Physiological Monitoring for Heat Stress Management

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Michael Schmoldt

Summary Statement

Michael's Schmoldt's PowerPoint, presented at the AIHA Conference on June 1, 2015 in Salt Lake City, outlines a physiological monitoring program to prevent heat-related illnesses at the Hanford Tank Farms. The presentation focuses on technologies available to measure heat strain because in many cases WBGT environmental monitoring is not sufficient or feasible. Additional information on worker heat stress is needed when work will occur in semi- or impermeable clothing ensembles or when heavy to very heavy work is performed, regardless of clothing level.
June 1, 2015

washington river protetion solutions logoTOC-Pres-15-2199
Mike Schmoldt, MS, MS, MBA, CIH, PE, CHMM, CPEA,
Principal Industrial Hygienist

June 1, 2015

Heat Stress


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

-Environmental Medicine. -Brooks.

Why monitor for heat stress?

AIHce 2003 Dallas TX PD Course 420

Major flaws in poor IH assessments:

  1. Numbers only analysis; reactionary, no prevention
  2. Superficial evaluation of heat stress, not heat strain
  3. No biological monitoring

What is a best practice? 2013 EFCOG Survey

  • Few responses (6)
  • Reliance on work/rest tables were common
  • Monitoring using WBGT used extensively
  • 10 CFR 851 was not always recognized as having a thermal stress limit
  • No consensus on application of OELs, methods or measurement
  • Little or no detailed data available

Recent OSHA Guidance

  • The OSHA Technical Manual is a primary source of guidance on how OSHA compliance officers conduct workplace monitoring.   It was updated in Feb. 2014 to modernize and clarify some sections.
    • Worker Monitoring Programs
      • Every worker who works in extraordinary conditions that increase the risk of heat stress should be personally monitored. These conditions include wearing semipermeable or impermeable clothing when the temperature exceeds 21°C (69.8°F), working at extreme metabolic loads (greater than 500 kcal/hour), etc.
      • Personal monitoring can be done by checking the heart rate, recovery heart rate, oral temperature, or extent of body water loss.
  • OSHA website.

Physiological Monitoring for Thermal Stress

Why do Physiological Monitoring?

  1. No OSHA specific requirements- except general duty clause, guidance document and requirements for selection of appropriate PPE limitations
  2. 10 CFR 851 Worker Safety and Health
    • 2005 ACGIH TLVs and BEIs ‘Heat Stress and Strain’
    • later ACGIH versions may/should be considered if more stringent
  3. ISMS programs and VPP
  4. Prior DOE-ORP repeat findings on heat stress management
  5. Series of internal corrective actions on: acclimatization, metabolic rate and clothing protection factors and work/rest schedules
  6. Need for documentation of worker exposure and hazard assessment

Hanford Tank Farms Thermal Stress Issues

  • Extended outdoor work in anti-contamination clothing and respiratory protection
  • Desert environment (high radiant loading/low humidity)
  • Tropical work shift schedule options
  • Record setting heat levels in 2014 and expected in 2015
  • High exertion work requirements
  • Past difficulty implementing engineering and admin. controls as part of planned work
  • Aging workforce/high bump and roll influx of newer workers
  • Worker job jeopardy concerns
  • Bargaining unit labor contract issues
  • Legacy issues of prior programs and practices
  • Past reliance on ‘self-identification’ of heat stress symptoms

Changes to Program Elements

  • Educate management and field work supervisors
  • Created a Heat Stress committee (IH/Mgt./labor)
  • Update heat stress procedure
  • Research and selection of instrumentation
  • Develop procedures and training for IH and IHT staff
  • Communication Plan
  • Memorandum Of Agreement with Bargaining Unit
  • Field application with field work supervisors IH/IHTs
  • Detailed data analysis of results for future work

Changing the Heat Stress Monitoring Program

  • Updated to address 2005 ACGH-TLV thermal stress requirements
  • Minimized used of acclimatization and work/rest schedules
  • Updated clothing protection factors and metabolic level tables
  • Trained IH and IHTs on use of equipment and documenting results
  • Required documented evaluation using a heat stress mitigation that documents the expected controls present, environmental conditions, PPE and level of exertion
  • Required field work supervisor monitoring >85°F dry bulb or if listed heat stress precursor conditions were likely

What is Physiological Monitoring?

  • A basic way to measure the level of an individual’s heat strain in response to heat stress conditions. This includes, but is not limited to, heart rate monitoring & body temperature measurement.
  • It does not include parameters which may be considered medical monitoring (measuring blood pressure, oxygen saturation, urine testing, or cardiac rhythm).

By contrast: the WBGT measures environmental temperature conditions useful to establish work/rest schedules and exposure hazard evaluation (i.e., heat stress) but does NOT monitor worker specific physiological responses (heat strain response) to the thermal dose received.

Physiological Monitoring may be required when:

  • WBGT monitoring is not sufficient or feasible.
  • Work will occur that is likely outside of the established work/rest regimens
  • Additional information on worker heat stress is needed
  • Work will occur in semi- or impermeable clothing ensembles such as polyethylene coated Tyvek or vapor barrier coveralls
  • Heavy to very heavy work is performed, regardless of clothing level

Physiological Monitoring Instrumentation

  • Physiological monitoring is conducted using an IH approved device following manufacturer’s instructions (e.g., Nonin Onyx heart rate monitor, Polar sensor, Infrared tympanic membrane thermometer or other device
  • A variety of instruments were evaluated and the technical literature was reviewed to make an informed decision
  • Seminars and discussion with Dr. Thomas Bernard, U. of Florida (ACGIH/AIHA) were valuable in identifying limitations of each.
  • Instrument should be field practical, minimally invasive and accurate enough for heat stress evaluation
  • The IH program and Occupational Medical Provider (HPMC) reviewed and accepted the instruments selected

Temperature Monitoring

  • Physiological measurement is used to obtain a core body temperature for the purpose of evaluating heat strain to workers
    • graphic of a thermometerAvailable Methods:
      • Invasive (unacceptable to most people)
      • Biological sampling (urine stream)
      • Surface temperature (highly variable)
      • Oral (strongly affected by breathing/air temperature or drinking liquids)
      • Aural: ear canal or tympanic
  • This is an objective physiological measurement
    • It is not a medical or clinical procedure
    • It must be accurate enough for assessing heat strain

Temperature Monitoring

  • Braun Thermoscan or similar type of infrared ear thermometer
  • Used to collect and report baseline and periodic heat strain evaluation data

side view graphic of human headimage of a Braun THermoscan thermometer

Heat Stress Physiological Monitoring -- Tympanic Temperature

Principle of the method

  • This method measures tympanic temperature NOT ear canal temperature
  • Blood flow from the internal carotid artery supplies the hypothalamus and the area around the eardrum.
  • The hypothalamus is the part of the brain that senses and reacts to body core temperature
  • There is little ‘thermal inertia’ with the eardrum
  • Temperature changes are rapidly reflected
  • Temperature of the eardrum does not require a correction factor when read using an infrared thermometer to approximate body core temperature
  • Extreme environmental temperatures may require a minute to adjust air temperature to blood temperature

Theory of Operations -- Tympanic Temperature

Measurement requires a direct line of sight to the ear canal

  • Some people’s ear canal shape may make this impossible
  • Ear wax may impede the ability to get an accurate measurement
  • Pull UP and BACK to straighten the ear canal

graphic if ear canal - a cut-away view

Thermoscan Readings

  • If temperature measured is >100.4°F, discontinue exposure to thermal stress immediately and take precautions to cool the worker
  • Surveying workers out of radiation control areas may result in partial recovery and not represent peak exposure
  • Consider whether symptoms are present which require first aid or medical assistance

Thermoscan specifications

  • Operating Range 50-104° F.
  • Maximum humidity 95%
  • Allow 30 minutes for the instrument to stabilize in the environment where it will be used before taking a reading
  • Meets ASTM standard E1965-98: Infrared Thermometers for Intermittent Determination of Patient Temperatures

Nonin Pulse Rate Measurement

  • photo of Nonin pulse oximeterNonin pulse oximeter (Onyx or Vantage models)
  • Baseline and periodic heat strain evaluation data








Nonin Pulse Rate Measurement

  • Physiological heart rate measurements are used to obtain an estimate of heat strain experienced by a worker
  • This device collects a short time sample, but does not represent the overall worker heart rate variability over the work period
  • We do not use the oximeter reading as part of the heat stress control program (NFPA does)
  • This is an objective physiological measurement
    • It is not a medical or clinical procedure
    • It must be accurate enough to evaluate heat strain

Theory of operations, Nonin

line drawing of Nonin unit on fingerInfra red light is transmitted by an LED through the finger to a sensor where the intensity and rate of change of the light is read. A microcomputer calculates the transmissivity of the infrared light, which is proportional to hemoglobin concentration. The unit calculates both oxygen saturation and pulse rate from this information.





General Instructions for Use, Nonin

  • photo of Nonin unit on fingerCollect a baseline pulse rate prior to beginning work and donning PPE clothing
  • Collect periodic pulse rates based in instructions by the IH
  • Collect a recovery heart rate as soon as the work stress ends if possible. Record the time work ended and when the reading occurred




Applicable Standards, Nonin

The Nonin was designed and certified to meet the following ISO standards. No user calibration or adjustment is required. The device performs self-function checks and does not require calibration or periodic maintenance

  • ISO 9910:2005 criteria for heart rate testing
  • ISO 10993-1 Biological evaluation of medical devices –Part 1: Evaluation and testing

Continuous Heart Rate Monitoring

Physiological monitoring pulse rate using a Polar H7 pulse oximeter.

composite of 4 photos of monitoring using a Polar H7  pilse oximeter

Introduction, Pulse Oximeter

  • photo of a Polar pulse oximeterPhysiological heart rate measurements are used to obtain an estimate of heat strain experienced by a worker
  • This device can provide real time reading as well as continuous readings to allow peak rate and recovery rate data to be collected in graphical and data file format
  • This is an objective physiological measurement
    • It is not a medical or clinical procedure
    • It must be accurate enough to evaluate heat strain

General Instructions For Use, Pulse Oximeter

  1. Moisten the electrode areas on the back of the strap with water or electrode gel
  2. Attach the transmitter to the strap. Adjust the strap to fit tightly but comfortably

line drawing illustrating how to place the pulse oximeter

Linking Polar Monitor to IPAD Application

screen capture of Polar Monitor Ipad Application

screen capture of Polar Ipad Application

Theory of Operations, Pulse Oximeter

  • The body regulates metabolic activity by reacting with increases in heart rate, glucose metabolism, oxygen uptake and blood pressure
  • Electrocardiogram skin resistance is a direct indicator of cardiac muscle activity and heart rate
  • Resistance is measured by the chest strap, translated into heart rate data and transmitted to a receiver
  • Transmissions are digitally encrypted Bluetooth signal so multiple units don’t interfere with each other and data is only available to the receiving device selected
  • IPAD acts as both data logger, field notes record and real time graphical display on up to 20 workers at once.

Examples of Polar Heart Rate Results

images of Ploar heart rate screens

images of Ploar heart rate screens

Examples of Heart Rate Results

Examples of Heart Rate Results

Examples of Heart Rate Results

Examples of Heart Rate Results

Examples of Heart Rate Results

Heat Stress Monitoring Data for FY 2014

  • 328 employees were scheduled to work at heat stress related tasks
  • 318 of the 328 employees were monitored for heat strain utilizing physiological monitoring (10 of the 328 employees were not needed to perform assigned tasks and were not monitored)
  • 17 employees (5%) were removed from heat stress related tasks due to physiological monitoring.
    • NO EXCEEDENCES (>OEL were observed)

Results of Physiological Monitoring

  • Physiological monitoring removed employees from heat stress related tasks before exceeding the exposure limits or Heat Stress illnesses symptoms developed
  • Provided management with a quantitative measurement of each employee’s response to heat strain.
  • Helped build employee confidence in the IH Heat Stress Control Program
  • Provided data for detailed analysis to plan future exposure assessments, development of similar exposure group classifications and hazard analysis
  • No reported issues with job jeopardy or medical limitations (use of stimulants does raise heart rate)
  • Ability to demonstrate compliance with 10 CFR 851

Contact information for the authors

Questions:? Contact

Mike Schmoldt,

Edward Sinclair,
Mr. Sinclair is the current heat stress SME for Washington River Protection Solutions, LLC at the Hanford, WA site.