Critical Assessment of the Recommended Alert Limit Curves for Occupational Heat Exposure

Details

• Journal Article:
  American Journal of Industrial Medicine
• Personal Author:
  Hess, Hayden W. ; Hite, M. Jo ; Heikkinen, Molly E. ; Tarr, Macie L. ; Tourula, Erica ; Johnson, Blair D. ; Hostler, David ; Schlader, Zachary J.
• Description:
  Background: Occupational heat stress recommendations aim to achieve thermal equilibrium and keep core temperature (Tc) below 38.0 degrees C. We assessed the recommended alert limit curves when: (1) work-rest ratios are adjusted based on wet-bulb globe temperature (WBGT) at a fixed rate of metabolic heat production (Hprod) and (2) Hprod is adjusted based on WBGT at a fixed work-rest ratio. We tested the hypothesis that adhering to occupational heat stress recommendations results in thermal equilibrium and prevents TC from exceeding 38.0 degrees C. Methods: Unacclimated adults completed 4-hour exposures at a fixed WBGT, Hprod, and work-rest ratio. There were six iterations of compliant trials (n = 70 observations; A: 24.1 degrees C, 431 W, 60:0 min; B: 26.6 degrees C, 461 W, 45:15 min; C: 28.4 degrees C, 462 W, 30:30 min; D: 29.7, 453 W, 15:45 min; E: 27.3 degrees C, 412 W, 30:30 min; F: 31.6 degrees C, 290 W, 30:30 min) and two iterations of noncompliant trials (n = 24 observations; G: 31.6 degrees C, 413 W, 30:30 min; H: 36.1 degrees C, 453 W, 15:45 min). Results: Mean and peak TC across the compliant trials were 37.6 degrees C +/- 0.3 degrees C and 37.9 degrees C +/- 0.3 degrees C. Thus, 65/70 (93%) and 44/70 (63%) trials did not exceed a mean or peak core TC of 38.0 degrees C. Mean and peak TC across the noncompliant trials exceeded 38.0 degrees C in all trials. The rate of heat gain differed between compliant and noncompliant trials (0.08 degrees C +/- 0.07 degrees C/h vs. 0.41 degrees C +/- 0.34 degrees C/h; p < 0.0001) but on average thermal equilibrium was < 0.1 degrees C/h in the compliant trials. Conclusion: Compliance with the occupational heat stress recommendations resulted in thermal equilibrium and mitigated the development of excessive heat strain.
• Subjects:
  Heat Stress Disorders Occupational Health Occupationational Exposure Safety
• Keywords:
  Author Keywords: Heat Strain; Heat Stress; Hydration; Recommendations Heat Stress; Body Temperature; Thermal Effects; Recommendations; Dehydration; Rest Periods; Heat Exposure;
• Source:
  Am J Ind Med 2025 Nov; 68(11):1004-1012
• ISSN:
  0271-3586
• Document Type:
  Text
• Funding:
  Grant
• Genre:
  Journal Article
• Place as Subject:
  Indiana ; New York ; Chicago Region [OSHA] ; New York City Region [OSHA]
• CIO:
  National Institute for Occupational Safety and Health (NIOSH)
• Topic:
  Workplace Safety & Health
• Location:
  North America
• Pages in Document:
  9 pdf pages
• Volume:
  68
• NIOSHTIC Number:
  nn:20071286
• Contact Point Address:
  Zachary J. Schlader, Department of Kinesiology, Indiana University School of Public Health, Bloomington, Indiana, USA
• Email:
  zschlade@iu.edu
• Federal Fiscal Year:
  2026
• Performing Organization:
  Indiana University, Bloomington
• Peer Reviewed:
  True
• Start Date:
  20190901
• End Date:
  20240831
• Collection(s):
  National Institute for Occupational Safety and Health
• Main Document Checksum:
  urn:sha-512:c73b77512225a1d852cf4c304f576fbcbb766eaa49f3f2da46e65c5b3200545325b6586b9acee42ef46616cbc5edcb9639be405ee9e9564245aba89fd0d71cea
• Download URL:
  https://stacks.cdc.gov/view/cdc/258763/cdc_258763_DS1.pdf
• File Type:
  [PDF - 821.07 KB ]