Micro-environment changes inside impermeable protective clothing during a continuous work exposure

Protective clothing (PC) results in a micro-environment between itself and the body. Workers are then exposed to a heat stress greater than the ambient environment alone, which is a reflection of micro-environment, metabolic rate and time. Adjustments to the ambient environment to account for the micro-environment have been formulated as a means to predict heat strain for safety and productivity purposes. Measurement of the actual micro-environment was made for a mean of 63.1 - 7.9 min using a remote sensor at the shoulder, hip and thigh levels on 15 subjects during a continuous work protocol (300 kcal/h) in impermeable PC at an ambient temperature of 30.1°C wet bulb globe temperature (WBGT) (32°C dry, 29°C wet, 33°C globe). Micro-environment temperature increased over the duration of the work period. There was no statistically significant difference (p >0.05) between the measurements made at the three different body sites for temperature or humidity. The mean micro-environmental WBGT at the end of work was 34.6°C WBGT. Micro-environment WBGT increased rapidly in the first 20 min of work then slowed, rising only 0.5°C WBGT from 40 to 60 min. These results suggest that at this particular high ambient temperature (30.1°C WBGT) an adjustment factor of 5°C WBGT would give a more accurate indication of thermal stress for up to 1 h of continuous moderate work within PC. For shorter work durations, an even smaller adjustment would be appropriate.