ]------[ ]------inside the --[ ] Footwear

Unacceptable Poor Neutral Good

Excellent

Overall [N/A] [ ]------[ ]------[ ]------[ ]------Comfort --[ ]

Pedometer

reading:

Use the image and space below to indicate and describe areas of discomfort or positive properties during the wear trial:

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Second Liner Post-Task Questionnaire (circle): Stretch / Non-Stretch Please indicated your impression of the following properties about how the liner felt during the task sequence.

Unacceptable Poor Neutral Good Excellent

Ease of [N/A] [ ]------[ ]------[ ]------[ ]------Donning --[ ]

Ease of [N/A] [ ]------[ ]------[ ]------[ ]------Doffing --[ ]

Fit at end [N/A] [ ]------[ ]------[ ]------[ ]------of Toes --[ ]

Fit on top [N/A] [ ]------[ ]------[ ]------[ ]------of Toes --[ ]

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[N/A] [ ]------[ ]------[ ]------[ ]------Fit in Heel --[ ]

Fit [N/A] [ ]------[ ]------[ ]------[ ]------Around --[ ] Calf

Impression [N/A] [ ]------[ ]------[ ]------[ ]------of --[ ] Durability

Excessive Very noticeable Somewhat noticeable

Minimal Non-existent

Material [N/A] [ ]------[ ]------[ ]------[ ]------Bunching --[ ]

Sensation [N/A] [ ]------[ ]------[ ]------[ ]------of Heat --[ ]

Sensation of Slipping [N/A] [ ]------[ ]------[ ]------[ ]------inside the --[ ] Footwear

Unacceptable Poor Neutral Good

Excellent

Overall [N/A] [ ]------[ ]------[ ]------[ ]------Comfort --[ ]

Pedometer

reading:

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Use the image and space below to indicate and describe areas of discomfort or positive properties during the wear trial:

End of Session Comparative Questionnaire AFTER BOTH LINERS HAVE BEEN WORN After completing the task procedure with both liners elect your preferred candidate liner or select “no preference” for the following features:

Ease of Donning No Preference Stretch Non-Stretch

Ease of Doffing No Preference Stretch Non-Stretch

Fit at end of Toes No Preference Stretch Non-Stretch

Fit on top of Toes No Preference Stretch Non-Stretch

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Fit in Heel No Preference Stretch Non-Stretch

Fit Around Calf No Preference Stretch Non-Stretch

Impression of Durability No Preference Stretch Non-Stretch

Material Bunching No Preference Stretch Non-Stretch

Sensation of Heat No Preference Stretch Non-Stretch

Sensation of Slipping No Preference Stretch Non-Stretch inside the Footwear

Overall Comfort No Preference Stretch Non-Stretch

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Appendix B. Additional User Evaluation Data

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B.2 Mean Liner Assessment Responses for Each Footwear

Mean Responses in Combat Footwear Non- Stretch Stretch

5.0 4.584.58 4.424.58 4.25 4.17 4.25 4.33 4.5 4 3.92 4.08 44.08 4 3.91 3.67 3.75 4.0 3.5 3.42 3.5 3.25 3.17 3.33 3.0 2.5 2.0 1.5 Rating 1.0 0.5 0.0

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Mean Responses in Fire Fighter Footwear Non- Stretch Stretch 5.0 4.58 4.424.42 4.33 4.5 4 3.92 3.92 3.92 3.75 3.75 4.0 3.58 3.5 3.583.67 3.33 3.33 3.253.42 3.25 3.25 3.5 3 3.0 2.5 2.5

Rating 2.0 1.5 1.0 0.5 0.0

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Mean Responses in Low-Profile Footwear Non- Stretch Stretch 5.0 4.5 4.33 4.334.25 4.5 4.17 4 4 4.17 3.92 3.75 3.833.92 3.83 3.75 4.0 3.67 3.5 3.58 3.25 3.42 3.5 3.17 3.08 3 3.0 2.5

Rating 2.0 1.5 1.0 0.5 0.0

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B.1 Summary of preference data for each footwear and comfort property in the comfort evaluations

Table 20. Summary of preference data for each footwear and comfort property

Combat Fire Fighter Low Profile No Non- No Non- No Non- Comfort Property Stretch Stretch Stretch Preference Stretch Preference Stretch Preference Stretch Ease of donning 6 3 3 8 2 2 4 3 3 Ease of doffing 5 4 3 8 3 1 4 3 3 Fit at end of toes 3 2 7 1 3 8 1 2 7 Fit on top of toes 3 2 7 2 4 6 3 0 7 Fit in heel 4 2 6 2 4 6 1 3 6 Fit around calf 6 1 5 7 1 4 4 2 4 Impression of 5 2 5 6 3 3 4 2 4 durability Material bunching 2 4 6 0 5 7 1 3 6 Sensation of heat 3 3 6 1 7 4 1 3 6 Sensation of slipping 4 2 6 3 5 4 1 4 5 Overall comfort 1 3 8 1 4 7 0 3 7 Sum: 42 28 62 39 41 52 24 28 58

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Appendix C. Images

C.1 Images of the comfort evaluation tasks

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