Abstract : A new concept of immersion suit, the nearly dry suit, was recently developed to overcome the main limitations of the wet and dry suits. The main new feature of the suit is the adjustable seals that can be closed before or upon entry in water. The purpose of the present study was to test the new suit at sea against a standard dry suit. Seven male subjects were immersed for over one hour in 3 deg water in the Atlantic ocean. Three conditions were tested during which the subjects were wearing a dry suit (DRY), a nearly dry suit with the seals closed (NEAR-DRY-C) or a nearly dry suit with the seals opened upon entry in water (NEAR-DRY-O). The thermal resistance of the suit, measured from the skin heat loss data and the temperature difference between the skin and the outside surface of the suits, were 0.95 +/- 0.14, 0.69 +/- 0.13 and 0.58 +/- 0.09 Clo for DRY, NEAR-DRY-C and NEAR-DRY-O conditions, respectively, with the thermal resistance being significantly lower (p <- 0.05) for the NEAR-DRY conditions. The decrease in insulation for the NEAR-DRY-O condition was attributed to a significantly larger water leakage through the seals (1.37 +/- 0.29 L) as compared to the other conditions (DRY: 0.41 +/- 0.20 L; NEAR-DRY-C: 0.35 +/- 0.28 L). It was concluded that the nearly dry suit concept, while maintaining a greater comfort when the seals were opened before immersion, successfully limited the water leakage into the suit to a level observed with a dry suit when the seals were closed upon entry in water. The thermal insulation provided by the nearly dry suit when closed is not inferior to 0.75 Clo, the recommended insulation to obtain adequate thermal protection in cold water. During immersion in the open mode, the nearly dry suit can decrease the survival time by a factor a two.
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