ABSTRACT CARLTON, NIGEL PATRICK. Effective Methods for The

ABSTRACT

CARLTON, NIGEL PATRICK. Effective Methods for the Evaluation of Thermal Protective Performance of Firefighter Protective Hoods (Under the direction of Dr. R. Bryan Ormond and Dr. Roger L. Barker).

In recent years, firefighting and cancer have become nearly synonymous with one another.

To combat the infiltration of the possibly carcinogenic materials in soot and smoke, an optional particulate blocking layer has been added to the firefighter protective hoods in the NFPA 1971 standard which governs the protective equipment of structural firefighters. However, the performance of these materials under flashover conditions must be evaluated first and foremost.

There are several test methods that evaluate the performance of materials and garments under flashover conditions, but these test methods must also be evaluated for efficacy and efficiency of their procedures and results.

Firefighter protective hood materials and composites were tested using two bench-level thermal protective performance test methods. These were used to evaluate a material’s and composite’s performance under flashover conditions. The first test method used was with a continuous exposure until predicted second-degree burn while the second involved an abbreviated exposure with continued data collection until a predicted second-degree burn is realized. These methods showed that the addition of a particulate blocking layers increases the thermal protective performance of composites. Thickness and weight also were shown to have a significant effect on thermal protective performance.

Manikins are frequently used to evaluate thermally resistant garments to incorporate the addition of garment design and air gaps into thermal protective performance. The PyroHead™ Fire

Test System is a tool used for the evaluation of flame-resistant headgear and was originally developed for the evaluation of military balaclava testing at four seconds. However, since firefighter protective hoods are designed to give more protection than military balaclavas, four seconds was hypothesized to be too short of an exposure time and therefore a standard testing procedure had to be determined for effective evaluation. After rounds of testing and evaluation, the suggested testing procedure for testing firefighter protective hoods on PyroHead™ was to follow ASTM F1930 and test just the hood on the head form at seven seconds and run five replicates.

On-market hoods, both traditional and particulate blocking, were tested and evaluated using the proposed standard testing procedure. This tested was designed and conducted to determine what aspects of firefighter protective hoods influence the thermal protective performance as shown by PyroHead™ results. Aspects such as material, thickness, weight, layering, particulate blocking layers, and design were specifically taken into consideration when correlating variables with predicted head burn percentage. The results found that of the variables explored, the layering had the greatest effect on the predicted head burn percentage produced on

PyroHead™.

by Nigel Patrick Carlton

A thesis submitted to the Graduate Faculty of North Carolina State University in partial fulfillment of the requirements for the degree of Master of Science

Textile Engineering

Raleigh, North Carolina 2019

APPROVED BY:

______Dr. R. Bryan Ormond Dr. Roger L. Barker Committee Co-Chair Committee Co-Chair

______Dr. Jeffrey A. Joines Dr. Cassandra H. Kwon ii

DEDICATION

First and foremost, this research is dedicated to and intended for our men and women in not only the fire service, but our first responders and military personnel whom put their lives on the line every day for ideas of safety, liberty, justice and freedom. My only hope is that this research is able to assist you in some way, shape, or form while you are protecting these ideologies.

More thanks are due to the following people have also made a significant impact on my life, well-being, drive and continued success as an individual:

• My mom, Barbara, whom through it all, loved, taught, challenged and shaped four young

people to be the best versions of themselves. We will forever be thankful for being brought

into this world by such a woman whom we are slowly finding traits about ourselves that

are exactly like her.

• My dad, A. Nigel, whom taught us discipline and accountability through three simple rules:

“mind, do your homework and listen to your momma.”

• My siblings, whose annoyance and admiration taught me that someone is always watching

and looking up to you, so always set a good example.

• My friends and roommates in Raleigh, who distracted me from my studies more than I

needed but less than I wanted.

• My a cappella groups, Acappology and Triadic, who gave me an outlet from the everyday

and allowed me to add diversity to my life and friends.

• Brooke, who always showed her dedication and support, no matter the situation or

circumstance.

• All of my friends, classmates, teammates, and colleagues I have met during my six years

at NC State, I will never forget these years and will cherish every memory.

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BIOGRAPHY

Nigel (phonetically: nɪgɛl, not traditional British pronunciation) Patrick Carlton was born on November 22, 1994 to A. Nigel (same pronunciation) and Barbara Carlton in Burlington, NC.

Nigel is the eldest of four children. His brother Mendé, is four years younger and his twin sisters,

Lauryn and Silken, are six years younger. Nigel grew up in an athletic household and participated in a combination of American football, basketball, and baseball up through his time at Western

Alamance High School. Nigel went to The North Carolina State University for his undergraduate degree in pursuit for an engineering degree of some sort.

To put his love for sports and the sciences together he chased a degree in Textile

Engineering. Throughout undergrad, he was involved in intramural sports, a Resident Advisor for two years, an intern at Cotton Incorporated and a member of the a cappella group Acappology.

Nigel graduated with his undergraduate degree in May of 2017 and had the unique opportunity to go to graduate school in the Wilson College of Textiles at The North Carolina State University and work as a Graduate Research Assistant in the Textile Protection and Comfort Center (TPACC).

In graduate school, Nigel was also able to join a semi-professional a cappella group known as

Triadic. After graduation, Nigel intends to work in materials research, development, and innovation.

ACKNOWLEDGMENTS

My journey through graduate school would not have been possible without the help and confidence of Dr. Bryan Ormond. If he did not believe that every interaction is an interview, then

I may not have been able to have the unique opportunity to work and learn in a place such as the

Textile Protection and Comfort Center. You are invaluable to not only TPACC but also the Wilson

College of Textiles and NC State as a whole. The way you are able to understand the needs of your research and students while also using undeniable experience and logic to drive your decisions should not go overlooked and will propel you forward for years to come. You have been a true friend and mentor and I can only hope that your future students will appreciate you as much as I have the past two years.

Thank you to my committee, Drs. Roger Barker, Bryan Ormond, Cassandra Kwon and

Jeffrey Joines, for advising me through the process of preparing a thesis and for reading this ridiculously long paper. I would also like to acknowledge John Morton-Aslanis and Shawn Deaton for teaching me how to run the testing apparatuses and for helping with my PyroHead™ testing.

My undergraduate researchers, Emilie Phan, Jamie Honeycutt and Ryan Adams helped me tremendously from doing some of the duties I did not want to do, to taking their own initiative with the research projects I assigned them. Finally, I would like to thank the other TPACC graduate students for the advice and help they have provided me and would also like to wish them luck finishing out strong and in whatever they decide to pursue next. Thank you.

TABLE OF CONTENTS

LIST OF TABLES ...... viii LIST OF FIGURES ...... x LIST OF EQUATIONS ...... xiii

CHAPTER 1: Introduction and Proposal ...... 1 1.1. Purpose ...... 1 1.2. Research Objectives ...... 2 CHAPTER 2: Firefighting Tactics and Personal Protective Equipment ...... 3 2.1. Evolution of Tactics ...... 3 2.1.1. Cohorts of the Watchmen ...... 3 2.1.2. Middle Ages Europe ...... 4 2.1.3. American Colonization through Industrial Revolution ...... 4 2.1.4. Layman versus Modern Tactics ...... 5 2.2. Changes in Turnout Gear ...... 8 2.2.1. Legacy Turnout Gear ...... 9 2.2.2. Modern Structural Turnout Gear ...... 11 2.3. Protective Hoods ...... 12 2.3.1. NFPA 1971-18 Hood Requirements ...... 13 2.3.2. Response to Hoods ...... 16 2.3.3. Cancer Problem ...... 18 2.4. Protective Hood Materials ...... 22 2.4.1. Aramids ...... 22 2.4.2. Fire-Resistant Viscose Rayon ...... 26 2.4.3. Oxidized Polyacrylonitrile (OPAN) ...... 28 2.4.4. Polybenzimidazole (PBI) ...... 29 CHAPTER 3: Skin and Thermal Protection ...... 33 3.1. Skin Burns ...... 33 3.2. Skin Burn Models ...... 34 3.2.1. Studies of Thermal Injury – Henriques ...... 35 3.2.2. Stoll Curve ...... 36 3.3. Bench-Level Test Methods ...... 38 3.3.1. ISO 17492 ...... 38 3.3.2. ASTM F2703 ...... 40 3.4. Manikin Test Methods ...... 41

3.4.1. PyroMan™ Fire Test System ...... 41 3.4.2. PyroHands™ Fire Test System ...... 43 3.5. PyroHead™ Fire Test System ...... 45 3.5.1. Overview ...... 45 3.5.2. Burn Model Parameters – Head Skin Thicknesses ...... 46 3.5.3. Military Flash Hood Testing ...... 47 CHAPTER 4: Bench-Level Thermal Protective Performance Testing on Firefighter Protective Hood Materials ...... 50 4.1. Introduction and Background ...... 50 4.2. Materials and Methods ...... 50 4.3. Results and Discussion ...... 54 4.3.1. Full Results ...... 54 4.3.2. Addition of Particulate-Blocking Layer...... 55 4.3.3. Effect of Rayon ...... 59 4.4. Conclusions ...... 61 CHAPTER 5: Determining a Standard Testing Procedure for Testing Firefighter Protective Hoods on PyroHead™ Fire Test System ...... 62 5.1. Introduction and Background ...... 62 5.2. Materials and Methods ...... 62 5.2.1. Materials ...... 62 5.2.2. Methods...... 65 5.3. Results and Discussion ...... 67 5.3.1. Determining Exposure Time ...... 67 5.3.2. Determining a Mounting Configuration ...... 69 5.3.3. Determining Number of Replicates ...... 72 5.4. Conclusions ...... 75 CHAPTER 6: Testing of Firefighter Protective Hoods on PyroHead™ Fire Test System using Determined Standard Testing Procedure ...... 77 6.1. Introduction and Background ...... 77 6.2. Materials and Methods ...... 77 6.2.1. Materials ...... 77 6.2.2. Methods...... 79 6.3. Results and Discussion ...... 80 6.4. Conclusions ...... 85

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CHAPTER 7: Comparison of Bench-Level Flashover Exposure Test Methods to PyroHead™ Fire Test System...... 86 7.1. Introduction and Background ...... 86 7.2. Materials and Methods ...... 86 7.3. Results and Discussion ...... 86 7.4. Conclusions ...... 89 CHAPTER 8: Conclusions and Future Works ...... 90 8.1. Bench-Level Conclusions ...... 90 8.2. PyroHead™ Conclusions ...... 90 8.3. Suggestions for NFPA 1971 ...... 91 8.3.1. Certification Testing ...... 91 8.3.2. The Certifying TPP Rating ...... 92 8.4. Future Works ...... 93

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LIST OF TABLES

Table 2.1: Descriptions of the divisions of firefighting tactics as described by Layman [5]...... 6

Table 2.2: Description of the divisions of firefighting tactics as described by NFPA [7]...... 7

Table 2.3: Compares the Modern NFPA tactical divisions with their origin Layman divisions [6], [7]...... 8

Table 2.4: Outlines the turnout gear components and their governing sections in NFPA 1971, descriptions, and popular materials used in each component [12]-[15]...... 12

Table 2.5: Mandatory protective hood performance requirements described in NFPA 1971- 18 [12]...... 15

Table 2.6: Protective hood requirements for the optional protective barrier hoods described in NFPA 1971-18 [12]...... 15

Table 2.7: Likelihood of Cancer Risk and Summary Risk Estimate for different types of cancers [19]...... 20

Table 2.8: Properties of para-aramid fibers [24]-[27]...... 24

Table 2.9: Properties of meta-aramid fibers [24], [26], [27]...... 26

Table 2.10: Properties of Fire-Resistant Viscose Rayon [30], [31]...... 27

Table 2.11: Properties of oxidized polyacrylonitrile (OPAN) [30]...... 29

Table 2.12: Properties of Polybenzimidazole Fiber [26], [33], [37]-[39]...... 31

Table 2.13: Physical property comparison of high performance fibers used in firefighter protective hoods...... 32

Table 3.1: Estimated values of the depth of the different layers of skin at different areas around the head, face and neck compared to the estimated values used in ASTM F1930...... 47

Table 4.1: An explanation as to what each material and composite was composed of in this study...... 52

Table 4.3: All bench-level test method material results. Where the ISO 17492 test method is the continuous heating TPP method, and the ASTM F2703 test method is the abbreviated heating TPP method...... 54

Table 4.4: Regression R2 values of material properties with test results...... 59

Table 4.5: Thermal Inertia of hood materials and water for reference [52]-[54]...... 61

Table 5.1: Table outlining the compositions of the hoods used in the STP studies...... 64

Table 5.2: Number of random data sets generated for each sample size...... 73

Table 6.1: A description of the hoods in use and what their layering looks like, where the bottom layer is closest to the skin...... 79

Table 7.1: Regression R2 values of material properties versus test method results...... 87

LIST OF FIGURES

Figure 2.1: Typical turnout gear for firefighters around the 1950s, including rubber trench coat and three-quarter length rubber boots [9]...... 10

Figure 2.2: An indirect method of attack through a corner of a window while the nozzleman makes sure they are keeping below the opening to avoid escaping smoke and steam [6]...... 10

Figure 2.3: Shows the turnout ensemble from the chest up to the head with a protective hood being utilized, concealing any skin from environmental exposure...... 13

Figure 2.4: Shows turnout ensemble from the chest up to head without a protective hood being utilized, exposing skin around the neck to environmental exposure...... 13

Figure 2.5: Before and After photos of the head and neck areas showing particle penetration produced from the Fluorescent Aerosol Screening Test performed by RTI International in 2015 [65]...... 21

Figure 2.6: Comparison of normal polyamides versus aromatic polyamides [62]...... 22

Figure 2.7: Chemical structure of the para-aramid polymer [21]...... 23

Figure 2.8: Chemical structure of the meta-aramid polymer [21]...... 25

Figure 2.9: Chemical structure of the Exolit® 5060 FR additive [29]...... 27

Figure 2.10: Chemical structure change of PAN into OPAN after oxidation [63]...... 28

Figure 2.11: Original preferred polybenzimidazole as discussed by Clark and Maxwell [35]. .... 30

Figure 2.12: Poly-2,2'-(m-phenylene)-5,5'-bibenzimidazole [33]...... 30

Figure 3.1: Illustrations of the layers of normal, healthy skin versus skin that has suffered from first, second, and third-degree burns [64]...... 34

Figure 3.2: Stoll curve that models second-degree burns at varying levels of exposure at different durations [49]...... 37

Figure 3.3: Visualization of Equation 3.2 and where the burn/no burn criterion lies on the resultant raw data graph...... 37

Figure 3.4: TPP testing device in use...... 39

Figure 3.5: Chart showing that the intersection of the Stoll curve and temperature data results in a predicted second degree burn for an ISO 17492 test...... 39

Figure 3.6: Chart showing that the intersection of the Stoll curve and temperature data results in a predicted second degree burn for an ASTM F2703 test...... 41

Figure 3.7: The mounted PyroMan™ Fire Test System in use [49]...... 42

Figure 3.8: Typical display after a PyroMan™ test where yellow indicates No Burn, red indicates Second-Degree Burn and purple indicates Third-Degree Burn [49]...... 43

Figure 3.9: The mounted PyroHands™ Fire Test System [49]...... 44

Figure 3.10: Typical display after a PyroHands™ test where yellow indicates No Burn, red indicates Second-Degree Burn and purple indicates Third-Degree Burn [49]...... 44

Figure 3.11: The mounted PyroHead™ Fire Test System...... 45

Figure 3.12: Typical display after a PyroHead™ test where yellow indicates No Burn, red indicates Second-Degree Burn and purple indicates Third-Degree Burn...... 46

Figure 3.13: Graph showing that the results of the effect of exposure time on the PyroHead™ test during its development [51]...... 48

Figure 3.14: Graph showing that the results of the predicted standard error for multiple burns on the PyroHead™ fire Test System [51]...... 49

Figure 4.1: A visual representation of the firefighter protective hood materials used in this study...... 51

Figure 4.2: Time to second-degree burn for two-layer PBI/FR rayon compared to three-layer particulate-blocking composite. Error bars indicate the maximum and minimum values for the ISO bars and the 95% confidence interval for the ASTM bars...... 56

Figure 4.3: Time to second-degree burn for two-layer OPAN carbon compared to three-layer particulate-blocking composite. Error bars indicate the maximum and minimum values for the ISO bars and the 95% confidence interval for the ASTM bars...... 58

Figure 4.4: The time after exposure values for the materials using the ASTM F2703 test method. Materials A, C, D, and C.1 are composed of greater than 50% FR rayon. . 60

Figure 5.1: The three different hoods used for the exposure time study donned on PyroHead™. From left to right: Hood 1, Hood 2, Hood 2.1...... 63

Figure 5.2: Locations of the heat flux sensors on PyroHead™...... 66

Figure 5.3: The three different mounting configurations donned on PyroHead™. From left to right: Hood Only, Hood/Mask, Hood/Mask/Helmet...... 67

Figure 5.4: Demonstration of the effect of changing exposure times in a test using PyroHead™. Error bars represent the maximum and minimum test results for each condition...... 68

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Figure 5.5: Demonstration of the effect of adding masks and helmets to a test at a seven second exposure using PyroHead™. Error bars represent the 95% confidence interval...... 70

Figure 5.6: Different angles of a mask donned on PyroHead™ to show that a large proportion of sensors are either partially or fully covered...... 70

Figure 5.7: Demonstration of the intraday variability of using PyroHead™ with different mounting configurations. Error bars represent the maximum and minimum values...... 71

Figure 5.8: Plot of the change in variability of PyroHead™ test results as sample size increases...... 74

Figure 5.9: 95% confidence interval of sample size standard error of the estimated sample standard deviations of every hood tested on PyroHead™ in this research project. .. 75

Figure 6.1: Traditional (top) and particulate-blocking (bottom) hoods. Traditional hoods (from left to right) are 4, 5, and 6. Particulate-blocking hoods (left to right) are 4.2, 5.1, and 6.1...... 78

Figure 6.2: Custom hoods made with particulate blocking layers of different air permeability. Hoods from left to right starting at top left are as follows: 4, 4.1, 4.2, 4.3, 4.4...... 78

Figure 6.3: Graph of the percent change in predicted percent head burn from the traditional hood to its particulate blocking counterpart. Percent change was calculated by the difference divided by the traditional hood burn percentage...... 80

Figure 6.4: Post-test PyroHead™ sensor schematics in the Traditional vs. Particulate Blocking Study...... 81

Figure 6.5: Effect of adding or replacing a knit layer with a particulate-blocking layer on thermal protection. Error bars represent the 95% confidence interval...... 82

Figure 6.6: Graph of the effect of air permeability of particulate blocking layers on PyroHead™. Error bars represent the 95% confidence interval...... 83

Figure 6.7: T-test run to compare the true means of predicted head burn of the different air permeable particulate blocking layers on PyroHead™...... 84

Figure 6.8: Photograph demonstrating the cinching of a firefighter protective hood to mitigate openings where heat and flames could travel...... 85

Figure 7.1: Averages of the results of all the hoods run on PyroHead™. The three on the right are three-layer hoods while the other 10 are two-layer hoods...... 88

Figure 7.2: T-test to compare the true means of predicted head burn of the different numbers of layers on PyroHead™...... 89

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LIST OF EQUATIONS

Equation 3.1: Predicted Burn Injury Equation ...... 35

Equation 3.2: Stoll Curve Mathematical Criterion Model ...... 36

Equation 3.3: Calculation of Standard Error...... 49

Equation 5.1: Estimation of Standard Deviation using Moving Range ...... 72

CHAPTER 1: Introduction and Proposal

1.1. Purpose

Firefighters put themselves in harm’s way every day to protect and rescue those who have been affected by disaster. Structure fires could become catastrophic when the fuel of home décor and furnishings was all wood and other natural materials. However, with the rise in cheap, synthetic modern home décor and furnishings, structure fires are reaching their most dangerous levels more quickly and the by-products of combustion are as frightening. Even though firefighters are adequately trained and protected from the fires themselves, they are experiencing alarmingly high rates of cancer. This rise in cancer rates is believed to be attributed to the large number of carcinogens in the potential toxic by-products found in smoke and soot.

A study by RTI International in 2015 showed the penetration of particles similar to soot and smoke through the turnout gear to be a major issue and source of exposure, with one of the areas of concern being around the head and neck. The rise in concern over the effects of smoke and soot in structure fires has increased the amount of research and development done to protect the firefighters from these exposures, thus the creation and implementation of particulate protective layers in firefighter protective hoods. However, since the particulate protective layers in the hood are relatively novel, it must be sure that the thermal protection properties and requirements stated in the National Fire Protection Association (NFPA) standard, NFPA 1971, are adequately maintained. The goal of this research project could create a perfect firefighter protective hood, but chances are that hood would be expensive and only positively affect those that bought said hood. By looking at the standards that govern performance and design of the protective hoods and making sure that the minimum standards are adequate to protect all firefighters, this research is able to broaden its reach and have an effect on every single firefighter.

The purpose of this research is to delve deeper into looking at the thermal protective performance of these hoods and their prospective materials. There are many methods and tools of evaluating fabric and garment performance under flashover exposures and this research will explore and evaluate those methods against themselves and against each other. In order to understand the relationships these methods have with different material properties as well as with each other. A successful research project will be able to identify the factors affecting these relationships and through working with the standard committee, impact the NFPA 1971 requirements. All this is done to ensure that firefighters present and future not only come home at the end of their shifts but allow them to fully use their pensions when they decide to retire.

1.2. Research Objectives

The research objectives this project assesses are:

1. To determine how added particulate blocking layers affect the thermal protection of hoods

at both the material and hood-level.

2. To determine how hood-level results compare with legacy bench-level thermal protection

test methods and their results.

3. To determine what additional information, data and/or insights on protective hood

performance that hood-level evaluations can provide that the bench-level testing cannot.

CHAPTER 2: Firefighting Tactics and Personal Protective Equipment

2.1. Evolution of Tactics

Ever since its discovery, fire has been one of mankind’s greatest allies as well one of its greatest foes. From being used for cooking and keeping warm to accidentally resulting in destruction and loss of life, fire has been present through it all. This beautiful product of combustion has captured the hearts and minds of mankind throughout time and new scientific discoveries dealing with fire are being made on a regular basis. Figuring out how to control and mitigate unwanted losses have and will continue to be on the minds of mankind so long as all the necessary ingredients for combustion are available: heat, fuel, and oxygen. This review will explore the evolution of the tactics and the equipment used by those who attempt to contain rogue fires.

2.1.1. Cohorts of the Watchmen

The first permanent fire brigade was established by the Romans after a major conflagration tore through Rome in the early first century AD [1]. Emperor Augustus created the “Cohortes

Vigilum” or “Vigiles” and translated to “Cohorts of the Watchmen” as the first recorded instance of a permanent firefighting organization. Just as the Night’s Watch in George R. R. Martin’s fantasy novel series “A Song of Ice and Fire” are the watchers of the wall and protectors of the realm from ice demons called White Walkers, these Vigiles were watchers of the city and protectors of Rome from the fire demons known as conflagrations [2]. This organization was split up into seven stations of 1,000 men setup in different areas of the city [1]. These early firefighters did not have any sort of protection from the flames themselves and their equipment and tactics demonstrated the lack of protection. Tools such as buckets, force-pumps, axes, ladders, grappling hooks, and water or vinegar-soaked blankets were used to attempt to control fires that broke out, but these tools were mainly only successful if the fire was found in its early stages. If the fires

4 were too large to control, the Vigiles would begin tearing off roofs and walls of the lit building or by destroying surrounding buildings in an attempt to mitigate the further spread of the fire and contain it to one specific area [3].

2.1.2. Middle Ages Europe

After the fall of the Roman Empire, another dedicated fire service was not seen or implemented until the 11th or 12th century [1]. Technology for fire control was still in its infancy and as a result, advancements were made socially instead of technologically. From the 12th to 17th centuries, laws were put into place to assist those that monitored towns at night looking for fires.

These laws consisted of requiring residents to have ladders and buckets available for quick use of neighbors and fire servicemen so that they did not have to waste time going back and forth from a water source, especially if the fire was still small upon its discovery [1]. At this point in time, tactics were still centered around prevention of fire and spreading of conflagration as opposed to fire combat.

2.1.3. American Colonization through Industrial Revolution

The 17th through 19th centuries were a time of enormous growth and technological advancement, especially for the United States. As the colonized areas of the United States experienced and suffered from tragic accidents as a result of structure fires, towns, cities, and the entire country placed rules and regulations on buildings to prevent future fires [4]. The first written regulation was by the Puritans in 1630, whom had many of the same type of fires over an eight- month period, hence drafted a regulation that banned wooden chimneys and thatch roofs [4]. A devastating fire in 1908 in the Lake View Elementary School in Ohio forced the rest of America to rethink school construction and led to new laws and standards for the construction of schools such as multiple exits and outward opening doors [4]. The early 1900s was also a time where the

5 foundations were laid for modern fire protection, departments, prevention, and suppression. To help with the inherent dangers of firefighting, the fire service was quick to adopt ideas and innovations from inventors during the industrial revolution. Larger and more powerful water pumps, silhouettes of modern American fire helmets and steam powered engines were all designed or redeveloped in the 1800s and were shown as a testament to how much innovation occurred during this period. In the late 1800s, the National Fire Protection Association (NFPA) was created to govern and standardize fire protection efforts across the country [1].

2.1.4. Layman versus Modern Tactics

2.1.4.1. Layman Tactics

Lloyd Layman was a former fire chief from the 1930s to 1960s whose research and implementation of firefighting methodologies and tactics transformed the way the fire service assesses and attacks a situation. Layman defines firefighting tactics as “the art of using man power, apparatus and equipment on the fireground” or “the method or procedure by which the officer in charge seeks to attack, control and extinguish the fire” [5]. Layman’s fundamentals of firefighting tactics were split up into six different divisions: size-up, rescue, exposures, confine fire, extinguish fire, and overhaul [5]. The final division, overhaul, is split into two subdivisions, ventilation and salvage. All these divisions are explained in Table 2.1.

Table 2.1: Descriptions of the divisions of firefighting tactics as described by Layman [5]. Division Description Situational estimate by the officer in charge where they decide 1 Size-Up what to do and how to do it. Remove any people out of harm’s way from the building to 2 Rescue safety.

3 Exposures Preventative methods of the spreading of fire to other structures.

Preventative methods of the spreading of fire to other parts of 4 Confine Fire the building on fire.

5 Extinguish Fire Attack and extinguishing of the main body of fire.

Procedures to prevent rekindling after the fire has been 6 Overhaul extinguished.

6a Ventilation Removal of smoke, gasses and hot air.

Protect building and contents from unnecessary damage from 6b Salvage water, smoke and other elements.

Layman also came up with a methodology called “the indirect method of attack” [6]. This methodology was developed during his time with the United States Coast Guard in 1943 to extinguish fuel oil fires in confined spaces on commercial and military boats and ships. This methodology showed that it was possible to control and extinguish fires in confined spaces without having to apply water directly to the surface of the burning oil. Previously, directly applying water had the potential to spread the fire as water and oil do not mix. This new methodology also allowed those fighting the fire the opportunity to diminish the conditions down to a suitable level for firefighters to enter the room or structure. After he left the U.S. Coast Guard, Layman brought these findings back to his home fire department and implemented this methodology in the late

1940s to early 1950s [6].

2.1.4.2. Modern Tactics

Modern firefighting tactics are essentially based on the research and methodologies suggested originally by Layman. The NFPA has put together a Fire Behavior Position Statement

7 that outlines suggested procedure on a fire ground. This statement is split up into nine divisions and were developed from years of research and experience. These divisions are outlined and described in Table 2.2. [7]

Table 2.2: Description of the divisions of firefighting tactics as described by NFPA [7]. Division Description Get a 360-degree view of structure, and report fire location, 1 Size-Up extent, and smoke conditions. Figure out smoke and fire entry and exit points, where to send 2 Identify the Flow Path attack crews, and where ventilation is happening. Cooling gases improves interior conditions, apply solid stream to 3 Soften the Target ceiling or seat of fire. A rapid intake of air could indicate a ventilation-limited fire (the 4 Read Smoke fire needs more air to grow). Vent Close to Fire Venting far away from the fire can increase chances of spreading 5 Origin and quicken flashover. Coordinate Ventilation Venting causes fire to grow, use water in tandem with ventilation 6 with Hose Attack to take fire from ventilation-limited to fuel limited. Vent, Enter, Isolate, Closing door of occupied room increases tenability while smoke 7 Search (VEIS) vents and gives ability to search isolated space.

8 Close the Door Room will remain tenable and increases survivability.

Control the Access Limits airflow until attack crew gets leverage on fire, then door 9 Door can be opened to release hot gasses and smoke.

2.1.4.3. Comparison of Tactics

There are apparent similarities between the different tactics of modern times, especially along the lines of what the newer tactical procedures have emulated from Layman practices.

Modern tactics have essentially reordered and modified what steps and procedures take a priority on the fireground. Table 2.3 lists the Layman tactics divisions and identifies which of the NFPA tactical procedures stemmed from each division.

Table 2.3: Compares the Modern NFPA tactical divisions with their origin Layman divisions [6], [7]. Layman Division Corresponding Modern NFPA Division(s) 1 Size-Up 1, 2 Size-Up, Identify Flow Path

2 Rescue 7, 8 VEIS, Close Door

3 Exposures 3, 4 Soften the Target, Read Smoke

4, 5, 6, Read Smoke, Vent Close to Fire Origin, Coordinate 4 Confine Fire 7, 8 Ventilation, VEIS, Close Door

5 Extinguish Fire 6, 9 Coordinate Ventilation, Control Access Door

6 Overhaul N/A N/A

There is no doubt that technology influences all phases of life and the fire service’s tactical procedures are no different. Changes in turnout gear are a heavy influence in why the fire service has felt the need to change and update how they approach and attack a fire. Modern turnout gear has given those in the fire service more of an opportunity to go deeper into the fire to perform their duty to protect others and property. This is apparent in the tactical procedures because modern tactics mandate ventilation close to the source of the fire, which was not possible with legacy personal protective equipment. Also, rescue operations are performed later in the order of duties, showing that firefighters can control the fire enough to increase survivability for potential occupants.

2.2. Changes in Turnout Gear

As mankind learned more about the world around them and explored properties and uses for different materials and processes, life became easier is some aspects and more complicated in others. These technological advances were apparent in the fire service as different materials were invented and advancements to turnout gear were made. As mentioned, the earlier tactics did not

9 require interior fire attack and focused mainly on disrupting spread of fire to other structures, therefore, turnout gear was not necessarily needed.

2.2.1. Legacy Turnout Gear

In reference to the short boots and protective pants that firefighters would put on in their bunk rooms before night calls, their gear was affectionately referred to as “bunker gear” [8].

However, during the day, firefighters would typically wear protective clothing that consisted of long trench coats and three-quarter length boots like those shown in Figure 2.1 [9]. The outer shells of both the coats and the boots were rubber to protect the firefighters from hot embers and water that had the potential to fall on them in the line of duty. For insulation from the heat emitted from the fire or to keep the firefighters warm from the cold during the winter, the coats and boots were lined with wool or cotton [8]. This version of gear allowed firefighters to go interior to attack but had to use “indirect methods of attack” as discussed by Layman [6]. With a proper indirect method of fire attack, firefighters should be able to lower the residual heat to tolerable levels for entering and operating within. Figure 2.2 illustrates the indirect method of fire attack where firefighters spray through the corner of a window while stressing that the nozzleman should stay below the hole in the window to avoid any hot smoke or steam that could escape out of said hole [6].

Figure 2.1: Typical turnout gear for firefighters around the 1950s, including rubber trench coat and three-quarter length rubber boots [9].

Figure 2.2: An indirect method of attack through a corner of a window while the nozzleman makes sure they are keeping below the opening to avoid escaping smoke and steam [6].

However, with the passing of NFPA 1500: Standard on Fire Department Occupational

Safety, Health, and Wellness Program, the trench coat and three-quarter boots combination was banned in 1987 [10], [11]. NFPA 1500 states that both the coat and pants must pass NFPA 1971:

Standard on Protective Ensembles for Structural Fire Fighting and Proximity Fire Fighting [11].

According to NFPA 1971 section 6.5.1, the “garments and their closure systems, including the coat front and the trouser fly, shall be constructed in a manner that provides continuous moisture and thermal protection” [12]. This requirement does not include the trench coat and boot combination because of the gaps in the bottom of the trench coat up into the legs of the firefighter wearing the uniform as can be noticed in Figure 2.1.

2.2.2. Modern Structural Turnout Gear

The addition of NFPA 1500 and NFPA 1971 made way for the rise in turnout gear as is recognized today. Turnout coats and pants make up the majority of the turnout ensemble, and therefore, NFPA mandates that these garments that are used for structural firefighting be made up of three parts as shown in Table 2.4: outer shell, moisture barrier, and thermal barrier [12]. As defined by NFPA 1971, “the outer shell is the outermost part of an item and does not include the supplementary parts of the item such as trim or reinforcing material” [12]. “The moisture barrier is the component that inhibits liquid transfer through the system” and finally, “the thermal barrier is the element of the item that provides the majority of the thermal protection” [12]. The increase in standard requirements coupled with technological advancements allowed firefighters to withstand more extreme environments and get closer to the main areas of the fire to control ventilation.

Table 2.4: Outlines the turnout gear components and their governing sections in NFPA 1971, descriptions, and popular materials used in each component [12]-[15]. Governing Layer NFPA 1971 Purpose Popular Materials Sections

Protects from direct flame as well polybenzimidazole (PBI), Outer 3.3, 6.1, 7.1 as gives abrasion and cut meta-aramid, para-aramid, Shell protection. polybenzoxazole (PBO)

Substrate: Prevents the transfer of liquids such PBI, meta-aramid, para- as water, aqueous film-forming- aramid, FR rayon Moisture 3.3, 6.1, 7.1 foams, gasoline, and blood-borne Barrier pathogens. Also allows perspiration Film: to move away from the body. polytetrafluoroethylene (PTFE), polyurethane (PU)

Provides most of the thermal Thermal polyimide, PBI, FR rayon, 3.3, 6.1, 7.1 protection from ambient heat. Barrier meta-aramids, para-aramids Consists of facecloth and batting.

2.3. Protective Hoods

Firefighters are asked on a normal basis to face conditions too extreme for the human body to bear, which is why turnout gear was first incorporated. Turnout gear is tasked with protecting a firefighter’s entire body from the heat and flames that they could potentially be exposed to. As a result, the turnout gear must effectively seal off any gaps and openings that could allow flames to reach any exposed skin. In 1997, NFPA updated the NFPA 1971 standard to require firefighters to wear protective hoods under their helmets and around their self-contained breathing apparatus

(SCBA) mask [16]. Firefighter protective hoods are a part of a firefighter’s standard personal protective equipment and is considered an interface item. Interface items are those that cover gaps in the protective ensemble that might not be covered by the bulk of the ensemble [17]. Other than the protective hood, the parts of the turnout gear that cover sections around the head and neck area are the coat collar, SCBA mask, helmet, and helmet earflaps as shown in Figure 2.3. Without the

13 protective hood, since the earflaps are relatively loose fitting on the wearer, it is possible for extreme heat and flames to come up into the sides and back of the neck and face as shown in Figure

2.4. However, since the protective hood is an interface item, it is not subject to some of the rigorous testing that the rest of the turnout gear is required to go through.

Figure 2.3: Shows the turnout ensemble Figure 2.4: Shows turnout ensemble from from the chest up to the head with a the chest up to head without a protective protective hood being utilized, concealing hood being utilized, exposing skin around any skin from environmental exposure. the neck to environmental exposure.

2.3.1. NFPA 1971-18 Hood Requirements

To be eligible for on-market use, any and all structural firefighter gear must pass all of the design and performance requirements mandated by the newest version of NFPA 1971, including protective hoods. NFPA 1971-2018 defines a Structural Fire Fighting Protective Hood as “the interface element of the protective ensemble that provides limited protection to the coat/helmet/SCBA facepiece interface area” [12]. NFPA 1971-18 also goes on to specify design requirements for protective hoods in section 6.13 Protective Hood Interface Component Design

Requirements for Both Ensembles. Design requirements such as the types of threads to be used,

14 what parts the hood is supposed to protect with measurements, and size of the face opening. In the

2018 edition of NFPA 1971, an optional protective barrier hood was introduced, and its design requirements are outlined in 6.14 Optional Protective Barrier Hood Interface Component Design

Requirements. These requirements include all of those specified in section 6.13 as well as how much of the hood must contain particulate blocking material [12].

Arguably, the most important directives that potential materials and hoods must pass are the performance requirements. Described in section 7.13 Protective Hood Interface Component

Performance Requirements for Both Ensembles are mandatory performance requirements that all protective hoods must meet or exceed. Then there are requirements that the optional protective barrier hoods must abide by are described in section 7.14 Additional Performance Requirements for Optional Structural Fire Fighting Protective Hood Interface Components Providing Particulate

Protection. The requirements of section 7.13 are outlined in Table 2.5 and the requirements of section 7.14 are outlined in Table 2.6.

Table 2.5: Mandatory protective hood performance requirements described in NFPA 1971-18 [12]. Test Method/ NFPA 1971 Protective Hood Property Measurement Requirement Hood Opening Size Shape Retention Shall not exceed 110% of original size Retention Test Thermal Protective Thermal Insulation Performance (TPP) TPP rating of no less than 20.0 Test – ISO 17492 Shall not have a char length of more Flame Resistance Test than 100 mm (4 in) average, after Resistance to Flame One – ASTM D6413 flame of more than 2.0 seconds, no melt or drip Heat and Thermal Resistance to Heat Shrinkage Resistance Shall not shrink more than 110% Test – ISO 17493 Cleaning Shrinkage Resistance to Shrinkage Resistance Test – Shall not shrink more than 5% AATCC 135

Thread Melt Resistance Thread Melting Test Shall not melt below 260°C (500°F)

Knit Hood Material Burst Strength Test – Burst strength not less than 225 N (51 Strength ASTM D6797 lbf) Seam Breaking Knit Hood Seam Burst strength not less than 181 N (41 Strength Test – ASTM Strength lbf) D3940

Table 2.6: Protective hood requirements for the optional protective barrier hoods described in NFPA 1971-18 [12]. Test Method/ NFPA 1971 Protective Hood Property Measurement Requirement Particulate Blocking Efficiency of no Particulate Blocking Particulate Blocking less than 90% of particle sizes between Efficiency Test – ASTM F2299M 0.1 and 1.0 µm Evaporative Heat Total Heat Loss Test – Total Heat Loss shall be no lower than Transfer ASTM F1868 325 W/m2

2.3.2. Response to Hoods

No matter how much added performance or value a product can give, there will typically be pushback by users, especially by those who have been doing things one particular way for so long. In this case, protective hoods are that product that had a great deal of additional value, but still received pushback. There is a consistent consensus between firefighters, especially experienced ones, that feel as though the protective hood impedes their instincts and how they perceive a situation. For example, before the addition of the hoods, firefighters used to use their ears as indictors as to when the environment was getting too dangerous, as told by a firefighter in the doctoral dissertation by Ward:

The turnout gear has improved our protection, but it also gives you a false sense of

security because you don’t feel what you used to. And the thing that I’ve done and

take a beating over is I won’t wear my hood the whole way. I’ll keep an ear open.

And the reason being is because I don’t feel the heat in my gear…I know it’s an old

indicator; it’s probably not the best thing [18].

With the full encapsulation of the firefighter’s person, they feel as if the turnout gear is giving them a false perception that they are safe and are going deeper into the fires. Firefighters used the exposed areas of the skin to ascertain the current environmental situation and how it is changing, while balancing that information with an understanding of one’s own limits to make split second decisions as to where one should go and how long they should stay [16]. Another firefighter commented regarding this:

Back when I first came in you always left your ears exposed so when you crawled

down the hall, you know, depending on how hot it was, your ears were always

telling you… If the place wasn’t being ventilated properly, you knew it because; of

course you get close to the ground where it was a little cooler and as soon as you

pick your head up, you could tell how hot it was. And when your ears start tingling

you know that the truck company is not ventilating the place, so back up a little bit.

Right now you’re so well protected that you feel nothing. We’ve had people, their

helmets, they just absolutely melt. And they can stay there because they’re so well

protected – which is bad… You know [Laughs], it’s good that you’re protected that

well, but it’s bad because now you’re in an environment where if something

happens to your mask, you’re dead [16].

In general, firefighters seemed to prefer the minor to moderate burns on their neck and ears and be able to sense life-threatening situations well before they arise as opposed to mitigating these burns but potentially venturing too far into the fire.

However, even with all the pushback given by firefighters regarding the protective hoods, there is a minority positive view that is shared between some of those in the fire service. According to the firefighters, the protective hoods impede their ability to prevent themselves getting into a life-threatening situation but have stated that the hoods have helped them survive flashovers and other life-threatening situations. Here is one of those firefighters’ takes with this minority view:

But, you know, the older school mentality was you know, if you got in there and the

thing started to heat up too much you could feel it. Now you can’t really feel it when

you wear that hood. It’s almost like you don’t feel it until it’s really biting you and

then it’s almost like, “Uh oh.” You know, you got to get out. But on the other hand,

if it did flashover you’d have a better chance of survival if you had it on compared

if you didn’t have it on [16].

2.3.3. Cancer Problem

Firefighters are a people of habit and tradition, and some of those traditions die hard. The incorporation of protective hoods is a prime example of the pushback firefighters give when they are asked to change their ways. As stated in the previous section, before the late 1990s, firefighters would use the exposed parts of their person to feel the environment and assess if they were going into an area too dangerous for them to be in. Most of the firefighters were trained this way and have even trained those that may have started after protective hoods were incorporated to feel the environment with their ears. Consequently, this has resulted in firefighters wearing their gear incorrectly and exposing parts of their body that should not be exposed, especially in areas around the head and neck. Little did these firefighters know that purposefully exposing themselves to the burning environment could arguably be more detrimental to their health than they might realize.

Thanks to the new technologies that go into firefighter turnout gear, firefighters are able to survive and withstand previously insurmountable conditions and come home to their families at the end of their shift. Since firefighters are, for the most part, protected from the immediate threat of extreme heat and flames, that increases the number of fires that a firefighter is involved in which also increases the amount of soot and smoke they are exposed to. However, with the mitigation of one threat to firefighters’ lives, another threat rears its head: cancer. In recent years, the fire service has been hit hard by a great deal of both active and retired firefighters being diagnosed with cancer

19 and many subsequently dying. The words “firefighter” and “cancer” have almost become affixed to each other as one cannot be brought up without the other following close behind. The threat of cancer in the fire service is a relatively new subject and recent studies are being carried out to confirm or deny the enhanced occupational risk firefighters have while doing their everyday jobs.

One group that did a meta-analysis on other smaller studies, compared the occupational risk that firefighters are diagnosed with cancer to the general population being diagnosed with the same types of cancers [19]. For example, they found that firefighters have a 2.02 times greater risk of being diagnosed with testicular cancer than the general public and a 1.53 times greater risk of being diagnosed with multiple myeloma [19]. The other types of cancers are outlined in Table 2.7 and show the estimated risk (if the general public has a risk of 1.00) and the likelihood of cancer risk which ranks from highest risk to lowest risk: probable, possible, unlikely.

Table 2.7: Likelihood of Cancer Risk and Summary Risk Estimate for different types of cancers [19]. Summary Risk Estimate Likelihood of Cancer Risk by Cancer Site (95% CI) Criteria Multiple myeloma 1.53 (1.21 – 1.94) Probable

Non-Hodgkin lymphoma 1.51 (1.31 – 1.73) Probable

Prostate 1.28 (1.15 – 1.43) Probable

Testis 2.02 (1.30 – 3.13) Possible

Skin 1.39 (1.10 – 1.73) Possible

Malignant melanoma 1.32 (1.10 – 1.57) Possible

Brain 1.32 (1.12 – 1.54) Possible

Rectum 1.29 (1.10 – 1.51) Possible Buccal cavity and 1.23 (0.96 – 1.55) Possible pharynx Stomach 1.22 (1.04 – 1.44) Possible

Colon 1.21 (1.03 – 1.41) Possible

Leukemia 1.14 (0.98 – 1.31) Possible

Larynx 1.22 (0.87 – 1.70) Unlikely

Bladder 1.20 (0.97 – 1.48) Unlikely

Esophagus 1.16 (0.86 – 1.57) Unlikely

Pancreas 1.10 (0.91 – 1.34) Unlikely

Kidney 1.07 (0.78 – 1.46) Unlikely

Hodgkin’s disease 1.07 (0.59 – 1.92) Unlikely

Liver 1.04 (0.72 – 1.49) Unlikely

Lung 1.03 (0.97 – 1.08) Unlikely

All cancers 1.05 (1.00 – 1.09) Unlikely

In a 2015 study conducted by the International Association of Fire Fighters (IAFF) and

International Personnel Protection, Inc. at RTI International (Research Triangle Park, NC), revealed that particles from soot and smoke in structure fires could penetrate the turnout gear and could potentially be the cause of spikes in cancer rates [20]. The images shown in Figure 2.5 from the Fluorescent Aerosol Screening Test (FAST) of firefighter turnout gear were some of the first qualitative pieces of data that both researchers and the fire service had that exhibited how soot and smoke had the potential to penetrate through the turnout gear and enter the bodies of the men and women in the fire service. Seeing that a great deal of particulate penetration was entering around the head and neck areas, the fire service as a whole started to embrace the protective hoods and research and development on how to mitigate these harmful chemicals from entering the turnout gear and reaching the body started and quickly became the new topic of discussion for researchers and those in the fire service alike.

Figure 2.5: Before and After photos of the head and neck areas showing particle penetration produced from the Fluorescent Aerosol Screening Test performed by RTI International in 2015 [65].

2.4. Protective Hood Materials

2.4.1. Aramids

Some of the first synthetic polymers developed were aliphatic polyamides, or nylons, and were developed by a DuPont researcher named Wallace Carothers. However, DuPont first introduced aramids to market in 1961 with the release of their Nomex® meta-aramid fiber [21].

Aramids are in the same family as polyamides as their chemical structures are extremely similar.

The only difference in these two structures is that the methylene groups in typical polyamides like nylon 6 and nylon 66, are replaced with an aromatic ring as shown in Figure 2.6, hence, the name to ‘aromatic polyamide’ or ‘aramid’ for short [22]. There are two main types of aramids, meta- aramids and para-aramids and in general, aramids are very strong and have a remarkably high resistance to heat, chemicals, and abrasion, which will be explained in the following sections.

Polyamide Aromatic Polyamide

Figure 2.6: Comparison of normal polyamides versus aromatic polyamides [62].

2.4.1.1. Para-aramids

2.4.1.1.1. Structure

Para-aramids, or poly(p-phenyleneterephthalamide), are a type of aramid with para linkages connecting the carbonyl and amine groups to the phenylene rings of the polymer. A para linkage is a linkage of a six-membered ring in the 1,4 positions as shown in Figure 2.7. Having linkages that are opposite of each other allows the polymer to be rod-like and have an affinity for tight packing and as a result, has a high degree of crystallinity and symmetry [23].

Figure 2.7: Chemical structure of the para-aramid polymer [21].

2.4.1.1.2. Properties

Since para-aramids have such a linear structure and high degree of crystallinity, they have extremely high tensile strength and modulus. Their performance-to-weight ratio indicates that para-aramids perform better than fiber-glass and steel [21]. As an added result of its highly regular structure and crystallinity, para-aramids have great thermostability and negligible shrinkage at high temperatures. Para-aramids’ high performance capabilities are also contributed to bonding characteristics such as aromatic and amide groups, and intermolecular hydrogen bonding between polymer chains [24]. Table 2.8 lists some of the important properties of para-aramids and para- aramid fibers.

Table 2.8: Properties of para-aramid fibers [24]-[27]. Property Value Units Glass Transition Temperature 322 °C (Tg)

Degradation Temperature (Td) 500 °C

Limiting Oxygen Index (LOI) 29 %

Density 1.45 g/cm3

Tenacity 190-240 cN/tex

Elongation at Break 1-4 %

Thermal Conductivity 0.04 W/m-K

Specific Heat 1,400 J/kg-K

2.4.1.2. Meta-aramids

2.4.1.2.1. Structure

Meta-aramids are extremely similar to para-aramids and are again characterized by their backbone linkages. Meta-aramids have meta-linkages connecting the carbonyl and amine groups to the phenylene rings, which are connections at the 1,3 positions on the phenylene ring, as shown in Figure 2.8. Meta-linkages in the backbone create a zigzag-like backbone structure [23]. This, coupled with the high energy barrier of internal rotations of the strong bonds in the backbone do not allow the polymer chain to extend completely [27]. Since the polymer chain is not allowed to extend completely, meta-aramids have a semi-crystalline structure with the fibers containing both partially oriented and partially crystalline regions.

Figure 2.8: Chemical structure of the meta-aramid polymer [21].

2.4.1.2.2. Properties

With meta-aramids being flexible, chain-folding, semi-crystalline polymers, they typically show signs of lower performance than their para-linked counterparts. However, because of the phenylene-amide and carbon-nitrogen bonds and overall strength of the backbone, meta-aramids still show mechanical properties that rival many high-performance polymers and fibers and are shown in Table 2.9. Meta-aramids also do not melt but degrade once at a high enough temperature.

Unlike para-aramids, once exposed to an open flame or heat source, meta-aramids will shrink [24].

This shrinking is the result of meta-aramids being semi-crystalline and less regular than para- aramids but are drawn out to be oriented and somewhat aligned during fiber spinning. Since meta- aramids have amorphous regions and are considered chain-folding polymers, the subsequent heating of the polymer causes energy to enter the amorphous regions, causing an entropic reaction.

This entropy change makes the bonds in the amorphous regions to rotate and become disordered, subsequently shortening the distance between crystalline regions, forcing the polymer to contract

[28].

Table 2.9: Properties of meta-aramid fibers [24], [26], [27]. Property Value Units Glass Transition Temperature 280 °C (Tg)

Degradation Temperature (Td) 415 °C

Limiting Oxygen Index (LOI) 28-30 %

Density 1.35 g/cm3

Tenacity 40-50 cN/tex

Elongation at Break 20 %

Thermal Conductivity 0.13 W/m-K

Specific Heat 1,200 J/kg-K

2.4.2. Fire-Resistant Viscose Rayon

2.4.2.1. Structure

Viscose rayon is a manmade fiber that comes from the building block of most plants, cellulose. However, cellulose does burn very easily and to prevent cellulosic product from catching fire, treatments to make the products fire-retardant or fire-resistant (FR) are added. These treatments can either be added as a finish in the fiber or fabric or added pre-extrusion so that the fibers are inherently FR. FR viscose rayon used for protective garments typically use the fibers that are inherently FR so that the treatment will not come off during any laundering that will take place during a garment’s lifetime [29]. When undergoing combustion, these additives typically will form a char which takes away the fuel source of the cellulose away from the combustion equation, limiting how much cellulose burns. The most used additive for protective clothing is called Exolit® 5060 and its chemical structure is shown in Figure 2.9 [29]. This additive is an insoluble solid that look like rod-shaped particles that are dispersed into the dope just before extrusion [29].

Figure 2.9: Chemical structure of the Exolit® 5060 FR additive [29].

2.4.2.2. Properties

As with any solid material, when impurities are added, typically the physical properties of the material are reduced, and adding FR particles to a viscose dope is no different. However, since

FR viscose is used in protective equipment, higher quality materials are used more often. Typical viscose is not used in the making of FR viscose, but instead a different process is used that yields a better manmade cellulosic fiber, modal. Once the FR particles are added, the modal is weaker than what it would be in its pure form, but the FR treated modal is superior in performance compared to normal viscose. Properties of FR viscose rayon are outlined in Table 2.10 [29].

Table 2.10: Properties of Fire-Resistant Viscose Rayon [30], [31]. Property Value Units

Degradation Temperature (Td) 150-200 °C

Limiting Oxygen Index (LOI) 28 %

Density 1.52 g/cm3

Tenacity 15-24 cN/tex

Elongation at Break 15-20 %

Thermal Conductivity 0.23 W/m-K

Specific Heat 1,400 J/kg-K

2.4.3. Oxidized Polyacrylonitrile (OPAN)

2.4.3.1. Structure

Oxidized polyacrylonitrile (OPAN) is carbon fiber that has been derived from polyacrylonitrile (PAN) fibers. To become a carbon fiber, PAN must go through cyclization, oxidation, and stabilization phases to effectively reorganize the backbone structure to mimic true carbon fiber as much as possible without going through the complete carbonization process which takes a lot of time, energy, and money. To become oxidized, PAN fiber goes through an oxidation oven which heats the PAN in air at 300°C so that the structure can become cyclic, as shown in

Figure 2.10 [32] .

Figure 2.10: Chemical structure change of PAN into OPAN after oxidation [63].

2.4.3.2. Properties

Since OPAN has not completely gone through the complete carbonization process to become pure graphitic crystals and still has elements such as oxygen and nitrogen in the structure, it typically has lower physical properties than its pure counterpart. Even with inferior physical properties than pure carbon fiber, OPAN, will not melt, burn, nor shrink when exposed to heat and direct flame [30]. The fewer processes allow OPAN to be much cheaper for applications that need high performance for wearables, but not exceptional performance like what would be needed in aircrafts and pressure tanks. Table 2.11 highlights some of OPAN’s physical properties.

Table 2.11: Properties of oxidized polyacrylonitrile (OPAN) [30]. Property Value Units

Degradation Temperature (Td) >450 °C

Limiting Oxygen Index (LOI) 45-55 %

Density 1.37-1.40 g/cm3

Tenacity 18.5-23 cN/tex

Elongation at Break 22-28 %

Thermal Conductivity 0.033 W/m-K

Specific Heat 740 J/kg-K

2.4.4. Polybenzimidazole (PBI)

The first time that anyone patented polybenzimidazole (PBI) technology was in 1959 by the researchers, Keith Clark Brinker and Ivan Maxwell Robinson, whom were working at DuPont at the time. After extensive research was conducted on linear condensation polymers like polyamides for example, there were still some downfalls regarding their stiffness and toughness, softening points, and resistance to water, as well as other properties. Clark and Maxwell wanted to solve these issues so continued to do research and the polymer PBI was the result of their hard work and research [33]. PBI is a unique polymer with a variety of possible variations of end group structures and synthesis techniques to create different derivatives of one of the most stable extreme environment amorphous polymers on market.

2.4.4.1. Structure

There are a number of different variations of PBI that have been researched with different types of end groups such as different substituent positions on the aromatic rings to having methylene end groups [34]. For example, the patent submitted and approved by Clark and Maxwell

30 stated that their preferred method at the time of invention contains four to eight methylene groups in the monomer, as shown in Figure 2.11 [35].

Figure 2.11: Original preferred polybenzimidazole as discussed by Clark and Maxwell [35].

However, after sixty plus years of knowledge and technology later, other structures have been experimented with and are preferred. PBI Performance Products, Inc. is the only distributer of PBI fiber in the world, therefore, the focus of this review will be on the variation that PBI

Performance Products, Inc. produces, which is poly-2,2’-(m-phenylene-5,5’-bibenzimadozle as illustrated in Figure 2.12 [36].

Figure 2.12: Poly-2,2'-(m-phenylene)-5,5'-bibenzimidazole [33].

2.4.4.2. Properties

What makes PBI extremely unique is the fact the it is an amorphous polymer yet still when it has a high molar mass, it has the highest thermal stability of those in the advanced engineering thermoplastics family. However, even though it is amorphous and considered a thermoplastic, because of its high thermal stability, PBI is not melt processable at temperatures and pressures that are easily achieved [37]. Some of the more important properties of PBI and PBI fibers are listed in Table 2.12. All previous material properties mentioned are outlined in Table 2.13.

Table 2.12: Properties of Polybenzimidazole Fiber [26], [33], [37]-[39]. Property Value Units Glass Transition Temperature 427 °C (Tg)

Degradation Temperature (Td) 760 °C

Limiting Oxygen Index (LOI) 58 %

Density 1.3 g/cm3

Tenacity 240-270 cN/tex

Elongation at Break 3 %

Thermal Conductivity 0.41 W/m-K

Specific Heat 930 J/kg-K

Table 2.13: Physical property comparison of high performance fibers used in firefighter protective hoods. Glass Limiting Degradation Elongation Thermal Specific Transition Oxygen Density Tenacity Fiber Temperature at Break Conductivity Heat Temperature Index [g/cm3] [cN/tex] (Td) [°C] [%] [W/m-K] [J/kg-K] (Tg) [°C] (LOI) [%]

Para- 322 500 29 1.45 190-240 1-4 0.04 1,400 aramid Meta- >230 415 28-30 1.35 40-50 20 0.13 1,200 aramid FR Viscose - 150-200 28 1.52 15-24 15-20 0.23 1,400 Rayon

OPAN - >450 45-55 1.37-1.40 18.5-23 22-28 0.033 740

PBI 427 760 58 1.3 240-270 3 0.41 930

CHAPTER 3: Skin and Thermal Protection

3.1. Skin Burns

Protective clothing is used so that humans are able to perform tasks with materials and in environments that are inherently too dangerous for the body to naturally handle. From uses in cooking to firefighting, protection from fire and extremely heated surfaces and environments are of the highest demand. Without protection from fire and heat energy, the skin is open to take the brunt force of the energy transfer and can result in different levels of burn injury depending on the level of exposure and the duration of exposure.

There are three main layers that makeup the anatomy of skin: epidermis, dermis, and hypodermis (or subcutaneous tissue) [40]. The epidermis is the topmost layer of the skin that consists of dead cells that shed and are replaced frequently. The second layer, dermis, produces melanin that gives skin its pigmentation and protects the lower layers and cells from ultraviolet rays. The dermis is where most of the functions of the skin take place. Blood vessels, nerves, sweat glands, hair follicles, as well as the elastic structures that enable the skin to be flexible and pliable are all contained in the dermis. The final layer, the hypodermis, is where most of the fat is stored in the skin which acts as both insulation as well as cushioning from impacts [40] .

If exposed to too much heat energy for an extended amount of time, the skin can burn, resulting in one of three levels of burn: first-degree, second-degree and third-degree. A first-degree burn will only affect the epidermis, this first layer will get red and dry and will be slightly painful, a sunburn is an example of a first-degree burn. Second-degree burns are partial thickness burns that affect both the epidermis and dermis and will often redden, swell, and blister. If a burn destroys the epidermis and dermis and begins to affect the hypodermis, is considered a third-degree burn and will appear to look discolored or even charred [41]. Figure 3.1 illustrates the layers of heathy skin as well as after a first, second and third-degree burns.

Figure 3.1: Illustrations of the layers of normal, healthy skin versus skin that has suffered from first, second, and third-degree burns [64].

3.2. Skin Burn Models

Modeling must be used to predict whether a human will sustain a burn when wearing a specific garment. Other than the fact that this type of testing for every material and garment would take too much time and money, advancements in ethics of the treatment of human subjects has prevented further burn injury testing on live subjects. Before ethical treatment was widely considered, the research and burn modeling of two researchers, Henriques and Stoll, have been the basis of burn injury prediction in most standard thermal protection test methods.

3.2.1. Studies of Thermal Injury – Henriques

In response to the high rates of injury and death caused by heat energy and fires in World

War II, Henriques and Moritz were inspired to study the effects of thermal conduction on skin.

Henriques and Moritz released multiple articles all under the title “Studies of Thermal Injuries”

[42]-[44]. Most of these studies showed the relationships between time and temperature for causing skin burns. However, the fifth paper used the data gathered in the four previous studies to derive a model for predicting when and how serious a skin burn could be expected. The Predicted

Skin Burn Injury equation (Equation 3.1) is the resulting mathematical model that Henriques and

Moritz came up with [44]. A second or third-degree burn can be predicted when the equation is integrated and the arbitrary value of Ω ≥ 1 for a specified temperature or depth of skin. A second- degree burn is predicted when Ω ≥ 1 for depths of ≥75e-6 m and <1200e-6 m, which corresponds to around the depth of the epidermal/dermal intersection. A third-degree burn is predicted when Ω

≥ 1 at a depth >1200e-6 m, which corresponds with the depth of the main portion of the dermal layer of the skin [45]. This particular predictive burn model lays the ground work for many human skin burn models, including those used in predicting burn in the ASTM F1930 Standard Test

Method for Evaluation of Flame-Resistant Clothing for Protection Against Fire Simulations Using an Instrumented Manikin [45].

푡 Ω = 푃 ∫ 푒−∆퐸/푅푇푑푡 (3.1) 0

Where,

Ω = burn injury parameter; value, ≥1 indicates predicted burn injury, unitless t = time of exposure and data collection period, s

P = pre-exponential term, dependent on depth and temperature, 1/s

ΔE = activation energy, dependent on depth and temperature, J/kmol

R = universal gas constant, 8314.5 J/mol·K

T = temperature at specified depth, K

3.2.2. Stoll Curve

Basing their study on the work done by Henriques and Moritz, Stoll and Greene continued the work of finding the relationship between skin injury due to thermal energy transfer but instead of using porcine skin, they tested using humans. In their initial study, they used three different subjects and applied thermal radiant exposures to their forearms [46]. They used the model created by Henriques, Equation 3.1, however found that the issue was that the damage during the cooling process was much more important for high intensity, short-term exposures than originally believed

[47]. Therefore, a different model was developed, called the “Stoll Curve” (shown in Figure 3.2) which is a burn/no burn criterion where if the heat exposure exceeded the threshold line, a second- degree burn was predicted. The Stoll Curve is widely used in test methods today and is employed in the Thermal Protective Performance (ISO 17492, ASTM F2700, ASTM F2703) tests as well as others. However, these test methods utilize a modified version of the Stoll Curve that has the axes of Temperature vs. Time, rather than the original Heat Exposure vs. Time. This modified version is modeled by Equation 3.2 and demonstrated by Figure 3.3.

푠 0.2901 푐푎푙/푐푚 = 1.1991 ∗ 푡푖 (3.2)

Where, ti = time value of the elapsed time since the initiation of the thermal exposure, s

Figure 3.2: Stoll curve that models second-degree burns at varying levels of exposure at different durations [49].

Stoll Curve 25

20 BURN

10 SAFE

Total Flux Total(cal/cm2sec) Flux 5

0 0 2 4 6 8 10 12 14 16 18 Time (sec)

Figure 3.3: Visualization of Equation 3.2 and where the burn/no burn criterion lies on the resultant raw data graph.

3.3. Bench-Level Test Methods

3.3.1. ISO 17492

NFPA 1971 calls out the ISO standard, ISO 17492: Clothing for protection against heat and flame – Determination of heat transmission on exposure to both flame and radiant heat in

Section 8.10 [12], [48]. A Thermal Protective Performance (TPP) Testing Device is shown in

Figure 3.4. However, there are a few modifications to the testing standard that were mentioned in the NFPA standard, such as a slight change in the exposure flux as well as the configuration of the specimens. The biggest modification to the test method was that the exposure heat flux was changed from 80 kW/m2 to 84 kW/m2 to convert easily to 2.0 cal/cm2-s [12]. These exposure heat fluxes are used because typical house fires range in temperatures from 800 - 1200°C, which can be converted into heat fluxes ranging from 75 – 250 kW/m2 (1.8 – 6.0 cal/cm2-s) [49]. At its core, the test is a continuous heating method that is used to generally characterize the amount of protection from burn injury that a clothing ensemble would give in a flashover exposure. For a properly run test, the method requires for three replicates. Figure 3.5 shows the results from a single test run. The bottom curve increasing with a greater slope is the total heat flux through the sample, while the top curve increasing at a lower rate represents the Stoll predicted burn threshold.

The intersection of the two curves is the time of a predicted second degree burn. ISO 17492 is used as the certification test that all structural firefighter protective materials and composites must undergo to be certified for garments. The turnout coat and pants must have a TPP Rating of at least

35 cal/cm2 and the protective hoods must be at minimum 20 cal/cm2 [12].

Figure 3.4: TPP testing device in use.

ISO 17492 Testing on Hood Material 35

10 Total Flux Total(cal/cm2sec) Flux 5

0 0 2 4 6 8 10 12 14 16 18 20 Time (sec) Burn Time: 12.84 sec TPP Rating: 25.6 Raw Flux Stoll Burn Data

Figure 3.5: Chart showing that the intersection of the Stoll curve and temperature data results in a predicted second degree burn for an ISO 17492 test.

After testing, a TPP Rating is reported, which is the target exposure heat flux (2.0 cal/cm2- s) multiplied by the time to predicted second-degree burn, in seconds. Some sources have led firefighters to believe that a TPP Rating is indicative of how long a wearer has in a flashover environment before a second-degree burn is suffered. One of these is in a widely used Firefighter’s

Handbook where it states: the current TPP for a structural coat is 35, that is, the wearer has 35 seconds of protection before a second degree burn is likely to be sustained” [8]. However, the

40 resulting TPP Rating has units of cal/cm2, indicating that a TPP Rating is how much heat energy per unit area a sample can withstand before a predicted second-degree burn, not the amount of time a wearer has in a flashover environment. Therefore, a TPP Rating of 35 would correspond to about 17.5 seconds of protection before a predicted second-degree burn.

3.3.2. ASTM F2703

ASTM F2703 Standard Test Method for Unsteady-State Heat Transfer Evaluation of Flame

Resistant Materials for Clothing with Burn Injury Prediction, is used as an abbreviated test that accounts for the thermal energy that may be contained inside the sample [50]. The ASTM F2703 test method is also performed using the TPP testing device used for the ISO 17492 test method.

Figure 3.6 is an illustration of the output from one sample of the ASTM F2703 test. The top curve is the same Stoll predicted burn threshold as is in the ISO standard and the bottom curve is still the total heat flux through the sample. However, the vertical line is where the exposure on the sample was taken away and is the cause of the decrease in the rate of increase in total heat flux after the first 8.5 seconds. After testing, a Thermal Performance Estimate (TPE) Rating is reported, which is the target exposure heat flux (2.0 cal/cm2-s) multiplied by the abbreviated exposure time, in seconds.

ASTM F2703 Testing on Hood Material

Total Flux Total(cal/cm2sec) Flux 5

0 0 5 10 15 20 25 30 35 40 Time (sec) Exposure Time: 8.5 sec Burn Time: 20.83 sec Stoll Burn Data Raw Flux End Exposure

Figure 3.6: Chart showing that the intersection of the Stoll curve and temperature data results in a predicted second degree burn for an ASTM F2703 test.

3.4. Manikin Test Methods

3.4.1. PyroMan™ Fire Test System

The previously mentioned bench-level methods only test thermal protection when the material or composite is flat. Garments are not worn as flat pieces of fabric and these methods do not account for the airgaps and drape that is associated with actual thermal protective garments.

Therefore, NC State’s Textile Protection and Comfort Center (TPACC) developed the PyroMan™

Fire Test System pictured in Figure 3.7. PyroMan™ is used by many research, certification, and manufacturing institutions to evaluate the thermal protective performance afforded by thermal and fire-resistant clothing. PyroMan™ is in a chamber surrounded by eight propane burners, and when ignited, like the TPP test methods, exposes the garment and manikin to 2.0 cal/cm2-s (84 kW/m2).

To simulate skin response and predict burn, PyroMan™ is covered with 122 heat flux sensors to measure the amount of heat flux that may penetrate through the garment. After the test, data

42 collected from each sensor goes through an algorithm and predicted burn injuries are calculated using the damage integral model (Equation 3.1) [45]. For each sensor, one of three displays will be shown for that sensor area: no burn, second-degree burn, or third-degree burn. On the example graphical display that is provided after a PyroMan™ test shown in Figure 3.8, yellow represents no burn, red represents second-degree burn, and purple represents third-degree burn. A total body burn is then calculated by taking the total number of sensors that received a burn and dividing it by the total number of sensors (122) and multiplying by 100% to get a final total body burn percentage. However, PyroMan™ has limitations as there are no sensors in the hands nor feet, therefore those regions are excluded. The head is also rarely dressed because of the cord escape/support out of the side of its neck. Hence, the development of PyroHands™ and

PyroHead™ were necessary.

Figure 3.7: The mounted PyroMan™ Fire Test System in use [49].

Figure 3.8: Typical display after a PyroMan™ test where yellow indicates No Burn, red indicates Second-Degree Burn and purple indicates Third-Degree Burn [49].

3.4.2. PyroHands™ Fire Test System

To combat the issue that PyroMan™ did not have sensors in its hands, NC State TPACC developed the PyroHands™ Fire Test System. Shown in Figure 3.9, PyroHands™ are two standalone hand forms that are used to test thermal protective gloves under flashover conditions.

The hand forms are surrounded by four propane burners that expose them to 2.0 cal/cm2-s (84 kW/m2). The hands have 20 sensors total along the palm and back of the hand as well as the wrist, while also having an extra sensor in the middle finger of the right hand. Henriques’ burn model

(Equation 3.1) is used for the calculation of burn prediction after the exposure in nearly the same way it is used in PyroMan™ and ASTM F1930. However, the only difference is that some of the model’s constants have been modified to account for the skin thickness difference between the skin in the torso versus the skin in the hands, fingers, and wrists. Total hand burn percentage is calculated the same in PyroHands™ as it is in PyroMan™, number of sensors detecting a burn

44 divided by total number of sensors (20), then multiplied by 100%. These results are then displayed in a similar graphic to PyroMan™, as shown in Figure 3.10.

Figure 3.9: The mounted PyroHands™ Fire Test System [49].

Figure 3.10: Typical display after a PyroHands™ test where yellow indicates No Burn, red indicates Second-Degree Burn and purple indicates Third-Degree Burn [49].

3.5. PyroHead™ Fire Test System

3.5.1. Overview

The PyroHead™ Fire Test System in TPACC at NC State is a modified version of the instrumented flame test manikins described and outlined in ASTM F1930-18 [45]. As shown in

Figure 3.11, it is placed in a chamber with propane burners that expose the head form and the garment to an average of 2.0 cal/cm2-s (84 kW/m2) of heat flux. PyroHead™ has 22 heat flux sensors located at different parts of the manikin head to predict levels of burn injury to areas of the head and neck that are calculated after the burn exposure. On the display that is provided after a

PyroHead™ test shown in Figure 3.12, yellow represents no burn, red represents second-degree burn, and purple represents third-degree burn. A total body burn is then calculated by taking the total number of sensors that received a burn, dividing it by the total number of sensors (22) and multiplying by 100% to get a final total body burn percentage.

Figure 3.11: The mounted PyroHead™ Fire Test System.

Figure 3.12: Typical display after a PyroHead™ test where yellow indicates No Burn, red indicates Second-Degree Burn and purple indicates Third-Degree Burn.

3.5.2. Burn Model Parameters – Head Skin Thicknesses

The PyroHead™ predicted burn calculation is the same as outlined for ASTM F1930 and employs Henriques predictive burn model (Equation 3.1). The PyroHead™ mathematical model uses some of the skin properties such as thermal conductivity, heat capacity and density, however, because of differences in skin thicknesses of the head as compared to the torso and forearms, some of the parameters of the model should be changed, like how they were changed in PyroHands™ development. The default skin thicknesses used in ASTM F1930 gathered from the forearm and torso are 75, 1125, and 3885 µm, respectively. Whereas there are vast differences depending on the part of the head, as outlined in Table 3.1, gathered from the final report of the development of

PyroHead™ [51].

Table 3.1: Estimated values of the depth of the different layers of skin at different areas around the head, face and neck compared to the estimated values used in ASTM F1930. Body Location Epidermis (µm) Dermis (µm) Subcutaneous (µm)

Eyelid1 50 550 600

Temple1 50 1,800 3,400

Chin1 85 1,865 1,300

Forehead1 75 1,675 3,400

Cranium1 70 1,430 3,400

Ears1 50 750 600

Cheek1 85 1,665 4,000

Neck1 85 1,765 9,900

Forearm/Torso2 75 1,125 3,885

3.5.3. Military Flash Hood Testing

PyroHead™ was originally made and developed for military head gear. The anti-flash hoods used for the military are typically single-layer hoods with just the eyes exposed. As explained in the PyroHead™ development report, to demonstrate and determine how well the

PyroHead™ system could differentiate between exposures and material thicknesses, a standard hood was chosen that was tested ten times at three different exposure times, resulting in 30 total tests. The chosen exposure times were 3.5, 4.0, and 4.5 seconds to show that the test was able to show differences between diverse levels of intensity and those results are shown in Figure 3.13.

1 Taken from PyroHead™ Development Report [51] 2 Taken from ASTM F1930 [45]

There were third-degree burns on all of the testing results because the two sensors that represent the eyes were not covered and took the brunt of the heat energy for the entire duration of the exposure. Otherwise, the study stated that the test was able to differentiate between exposure levels as evident by the increase in total predicted burn with the increase in exposure time [51].

Average Total Predicted Burn 35

30 9.09 25

15 9.09

Burn PercentageBurn 22.5 10

5 9.09 9.09

0 0 3.5 Seconds 4.0 Seconds 4.5 Seconds 2nd Degree 3rd Degree Exposure Time

Figure 3.13: Graph showing that the results of the effect of exposure time on the PyroHead™ test during its development [51].

To determine the proper number of replicates for a PyroHead™ test and provide a statistical basis, TPACC ran the standard hood 20 times at both 4 and 4.5 seconds to be able to estimate and then predict a standard error with a 95% confidence interval (Equation 3.3). The idea was to make sure that the number if replicates on PyroHead™ produced a similar Standard Error to that of

PyroMan™. After the 20 replicates, the standard deviations for the 4 and 4.5 second exposure times were 4.89 and 4.77, respectively. The assumption was made that all further tests with all possible materials and any number of replicates will have the same standard deviations at the respective exposure times. Standard error was then calculated using each standard deviation and substituting a new sample size (n) for each data point. These data points were then graphed (Figure

3.14) and the sample size with the most comparable standard error to that of PyroMan™ was chosen as the ideal number of replicates to use in a study that utilizes the PyroHead™ Fire Test

System. According to these parameters, it was chosen that five replicates would be the set number.

푠 푆퐸 = 푡훼/2 (3.3) √푛 Where,

SE = standard error tα/2 = t-distribution, α = 0.05 s = standard deviation n = sample size

Standard Error 4

0 3 4 5 6 7 8 9 10 11 12 Number of Burn Repititions 4 sec 4.5 sec PyroMan™

Figure 3.14: Graph showing that the results of the predicted standard error for multiple burns on the PyroHead™ fire Test System [51].

CHAPTER 4: Bench-Level Thermal Protective Performance Testing on Firefighter Protective Hood Materials

4.1. Introduction and Background

As a novel layer being added into the firefighter protective hoods, there must be discussion as to how these particulate-blocking layers effect the overall performance of the hoods. This section discusses an evaluation of the thermal protective performance of firefighter protective hood materials. The eleven materials/composites used are all available on the market and the composites are tested both with and without particulate blocking layers. This section also discusses different bench-level methods of testing the thermal protection of these materials.

4.2. Materials and Methods

4.2.1. Test Materials

All the materials shown in Figure 4.1 and explained in Table 4.1 that were used in this study are either able to be found and purchased in the marketplace or were made by manufacturers of hood outer materials and/or particulate-blocking layers. The samples prepared for testing were constructed either in accordance with how they are found in a firefighter protective hood on the market, tested as a two-layer composite, or as a three-layer composite where the outer layers are identical, and the inner layer is a particulate-blocking layer. Materials were all tested as received as rolled goods and after at least 24 hours of conditioning in an environment of 21°C (±2°C) and

65% (±5%) relative humidity and may not reflect results given by the manufacturer because of the preconditioning methods required in NFPA 1971 [12].

Figure 4.1: A visual representation of the firefighter protective hood materials used in this study.

All the methods used in this study are standard methods and procedures found in NFPA,

International Organization for Standardization (ISO) and American Society for Testing and

Materials (ASTM) guidelines. The two methods used in this study were ISO 17492 and ASTM

F2703 which are mentioned and outlined in Sections 3.3.1 and 3.3.2, respectively. This study tested specimens that were all new, unused materials coming from an unused roll of fabric. Each sample was conditioned and tested as a six-inch by six-inch square. All results from the TPP methods will be expressed in seconds to keep consistency in comparisons. A third data point was collected from the difference between the ASTM F2703 exposure time and the total time-to-burn to give the time after exposure. The ISO 17492 test method calls for three replicate samples while the ASTM F2703 test method calls for five replicate samples.

Table 4.1: An explanation as to what each material and composite was composed of in this study. Air Permeability Weight for Particulate Sample Number Thickness of Particulate Material Composition Composite Blocking Name of Layers (mm) Blocking Layer (osy) (Y/N) (CFM) 80% FR rayon 20% meta-aramid A 2 13.9 1.68 N - 1x1 rib knit 7.0 oz/yd2 (osy) 100% meta-aramid B 1x1 rib knit 2 17.1 2.02 N - 8.5 osy 80% FR rayon 20% polybenzimidazole C 2 12.3 1.50 N - 1x1 rib knit 6.5 osy 40% polyimide (trilobal fiber cross section) 55% FR rayon D 5% para-aramid 2 16.7 1.89 N - 1x1 rib knit 8.0 osy 65% oxidized polyacrylonitrile (OPAN) 35% artificial triblend E 2 14.2 1.87 N - 1x1 thermal knit 6.5 osy 65% oxidized polyacrylonitrile (OPAN) 35% artificial triblend F 2 15.3 1.83 N - 1x1 rib knit 6.5 osy Material C is the outer layering C.1 Nonwoven particulate layer [0.8 osy] 3 14.4 1.80 Y - All layers are quilted together

Table 4.1 (continued).

Material F is the outer layering F.1 3 18.8 2.42 Y 761.2 Two laminated knit structures

Material F is the outer layering Polytetrafluoroethylene (PTFE) particulate F.2 3 19.0 2.46 Y 12.2 blocking layer with “high” air permeability Laminated between two knit structures Material F is the outer layering PTFE particulate blocking layer with “low” F.3 3 20.0 2.52 Y < 0.56 air permeability Laminated between two knit structures Material F is the outer layering PTFE particulate blocking layer with an F.4 impermeable polyurethane (PU) coating 3 21.5 2.50 Y < 0.56 Laminated between two knit structures – similar to a turnout moisture barrier

The hood materials used in this study (outlined in Table 4.1) were chosen because they are all representative of particulate and non-particulate blocking firefighter protective hoods on the market. They were also selected to be able to evaluate the difference between a range of available materials used for firefighter protective hoods, as well as evaluate the effects of different types of particulate blocking layers.

4.3. Results and Discussion

4.3.1. Full Results

All results gathered as a part of this study for each material is outlined in Table 4.2 and are listed as the average results from each test methods.

Table 4.2: All bench-level test method material results. Where the ISO 17492 test method is the continuous heating TPP method, and the ASTM F2703 test method is the abbreviated heating TPP method. ISO 17492 ASTM F2703 ASTM F2703 Time ASTM F2703 Time Material (sec) Exposure Time (sec) to Burn (sec) After Exposure (sec) A 9.6 7.0 12.8 5.8 B 11.2 9.0 21.9 12.9 C 9.5 8.7 13.2 4.5 D 9.6 8.0 11.7 3.7 E 13.0 8.8 20.1 11.3 F 13.2 8.0 19.4 11.4 C.1 12.6 11.8 17.7 5.9 F.1 15.4 9.7 25.0 15.3 F.2 17.2 10.7 23.2 12.5 F.3 17.6 11.7 28.1 16.4 F.4 19.9 11.2 33.7 22.5

4.3.2. Addition of Particulate-Blocking Layer

There were two different types of particulate-blocking layers added to two separate outer materials so that the particulate-blocking layers could be directly compared. Material C, the

PBI/FR rayon blend, had an air permeable flame resistant nonwoven particulate-blocking layer added to create Material C.1. While Material F, the carbon knit, were made with four different variations of PTFE particulate-blocking layers that differed by their air permeability.

To assess the effect of an air permeable particulate-blocking layer, the PBI/FR rayon knit,

Material C, was evaluated as the two-layers of knit and three-layers with particulate-blocking material as the inner layer, Material C.1. The two-layer composite showed an average time-to- second-degree burn using the ISO 17492 method of 9.9 seconds, which was on the lower end of performance for the materials. On the ASTM F2703 method, the composite performed poorly on both the average exposure time as well as the average time-to-burn, with times of 8.7 seconds and

13.2 seconds, respectively. When the nonwoven particulate barrier was added, the average time- to-burn for each of the thermal performance methods were increased to 12.6 (ISO), 11.8 (ASTM exposure time), and 17.7 (ASTM time-to-burn) seconds, respectively. All these results are shown on Figure 4.2. These test results show that the added particulate-blocking layer increases thermal protection because of the longer times of exposure and predicted second-degree burn. This is attributed to the extra layering of the composites and reinforces the notion of added thickness equates to added insulation and protection. The two methods give different time-to-burn values because the ASTM method allows heat energy to escape to the surroundings after the exposure is finished, while the ISO method saturates the sample until a predicted burn.

ISO 17492 ASTM F2703 Exposure ASTM F2703 Total

20.00 18.00 16.00 14.00 12.00 10.00

Time Time (sec) 8.00 6.00 4.00 2.00 0.00 C C.1 Material

Figure 4.2: Time to second-degree burn for two-layer PBI/FR rayon compared to three- layer particulate-blocking composite. Error bars indicate the maximum and minimum values for the ISO bars and the 95% confidence interval for the ASTM bars.

To evaluate the effect of membrane-based particulate-blocking layers with varying levels of air permeability, five composites (one two-layer and four three-layer) were constructed with the oxidized polyacrylonitrile carbon knit (Material F). The three-layer composites (F.1, F.2, F.3, and

F.4) were arranged in decreasing air permeability. The base, two-layer carbon knit (representing a traditional protective hood) showed an average time-to-burn on the ISO 17492 method to be 13.2 seconds which was the highest performance of any of the two-layer knit non-particulate blocking composites. When the ASTM F2703 method was performed, the sample performed on the lower end of the samples tested for both the exposure time as well as the time-to-burn with average times of 8.0 and 19.4 seconds, respectively.

The addition of the PTFE membrane-based particulate layers also increased the time-to burn of the composites in all the methods performed, showing an increase in thermal protection.

For Materials F.1, F.2, F.3, and F.4, they all resulted in average time-to-burn in the ISO 17492 method of 15.4, 17.2, 17.6, and 19.9 seconds, respectively. After the ASTM F2703 tests were

57 performed, these materials all resulted in average exposure times of 9.7, 10.7, 11.7, and 11.2 seconds, with total time-to-burn of 25.0, 23.2, 28.1, and 33.7 seconds, all respectively. All these data points are shown on Figure 4.3. The increase in protection from the traditional hood composite to the particulate-blocking composite can again be contributed to the added layering and thickness.

The steady increase in thermal protection in the ISO test results for the four PTFE membrane- based composites indicate that the increase in mass allowed the composites to hold more heat energy and prevent that energy from penetrating through to the heat flux sensor. There is a sharp decrease in the ASTM total time-to-burn between F.1 and F.2 because of the PFTE laminate F.2 has that F.1 does not. Without the laminate layer, the “particulate-blocking” layer that is in F.1 is extremely porous and therefore acts like an air trap where air is able to be kept still and can act like an insulator for the composite, increasing the time that it takes for energy to pass through the composite. The amount of protection shown by the ASTM test method was offset by weights and low permeability of the F.3 and F.4 materials when compared to the amount given by the extra air layer in F.1.

ISO 17492 ASTM F2703 Exposure ASTM F2703 Total 40.00

35.00

30.00

25.00

20.00

Time Time (sec) 15.00

10.00

5.00

0.00 F F.1 F.2 F.3 F.4 Material

Figure 4.3: Time to second-degree burn for two-layer OPAN carbon compared to three- layer particulate-blocking composite. Error bars indicate the maximum and minimum values for the ISO bars and the 95% confidence interval for the ASTM bars.

At all facets, the addition of these particulate-blocking layers resulted in an increase in predicted thermal protection. This increase in thermal protection can most significantly be attributed to the added thickness of the composites. As additional layers were added and the thickness of the composite increased, there was a relatively significant positive correlation between the results of the ISO 17492 method as well as the ASTM F2703 test method. The R2 values of the material thicknesses and weights versus each of the TPP test results that illustrate their correlations are shown in Table 4.3. Relative to the other categories, the ASTM exposure time had a low correlation with the thickness and the weight of the samples. This is likely because the exposure time was kept as constant as possible so that each sample tested with the ASTM test method would receive the level of exposure. The other three categories were results of a specific exposure and are more indicative of thermal protection, hence the high correlations with thickness and weight.

Table 4.3: Regression R2 values of material properties with test results. Correlation R2 Value Thickness vs. ISO 0.8277

Weight vs. ISO 0.7304

Thickness vs. ASTM Exposure Time 0.4368

Weight vs. ASTM Exposure Time 0.3358

Thickness vs. ASTM Total Time 0.7498

Weight vs. ASTM Total Time 0.7127

Thickness vs. ASTM Time After Exposure 0.6889

Weight vs. ASTM Time After Exposure 0.6848

4.3.3. Effect of Rayon

Four of the eleven materials tested had greater than 50% fire resistant (FR) rayon in the construction. There was a significant effect that FR rayon had on the amount of time that it took the samples to reach a second-degree burn after the exposure in the ASTM F2703 test, which is shown on Figure 4.4. All the samples with FR rayon (samples A, C, D, C.1) reached a second- degree burn much quicker (all less than six seconds) than the rest of the samples (all above eleven seconds).

30.00

25.00

20.00

15.00

Time Time (sec) 10.00

5.00

0.00 A B C D E F C.1 F.1 F.2 F.3 F.4 Material Figure 4.4: The time after exposure values for the materials using the ASTM F2703 test method. Materials A, C, D, and C.1 are composed of greater than 50% FR rayon.

A short amount of time to a burn after the exposure had been taken away from the sample shows that the sample in question is able to not only store a large amount of heat energy that is exposed to but is also able to transfer that energy very quickly through the sample and to the sensor, resulting in a predicted burn. All the samples with over 50% rayon showed these shorter times in between the time the exposure was removed to the time-to-burn. When looking at thermal inertia values calculated and shown for different materials in Table 4.4, rayon has one of the highest.

Thermal inertia was calculated by multiplying thermal conductivity (k), density (ρ), and specific heat (c) together as stated by Stoll and Greene [46]. This shows that rayon has a relatively high resistance to temperature change. Therefore, once the sample is taken away from the exposure, it has a difficult time releasing that heat energy to the surrounding air, leaving all the energy in the sample available for conductive transfer to the body.

Table 4.4: Thermal Inertia of hood materials and water for reference [52]-[54]. Thermal Inertia (k*ρ*c) Material [105 J2/m4-K2-s] OPAN 0.342

Para-aramid 0.812

Meta-aramid 2.106

Polyimide 3.708

Rayon 4.894

PBI 4.957

PU 4.420

PTFE 6.766

Water 25.367

4.4. Conclusions

Each test method has their own advantages and pitfalls. The ISO test method is easy to run, quick to run, low maintenance and consistent. However, the ASTM method is a relatively difficult test method to keep consistent if the user is attempting to find the maximum exposure time a composite can withstand. The addition of these particulate-blocking layers resulted in an increase of thermal protection, adding to the thickness and weight of the hood composites which has shown a correlation to thermal protection. Rayon has a higher thermal inertia than most of the other materials and therefore can only transfer the heat from the exposure through conduction to the body, resulting in protective hoods with rayon to allow for little time to be removed after a flashfire exposure before a burn can occur. We have the basis of the effects of the particulate-blocking layer from a bench level standpoint, the performance requirements of the hoods can now be properly assessed and evaluated.

CHAPTER 5: Determining a Standard Testing Procedure for Testing Firefighter Protective Hoods on PyroHead™ Fire Test System

5.1. Introduction and Background

In the late 1990s into the early 2000s, the British Royal Navy developed and tested with an instrumented manikin head form for flash fire protection [55]-[58]. The Royal Navy developed this head form for the same reasons as TPACC developed theirs: it provided an increase in sensors for the head and neck area as compared to the full body manikin, and garments for the head are able to be tested properly and how they would be worn in real life situations [56].

As previously stated in Section 3.5, PyroHead™ was originally developed for the assessment and evaluation tool for military flash hoods. These military flash hoods typically consist of one to two layers of relatively lightweight material so that military personnel may run missions and perform other tasks unhindered by the looming threat of heat strain. As firefighter protective hoods are typically constructed of more layers and heavier-weight materials, the same procedures for military flash hood testing on PyroHead™ may not be adequate. Changes in materials, layers and weight have a significant impact on thermal protection and therefore, could potentially have a significant impact on the necessary burn duration and mounting configurations.

This section will go through the methodology and analysis of determining a Standard Testing

Procedure (STP) for testing firefighter protective hoods on PyroHead™.

5.2. Materials and Methods

5.2.1. Materials

5.2.1.1. Exposure Time Study Materials

The study to determine the proper exposure time utilized three different types of on market firefighter hoods with one having a particulate blocking layer and the other two not having the extra layer. Each hood was provided by manufacturers and were tested brand new out of the

63 package and after at least 24 hours of conditioning in an environment of 21°C (±2°C) and 65%

(±5%) relative humidity. The selected hoods were as follows:

• Hood 1 was a two-layer, 65/35 OPAN/artificial triblend blend, 1x1 thermal knit, non-

particulate blocking hood.

• Hood 2 was a two-layer, 20/80 meta-aramid/FR rayon blend, 1x1 rib knit, non-particulate

blocking hood.

• Hood 2.1 was a three-layer hood with the outer layers being the same blend as in Hood 2

with the layer in between being a PTFE film particulate blocking layer laminated on a

meta-aramid knit.

Each type of hood was tested nine times with a total of 27 hoods being used and tested by the end of the study. Mounted hoods that were used in this study are shown in Figure 5.1..

Hood 1 Hood 2 Hood 2.1 Traditional hood Traditional hood Particulate-blocking hood oxidized PAN meta-aramid blend meta-aramid blend

Figure 5.1: The three different hoods used for the exposure time study donned on PyroHead™. From left to right: Hood 1, Hood 2, Hood 2.1.

5.2.1.2. Mounting Configuration Study Materials

The mounting procedure study employed the use of all consistent types of firefighter protective hoods, self-contained breathing apparatus (SCBA) masks, firefighter helmets and earflaps. The hoods (listed here as Hood 3) were all new, unused two-layer, 100% meta-aramid, non-particulate hoods that were each tested one time to evaluate performance. This hood was chosen because meta-aramid based hoods are widely used in the fire service due to their protective performance abilities and low cost, and it was also anticipated that this hood could become a control hood for future testing to maintain consistency. The masks used were Scott™ AV-3000 full-face mask respirators and the helmets were LION® American Legend™ helmets with LION® issued earflaps with the fittings and visors removed. The masks and helmets were used because they were the materials that were on hand or provided by a manufacturer. As a result of material limitations, cost restrictions and material durability, masks and helmets were replaced after three tests. However, the earflaps were replaced after each test since they were destroyed after each test.

A total of 27 hoods, six masks, three helmets and nine earflaps were used and tested.

Table 5.1: Table outlining the compositions of the hoods used in the STP studies. Hood Skin Layer Particulate Layer Outer Layer 1 OPAN thermal knit - OPAN thermal knit

80/20 Meta-aramid/ 80/20 Meta-aramid/ 2 - FR rayon blend FR rayon blend 80/20 Meta-aramid/ Laminated PTFE 80/20 Meta-aramid/ 2.1 FR rayon blend Film on Meta-aramid FR rayon blend

3 100% Meta-aramid - 100% Meta-aramid

5.2.2. Methods

The PyroHead™ Instrumented Fire Test Manikin Head in the Textile Protection and

Comfort Center (TPACC) at North Carolina State University is a modified version of the instrumented flame test manikins described and outlined in ASTM F1930-18: Standard Test

Method for Evaluation of Flame-Resistant Clothing for Protection Against Fire Simulations Using an Instrumented Manikin [45]. PyroHead™ has 22 heat flux sensors located at different parts of the manikin head (shown in Figure 5.2) to predict levels of burn injury to areas of the head and neck that are calculated after the burn exposure. This test chamber was set up in accordance with

ASTM F1930-18 using six propane fuel burners all positioned equidistant from one another. The donning methods for each mounting configuration are listed as follows:

• Hood Only: Place hood fully over the head form and make sure that other than those

representing the eyes, all sensors are covered and cannot be potentially subject to

unnecessary heat and flame exposure.

• Hood and Mask: Place hood fully over and through the head form so that the face opening

of the hood is around the neck of the head form. Fit mask on the face and straps over the

top and back of the head form and tighten straps. Bring the face opening of the hood over

the top of the head so that the face opening of the hood fits flush around the gasket of the

mask. Make sure all sensors are covered and cannot be potentially subject to unnecessary

heat and flame exposure.

• Hood, Mask, Helmet and Earflaps: Follow directions for Hood and Mask configuration.

Place helmet on top of the head form, making sure that the brim of the helmet is flat and

not leaning. Then make sure the earflaps are hanging down freely over the back and sides

of the head form.

Figure 5.2: Locations of the heat flux sensors on PyroHead™.

5.2.2.1. Exposure Time Study

Exposure time of important value because if the exposure is not intense enough, all the hoods tested will receive low amounts of head burn and there will be little to differentiate between hoods. On the contrary, if the exposure is too intense, all hoods will receive a high burn percentage and yet again, there will be little differentiate performance between hoods. Therefore, an optimal exposure intensity must be found in order to differentiate between hoods and their performance levels, which was the main goal of this study. This study looked at the effects of three different exposure times: five seconds, seven seconds, and nine seconds. Each exposure time was tested on three different commercially available firefighter protective hoods, with three replicates per hood.

This study was run strictly with the hood only configuration

5.2.2.2. Mounting Configuration Study

The second study utilized the single meta-aramid hood type with three different mounting procedure/head ensembles: mounting with just the hood, mounting with the hood and mask, and then mounting with the hood, mask, and helmet with earflaps. Each mounting configuration was tested three times over three separate days for nine total replicates. The masks all have holes in the front of the face piece where the SCBA regulator is attached and, so to prevent heat and flames from entering the mask through the connection at the mouth, the hole was filled and insulated with turnout gear thermal liner. Mounting procedure options are shown in Figure 5.3..

Figure 5.3: The three different mounting configurations donned on PyroHead™. From left to right: Hood Only, Hood/Mask, Hood/Mask/Helmet.

5.3. Results and Discussion

5.3.1. Determining Exposure Time

A preliminary study was run to have a general understanding about where the exposure time should be led to the decision of testing hoods at five, seven, and nine seconds. For the exposure durations, there was a general increase in predicted head burn with the increase in exposure time which shows a decrease in protection, evident in Figure 5.4. Both the two-layer

68 hoods (Hood 1 and 2) afforded roughly the same amount of protection at all three levels of exposure. The three-layer particulate blocking hood (Hood 2.1) showed an increase in protection as compared to the two-layer hoods as can be seen by the decrease in predicted percent burn at all three exposure durations. From the results of the three tested exposure times, the seven second exposures showed the largest difference in predicted burn between the three-layer hood and the two-layer hoods, showing that a time of seven seconds gives more opportunity to spot performance differences between traditional and particulate-blocking hoods. As each hood at each exposure time was tested at three repetitions, the small sample size could potentially be a false indicator of the true predicted burn percentage of each hood. Statistical analysis of sample sizes will be discussed in Section 5.3.3.

Hood 1 Hood 2 Hood 2.1 100.00 90.00 80.00 70.00 60.00 50.00

40.00 Head (%)Burn 30.00 20.00 10.00 0.00 5 sec 7 sec 9 sec Exposure Time

Figure 5.4: Demonstration of the effect of changing exposure times in a test using PyroHead™. Error bars represent the maximum and minimum test results for each condition.

5.3.2. Determining a Mounting Configuration

Although these test results suggest high predicted burn percentages, firefighters should still have much more protection due to the mandatory wear of masks and helmets. Predicted thermal protection increased as the mask, helmet and earflaps were added to the mounting configuration.

However, there was a massive increase in predicted thermal protection when the mask was added.

As shown in Figure 5.5, the average head burn percentage dropped from around 68% for the hood only configuration to approximately 14% when the mask was donned with the hood. This significant increase in thermal protection can be related to the number of sensors that are covered by the face piece and straps of the mask. Figure 5.6 shows PyroHead™ from different angles to demonstrate the number of sensors either partially or fully covered by the mask and head strap. In all, of the 22 sensors that PyroHead™ has on its head and neck regions, the mask and head straps cover roughly 15 of those sensors, leaving only seven of the sensors available to measure heat flux able to penetrate through only the hood, the equivalent of 31.82% of the head form. Since the mask and head straps covered so many of the sensors, adding the helmet only marginally increased the thermal protection by dropping the average predicted burn results for the mask from around 14% to around 4%. Therefore, this proves that if the required head gear is worn properly, firefighters can significantly increase the amount of thermal protection the gear provides.

80.00

70.00

60.00

50.00

40.00

30.00 Head (%)Burn

20.00

10.00

0.00 Hood Hood/Mask Hood/Mask/Helmet Mounting Method

Figure 5.5: Demonstration of the effect of adding masks and helmets to a test at a seven second exposure using PyroHead™. Error bars represent the 95% confidence interval.

Figure 5.6: Different angles of a mask donned on PyroHead™ to show that a large proportion of sensors are either partially or fully covered.

Flames are inherently hard to control because of their light weight and turbulent flow of the combustible gases. Therefore, the intra-day variability of the PyroHead™ test for firefighter hoods was explored and shown in Figure 5.7. There was some variability between days of testing, however, the trends of an increase or decrease in average protection by day was consistent

71 throughout the mounting configurations and seem to be close enough in value that any suspicions suggesting that the test is too variable are not warranted.

Hood Hood/Mask Hood/Mask/Helmet 90.00 80.00 70.00 60.00 50.00 40.00

30.00 Head (%)Burn 20.00 10.00 0.00 Day 1 Day 2 Day 3 Testing Day Figure 5.7: Demonstration of the intraday variability of using PyroHead™ with different mounting configurations. Error bars represent the maximum and minimum values.

After testing and data analysis, it was concluded that the mounting configuration to be used in the final STP was the hood only configuration. Although the hood only configuration had the highest amount of variability of the tested configurations, it was not hindered by the fact that most of the sensors were covered by anything that could artificially block heat from penetrating through to the sensors. This coupled with the fact that burning masks and helmets is cost prohibitive for research and standardized testing, in limited supply, and/or difficult to get donated from a manufacturer, the hood only configuration offered the easiest, most cost-effective way for firefighter protective hood thermal protection analysis using PyroHead™. Since the configurations using the mask and helmet received such low predicted burns at a seven second exposure, increasing the exposure time could be plausible, in the case of testing requiring the full head ensemble.

5.3.3. Determining Number of Replicates

As mentioned in Sections 3.4 and 3.5 detailing the development of PyroHands™ and

PyroHead™, both development studies found that to produce data with roughly the same 95% confidence interval as that produced on PyroMan™, each must run five replicates of a sample. The

PyroHead™ development, again, was run using military flash hoods, therefore, this study used statistical analysis of the results of the hood only configuration to determine if a five replicate test is the proper sample size for testing firefighter protective hoods on PyroHead™.

For data sets with sample sizes smaller than 10, a typical calculation of standard deviation cannot be considered representative of the population standard deviation. Therefore, the standard deviation must be estimated (푠̂) using the moving range of the sample, as shown in Equation 5.1, for samples smaller than six where 퐷2 is a constant based on the sample size which is based off years of research in control charts where the typical sample size is five [59]-[61].

푀푅 max() − min() 푠̂ = = (5.1) 퐷2 퐷2 Where,

푠̂ = estimated standard deviation

푀푅 = moving range

퐷2 = D2 constant

In order to account for variation due to material and design differences, all the data gathered on PyroHead™ throughout this research project was analyzed. Of the 27 tests run during the mounting configuration portion of this study, the nine tests run with the hood only configuration plus another three tests were used for further statistical analysis. To see what the impact of sample size has on the standard deviation of the hood only configuration, a Monte Carlo simulation technique was utilized to estimate standard deviations. Therefore, random samples of two to 11

73 were chosen out of the 12 data points to calculate if that many had been tested. The number of sample sets taken for each sample size outlined in Table 5.2 which was based on a percentage of the total number of combinations of the sample size exist in the 12-sample total set. Both the average and standard deviations of the estimated standard deviations of the random sets were calculated and Figure 5.8 depicts the variation of the estimated standard deviations. This was done to visually plot how variable the variation could be with a change in sample size, as it cannot be assumed that all materials and designs of hoods will have the same variability. As the change in sample size can be seen to become steady-state around sample sizes five, six, and seven, it is suggested that the sample size should be kept within that range. Going past seven will result in a point of diminished return and will be unnecessarily expensive for the results shown. In order to keep a consistent sample size within PyroHands™ and the testing of military balaclavas on

PyroHead™, it was concluded that a sample size of five will be used to test firefighter protective hoods on PyroHead™.

Table 5.2: Number of random data sets generated for each sample size. Sample Size Data Sets 2 20 3 70 4 170 5 260 6 300 7 260 8 170 9 70 10 20 11 6

1.2000%

1.0000%

0.8000%

0.6000%

0.4000% Standard Deviation 0.2000%

0.0000% 2 3 4 5 6 7 8 9 10 11 Sample Size

Figure 5.8: Plot of the change in variability of PyroHead™ test results as sample size increases.

The previous analysis looked at one configuration. When calculating a confidence interval, the standard error which is the sample standard deviation (푠̂) divided by the square root the number of samples (n). To demonstrate that variation of each configuration can have impact on the standard error, the sample standard deviation was estimated for each of the 13 hoods tested throughout this research project. Using the average and standard deviation of all the sample standard deviations, the 95% confidence level of the standard error for different samples is calculated and shown in

1 Figure 5.9. So, one cannot simply look at the with a constant variation but must understand that √푛 there is a potential range when selecting the sample size. With a sample size of five, the upper confidence level of the standard error was 3% which is reasonable.

0.06

0.05

0.04

0.03 Standard Error 0.02

0.01

0 2 3 4 5 6 7 8 9 10 11 Mean LCI UCI Sample Size Figure 5.9: 95% confidence interval of sample size standard error of the estimated sample standard deviations of every hood tested on PyroHead™ in this research project.

5.4. Conclusions

At each tested exposure time of five, seven, and nine seconds, the range of the average predicted burn percentages were 22.73, 59.09, and 33.33 respectively. The exposure time of seven seconds was chosen for the evaluation of firefighter protective hoods because its results show the greatest opportunity to spot performance differences between hoods. Adding masks and helmets covers 15 of the 22 available sensors on PyroHead™, which leaves too few inhibited sensors to show accurate, quantitative performance differences between different hoods and their thermal protective performance. At the used exposure time of seven seconds found in the exposure time study, the addition of helmets to the mask configuration adds about five percent predicted burn percentage. This change is a relatively marginal amount protection if, and only if, trying to distinguish hood performance for research purposes. The change in standard deviation with the

76 increase of sample replicates reaches a steady-state from five to seven replicates. Therefore, a sample size of five replicates was chosen to stay consistent with previous research and development of PyroHands™ and PyroHead™. The determined Standard Testing Procedure

(STP) for testing performance of firefighter protective hoods will be hood configuration, at seven seconds, using five replicates.

CHAPTER 6: Testing of Firefighter Protective Hoods on PyroHead™ Fire Test System using Determined Standard Testing Procedure

6.1. Introduction and Background

As an interface component and the component that protects the head and neck areas of firefighters, the protective hood is the last line of defense for firefighters from the soot and smoke at fire scenes. The effects of the particulate-blocking layer on thermal protective performance has been explored at bench-level test methods, the next step is to explore what effects these particulate- blocking layers have when incorporated into a firefighter protective hood. This section will serve as a comparison of commercially available, traditional hoods to their commercially available particulate-blocking counterpart, as well as serve as a comparison of a set of particulate-blocking hoods of with levels of air permeability.

6.2. Materials and Methods

6.2.1. Materials

All hoods were provided by manufacturers and were tested brand new and after at least 24 hours of conditioning in an environment of 21°C (±2°C) and 65% (±5%) relative humidity. Each non-particulate blocking hood is denoted with a number (Hood #) and its particulate blocking counterpart is denoted with the same number, followed by a decimal and an iteration number

(Hood #.#). Both studies used some, but not all of the hoods listed in Table 6.1. The traditional versus particulate-blocking hood study used Hoods 4, 4.2, 5, 5.1, 6 and 6.1, are shown in Figure

6.1. The levels of air permeability study utilized Hoods 4, 4.1, 4.2, 4.3, and 4.4, are shown in

Figure 6.2.

Figure 6.1: Traditional (top) and particulate-blocking (bottom) hoods. Traditional hoods (from left to right) are 4, 5, and 6. Particulate-blocking hoods (left to right) are 4.2, 5.1, and 6.1.

Figure 6.2: Custom hoods made with particulate blocking layers of different air permeability. Hoods from left to right starting at top left are as follows: 4, 4.1, 4.2, 4.3, 4.4.

Table 6.1: A description of the hoods in use and what their layering looks like, where the bottom layer is closest to the skin. Hood Cross-section Composition Name Visualization

4 Two layers of 100% meta-aramid knits

Two Layers: 4.1 Hood 4 outer layer Two laminated meta-aramid knit structures Two Layers: Hood 4 outer layer 4.2 PTFE film with “high” air permeability Laminated between two meta-aramid knits Two Layers: Hood 4 outer layer 4.3 PTFE film with “low” air permeability Laminated between two meta-aramid knits Two Layers: Hood 4 outer layer 4.4 PTFE film with PU coating Laminated between two meta-aramid knits – similar to a turnout moisture barrier

5 Two layers of 80% FR rayon 20% PBI knits

Three Layers Quilted: 5.1 Hood 5 outer layers

Nonwoven particulate blocking middle layer SKIN

6 Two layers of 65% OPAN 35% artificial triblend knits Three Layers: Hood 6 outer layers 6.1 PTFE film middle layer Laminated on meta-aramid knit

6.2.2. Methods

This section is governed by the modified version of the ASTM F1930-18 test method for

PyroHead™ while employing the Standard Testing Procedure (STP) discussed in Chapter 5:, of hood configuration, exposure time of seven seconds, and five replicates.

6.3. Results and Discussion

6.3.1.1. Traditional versus Particulate Blocking Hoods

As particulate-blocking layers are typically stiffer and not permeable like normal knit structures, it was hypothesized that there would be a general increase in thermal protection as particulate-blocking layers either replaced or added to the existing knit fabrics in hoods. This hypothesis was correct and there was an increase in thermal protection as all the particulate- blocking hoods as compared to their traditional counterparts as shown in Figure 6.3. Another visual that shows the increase in protection comes from the PyroHead™ sensor schematic after a finished test, as shown in Figure 6.4. For Hood 4, the percent change in predicted head burn was -6%, for

Hood 5, it was -66%, and for Hood 6, it was -60%. However, when looking at Figure 6.5, it is apparent that all hoods that have two layers performed similarly, and both the three-layer hoods also performed similarly.

-10%

-20%

-30%

-40% PercentChange -50%

-60%

-70% 4 to 4.2 5 to 5.1 6 to 6.1 Relationship

4 5 6

4.2 5.1 6.1

Figure 6.4: Post-test PyroHead™ sensor schematics in the Traditional vs. Particulate Blocking Study. Yellow indicates No Burn, Red indicates 2nd-Degree Burn, Purple indicates 3rd- Degree Burn. (If in greyscale, lightest is No Burn, darkest is 3rd-Degree Burn)

Traditional Particulate 100.00 90.00 80.00 70.00 60.00 50.00 40.00 % Head % Burn 30.00 20.00 10.00 0.00 4 4.2 5 5.1 6 6.1 Hood

Figure 6.5: Effect of adding or replacing a knit layer with a particulate-blocking layer on thermal protection. Error bars represent the 95% confidence interval.

6.3.1.2. Levels of Air Permeability

More air permeable materials are typically more open and therefore can allow air to pass through them. It was hypothesized that if a sample was not as air permeable as another, then it would provide more thermal protection. It must be noted the air permeability values were not run a part of this study and relative air permeability of each sample as told by the manufacturer was trusted by the researchers. The results shown in Figure 6.6 show that there was a slight increase in thermal protection when the particulate blocking layer was incorporated and as air permeability decreased.

Head (%)Burn 30

0 4 4.1 4.2 4.3 4.4 Hood

Figure 6.6: Graph of the effect of air permeability of particulate blocking layers on PyroHead™. Error bars represent the 95% confidence interval.

Since the average values are all so close together, statistically, it is not possible to say that the true means of each set of data is different. Figure 6.7 shows that a t-test confirms that it is not possible to reject that Hoods 4.1 through 4.4 have different true means. This t-test did show that it is possible for Hood 4 to have a different true mean than the other four hoods. However, it must be noted that Hood 4 had a much tighter fit on the head form than the other four hoods (Figure

6.8), which restrict the air gaps that can add extra insulation and more thermal protection.

Figure 6.7: T-test run to compare the true means of predicted head burn of the different air permeable particulate blocking layers on PyroHead™.

It must be noted that Hoods 4.1 through 4.4, and (to a lesser extent) hood 5.1 were designed to be worn very loosely as their particulate blocking layers restrict the hoods from being form- fitting. With that being said, these five hoods needed to be cinched down (Figure 6.8) by rolling up the front of the bib so that there would be as small of gaps around the face seal as possible to prevent unnecessary heat and flames from entering. This could potentially be combatted by donning a mask for testing firefighter protective hoods on PyroHead™, but as mentioned in

Section 5.3.2, other potentially detrimental trade-offs could occur.

Figure 6.8: Photograph demonstrating the cinching of a firefighter protective hood to mitigate openings where heat and flames could travel.

6.4. Conclusions

The addition or incorporation of particulate-blocking layers does increase the thermal protective performance of firefighter protective hoods when tested on PyroHead™ Fire Test

System. However, the number of layers seem to take on an even more important role when determining thermal protection afforded by firefighter protective hoods, even in those with particulate-blocking layers. The added weight and thickness that an extra layer has shown to be more influential in effecting the thermal protective performance on PyroHead™ than the effects influenced by materials. Larger air gaps between the hood and the person increases thermal protection as evidence of the tight-fitting hoods 4 and 5 as compared to their loose-fitting counterparts. Therefore, PyroHead™ is seen to be more effective at recognizing the effect of bulk garment properties like design and number of layers.

CHAPTER 7: Comparison of Bench-Level Flashover Exposure Test Methods to PyroHead™ Fire Test System

7.1. Introduction and Background

For certification of thermal protection, NFPA 1971-18 requires that all firefighter protective hood materials must exceed a TPP Rating of 20 (last at least 10 seconds tested using the

ISO 17492 modified method called out in the standard) when tested as would-be-worn composites.

Some have argued that flat bench-level methods are not how fabrics are worn and therefore do not truly represent how a garment would respond under flashover conditions. Product-level tests such as the PyroMan™ family of tests have been able to show performance aspects of garments that were design or material specific that would not have been seen on traditional bench-level testing methods. This study will explore what factors correlate most with the results from each testing method and then correlate the results of each bench-level test method with the PyroHead™ results.

7.2. Materials and Methods

This study will be running statistical analysis on the results gathered from the materials and methods used for the previous chapters. The two main tools used for statistical analysis of these results was linear regression R2 values for correlation, and the use of t-tests for comparison of true means. There are mentions of linear regression and t-tests in previous sections (Sections

4.3.1 and 6.3.1.2), however, these studies only used the data gathered specifically for that analysis.

Thus, this study will use all data gathered throughout the project and may result in different conclusions than those analyzed previously.

7.3. Results and Discussion

Before test methods are run, physical data such as material thickness and weight are gathered. Material thickness and weight are said to be the two driving factors in thermal protective performance testing, and the linear regression R2 values shown in Table 7.1 seem to loosely back

87 that statement up, with thickness and weight having positive correlations throughout the test results. The only test method that has R2 values above 0.5 are the correlations of thickness and weight versus the ISO 17492 test method at 0.6683 and 0.6962, respectively. These values are smaller than those found in Chapter 4:, at 0.8277 and 0.7304, respectively. This could be attributed to the fact that thickness and weight do not hold as heavy of a correlation as once thought, or quite simply there were too few samples run in previous chapters to get a full understanding of how thickness, weight and the ISO 17492 method all relate to one another. It was a surprise to notice that all the rest of the regression results have such low correlation values. This is possibly related to how each of these test methods are run that adds more variability. The ISO method is purely a material-based test and for the most part, the data acquisition only relies on how well heat travels through the sample. On the other hand, the other tests expose a sample and then continues acquiring data after the exposure has ended, introducing other uncontrollable variables such as heat release to the surroundings.

Table 7.1: Regression R2 values of material properties versus test method results. Correlation R2 Value Thickness vs. ISO 0.6683

Weight vs. ISO 0.6962

Thickness vs. ASTM Exposure Time 0.3263

Weight vs. ASTM Exposure Time 0.4168

Thickness vs. ASTM Total Time 0.4723

Weight vs. ASTM Total Time 0.4684

Thickness vs. ASTM Time After Exposure 0.3833

Weight vs. ASTM Time After Exposure 0.3514

Thickness vs. PyroHead™ 0.1880

Weight vs PyroHead™ 0.1716

Although thickness and weight had a very low correlation with the PyroHead™ test results, there was a much simpler physical property of the materials that had a much greater role in explaining the data, the number of layers. Although the number of layers directly correlates with the thickness and weight of a sample, because of the sheer number of different materials and variations of those materials to choose from, using thickness and weight data to characterize

PyroHead™ results breaks them up by number of layers naturally. This can be shown in a graph of all the PyroHead™ testing results (Figure 7.1), because all the hoods with two layers are all above the 60% head burn mark and while the hoods with three layers are all under 40% head burn.

When running a t-test on the number of layers by the PyroHead™ results, it is possible to say that hoods with two layers have a different true mean than hoods with three layers which is shown graphically in Figure 7.2.

90.00 80.00 70.00 60.00 50.00 40.00

% Head % Burn 30.00 20.00 10.00 0.00 Two-Layer Three-Layer Hoods

Figure 7.1: Averages of the results of all the hoods run on PyroHead™. The three on the right are three-layer hoods while the other 10 are two-layer hoods.

Figure 7.2: T-test to compare the true means of predicted head burn of the different numbers of layers on PyroHead™.

7.4. Conclusions

Thickness and weight are the main driving factors for the results shown on the bench-level flashover exposure test methods such as ISO 17492 and ASTM F2703. However, the PyroHead™ test method is a test that assesses thermal protective performance based on many variables such as material, design, and size, the bulk properties that should be taken into consideration when trying to figure out what properties govern the results on PyroHead™. Therefore, it was found that the number of layers in a firefighter protective hood holds more weight in governing the results on

PyroHead™ than material properties such as thickness and weight.

CHAPTER 8: Conclusions and Future Works

The increased threat of being diagnosed and potentially dying from working is a nightmare for many firefighters that will unfortunately come to fruition. The head and neck areas have been identified as potential areas that carcinogens in soot and smoke are able to penetrate turnout gear and deposit onto and be absorbed by the skin. Therefore, protective hoods have been on the forefront of the fire industry’s mind for protection against these carcinogens. This project has looked at the incorporation of the particulate-blocking layers and their effects on thermal protection. This research has been done so that the combined results of the overarching project will be greater than the sum of its parts.

8.1. Bench-Level Conclusions

The addition and incorporation of particulate blocking layers resulted in an increase of thermal protection, which adds to the thickness and weight of the hood composites which has shown a correlation to thermal protection on bench-level thermal protective performance results.

Thermal inertia is the resistance to temperature change and therefore materials with high thermal inertia values can only transfer the heat from the exposure through conduction to the body, resulting in little time for protective hoods to be removed after a flashfire exposure before a burn can occur. In other words, as it relates to firefighter gear, equipment made from materials with high thermal inertia values will hold heat energy well and should be doffed as soon as possible to prevent unnecessary burns.

8.2. PyroHead™ Conclusions

Before the evaluation of firefighter protective hoods on PyroHead™ could occur, a

Standard Testing Procedure (STP) had to be determined to ensure consistent and accurate data.

Two studies and a statistical analysis of the results concluded that the proper STP for testing firefighter protective hoods on PyroHead™ would include three parameters: hoods will be tested

91 in a hood only configuration, the testing exposure time will be seven seconds, and hoods will be tested at five replicates per sample. The hood only configuration was chosen because adding masks and helmets covered too many sensors to be used to show thermal protective performance differences between different hoods. The exposure time of seven seconds was thought to be ideal because there was the greatest range in results between types of hoods and exhibits the greatest opportunity to identify performance differences between hoods. Starting at five replicates, the change in standard deviation with the increase of sample replicates reached a steady-state and was chosen to stay consistent with previous research and development of PyroHands™ and

PyroHead™.

PyroHead™ and other full garment testing methods are as close to real life scenarios as repeatable lab tests get. According to this research, the number of layers is the most important variable that goes into evaluating the thermal protective performance on PyroHead™. PyroHead™ is a bulk result type of test, meaning there are many variables that go into the results that are given.

Therefore, bulk properties, like design, material, and number of layers should go into the characterization of the testing of garments like PyroHead™. Layering does indeed add to the thickness and weight of a sample but adding variables to an already complex test is splitting hairs.

8.3. Suggestions for NFPA 1971

8.3.1. Certification Testing

Currently, the test method for certifying if a composite has adequate thermal protection is

ISO 17492, a thermal protective performance bench-level method that is relatively cheap and easy to conduct. This project was partially tasked with seeing if PyroHead™ could potentially become the new certification test for evaluating thermal protection in firefighter protective hoods since it is a more realistic test. After this research had been conducted, it was concluded and suggested

92 that NFPA should stick with the bench-level thermal protective performance test method. The

PyroHead™ test method has too many issues that need to be solved before it could be considered to replace the ISO method. For example, because of the head form’s small size and design differences between hoods, some hoods’ face openings are not able to fit flush on the surface of the head form and gives less than ideal potential for heat and flames to reach the heat flux sensors.

Its issues coupled with the cost for certification testing would unnecessarily inflate the price of these lifesaving protective hoods, therefore limiting access to proper protective equipment for firefighters that service smaller, low income communities.

8.3.2. The Certifying TPP Rating

The current certifying thermal protective performance (TPP) rating is 20 for firefighter protective hood composites, meaning that a sample must last for at least 10 seconds under a radiant and convective heat before a predicted second-degree burn is realized to be considered for use in a protective hood. The research done in this study has concluded that according to the mounting configuration method study in Section 5.3.2, if, and only if, all personal protective equipment

(PPE) for the head and neck areas are worn correctly, then the PPE could provide enough protection for a firefighter caught in a flashover exposure. However, citing the qualms that firefighters formerly had with the incorporation of protective hoods in Section 2.3.2, and with the newfound necessity of particulate-blocking layers in hoods, the argument will be made that the certifying TPP rating could be lowered. Before protective hoods, firefighters would use their ears as instinctive indicators of when to leave the fire, and since the incorporation of hoods, firefighters are not able to feel with their ears and are finding themselves going further and deeper into fires than they probably should. In the dissertation by Ward [18], he referenced firefighter fatality statistics and fatalities caused by on-duty accidents have stayed steady throughout the

93 incorporation of protective hoods. Therefore, it seems that either firefighters are not being adequately protected, or the more likely causes are that they are getting caught too far into fires and that they are dying on-duty from other factors such as heat stroke. Therefore, this warrants the argument that the certification TPP rating could be lowered to allow for firefighters to be able to feel the heat with their ears as well as give them adequate particulate protection.

8.4. Future Works

As mentioned before, PyroHead™ needs improvement before it can be used to adequately evaluate thermal protective performance of firefighter protective hoods. The biggest issue found was that some designs of hoods had face openings that would not fit around the face of the head form, allowing the potential for heat and flames to enter the hood. Since masks are expensive, a reusable mask bracket should be developed for PyroHead™ that allows all hoods to fit flush to mitigate the potential for heat and flames to enter the hood. According to a presentation given at an ASTM conference in 2018, the U.S. Army Natick Soldier Systems Center (Natick) has been working on 3D printed flame test manikins and could potentially help with the design, fabrication, and implementation of a cheap, potentially reusable mask bracket.

This research was conducted by using the materials and hoods of only two different hood manufacturers. Further work should utilize the STP developed in this project to test hoods from other manufacturers and assess differences in thermal protection based on design and material.

The work with particulate-blocking layers with different air permeability was the effect of material that was unintentionally received. The research team was seeking particulate blocking layers with different levels of particulate blocking efficiency but received levels of air permeability instead. Further work should include working with particulate blocking layers of different particulate blocking efficiencies.

Flashover conditions are important, as that is the worst possible scenario for a structural firefighter to be in. However, a structural firefighter is taught from day one to notice the signs of a room reaching its flashover point and avoid those at all costs. They may occasionally get caught in that situation, but it is rare. A more practical and arguably more important environmental condition that structural firefighters are exposed to is low to moderate levels of radiant exposures.

From being on the fire ground 40 feet away from the fire to being in a room close to the seat of a fire, radiant forms of heat energy are exposed on firefighters regularly and should be explored if any future work is done on firefighter protective hoods with particulate-blocking layers.

REFERENCES

[1] R. J. Coleman, "Overview if the History, Tradition, and Development of the American Fire Service," The Firefighter's Handbook: Essentials of Firefighting and Emergency Response, 2000.

[2] G. R. R. Martin, "A Song of Ice and Fire," Aug, 1996.

[3] J. Hirst, "On the Methods Used by the Ancient Romans for Extinguishing Conflagrations," Journal of the Royal Archaeological Institute of Great Britain and Ireland, vol. 41, pp. 131, 1884. Available: https://play.google.com/books/reader?id=Nf8dAAAAMAAJ&pg=GBS.PA1.

[4] D. Smith, "Dennis Smith's History of Firefighting in America," 1978.

[5] L. Layman, Fundamentals of Fire Fighting Tactics. Parkersburg, WV: Magruder Publishing Company, 1940.

[6] L. Layman, Attacking and Extinguishing Interior Fires. (Fourth ed.) Boston, MA: National Fire Protection Association, 1973.

[7] S. Kerber, "Top 20 Tactical Considerations from Firefighter Research," UL Firefighter Safety Research Institute, 2014.

[8] D. W. Dodson, "Personal Protective Clothing and Ensembles," The Firefighter's Handbook: Essentials of Firefighting and Emergency Response, 2000.

[9] JST, "JST Southwestern Ontario Boots," .

[10] M. E. Loflin, "NFPA 1500 Standard For a Fire Department OSH Program," Professional Safety, vol. 34, (4), pp. 15, 1989. Available: https://search.proquest.com/docview/200366079.

[11] NFPA, "NFPA 1500 Standard on Fire Department Occupational Safety, Health, and Wellness Program," 2018.

[12] NFPA, "NFPA 1971 Standard on Protective Ensembles for Structural Fire Fighting and Proximity Fire Fighting," 2018.

[13] Globe, "Turnout Gear Moisture Barriers," Globe Holding Company, LLC, 2017.

[14] Globe, "Turnout Gear Outer Shells," Globe Holding Company, LLC, 2017.

[15] (). Turnout Gear Thermal Liners. Available: http://globeturnoutgear.com/education/materials/turnout-gear/turnout-gear-thermal-liners.

[16] B. W. Ward, "Reaction to Safety Equipment Technology in the Workplace and Implications: A Study of the Firefighter's Hood," The Qualitative Report, vol. 22, (12), pp. 3286, 2017.

[17] J. O. Stull and G. G. Stull, "Understanding and Using Protective Hoods," FireRescue1, Jul 20, 2010.

[18] B. W. Ward, "Firefighting in the New Economy: Changes in Skill and the Impact of Technology", University of Maryland, College Park, College Park, MD, 2010.

[19] G. LeMasters et al, "Cancer Risk Among Firefighters: A Review and Meta-analysis of 32 Studies," Journal of Occupational and Environmental Medicine, vol. 48, (11), pp. 1189- 1202, 2006. Available: http://ovidsp.ovid.com/ovidweb.cgi?T=JS&NEWS=n&CSC=Y&PAGE=fulltext&D= ovft&AN=00043764-200611000-00014. DOI: 10.1097/01.jom.0000246229.68697.90.

[20] J. O. Stull and G. G. Stull, "Firefighter Research Shows PPE Exposure Risk," FireRescue1, Apr 13, 2015.

[21] J. N. Weber, "Polyamides," Kirk-Othmer Encyclopedia of Chemical Technology, vol. 19, pp. 713-738, 2007.

[22] B. L. Deopura and N. V. Padaki, "Synthetic textile fibres: Polyamide, polyester and aramid fibres," in Textiles and FashionAnonymous 2014, . DOI: 10.1016/B978-1-84569-931- 4.00005-2.

[23] G. Song and Y. Lu, "Flame resistant textiles for structural and proximity fire fighting," Handbook of Fire Resistant Textiles, pp. 520-548, 2013.

[24] M. Jassal and S. Ghosh, "Aramid Fibres - An overview," Indian Journal of Fibre and Textile Research, vol. 27, pp. 290-306, Sept, 2002.

[25] Anonymous "Kevlar - Polyaramide," Polymerdatabase.Com, 2015.

[26] R. R. Mather and R. H. Wardman, "High Performance Fibers," The Chemistry of Textile Fibers, pp. 226-259, Jun 15, 2015.

[27] H. H. Yang, "Nomex Aramid Fiber," Handbook of Fiber Science and Technology: High Technology Fibers, pp. 77-178, 1993.

[28] M. Trznadel and M. Kryszewski, "Thermal Shrinkage Of Oriented Polymers," Journal of Macromolecular Science, Part C: Polymer Reviews, vol. 32, (3-4), pp. 259-300, Aug, 1992.

[29] T. Burrow, "8 - Flame resistant manmade cellulosic fibres," Handbook of Fire Resistant Textiles, pp. 221-244, 2013.

[30] A. Handermann, "Oxidized Polyacrylonitrile Fiber Properties, Products and Applications," 2017.

[31] Engineering ToolBox, "Thermal Conductivity of common Materials and Gases," The Engineering ToolBox, 2003.

[32] Xiaosong Huang, "Fabrication and Properties of Carbon Fibers," Materials, vol. 2, (4), pp. 2369-2403, 2009. Available: https://search.proquest.com/docview/1528946037. DOI: 10.3390/ma2042369.

[33] PBI Polymer, "Celazole® PBI Polymer," PBI Performance Products, Inc., .

[34] H. Vogel and C. S. Marvel, "Polybenzimidazoles, new thermally stable polymers," Journal of Polymer Science, vol. 50, (154), pp. 511-539, 1961. DOI: 10.1002/pol.1961.1205015419.

[35] "Polybenzimidazoles,"K. C. Brinker and I. M. Robinson, , July 21, 2895948K. C. Brinker and I. M. Robinson, "Polybenzimidazoles," 2895948, July 21, 1959.

[36] PBI International, "The PBI Advantage," PBI Performance Products, Inc., .

[37] D. Kyriacos, "High-temperature engineering thermoplastics," in Brydson's Plastics Materials (Eighth Edition), M. Gilbert, Ed. Butterworth-Heinemann, 2017, pp. 593-603.

[38] D. J. Kemmish, "Polybenzimidazole," in Practical Guide to High Performance Engineering PlasticsAnonymous Smithers Rapra Technology, 2011, pp. 87-92.

[39] MakeItFrom, "Polybenzimidazole (PBI)," MakeItFrom.Com, Sept 8, 2018.

[40] J. G. Betts et al, "The Integumentary System," Anatomy and Physiology, .

[41] E. Perez, M. Foley and R. Karlin, "Classification of Burns," University of Rochester Medical Center, 2019.

[42] F. C. Henriques Jr. and A. R. Moritz, "Studies of Thermal Injury. I. The Conduction of Heat to and through Skin and the Temperatures Attained Therein. A Theoretical and an Experimental Investigation," The American Journal of Pathology, 1947.

[43] A. R. Moritz and F. C. Henriques Jr., "Studies of Thermal Injury II. The Relative Importance of Time and Surface Temperature in the Causation of Cutaneous Burns," The American Journal of Pathology, 1947.

[44] F. C. Henriques Jr., "Studies of Thermal Injury V. The Predictability and the Significance of Thermally Induced Rate Processes Leading to Irreversible Epidermal Injury," Archives of Pathology, 1947.

[45] Anonymous "ASTM F1930-17 Standard Test Method for Evaluation of Flame Resistant Clothing for Protection Against Fire Simulations Using an Instrumented Manikin," 2017. . DOI: //doi.org/10.1520/F1930-17.

[46] A. M. Stoll and L. C. Greene, "Relationship between pain and tissue damage due to thermal radiation," J. Appl. Physiol., vol. 14, (3), pp. 373-382, 1959. Available: http://jap.physiology.org/content/14/3/373.abstract.

[47] J. A. Weaver and A. M. Stoll, "Mathematical Model of Skin Exposed to Thermal Radiation," US Naval Air Development Center, 1967.

[48] Anonymous "ISO 17492 Clothing for protection against heat and flame -- Determination of heat transmission on exposure to both flame and radiant heat," 2003.

[49] A. C. Hummel, "Development of a Heat Flux Sensor to Predict Skin Burn Injury for the Fingers of the PyroHands™ Fire Test System." , ProQuest Dissertations Publishing, 2011.

[50] Anonymous "ASTM F2703-08(2013) Standard Test Method for Unsteady-State Heat Transfer Evaluation of Flame Resistant Materials for Clothing with Burn Injury Prediction," 2013. DOI: //doi.org/10.1520/F2703.

[51] Center for Research on Textile Protection and Comfort, (TPACC), "Development of an Instrumented Thermal Manikin Head for Characterizing the Thermal Protective Performance of Military Head Gear in Fire Environments," U.S. Army Soldier Systems Center (Natick), Dec, 2009.

[52] (Oct 18,). Thermal Properties. Available: https://www.tpu.covestro.com/en/Technologies/Properties/Thermal-Properties.

[53] DuPont, "Teflon PTFE," Properties Handbook.

[54] (). Overview of Materials for Polyimide. Available: http://www.matweb.com/search/DataSheet.aspx?MatGUID=ab35b368ab9c40848f545c35 bdf1a672&ckck=1.

[55] J. R. House, J. D. Squire and R. Staples, "Assessing Fire Protection Afforded by a Variety of Firefighters Hoods," Ergonomics of Protective Clothing, pp. 296-299, May, 2000.

[56] J. D. Squire, "Development of the research and technology group flammability manikin systems Squire," pp. 200-203, May, 2000.

[57] J. R. House and J. D. Squire, "Fire Hood Retains Fire Protective Qualities After Wear and Washing: The effect of wear and washing on the protection afforded by the new Royal Navy fire fighters' protective hood," International Journal of Clothing Science and Technology, vol. 16, (4), pp. 368-373, 2004.

[58] J. R. House, J. D. Squire and R. Staples, "Optimising the number of layers in firefighters' hoods," International Journal of Clothing Science and Technology, vol. 14, (2), pp. 111- 118, 2002. Available: http://www.emeraldinsight.com/doi/abs/10.1108/09556220210697466. DOI: 10.1108/09556220210697466.

[59] A. Milivojevich, "Range Statistics and d2 Constant – How to Calculate Standard Deviation," Aug 14, 2014.

[60] P. B. Patnaik, "The Use of Mean Range as an Estimator of Variance in Statistical Tests," Biometrika, vol. 37, (1), pp. 78-87, 1950. Available: http://www.jstor.org/stable/2332149. DOI: 10.2307/2332149.

[61] J. Borneman, "A Study of Estimates in Sigma in Small Sample Sizes".

[62] OpenStax, "Amines and Amides," Chemistry, Oct 1, 2014.

[63] V. Kelly, "The PAN Carbon Fiber Process".

[64] B. A. Khan, "Culture and Sensitivity of Micro-Organisms in Burn Wounds at Mayo Hospital Lahore," 2012.

[65] J. Hill and J. Hanley, "Fluorescent Aerosol Screening Test (FAST) Test Report," RTI International, Jan 7, 2015.