The effect of floor insulation and clothing wetness on thermal response of life raft occupants exposed to cold

摘要

Introduction: Inflatable life rafts are the primary evacuation units used by the majority of vessels at sea. In the event of an emergency evacuation from a vessel, all passengers don the provided survival equipment and enter the life raft from the vessel or water. If the passengers do not have additional thermal protection (such is the case of many passenger vessels) they are largely dependent on the thermal protection of the life raft to prevent or minimize heat loss to the environment. Although current life raft standards require every life raft to provide sufficient insulation against cold (IMO, 1996), the standard lacks performance standards. The aim of this study was to determine the thermal response of life raft occupants with no additional thermal protection in cold conditions.udMethods: Five male and three female participants (26.3 ± 6.1 yrs, 84.4 ± 18.5 kg, 175.7 ± 9.6 cm, 23.7 ± 9.1 BF%) were exposed to four randomly assigned life raft conditions: wet clothing with uninflated floor (WU), wet clothing with inflated floor (WI), dry clothing with uninflated floor (DU), and dry clothing with inflated floor (DI). Trials were terminated based on any one of the following criteria: core temperature (both Tre and Tty) dropped to 35ﾟC, the scheduled trial end time was reached (max 8.25 hrs), or the participant refused to continue. For all trials the ambient conditions were: 5ﾟC air and water temperature, 5m∙s-1 wind speed, and 0.5m∙s-1 towing speed. During each trial two participants and one researcher occupied a 16 person life raft. Participants wore a full zip cotton coverall, cotton t-shirt, cotton briefs, and a safety of life at sea (SOLAS) approved lifejacket. The extremities were protected against non-freezing cold injuries with wool lined leather mittens, wool socks and 5 mm neoprene boots. Measures of rectal and tympanic temperatures (Tre and Tty), skin temperature (Tsk) and heat flow (HF) at 13 sites, and metabolic rate (MR) were recorded continuously during each trial. All trials were conducted at the National Research Council – Institute for Ocean Technology’s indoor ice tank.udResults: Baseline measurements were similar across all four conditions (Tre: 36.85±0.04ﾟC; Tty: 36.39±0.01ﾟC; Tsk: 33.02±0.03ﾟC; HF: 60.31±2.47W·m-2; MR: 106.30±49.44W). The duration of exposure for DI (7.76±0.52h) was significantly longer compared to DU (6.49±1.07h) and WI (6.10±1.29h), with the exception of WU (6.37±2.15h). At the end of the exposures, Tre and Tty had decreased from the baseline measurements for all condition. Tre decreased more significantly for the un-inflated conditions, WU (34.95±0.73ﾟC) and DU (34.76±0.69ﾟC), compared to the inflated conditions, WI (35.65±0.50ﾟC) and DI (35.72±0.49ﾟC). However, the clothing wetness had no significant effect on the Tre cooling. Tty decreased similar amounts across all four conditions indicating that neither the clothing wetness nor floor insulation had a significant effect on Tty cooling: WU (35.63±0.47ﾟC), WI (35.12±0.82ﾟC), DU (35.34±0.58ﾟC), and DI (35.30±0.41ﾟC). Tsk decreased across all conditions but significantly more during the wet conditions, WU (23.48±2.44ﾟC) and WI (24.01±1.91ﾟC), compared to the dry conditions, DU (26.84±1.61ﾟC) and DI (27.72±1.52ﾟC). The difference between the baseline and exposure average HF was significantly greater for the wet conditions, WU (183.20±29.27W·m-2) and WI (171.95±29.63W·m-2), compared to the dry conditions, DU (124.59±32.53W·m-2) and DI (120.67±23.03W·m-2). The floor had no significant effect on Tsk or HF. The average MR was greater during the exposures than baseline for all conditions with a more significant increase during the wet conditions, WU (65.17±27.12W) and WI (69.48±44.39W), compared to the dry conditions, DU (37.90±28.89W) and DI (5.44±39.00W). Similar to Tsk and HF, the floor had no significant effect on the change in average MR.udConclusion: This study demonstrated that both clothing wetness and floor insulation have an effect on the thermal response of life raft occupants wearing minimal protective clothing. Clothing wetness had the biggest effect on Tsk, HF, and MR, with floor insulation having the biggest effect on Tre.