Helicopter crashes in cold water present a survival challenge to passengers especially if they are trapped underwater. We tested the effect of varying skin exposure and water temperature on underwater breath-hold time and subsequent minute ventilation. Twelve subjects (2 female) were studied in 8 and 20°C water while wearing a helicopter transport suit with a dive mask. At each temperature, subjects performed a maximum breath-hold and then breathed for 90 s (through a mouth piece connected to room air) in five skin-exposure conditions. The first trial was out of water for Control (suit zipped up, hood on, mask off). Four submersion trials were then conducted with exposure of the: Partial Face (hood and mask on); Face (hood on, mask off); Head (hood and mask off); and Whole Body (suit unzipped, hood and mask off). Decreasing temperature and increasing skin exposure reduced breath-hold time (to as low as 10 ± 4 s), generally increased minute ventilation (up to 40 ± 15 L.min-1), and decreased predicted endurance time (PET) of a 55-L Helicopter Underwater Emergency Breathing Apparatus (HUEBA); for example, in 8°C water, PET was 2 min 39 s (Partial Face) and decreased to 1 min 11 s (Whole Body) (P<0.05).
Results have significant applications for education and preparation of helicopter occupants. Thermal protective suits and dive masks should be provided and occupants must wear the suits zipped up with hoods on, and don the dive mask prior to crashing if possible. This will greatly increase survivability