By Dan Markiewicz

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Is the manufacturing sector prepared for rising heat?

WBGT meters and understanding how to determine risk


        ith record setting high temperatures globally, and heat hazards continually flamed by the news media, all work locations must be prepared for heat concerns among their workforce.

OSHA actions
OSHA published proposed rules for “Heat Injury and Illness Prevention in Outdoor and Indoor Work Settings” in October 2021. The agency established a National Emphasis Program on heat in April 2022.
    This past July 2023, when global news media claimed the month “saw the hottest temperatures in human history,” President Biden announced, “new actions to protect workers from extreme heat and new investments to protect communities.”
    These actions include: 1) Develop an enforcement initiative on heat hazards; 2) Launch a National Emphasis Program on heat inspection; 3) Create the National Advisory Committee on Occupational Safety and Health’s Heat Injury and Illness Prevention Work Group to understand challenges and share best practices to protect workers; and 4) Launch a Heat Illness Prevention campaign to educate employers and workers on the dangers of working in the heat.

Anticipated impact
A manufacturing client recently requested that I conduct side-by-side heat stress monitoring with an OSHA IH performing a complaint investigation. This was the first heat stress investigation that I have conducted at an indoor manufacturing facility in over 30 years of my OHS practice. Workers are concerned about heat but are uncertain about the threshold for employer actions to improve conditions. I expect this to be the new-normal.

Concerns with heat stress begin when there is worker “reports of discomfort or other symptoms associated with heat stress,” per the ACGIH® TLV® booklet. The subjectiveness among some workers that there is excessive heat at work is partly driven numerous factors such as the readily available NIOSH/OSHA Heat Stress app and other weather-related heat indexes that provide alerts based on temperature and humidity. But these clues only help identify a hazard. Risk, or the potential for harm, is complex.

Photo: naveebird / iStock / Getty Images Plus via Getty Images.

Complex topic
The TLV® booklet provides the following caveat about heat stress and strain: “More than any other physical agent, the potential health hazards from work in hot environments depends strongly on physiological factors that lead to a range of susceptibilities depending on the level of acclimatization. Therefore, professional judgment is of particular importance in assessing the level of heat stress and physiological heat strain to adequately provide guidance for protecting nearly all healthy workers with due consideration of individual factors and type of work.”

WBGT measurements
One definitive method for determining risk from a heat hazard is the screening criteria based on the WBGTeff, per TLV® booklet guidance. This involves obtaining measurements using a wet bulb globe temperature (WBGT) meter and compare the results with a worker’s metabolic work rate, with consideration for clothing adjustment values, address work/rest time, and determine if the worker is acclimatized or unacclimatized. Other risk considerations beyond determining the TLV® depend upon the expertise of the IH include fluid replacement, the age and weight of the worker, whether the worker is pregnant, or comments by the worker that they use prescription medications that may be influenced by heat.

WBGT meters
OSHA field manuals show that compliance officers use QuesTemp 34 or 44 WBGT meters during heat stress evaluations. New QuesTemp WBGT meters cost about $4,000. During my side-by-side heat stress monitoring with OSHA noted above, the compliance officer used a QuesTemp 44 WBGT meter. Although not a product endorsement, I elected to purchase an EXTECH® Model HT30 Heat Stress WBGT Meter for a little over $200. The manufacturer offers NIST traceable calibration for the meter. I obtained the meter in one day through purchase with Amazon Prime.
    I elected to purchase the inexpensive EXTECH® HT30 after review of the research article “An Evaluation of Portable Wet Bulb Globe Temperature Monitor Accuracy” published in the Journal of Athletic Training, 52(12):1161-1167, Dec. 2017. The article concluded that the QuesTemp 34 and EXTECH HT30 “had the smallest error compared with the reference unit.” The QuesTemp was found to have a root mean square error (RMSE) at 0.44-degree C while the EXTECH HT30 had an RMSE at 0.79-degree C. During side-by-side monitoring with OSHA the error difference between the two meters was observed and accounted for during the measurements.
    If you elect to purchase an inexpensive WBGT, of which there are many available online, you should choose one that offers NIST or similar calibration services. Calibration frequency should follow manufacturer's recommendations.

NASA thermal stress program
Given all that is happening, along with the scientific projection of continued rising global temperatures, it is important that your organization develop a Heat Stress Program in policy and procedure format.
    Whenever I am confronted with a new or evolving occupational health hazard, I look to see what the smartest OHS people I know are doing on the topic. In this case, I looked at NASA Glenn Research Center (Cleveland, OH) Thermal Stress Program. The program is publicly available online. Search online for <NASA GRC GLP-QS-1800.1.27 Occupational Health Programs Manual – Chapter 27, Thermal Stress Program>. Note that NASA’s “Initial release” effective date for the program is 1/20/2023.
    NASA was able to summarize the heat stress work/rest cycle in three easy to understand tables in two pages. Table 4, Work:Rest Cycle Calculator, is a simple GRC created method to obtain an adjusted temperature without the need for WBGT measurements.

Foundational understanding
All OHS pros will need to better understand heat stress concerns. A foundational understanding may be achieved by review information in the <NIOSH Publication No. 2016-106 “Criteria for a Recommended Standard – Occupational Exposure to Heat and Hot Environments – Revised Criteria 2016”> The 159-page document is available free online. Use search terms as shown.

Be aware that current heat stress concerns include politics. During worker training on heat stress, you should avoid taking a side whether rising global temperatures are man-made or not or whether your company contributes to global warming with their environmental practices. Be aware that union representation may see an advantage in adoption of expanding work/rest cycles for the entire workforce based upon a small amount of maximally exposed workers to heat. Be aware that intolerance to heat begins with subjective symptoms. Complaints that the workplace is “too hot” is a hazard but not necessarily a health risk. Be aware that worker heat concerns will exist in HVAC air-conditioned manufacturing facilities. Most importantly, be alert for future concerns because of rising heat as noted in Figure 10-1 “Relationship between climate change and occupational safety and health” found in NIOSH Publication No. 2016-106.

Dan Markiewicz, MS, CIH, CSP, CHMM, is an independent environmental health and safety consultant. He can be reached at (419) 356-3768 or by email at


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VOL. 57  NO. 7