Psychrometric Limits to Prolonged Work in Protective Clothing Ensembles

Abstract

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.

Psychrometric limits and critical evaporative coefficients for unacclimated men and women

“…In heat-acclimated subjects, T es typically equilibrates as a relatively horizontal line before the upward inflection forced by the changing environmental conditions (13)(14)(15). However, in the unacclimated subjects tested here, T es often increased gradually before its upward inflection.…”

Critical environmental limits for exercising heat-acclimated lean and obese boys

“…Thus the P a 2 min before the upward inflection point was defined as the P crit in the present study. Approximately 10–15 min prior to the T c inflection point, an upward rise in heart rate (Kamon and Avellini 1976; Kamon et al 1978; Kenney and Zeman 2002; Kenney et al 1988) was evident in all tests.…”

“…As opposed to separate tests in each environment, Kamon and Avellini later refined this protocol by defining P crit values at several T db ’s for heat-acclimated women by increasing P a throughout each test (Kamon and Avellini 1976). Subsequent studies determined critical environmental limits for lightly (Kamon et al 1978) and heavier (Kenney et al 1988) clothed heat-acclimated and lightly clothed (Kenney and Zeman 2002), unacclimated men and women. The present study extends these critical environmental heat stress limits to a novel population of heat-acclimated children.…”

Sweat management for military applications

“…Clothing creates an additional resistance to vapor transport, which results in increased thermal strain from elevated body temperatures, thus reducing worker tolerance and, in extreme cases, posing the risk of overheat sickness (Joy and Goldman, 1968;Kenny et al, 1988;Bishop et al, 1988;Faff and Tutak, 1989;Nunneley, 1989;Sun et al, 2000;White et al, 1989). Evaporation of perspiration becomes the only heat-dissipating channel.…”