Immersion suit insulation: the effect of dampening on survival estimates.

Immersion suit leakage values were obtained from realistic testing of helicopter passenger immersion suits using eight subjects. Simulated helicopter underwater escape resulted in mean leakages of 198 +/- 103, 283 +/- 127, 203 +/- 179, and 45.7 +/- 31.6 g (mean +/- S.D.) when wearing four different immersion suits. Suit leakages obtained from a 20-min swim test to simulate vital in-water survival actions produced leakages of 213 +/- 224, 1398 +/- 691, 145 +/- 96.5, and 177 +/- 139 g (mean +/- S.D.). Dampening of undergarments during simulated helicopter travel at an elevated cabin temperature of 30 degrees C was 115 +/- 47.3 (mean +/- S.D.; n = 4) when wearing an impermeable suit and 19 +/- 16.7 g (mean +/- S.D.; n = 4) when wearing a vapour-permeable suit. The commensurate loss of insulation with the impermeable suit at the upper level of temperature could reduce clothing insulation by 17%. A reduction of less than 5% may result under similar conditions when wearing the permeable suit. The combined dampening effect of sweating, helicopter underwater escape, and performance of vital survival actions could result in a total dampening of 247-1712 g, depending on the type of suit worn. The respective loss of insulation would be 15% and 50% respectively. This could reduce, for the 10th percentile thin man, his survival time in water at 5 degrees C from 3.5 h to between 2.4 h and 1.1 h, respectively.