Human temperature regulation in wind and waves
Student thesis: Doctoral Thesis
Many international and national standards exist for the testing and certification of immersion suits. Some require the thermal protective properties of immersion suits to be tested with human volunteers in calm, circulating 2°C water. The knowledge gap that currently exists between the benign testing conditions used in international standards and specifications, and the harsh environments that an immersed individual find themselves in following a marine accident, could result in unexpectedly poor levels of performance, with fatalities occurring sooner than expected following accidental immersion. Study 1 determined the heat loss from the skin of volunteers in immersion suits and immersed in wind and waves. Twelve healthy participants (Age: 25.8 [5.9] years old; Mass: 81.7 [13.1]kg; Height: 176.2 [7.7]cm) performed four, one hour immersions in the following conditions: Calm water; Wind-only; Waves-only; and Wind + Waves. Compared to Calm (67.21 [4.70]W·m-2), all the other immersion conditions produced a significantly greater increase in mean skin heat flow (MSHF) (Wind: 79.60 [6.70]W·m-2; Waves: 78.8 [4.52]W·m-2; Wind + Waves: 92.00 [8.39]W·m-2). The Wind + Waves condition produced a significantly greater increase in MSHF compared to all other conditions. Study 2 built upon the findings of the first by investigating the extent to which human thermal responses were related to the severity of weather conditions. Twelve healthy males (Age: 23.9 [3.3] years old; Mass: 83.2 [4.9]kg; Height: 181.0 [4.9]cm) performed three, three hour immersions in the following conditions: Calm water; Weather 1; and Weather 2. Compared to the calm water condition (62.96 [2.98]W·m-2], both weather conditions produced a significantly greater increase in MSHF (Weather 1: 76.75 [6.26]W·m-2; Weather 2: 79.53 [6.24]W·m-2). There were no significant differences in the change in gastro-intestinal temperature (TGI) across immersion conditions (Calm: -0.10 [0.31]°C; Weather 1: -0.29 [0.30]°C; Weather 2: -0.20 [0.28]°C]. There were no significant differences in V · O2 across immersion conditions (Calm: 0.325 [0.054]L·min-1; Weather 1: 0.332 [0.108]L·min-1; Weather 2: 0.365 [0.080]L·min-1). Study 3 investigated the effect of simulated water ingress under an immersion suit on human thermal responses during immersions in varying weather conditions. Twelve healthy males (Age: 25.6 [5.6] years old; Mass: 82.7 [10.2]kg; Height: 181.0 [4.7]cm) performed three, three hour immersions in the same conditions as Study 2, but with 500mL of water underneath the immersion suit. Compared to the calm water condition (79.45 [9.19]W·m-2), both weather conditions produced a significantly greater increase in MSHF (Weather 1: 102.06 [11.98]W·m-2; Weather 2: 107.48 [3.63]W·m-2). There were no significant differences in the change in TGI (Calm: -0.35 [0.14]°C; Weather 1: -0.38 [0.15]°C; Weather 2: 0.29 [0.25]°C) or V · O2 (Calm: 0.449 [0.054]L·min-1; Weather 1: 0.503 [0.051]L·min-1; Weather 2: 0.526 [0.120]L·min-1) across conditions. Survival times were calculated for the participants of Studies 2 and 3. There was no difference in the predicted survival times for the Study 2 participants for both the calm (> 36 hours) and wind and wave conditions (> 36 hours). The predicted survival times for the participants of Study 3 were significantly lower in the turbulent conditions (16 hours) compared to calm (27 hours). The predicted survival times of the participants in turbulent conditions were up to half those calculated for calm water immersions. The results collected in Studies 2 and 3 were used to calculate the change in total insulation in varying conditions compared to being dry. Immersions in wind and waves will reduce immersion suit insulation by 27%; 500mL of water leakage will reduce it by 24%; wind, waves and 500mL of water combined will reduce it by 43%. It is concluded that: immersions in wind and waves causes a significant increase in heat flow from the body compared to calm conditions. Testing individuals and immersion suits in conditions not representative of the area where they are to be used may, or may not, result in an over-estimation of performance depending on the capacity of an individual’s thermoregulatory system.
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