Psychrometric limits to prolonged work in protective clothing ensembles.

When work is performed by workers in protective clothing, sweat evaporation is limited and body temperature rises. In an attempt to quantify the limits such ensembles place on safe work, 6 acclimated men and women walked at 30% VO2max (150-200 W/m2) in 2 protocols involving environmental transients. In one, ambient water vapor pressure (Pw) was fixed at 10 torr, and after rectal temperature (Tre) plateaued, ambient dry-bulb temperature (Tdb) was raised 2 degrees C every 10 min. In the second, Tdb was constant and Pw was increased 2 torr every 10 min. Critical temperature (Tcrit) and pressure (Pcrit) were defined as the Tdb or Pw at which thermal balance could no longer be maintained and Tre rose sharply. Each test was performed in various clothing ensembles ranging from light cotton work clothes to "impermeable" suits. Lines connecting mean Tcrit and mean Pcrit define a limit for safe prolonged exposure/exercise for approximately 50% of the population in each ensemble. Similar lines, drawn to represent values 2 standard deviations below the mean, should provide critical environmental limits for 95% of the population.

Physiologically derived critical evaporative coefficients for protective clothing ensembles.

When work is performed in heavy clothing, evaporation of sweat from the skin to the environment is limited by layers of wet clothing and air. The magnitude of decrement in evaporative cooling is a function of the clothing's resistance to permeation of water vapor. A physiological approach has been used to derive effective evaporative coefficients (he) which define this ability to evaporate sweat. We refined this approach by correcting the critical effective evaporative coefficient (K for sweating efficiency (Ke,eta') since only a portion of the sweat produced under such conditions is evaporated through the clothing. Six acclimated men and women walked at 30% maximal O2 consumption (150-200 W.m-2) at a constant dry bulb temperature as ambient water vapor pressure was systematically increased 1 Torr every 10 min. Critical pressure was defined as the partial pressure of water vapor (Pw) at which thermal balance could no longer be maintained and rectal temperature rose sharply. Each test was performed in various clothing ensembles ranging from cotton shirt and pants to "impermeable" suits. This approach was used to derive he by solving the general heat balance equation, M - W +/- (R + C) = w.he.(Psk - Pw), where M is metabolic heat production, W is external work, R is radiant heat exchange, C is convective heat transfer, w is skin wettedness, and Psk is water vapor pressure of fully wet skin.(ABSTRACT TRUNCATED AT 250 WORDS)