Evaluation Of Occupational Heat Strain Under Dry And Humid Conditions With Equivalent WBGT

Abstract

PURPOSE: American Conference of Governmental Industrial Hygienist’s (ACGIH) Threshold Limit Value (TLV), based on Wet Bulb Globe Temperature (WBGT), is a commonly used tool to prevent occupational heat stress (core body temperature (Tc) elevation within +1°C or ≤ 38 °C). This study examined the hypothesis that a level of heat stress would be equivalent to different combinations of ambient temperature and relative humidity should it be matched to the equivalent in terms of WBGT. METHODS: All subjects provided informed consent approved by the NIOSH IRB. Eight healthy men (Age: 23±2 yrs.) wearing a cotton work coverall with a hardhat and work gloves underwent four cycles of an intermittent work-rest (15 min each, total 2 hours) under two ambient conditions characterized as either dry (45.5°C, 15% RH) (DRY) or humid (31°C, 84% RH) (HUM), but both equivalent to 30°C WBGT. The work was performed via a cycling exercise at a fixed rate of 350 watts metabolic heat production while the rest was given as sitting on a chair and removing gloves and headgear, with hydration ad lib. Tc, skin temperature (Tsk), Thermal sensation (TS), and Rating of Perceived Exertion (RPE) were measured during exercise. RESULTS: Measurement of Tc, TS, and RPE were not significantly different between DRY and HUM conditions. There was also no difference in Tc elevation (DRY: 0.8±0.4°C, HUM: 0.7±0.3°C) within the upper limit of TLV. However, Tsk was significantly higher in DRY condition than HUM during exercise (p≤0.05). The average amount of water intake was not significantly different between DRY (1187.5±258.8 ml) and HUMID (901.5±323.6 ml) throughout trials (P>0.05).Table: No title available.CONCLUSION: These data demonstrated that a level of heat stress is similar under different ambient temperature and RH when matched the same in WBGT. However, it is speculated that a prolonged working time (e.g. 4 to 8 hour work shift) would likely surpass the upper limit of ACGIH’s TLV.