Experimental Study and Modelling of Thermal Protection in Liferafts Using a Thermal Manikin and Human Subjects

Abstract

Experiments were conducted in cold conditions (5°C water temperature and 5°C air temperature) to assess the thermal protection of a 16-person, SOLAS approved, commercially available liferaft using a thermal manikin and human subjects. The comparison tests included four cases — 1. Inflated raft floor; dry clothing (Idry); 2. Inflated raft floor; wet clothing (Iwet); 3. Uninflated raft floor; dry clothing (Udry); 4. Uninflated raft floor; wet clothing (Uwet). The results demonstrated equivalence in insulation between human subjects and a thermal manikin for all cases of comparison (Idry: Manikin 0.236 (m2°C)/W versus Human 0.224 (m2°C)/W; Iwet: Manikin 0.146 (m2°C)/W versus Human 0.145 (m2°C)/W; Udry: Manikin 0.174 (m2°C)/W versus Human 0.185 (m2°C)/W; Uwet: Manikin 0.101 (m2°C)/W versus Human 0.116 (m2°C)/W). The results also showed the repeatability of the thermal manikin tests (0.177 (m2°C)/W versus 0.171 (m2°C)/W in Udry baseline case; and 0.101 (m2°C)/W versus 0.104 (m2°C)/W in Uwet baseline case). The results indicated that the insulation of a closed cell foam floor is comparable to an inflated floor (0.236 (m2°C)/W compared to 0.221 (m2°C)/W and 0.236 (m2°C)/W for closed foam floor from manufacturer A and B respectively). TPA provided considerable additional insulation than all baseline cases. A test with a human subject wearing a TPA in the Uwet case showed an improved insulation of 48% over the baseline case. TPA provided more additional insulation than a wet suit in all test cases except Udry case. In Uwet case, the worst test condition, the insulation obtained by sitting on a lifejacket (0.149 (m2°C)/W) is less than wearing a TPA (0.158 (m2°C)/W). Both of these are better than sitting directly on an uninflated floor (0.104 (m2°C)/W) or a closed cell foam floor (0.129 (m2°C)/W). There is a significant decrease in insulation value sitting in 10 cm of water (0.05 (m2°C)/W). Two human subject tests show an insulation value of 0.079 (m2°C)/W and 0.081 (m2°C)/W respectively. A liferaft occupant heat loss model was developed and integrated with Defense R&D Canada’s Cold Exposure Survival Model to predict survival time. For Uwet case, the worst test condition, the survival time is 32 hours and functional time is 24 hours for the experimental conditions.