Occupancy Time Limits for PersonsWorking in ToxicWarm Environments While Wearing Encapsulating Chemical-biological Protective Clothing with Self Contained Air Supply and Water/Ice Microclimate Cooling

Safe work time limits for persons wearing US Army's Self Contained Toxic Environment Protective Outfit (STEPO) were developed from human tests and human simulation. STEPO, a Level A HAZMAT protective garment, has CO2 scrubber, O2 supply and upper body liquid cooling. Rest/treadmill-exercise (10/20 min) cycle test results for a limited range of conditions were extended by simulating human responses to more environments. A rational 5 compartment lumped parameter thermo-physiological model was adapted to simulate responses with STEPO. The model's output showed close conformity with measured core temperatures and heart rates. The safe working time criterion was for the core temperature and heart rate not to exceed 38.3°C and 150bpm. For example, at 27 and 38°C the resulting recommended work limits are 240 and 70 min, respectively.