Impact of a Ventilated Hood on Heat Stress at High Relative Humidity

摘要

Heat stress is a major problem associated with use of encapsulating chemical protective garments. Metabolic and externally imposed heat loads can be degrade cognitive and physical performance and prove life-treating if not adequately extracted from within protective clothing ensembles. Two approaches have historically been used to actively remove heat from encapsulating clothing ensembles: (1) vapor phase cooling, where the heat transfer medium is a vapor such as air; and (2) liquid phase cooling, with water or freon acting as the heat transfer medium. Personal aircrew cooling systems tend to be vapor-based because of weight considerations and the risk of leaking coolant into the aircraft. In addition, air-cooled systems employing evaporative cooling can theoretically remove greater quantities of heat while using less external energy the liquid-based systems dependent on conductive or convective heat exchange. Wearing a helmet, however, compresses the protective hood worn with encapsulating protective garments and produces available airflow to the head and neck. This reduced airflow may limit heat loss from the head and neck and potentially eliminate a major route of body heat loss. The purpose of this study was to examine whether using a chemical protective hood contributes significantly to heat stress in a hot/humid environment.