Wind speed limits to work under hot environments for clothed men

Abstract

Four heat-acclimated clothed young adult men exercised (treadmill) at metabolic rate of 191 W.m-2 (27% VO2 max), under five air temperatures (Ta) between 36 and 53 degrees C and three wind velocities (v), 1, 2, and 4 m.s-1, for 2 h. The 2nd h of each experiment involved progressive increases in the ambient vapor pressure (Pa) to force an upward inflection of the rectal temperature (Tre). The Tre point of inflection identified the critical Pa (Pcrit) for each Ta. The average mean skin temperature (Tsk = 36 degrees C for all Pcrit. Straight-line isotherms for Tsk = 36 degrees C, which agreed with the negative regressions of the Pcrit on Ta, represented the limits of exposure for Ta less than or equal to 44 degrees C. The slope characteristics of the isotherms corresponded with skin wettedness (w) of 0.94, 0.71, and 0.58, respectively, for v of 1, 2, and 4 m.s-1. For Ta greater than 44 degrees C the limit line corresponded with steeper negative regressions indicating a lower w than for Ta less than or equal to 44 degrees C. Despite the increase in the ambient evaporative capacity due to the higher v the limit lines describing exposure limits were not significantly different either at Ta less than or equal to 44 degrees C for v of 2 and 4 m.s-1 or at Ta greater than 44 degrees C for all three v.