Physiological assessment of the RNZAF constant wear immersion suit: laboratory and field trials.

Laboratory and field immersion trials were undertaken to determine the thermal protection afforded by a constant wear immersion suit (CWIS) in operation with the Royal New Zealand Air Force (RNZAF). Six males wore each of two ensembles during head-out laboratory immersions in 5.0 +/- 0.1 degree C (mean +/- SD) water for a maximum of 3 h. Ensembles 1 and 2 consisted of the CWIS in addition to minimal and maximal likely undergarment insulations, respectively. Open sea field trials (water temperature = 13.8 +/- 0.7 degree C; Beaufort wind state = 0-4; Sea state = 0-2) were conducted for a maximum of 2 h, with subjects wearing ensemble two and remaining strike aircrew apparel (ensemble three). Analysis of rectal temperature (Tre) changes permitted calculation of time to hypothermia (t35) and the survival estimate of 34 degrees C (t34). Mean (+/- SEM) t35 was 78 +/- 11 (n = 6), 187 +/- 20 (n = 5, p < 0.05) and 98 +/- 5 min (n = 3) for ensembles one, two and three, respectively. Mean t34 was 96 +/- 15, 259 +/- 31 (p < 0.05), and 119 +/- 5 min, respectively. Immersed insulations of ensembles one and two were 0.035 +/- 0.002 and 0.150 +/- 0.015 degree C.m2.W-1, respectively. Thus, the difference between minimal and maximal operational insulation was a 4.3-fold increase in insulation, which facilitated a 2.7-fold increase in mean t34. The thermal protection afforded by the CWIS during field trials was not sufficient to ensure survival for the 12-h expected rescue time.(ABSTRACT TRUNCATED AT 250 WORDS)