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 no safe work, 6 acclimated men and women walked at 30% V̇O₂max (150-200 W/m²) in 2 protocols involving environmental transients. In one, ambient water vapor pressure (P(w)) was fixed at 10 torr, and after rectal temperature (T(re)) plateaued, ambient dry-bulb temperature (T(db)) was raised 2°C every 10 min. In the second, T(db) was constant and P(w) was increased 2 torr every 10 min. Critical temperature (T(crit)) and pressure (P(crit)) were defined as the T(db) or P(w) at which thermal balance could no longer be maintained and T(re) rose sharply. Each test was performed in various clothing ensembles ranging from light cotton work clothes to 'impermeable' suits. Lines connecting mean T(crit) and mean P(crit) define a limit for safe prolonged exposure/exercise for approximatelty 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.