Heat Stress of Helicopter Aircrew Wearing Immersion Suit

Abstract

The objectives of the present study were to define the lowest ambient air and cabin temperatures at which aircrews wearing immersion protection are starting to experience thermal discomfort and heat stress during flight operations, and to characterize during a flight simulation in laboratory, the severity of the heat stress during exposure to a typical northern summer ambient condition (25°C, 40% RH). Twenty male helicopter aircrews wearing immersion suits (insulation of 2.2 Clo in air) performed 26 flights within an 8-month period at ambient temperatures ranging between -15 and 25°C, and cabin temperatures ranging between 3 and 28°C. It was observed based on thermal comfort ratings that the aircrews were starting to experience thermal discomfort and heat stress at ambient and cabin air conditions above 18°C and at a WBGT index of 16°C. In a subsequent study, seven aircrews dressed with the same clothing were exposed for 140 min to 25°C and 40% RH in a climatic chamber. During the exposure, the aircrews simulated pilot flight maneuvers for 80 min followed with backender/flight engineer activities for 60 min. By the end of the 140 min exposure, the skin temperature, rectal temperature and heart rate had increased significantly to 35.7 ± 0.2°C, 38.4 ± 0.2°C and between 110 and 160 beats/min depending on the level of physical activity. The body sweat rate averaged 0.58 kg/h and the relative humidity inside the clothing was at saturation by the end of the exposure. It was concluded that aircrews wearing immersion suits during the summer months in northern climates might experience thermal discomfort and heat stress at ambient or cabin air temperature as low as 18°C.

Development of a perceptual hyperthermia index to evaluate heat strain during treadmill exercise

“…Thermal comfort in helicopter aircrew wearing immersion suits seemed to show an anecdotal positive trend with ambient temperature, cabin temperature, and the cabin wet-bulb globe temperature index. 18 Thermal sensation during exercise in cool and cold water is suggested to be moderately correlated with skin temperature and rectal temperature. …”

Performance of immersion suits: A literature review

“…The very nature of being impermeable contributed to the bad ventilation of immersion suits. As it was concluded by several research studies, the relatively high thermal resistance and extremely low water vapor permeability of clothing ensemble impede evaporative heat dissipation and thus elevate the rate of heat storage, creating a state of uncompensable heat stress [32][33][34].…”

“…Human trials were conducted in a climatic chamber at Defense Research and Development Canada to study the heat stress of the aircrews when carrying on a certain level of activity. The severity of heat stress was investigated during the flights of aircrew in a temperature range between À15 C and 25 C. It was concluded that during the summer in northern climates, aircrews wearing immersion suits might experience thermal discomfort and heat stress at ambient or cabin air temperature as low as 18 C [32]. One of the reasons that resulted in thermal discomfort is the impermeability of certain immersion suits.…”

“…Besides the suit, there are undergarments and accessories worn in accordance with the layered suits, i.e. top and bottom long cotton underwear, woolen socks, flying leather summer boots, flying gloves, helmet and un-inflated or inflated life vest [24,32]. Originally, the immersion suits were made of neoprene and chloroprene-coated rubber, which is impermeable to sweat.…”

Development of a Perceptual Hyperthermia Index to Evaluate Heat Strain during Treadmill Exercise

“…Thermal comfort in helicopter aircrew wearing immersion suits seemed to show an anecdotal positive trend with ambient temperature, cabin temperature, and the cabin wet-bulb globe temperature index. 18 Thermal sensation during exercise in cool and cold water is suggested to be moderately correlated with skin temperature and rectal temperature. 72…”