IH/OS-SIG WEBEX PRESENTATION JULY 22, 2020
WHAT DO HEAT STRESS MEASUREMENTS TELL US?
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MIKE SCHMOLDT, PE, CIH, CHMM [email protected] Senior Industrial Hygienist Argonne National Laboratory Graphic from NIOSH: Occupational Exposure to Heat and Hot Environments (2016) PANDA Apt # 161064
Argonne National Laboratory is a U.S. Department of Energy laboratory managed by UChicago Argonne, LLC. WHAT DO HEAT STRESS MEASUREMENTS TELL US? Objectives ▪ Why collect measurements? – To verify worker exposure is within limits – To inform and calibrate ‘professional judgement’ – To identify the need to for a ‘pause’ or safety intervention – For incident investigation ▪ Effective use of the measurements – Assess and document individual exposure – Generalize to other workers in cohort and similar work evolutions – Verify the effectiveness of selected controls for work – Build a library of site-specific detailed analysis scenarios – Improve planning for future similar task ▪ Program improvements – Examples for worker training and management/supervisors – Demonstrate effective program management – Retrospective analysis and comparison to other facilities – Analysis of trends and seasonal changes – Consistency, continuous improvement and risk reduction
2 WHAT DO HEAT STRESS MEASUREMENTS TELL US?
Three Types of Measurements
▪ Local/Regional Weather – Forecasts//historical, weather condition alerts ▪ Worksite Environmental Conditions (WBGT) – Baseline – Task specific & local – Predicted (for work planning) Complexity – Real time (for monitoring and verification) & Accuracy ▪ Physiological Monitoring – Observation of symptoms – Referral to occupational medicine provider – Heart rate (sustained and recovery) • Baseline, continuous or periodic – Body temperature • Baseline and periodic – Weight loss/urine volume
3 WHEN IS HEAT STRESS EXPECTED?
12-step decision path requires detailed data analysis if > low risk
Is excessive heat stress expected?
Is the Detailed Is the TWA screening TLV or AL table data exceeded? exceeded? analysis
Is Physiological monitoring data available?
Otherwise general or job-specific controls are required based on data
Adopted from ACGIH TLV & BEI’s Figure 1. Evaluating heat stress and strain
4 WHAT DO HEAT STRESS MEASUREMENTS TELL US?
WBGT comparison with Heat index
5 Methods described in ACGIH® documentation requiring measurements or estimated values:
• Need to determine ‘risk of excessive exposure’ Decision Logic (Figure 1) • Use of TWA-exposure limit (Figure 2) • Clothing Adjustment Factors (Table 1) • Screening Criteria for TLV and Action Limit for Heat Stress Exposure (Table 2) • Metabolic rate categories (Table 3) • Physiological monitoring • ‘Detailed analysis’
To know if worker exposure is near or above the screening criteria or TLV, you need to evaluate exposure quantitatively.
If exposure is expected to exceed limits, this may lead to physiological monitoring to objectively demonstrate that adequate protection is provided.
6 WHAT DO HEAT STRESS MEASUREMENTS TELL US?
• Additional controls • Detailed analysis • Physiological monitoring
• Work/rest cycle • Job Specific Controls
• Continuous work • General Controls
7 WIPP INCIDENT RETROSPECTIVE ANALYSIS Balancing Safety with Performance Goals (Source: User Submitted - ID: NWP-WIPP-2018-001) The Waste Isolation Pilot Plant (WIPP) ProForce organization has a strong "keep going - push through" culture that was not effectively balanced by a Safety Conscious Work Environment. This resulted in multiple employee injuries due to heat strain.
Based on the article and some conservative assumptions, the 50/50 work/rest period described is predicted to exceed the ACGIH TLV TWA for the workers.
Had an analysis like this been done during the planning state of this training, could this incident could have been anticipated and avoided?
8 COVID-19 SCREENING
At 90.3 F. WBGT, for continuous work, the TLV and Action limit would be predicted to be exceeded.
The predicted thermal exposure Time- Weighted-Average would be at the action limit but below the TLV, if a 50/50 work rest cycle is employed.
9 WHAT DO HEAT STRESS MEASUREMENTS TELL US?
Physiological Monitoring ▪ Primarily used when excessive heat strain is expected ▪ Monitors, provides feedback and documents heat strain to individual workers ▪ Variable depending on individual worker conditions – Multiple examples aid in confidence to interpreting results. ▪ Establishes a basis for evaluating similar work in comparable conditions ▪ Informs ‘professional judgement’ on effectiveness of controls and assumptions used to estimate heat stress and strain – Verifies if work/rest cycle and metabolic levels are effective as controls
Heart rate monitoring From OPEXshare by UCOR at Oak Ridge
10 Mixing and Loading depleted uranium in Cell
Graph 1: 315, Morning, Heart Rate Monitoring (heart rate limit-123)
Time In/ Out of Task Heart Rate containment (Bpm) 9:10 Out Entry 93 9:22 In Rearranging 55-gallon drum/ scooping 117 chemicals 9:33 Out Exiting 86 10:04 In Entry 92 10:23 In Doffing PPE 110 10:25 Out Exiting 104 10:45 Out Donning PPE 95 10:50 In Entry 95 11:07 In Scooping and weighing chemicals 110 11:11 In Doffing PPE 106 11:14 In Wiping Buckets 109 11:16 In Getting clearance on PAPR- re-wiping 119 11:20 Out Exiting 99
11 Removing Asbestos Calk and Elevated Window Removal
Day 1. Good recovery after initial peak, but subsequent recovery did not drop HR below 120 bpm until after stopping work
Day 2. After reviewing results from first day. Self-paced and reduced level of heat strain
12 Chemical Drum Loading, Outdoor Loading Dock
Exertional strain or heat strain?
4 minute HR peak while moving Brief HR peaks moving drums. HR consistently below Target HR value drums with rapid recovery Rapid recovery to < 120 bpm Conclusion: Exertion did not result in excessive heat strain. Spacing out high exertion tasks allowed for adequate recovery.
13 CONSIDER THIS What are the demographics (age, fitness, weight….) of your workforce now and in a few years? “…men over the age of 40 were found to be 10 times more susceptible to heat stroke than were younger men”. … however the risk of heat stroke is minimal if heat stress is kept within the limits of the TLV…” Environmental Medicine — Brooks Half of US workers in physically demanding occupations will be over the age of 45 years by 2020 –JOEH 10/2017
14 REFERENCES
Useful information on heat stress measurement
▪ Thermal Indices and Thermophysical Modeling for Heat Stress. Comprehensive Physiology (2016) George Havenith. ▪ Age, human performance and physical employment standards. Appl. Physiol. Nutr. Metb. (2016) Glen Kenney, et al. ▪ On the use of wearable physiological monitors to assess heat strain during occupational heat stress. (Review article) Appl. Physiol. Nutr. Metb. (2018) Sean Notley, et al. ▪ Occupational Heat Stress in the USA: Whither We Go? (Editorial) Industrial Health (2014) Thomas Bernard. ▪ Predicting and preventing heat stress related excessive exposures and injuries: A field-friendly tool for the safety professional. J. Chem. Health & Safety. Harry Elston, Mike Schmoldt (2019). ▪ DOE Safety and Health Regulatory Policy Response Line Documents : D19-08- 001 Thermal Stress and D19-08-0002 ACGIH TLVs (2019).
15 [email protected] Excel Spreadsheet for Heat Stress Analysis available upon request
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