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 degrees 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 degrees C WBGT.

Physiological Strains of Wearing Aluminized and Non-aluminized Firefighters’ Protective Clothing during Exercise in Radiant Heat

“…Since the WBGT was developed specifically for men working in shirt and trousers 17) , a clothing adjustment factor of WBGT for the workers wearing protective clothing has been suggested 18) . For example, ACGIH 2) suggested lowering the threshold WBGT 10°C for completely enclosed suits, Bernard 19) reviewed that a clothing adjustment factor of WBGT is 11°C for firefighter turn-out gear, and Kenny 20) suggested lowering the WBGT 7°C when a worker is wearing an enclosed suit.…”

Short-Term Heat Stress Exposure Limits Based on Wet Bulb Globe Temperature Adjusted for Clothing and Metabolic Rate

“…(5) The observed slope was −0.039 • C-WBGT per W m −2 (5) or about −0.02 • C-WBGT per W for a body surface area of 2 m 2 , the average for the study participants. (5) That is, the change in WBGT was related to the change in metabolic rate following Eq. 3.…”

“…The experimental design built in clothing adjustments by setting the L1 heat stress level based on critical conditions at a similar metabolic rate and relative humidity found in earlier studies in our laboratory. (4,5) The adjustment factors for clothing under similar conditions were 0 • C-WBGT for work clothes, 2.5 • C-WBGT for NexGen, and 6.5 • C-WBGT for Tychem QC. (4) Assuming that the clothing effect as an equivalent WBGT that is fixed over a range of heat stress levels, a clothing adjusted WBGT can be computed as the actual WBGT plus the clothing adjustment.…”

“…The WBGT was further adjusted by the difference from the average value by −0.039 • C-WBGT per W m −2 found previously. (5) That is, the adjusted WBGT is increased if the trial metabolic rate was less than the average and decreased if above average. The Adjusted WBGTs vs. the safe exposure time limit are shown in Figure 2.…”

“…3). (5) Because the baseline metabolic rate for Eq. 4 was 365 W, the third term of AdjWBGT was reflected as the difference from this baseline.…”