Abstract:

Objective Immersion suit is a type of personal protective equipment to prevent cold shock or even death caused by rapid heat loss when the wearer accidentally falls into cold water, which can effectively prolong the survival time of the wearer. The existing immersion suit has good thermal insulation, but there may be physiological heat load during the non-water state. Therefore, the development of protective clothing capable of dynamically adjusting thermal insulation to provide thermal comfort in different operating environments is necessary. The performance evaluation under pressure conditions is also in demand.

Method An air inflatable temperature-regulating immersion suit was developed, containing an inflatable layer with adjustable static air volume, between the waterproof layer and the aerogel thermal layer. The thermal insulation of the developed air inflatable immersion suit and the commercial immersion suit with polyester wadding were measured and compared using thermal manikin "Newton". The total and local thermal insulations were analyzed under conditions of two thermal insulating materials (aerogel and polyester wadding), three pressure states (no pressure, low pressure, high pressure), and four inflation volumes (CON, 1/3FULL, 2/3FULL and FULL). The thermal insulations were calculated using the parallel method and statistically analyzed using SPSS software.

Results The experimental results showed that the thermal insulating materials had significant effect on the total thermal insulation of immersion suit under no pressure. The thermal insulation of the air inflatable immersion suit was 3.85 clo, which was significantly higher than that of the polyester wadding immersion suit whose a thermal insulation is 3.28 clo (P<0.01). Meanwhile, the total thermal insulation was significantly reduced under high pressure. The thermal insulation of the air inflatable immersion suit was significantly higher than that of the polyester wadding immersion suit at the forearm, chest, abdomen, back, and buttocks (P<0.01), while the differences in other areas were not significant. With the increase of pressure, the total thermal insulation of the immersion suit was decreased, and the reduction rate of air inflatable immersion suit was 11.53% from no pressure to low pressure and 24.40% from low pressure to high pressure, with the reduction rate of thermal insulation from no pressure to high pressure for the commercial immersion suit being 7.05%. The difference of thermal insulation between the two immersion suits was no longer significant. This may be related to the fact that the immersion suit was squeezed, reducing its overall thickness and damaging the warmth wadding and the static air layer underneath the suit. The pressure also reduced the local thermal insulation. Under low pressure, the thermal insulation of the air inflatable immersion suit was decreased less at the upper arm and the back. Under high pressure, the thermal insulation of the abdomen, back and buttocks was decreased remarkably, and there was no longer a significant difference between the two suits at the abdomen and thighs. This result is related to the degree of extrusion of the air layer under the clothing. When the thermal manikin is standing still, there is more air under the clothing in the lumbar and abdominal areas, and less air under the clothing in the shoulders and hips, and consequently a greater decrease in the thermal insulation of the lumbar and abdominal areas when it is extruded by an external force. With the increase of the inflation volume, the total thermal insulation did not change significantly under no pressure, was increased significantly (P<0.05) and then decreased slightly under low pressure and continued to increase under high pressure. This may be be cause of the fact that immersion suit contained a certain air layer between the layers, and the increase in inflation without pressure instead squeezes out the presence of the air layer, and no difference exists in the total thermal insulation. Pressure causes the air layers between layers and underneath the suit to be squeezed, but inflation resists the squeezing of the air layers caused by pressure, so the higher the inflation, the greater the thermal insulation of the suit. However, the inflation volume did not have a consistent pattern of influence on the local thermal insulation for the air inflatable immersion suit.

Conclusion The total thermal insulation and local thermal insulation of the two immersion suits were decreased under pressures, and the reduction was more pronounced as the pressure became higher. The difference between the thermal insulation of the two immersion suits was no longer significant, but the air inflatable immersion suit was still better than the commercial immersion suit. Under pressures, the thermal insulation of the air inflatable immersion suit tended to increase with increasing inflation volume, and the higher is the pressure, the more pronounced is this trend. In summary, compared with the commercial immersion suit, the air inflatable immersion suit provided better thermal insulation and could dynamically adjust under a certain pressure.

Key words: inflatable suit, immersion suit, thermal insulation, thermal manikin, inflation volume