Psychrometric limits to prolonged work in protective clothing ensembles

Area of Science:

• Occupational Health
• Environmental Physiology
• Protective Clothing Technology

Background:

• Workers in protective clothing experience limited sweat evaporation, leading to elevated body temperatures.
• Quantifying the thermal strain imposed by protective ensembles is crucial for establishing safe work guidelines.

Purpose of the Study:

• To quantify the limits of safe work for individuals wearing various protective clothing ensembles under transient environmental conditions.
• To define critical environmental parameters (temperature and water vapor pressure) at which thermal balance is compromised.

Main Methods:

• Six acclimated men and women performed walking exercise (30% VO2max) in different clothing ensembles.
• Two environmental transient protocols were used: increasing dry-bulb temperature (Tdb) at fixed water vapor pressure (Pw), and increasing Pw at fixed Tdb.
• Critical temperature (Tcrit) and pressure (Pcrit) were identified as the points where rectal temperature (Tre) rose sharply, indicating loss of thermal balance.

Main Results:

• Critical environmental limits were determined for ensembles ranging from light cotton to impermeable suits.
• Lines connecting mean Tcrit and Pcrit define safe exposure limits for approximately 50% of the population.
• Lines representing two standard deviations below the mean provide critical limits for 95% of the population.

Conclusions:

• The study establishes a framework for defining safe environmental exposure limits for workers in protective clothing.
• These findings are essential for developing evidence-based guidelines to prevent heat stress and ensure worker safety.
• The methodology provides a means to assess the thermal burden of different protective ensembles under varying environmental conditions.