Ability to Discriminate Between Sustainable and Unsustainable Heat Stress Exposures – Part 1: WBGT Exposure Limits

Details

• Personal Author:
  Ashley CD ; Bernard, Thomas E. ; Garzón-Villalba XP ; Wu Y
• Description:
  Objectives: Heat stress exposure limits based on wet-bulb globe temperature (WBGT) were designed to limit exposures to those that could be sustained for an 8-h day using limited data from Lind in the 1960s. In general, Sustainable exposures are heat stress levels at which thermal equilibrium can be achieved, and Unsustainable exposures occur when there is a steady increase in core temperature. This paper addresses the ability of the ACGIH Threshold Limit Value (TLV) to differentiate between Sustainable and Unsustainable heat exposures, to propose alternative occupational exposure limits, and ask whether an adjustment for body surface area improves the exposure decision. Methods: Two progressive heat stress studies provided data on 176 trials with 352 pairs of Sustainable and Unsustainable exposures over a range of relative humidities and metabolic rates using 29 participants wearing woven cotton clothing. To assess the discrimination ability of the TLV, the exposure metric was the difference between the observed WBGT and the TLV adjusted for metabolic rate. Conditional logistic regression models and receiver operating characteristic curves (ROC) along with ROC's area under the curve (AUC) were used. Four alternative models for an occupational exposure limit were also developed and compared to the TLV. Results: For the TLV, the odds ratio (OR) for Unsustainable was 2.5 per 1 degrees C-WBGT [confidence interval (CI) 2.12-2.88]. The AUC for the TLV was 0.85 (CI 0.81-0.89). For the alternative models, the ORs were also about 2.5/ degrees C-WBGT, with AUCs between 0.84 and 0.88, which were significantly different from the TLV's AUC but have little practical difference. Conclusions: This study (1) confirmed that the TLV is appropriate for heat stress screening; (2) demonstrated the TLV's discrimination accuracy with an ROC AUC of 0.85; and (3) established the OR of 2.5/ degrees C-WBGT for unsustainable exposures. The TLV has high sensitivity, but its specificity is very low, which is protective. There were no important improvements with alternative exposure limits, and there was weak evidence to support metabolic rate normalized to body surface area. In sum, the TLV is protective with an appropriate margin of safety for relatively constant occupational exposures to heat stress. [Description provided by NIOSH]
• Subjects:
  Environment Heat Stress Disorders Hot Temperature Humidity Occupational Exposure Occupational Health Safety Temperature
• Keywords:
  Analytical Models Author Keywords: Heat Stress Body Temperature Environmental Factors Exposure Assessment Exposure Limits Heat Heat-exposure Heat-stress Hot Environments Humans Metabolic Equilibrium Metabolic Rate Occupational Exposure Occupational Exposure Limit Protective Measures Regression Analysis ROC Sustainable Temperature Effects Threshold Limit Values TLV Unsustainable WBGT Wet-bulb Globe Temperature

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• ISSN:
  2398-7308
• Document Type:
  Text
• Funding:
  Grant
• Genre:
  Journal Article
• Place as Subject:
  Florida ; OSHA Region 4
• CIO:
  National Institute for Occupational Safety and Health (NIOSH)
• Topic:
  Workplace Safety & Health
• Location:
  North America
• Volume:
  61
• Issue:
  6
• NIOSHTIC Number:
  nn:20049879
• Citation:
  Ann Work Expo Health 2017 Jul; 61(6):611-620
• Contact Point Address:
  Thomas E. Bernard, College of Public Health, University of South Florida, 13201 Bruce B Downs Boulevard, Tampa, FL 33612, USA
• Email:
  tbernard@health.usf.edu
• Federal Fiscal Year:
  2017
• Performing Organization:
  Sunshine Education and Research Center, University of South Florida
• Peer Reviewed:
  True
• Start Date:
  20050701
• Source Full Name:
  Annals of Work Exposures and Health
• End Date:
  20290630
• Collection(s):
  National Institute for Occupational Safety and Health
• Main Document Checksum:
  urn:sha-512:8fa994770af4a1d99e34ab1a4fbeea8bf5b6bfc66411e658d6873a720923c8057c42f9b28bbe2a942aae72554fcd0bfb568c2aa0c87429cde42ca1b2e05917bf
• Download URL:
  https://stacks.cdc.gov/view/cdc/210475/cdc_210475_DS1.pdf
• File Type:
  [PDF - 359.65 KB ]