Argonne National Laboratory is a U.S. Department of Energy laboratory managed by UChicago Argonne, LLC.

WHEN TO EXPECT THERMAL STRESS

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MIKE SCHMOLDT, PE, CIH, CHMMmschmoldt@anl.gov

Industrial HygienistArgonne National Laboratory

Cartoon licensed by Sidney Harris to M. Schmoldt 2019

OBJECTIVES

Recognize when excessive heat stress is expected.

1. Using screening criteria

2. By performing a more ‘detailed analysis’

3. Demonstrate calculation tools to make this process more effective and to communicate results.

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REQUIREMENTS FLOW DOWN 10 CFR 851 Worker Safety and Health Program (for Dept. of Energy sites) ACGIH® 2016 Heat Stress and Strain ACGIH® Supporting Documentation

Methods described in ACGIH® documentation:• 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)• ‘Detailed analysis’

To know if worker exposure is near or above the screening criteria or TLV, you may need to evaluate exposure quantitatively.

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3 OPTIONS FOR MANAGING HEAT STRESS

1) Screening Table: Heat Stress Exposure based on WBGTeff & Work Effort

OR2) Detailed Analysis:

• Based on objective data (historic or documented studies)• Consideration of the level Metabolic Activity (Time-Weighted Effort)• Data representing working conditions (Time-Weighted WBGTeff)

3). Physiological Monitoring (PM) • Provides real time feedback and control• Limits for ceasing exposure until recovery is complete• Basis for determining if existing controls are adequate or not

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CONSIDER THIS

“…men over the age of 40 were found to be 10 times more susceptible to heat stroke than were younger men”.

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Half of US workers in physically demanding occupationswill be over the age of 45 years by 2020 –JOEH 10/2017

… however the risk of heat stroke is minimal if heat stress is kept within the limits of the TLV…”

Environmental Medicine — Brooks

ACGIH TLV LOGIC

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Where estimated TWA-TLV / ALValues are needed

All paths lead here until you have data

Our GOALtoday

ACGIH SCREENING CRITERIA AND LIMITS

These are models based on the inputs for PPE, workload, and expected environmental conditions.

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Work in this region

HEAT STRESS EXPOSURE LIMITS

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Work in this region

Adopted from ACGIH TLV & BEI’s Figure 2 TLV and Action Limit

BEGIN WITH THE END IN MIND - STEPHEN COVEY

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The graphicaloutput makes it easy to effectively communicate the result and it’s relationship to the limits.

This often prompts meaningful discussion about what practical work control options are available and what their impact would be.

ELEMENTS OF CALCULATING TWA-TLV

Worker weight, age and acclimatization status Clothing adjustment factor for PPE What is the expected Wet Bulb Glob Temperature

(WBGT) environmental value? Metabolic level of resting, work and recovery periods Duration and number of resting, work and recovery

periods. Comparing result to TLV/AL value or screening table

values

For work planning purposes, monitoring current work or reconstructing incidents afterwards

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WHY I DEVELOPED A CALCULATION TOOL

Organizes data collection– Legibility– explanatory notes

Automates tedious chain calculation– Facilitates ‘what if’ alternative analysis– Easily modified for unique situations– Exposure reconstruction of heat incident investigations

QA review process– Provides documentation of inputs and assumptions– Eliminates errors in math and unit conversions

Communications– Consistency in methodology and communication of results– Graphical output that clearly puts the estimate into perspective– Improves communications at all levels (worker, IH staff and management)

Exposure assessment is fundamental to understanding and controlling hazards.

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YOU WILL BE DOING NUMERICAL MODELING

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“…when you can measure what you are speaking about and express it in numbers; you know something about it;

But when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meager and unsatisfactory kind…”

Lord Kelvin, 1883

EXCEL TOOL FOR TWA/AL CALCULATION

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Published in ACSJournal of Chemical Health and Safety 2019

AIHce 2019 presentation

CALCULATING WBGT FROM METEOROLOGICAL DATA

Essential for planning future work Conditions should be

chosen to represent actual work situation

Program developed by Argonne meteorologist James Liljegren et. al. Peer-reviewed

publications Referenced on

OSHA website

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CLOTHING ADJUSTMENT FACTORS

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Table 8 of the ACGIH Documentation contains an expanded list of clothing adjustment factors as well as Bernard et.al. in JOEH and other publications.

HOW HARD IS THE WORK?

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SOIL GAS FIELD INSTALLATION & SAMPLING 12 students & PI in Southern

Illinois Soybean fields Working in direct sunlight.

Record July heat. 20 min. hike from vehicle to

sites carrying equipment 40 min round trip if using

vehicle as recovery Light-Moderate level of

activity– Recommended work/rest

regimen of 40/20 based on calc.

– Provided portable shade structure

– Recommended pulse spot checks

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LANDFILL GAS FILTERS CHANGE OUT

TWA factors Time (min) WBGT (F)

Clothing Adjustment

Factor (F)WBGT

effective (F)Metabolic Level

(Watts)

outdoor task 1 15 89 0 89 300

inside task 25 72 0 72 115

outdoor task 2 20 89 0 89 300

total time (min) 60

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Multiple tasks ~ 10 min. each

Direct sunlight

Recovery in vehicle with AC between tasks

Light- Moderate level of activity

Recommended work/rest regimen of up to 20/40 based on calc. of TWA

DHS ENVIRONMENTAL CHAMBER PROJECT

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Work required insideChamber for 20 min.At 120 F.

(1) 200 lb. worker

No PPE, light exertion

Humidity (estimated byCalculation)

Radiant heat (est. but can be verified withWBGT)

WIPP INCIDENT RETROSPECTIVE ANALYSIS

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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, one can ESTIMATE that for an 50/50 work/rest period, that it is predicted to exceed the ACGIH TLV TWA for the workers.

PRECAUTIONS

Uncertainty in inputs results on a very conservative estimate Users must validate calculation methods,

assumptions and results. …….and still professional judgement must

be used

Physiological monitoring and observing signs & symptoms are the best methods to validate models and assess effectiveness of controls.

“All models are wrong….the practical question is how wrong do they have to be not to be useful.” -George Box

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SUMMARY

You must anticipate and recognize when heat stress conditions are expected

ACGIH TLVs provide an objective basis for evaluating potential heat stress conditions and identifying excessive heat strain

Tools for estimating environmental contribution to heat stress are available

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RESOURCES

Excel Worksheet: contact mschmoldt@anl.gov Preventing heat stress related Injuries: A field-friendly tool for the safety

Professional. H. Elston, M. Schmoldt. Journal of Chemical Health and Safety. Nov-Dec 2019. https://doi.org/10.1016/j.jchas.2019.03.007 Argonne National Laboratory (ANL). Wet Bulb Globe Temperature (WBGT)

Version 1.2. Chicago, IL, 2008. https://www.osha.gov/dts/osta/otm/otm_iii/otm_iii_4.html R. Liljegren, R. Carhart, P. Lawday, S. Tschopp, R. Sharp. Modeling the Wet Bulb

Globe Temperature Using Standard Meteorological Measurements. Journal of Occupational and Environmental Hygiene, 5:10, 645-655, 2008. OSHA Technical Manual Section III: Chapter 4 Heat Stress

https://www.osha.gov/dts/osta/otm/otm_iii/otm_iii_4.html

The Sept. 2017 Revision contains detailed instructions on using theArgonne WBGT calculator and the ACGIH approach to calculating TLV

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THANK YOU!MSCHMOLDT@ANL.GOV 630-252-1213

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