WBGT Clothing Adjustment Factors for Four Clothing Ensembles and the Effects of Metabolic Demands

Abstract

This study measured the clothing adjustment factors (CAFs) for four clothing ensembles (Cotton Coveralls, Tyvek 1427 Coveralls, NexGen Coveralls, and Tychem QC Coveralls; all coveralls were worn without hoods) against a baseline of cotton work clothes to determine whether the CAFs would be affected by the metabolic rate. Fifteen participants wore one of the five ensembles while walking on a treadmill at low, moderate, and high rates of work in an environment maintained at 50% relative humidity. A climatic chamber was used to slowly increase the level of heat stress by increasing air temperature. When the participant's core temperature reached a steady-state, the dry bulb temperature was increased. The point at which the core temperature began to increase was defined as the inflection point, and the WBGT recorded 5 min before the inflection point was the critical WBGT for each ensemble. A three-way mixed effects linear model with ensemble by metabolic rate category interactions demonstrated that the CAF did not change with metabolic rate, so CAFs can be used over a wide range of metabolic rates. The data at the moderate metabolic rate were combined with data on 14 participants from a previous study under the same conditions. The CAFs in °C WBGT were 0 for cotton coveralls, 1.0 for Tyvek 1422A, and 2.5 for NexGen. Although the value of 7.5 for Tychem QC was found, the recommendation remained at 10 to account for the effects of humidity. The standard error for the determination of WBGT _crit at 50% relative humidity was 1.60°C WBGT.

Keywords:

• heat stress
• metabolic rate
• protective clothing
• TLV

ACKNOWLEDGMENTS

The authors would like to thank the participants and laboratory support, including Christina Luecke. This research was supported by a grant from the National Institute for Occupational Safety and Health (R01-OH03983). Clothing was provided as a courtesy by DuPont and Red Kap Industries.

The contents herein are solely the responsibility of the authors and do not necessarily represent the official views of NIOSH, CDC, United States Air Force, or the Department of Defense.

Notes

^A Work Clothes, Cotton Coveralls, and Tyvek 1427 were not statistically different from each other.

^A All ensembles except work clothes in a coverall configuration without hood and gloves.

^B The same letters indicate no difference between ensembles at the α = 0.05 level.

^C Differences reported by Bernard et al. in Ref. 8.

^D For Tyvek 1424 only.

^E For 50% rh only.