THE EFFECT OF STANDARD WAVE CONDITIONS ON DRY SUIT INSULATION WHEN MEASURED ON HUMANS
Testing of immersion suits is commonly conducted in calm or circulatory water. Several investigators have argued that this is an unrealistic test for a suit that is designed to protect a human from hypothermia in open ocean conditions. In support of this argument, Steinman et al. (1) and Romet et al.(2) reported a significant reduction of suit insulation in turbulent water when compared to still water by an average of about 30% when measured on humans. Such differences were found for loose-fitting wet suits but were not investigated for dry suits. Recently, Sowood et al. (3) reported a reduction of dry suit insulation by about 30% in turbulent water (wave height of 60 cm) compared to still water when tested on a thermal manikin.
The Effects of Wave Conditions on Dry Immersion Suit Insulation: A Comparison Between Humans and Manikin,
Abstract : The objective of the present study was to investigate the effect of standard wave conditions (0 to 70 cm) on dry immersion suit insulation when tested on humans and a manikin simultaneously. Six human subjects and a thermal manikin dressed with the same dry immersion suit system (pile undergarment insulation, uninsulated immersion suit and neoprene gloves and hood) were immersed simultaneously for one hour in 16 deg C water rendered turbulent with an irregular wave pattein. One immersion was performed for each randomly chosen wave condition, from 0 to 70 cm wave height, changing by steps of 10 cm. In addition to the physiological parameters measured on the human subjects (skin and rectal temperatures, skin heat loss and heart rate), and the ambient temperature of water and air, heat fluxes and surface temperatures were measured at 12 sites on the subjects and manikin for each compartment of the dry suit system (skin, pile garment, suit garment). This allowed the calculation of the thermal resistance of every suit compartment in addition to the air and water boundary layer surrounding the suit. The results showed that none of the physiological parameters were significantly affected by the wave conditions, except for the skin heat flux which increased with wave height from 72.0 +/- 1.9 W m(-2) at 0 cm to 85.5 +/- 2.9 W m(-2) at 70 cm. The thermal resistance data showed that wave height up to 70 cm decreased dry suit system insulation by 14 and 17% when measured on human subjects and manikin, respectively; and that the only suit component significantly affected by the wave motion was the insulation of the water and air boundary layers surrounding the body. The body sites that were the most affected by the effect of wave motion were the head, and the proximal limbs with a 58% and 63% decrement in suit thermal resistance from 0 to 70 cm wave height for humans and mani
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.