deliverable 1.4. : Description of cooling protective clothing

Authors: Manuel Bühler, Herman Reezigt

Rationale:

In the Prospie project we aim to make a working prototype of comfortable PPE which is effective in hot situations. Therefore, cooling during operation is desired. We tested the effectiveness of salts for reduction of thermal strain using a thermal manikin.

Methods:

-     Heat absorbing modules containing salt based inflammable phase change materials (PCM) were prepared. They could be fixed on the external surface of the prototype PPE for reducing the conduction of thermal energy through the PPE. The efficiency of the modules was evalu-ated by irradiation tests.

By these tests it was possible to simulate a typical exposure to a ra-diant heat source.

-     Humidity absorbing modules containing hygroscopic endothermic salts were prepared. They were placed within the PPE for reducing the relative humidity what increased the wearer’s comfort and allowed more sweat to evaporate, leading to an additional cooling. The efficiency of the modules was evaluated by tests on a thermal manikin which is also able to sweat. A sweat rate of 400 g/h was chosen.

Both modules were tested on a manikin. The clothing included underwear and a permeable overall. The heat and humidity absorbing modules could be added separately.

Results:

-     The heat absorbing modules were shown to be efficient for approximately 5 minutes. After exposition to the hot environment they could be reactivated by exposing them to a cooler environment. The irradiation tests of the heat absorbing modules alone showed clear cooling effects. The results of the manikin tests were somewhat less clear because the total insulation with underwear, coverall and air layers was higher. However, the skin temperature of the manikin was observed to be lower when the heat absorbing module was used.

-     The additional uptake of water by the humidity absorbing modules during the manikin tests was small. Most effective was the encapsulated salt KSCN. However, the absorbed amount of water was small and the reduction of relative humidity within the clothing compared to the reference clothing was marginal.  The power needed to maintain the outside of the thermal manikin at 34°C was about 40% lower for the vests than the reference. This means that the heat loss restriction of the vests exceeded the cooling capacity.

Applicability:

-     The heat absorbing module is easy to process and can be attached onto the external layer of a PPE by suitable confection. Depending on the applications, salts with various phase change temperatures can be used.

-     If humidity absorbing modules are used together with a permeable overall it is important to integrate them within a light and breathable vest. Otherwise, the additional weight and thus reduction of comfort might be a larger inconvenient than what is possible to win in humidity comfort. Field tests (human subject study) will have to clarify this question. For suits with an impermeable coverall the salts could be more interesting. Also, the use of a salt type absorbing already at lower relative humidity (at around 50%) could eventually show a higher effect.