Wind speed limits to work under hot environments for clothed men

Area of Science:

• Environmental Physiology
• Human Thermoregulation
• Exercise Science

Background:

• Understanding human tolerance to heat stress is crucial for occupational safety and athletic performance.
• Heat acclimatization enhances the body's ability to cope with high ambient temperatures.
• Evaporative heat loss, primarily through sweating, is a key mechanism for thermoregulation in hot conditions.

Purpose of the Study:

• To identify critical ambient vapor pressures (Pcrit) that define thermal exposure limits for heat-acclimated individuals.
• To investigate the influence of air temperature (Ta) and wind velocity (v) on thermoregulatory responses.
• To quantify skin wettedness (w) at different environmental conditions.

Main Methods:

• Four heat-acclimated men exercised on a treadmill at a metabolic rate of 191 W.m-2 (27% VO2 max).
• Experiments were conducted across five air temperatures (36-53°C) and three wind velocities (1, 2, 4 m.s-1).
• Rectal temperature (Tre) inflection points were used to determine critical vapor pressure (Pcrit) at varying ambient conditions.

Main Results:

• Mean skin temperature (Tsk) remained constant at 36°C for all Pcrit determinations.
• Exposure limits were defined by straight-line isotherms for Tsk = 36°C, showing negative regressions of Pcrit on Ta.
• Skin wettedness decreased with increasing wind velocity at Ta ≤ 44°C, and further decreased at Ta > 44°C.

Conclusions:

• Critical vapor pressure decreases with increasing air temperature, indicating reduced evaporative capacity.
• Wind velocity significantly impacts skin wettedness, influencing heat tolerance thresholds.
• Despite increased evaporative potential with higher wind speeds, exposure limits did not significantly change above 44°C.