Heat strain while wearing the current Canadian or a new hot-weather French NBC protective clothing ensemble

Background: A new nuclear, biological and chemical (NBC) protective garment has been designed for use in hot environments. This NBC battle dress uniform (NBC-BDU) is intended to be worn over the skin or, at most, over underwear and an undershirt. It is unclear whether the documented reductions in heat strain associated with wearing this clothing configuration represent simply the removal of the combat clothing layer normally worn underneath a NBC protective overgarment or an improved heat transfer through the new NBC-BDU. Hypothesis: It was hypothesized that the removal of the combat clothing layer would produce a significant reduction in heat strain. As a result, it was also hypothesized that there would be no difference in heat strain between this new NBC-BDU and the current Canadian protective overgarment when the remaining clothing was standardized. Methods: There were 9 males who alternated 15 min of walking at 1.11 m . s(-1) and 15 min of seated rest for a maximum of 4 h in a chamber set at 40 degrees C, 30% relative humidity and a wind speed less than 0.1 m . s(-1) while wearing underwear, an undershirt and the current Canadian protective overgarment either with (C+C) or without (C-C) combat clothing underneath and the new NBC-BDU worn over underwear and an undershirt. Results: All indices of heat strain which included tolerance time, sweat rates, sweat evaporation, Tre, fsk, Skin and garment vapor pressures, and heart rate indicated a significant improvement when the combat clothing was removed regardless of which NBC protective garment was worn. The new NBC-BDU was associated with a lower Tre after 2 h of exposure and lower skin and garment vapor pressures compared with the Canadian overgarment. Other indices of heat strain were not different between the NBC-BDU and C-C configurations. Conclusions: During light intermittent exercise when the rate of heat production is low, the removal of the combat clothing layer as part of the Canadian NBC protective ensemble is recommended to significantly reduce the heat strain.