Heat stress risk profiles for three non-woven coveralls

ABSTRACT

The ACGIH® Threshold Limit Value® (TLV®) is used to limit heat stress exposures so that most workers can maintain thermal equilibrium. That is, the TLV was set to an upper limit of Sustainable exposures for most people. This article addresses the ability of the TLV to differentiate between Sustainable and Unsustainable heat exposures for four clothing ensembles over a range of environmental factors and metabolic rates (M). The four clothing ensembles (woven clothing, and particle barrier, water barrier and vapor barrier coveralls) represented a wide range of evaporative resistances. Two progressive heat stress studies provided data on 480 trials with 1440 pairs of Sustainable and Unsustainable exposures for the clothing over three levels of relative humidity (rh) (20, 50 and 70%), three levels of metabolic rate (115, 180, and 254 Wm⁻²) using 29 participants. The exposure metric was the difference between the observed wet bulb globe temperature (WBGT) and the TLV. Risk was characterized by odds ratios (ORs), Receiver Operating Characteristic (ROC) curves, and dose-response curves for the four ensembles. Conditional logistic regression models provided information on ORs. Logistic regressions were used to determine ROC curves with area under the curve (AUC), model the dose-response curve, and estimate offsets from woven clothing. The ORs were about 2.5 per 1°C-WBGT for woven clothing, particle barrier, and water barrier and for vapor barrier at 50% rh. When using the published Clothing Adjustment Values (CAVs, also known as Clothing Adjustment Factors, CAFs) or the offsets that included different values for vapor barrier based on rh, the AUC for all clothing was 0.86. When the fixed CAVs of the TLV were used, the AUC was 0.81. In conclusion, (1) ORs and the shapes of the dose-response curves for the nonwoven coveralls were similar to woven clothing, and (2) CAVs provided a robust way to account for the risk of nonwoven clothing. The robust nature of CAV extended to the exclusion of different adjustments for vapor barrier by rh.

KEYWORDS:

• CAV
• clothing
• exposure limit
• heat stress
• WBGT

Acknowledgments

The authors recognize and thank the many laboratory assistants and trial participants who made this study possible. We would like to especially recognize Victor Caravello along with Mathew D. Dooris, Brian E. Grace, and Patrick L. Rodriguez.

Funding

The data used in this study were collected under CDC/NIOSH R01-OH03983. Dr. Garzón was supported by the Republic of Ecuador through the Insituto de Fomento al Talento Humano. Caravello was supported by the US Air Force, Dooris by the US Coast Guard, and Grace and Rodriguez were supported by CDC/NIOSH T42-OH008438.

Disclaimer

The authors declare no conflict of interest relating to the material presented in this article. Its contents, including any opinions and/or conclusions expressed, are solely those of the authors.

One of the authors [TEB] has acted as an expert witness for both private companies and OSHA in litigation concerning heat stress exposures and may in the future serve as an expert witness in court proceedings related to heat stress.

The mention of trade names was to provide specifics about the clothing and do not represent an endorsement by the authors.