Protective clothing protects the body from external influence like heat, chemicals, mechanical hazards, foul weather, etc. To achieve this goal, the clothing has to shield the human body from the environment. From a physiological point of view, the human body feels comfortable at about 29 0C in an unclothed state (Wenzel and Piekarski 1982) and at about 26 0C with a clothing insulation of 0.6 clo (1 clo = 0.155 m K/W) (Olesen and Fanger 1973). However, protective clothing usually has a higher insulation. The bulkiness and the weight of the clothing lead to higher metabolic heat production. The British Standard (BS 7963 2000) provides estimations for the increase in metabolic rate due to the wearing of different types of protective clothing. This increase can be as high as 155 W/m2 when wearing highly insulating firefighters' personal protective equipment (including helmet, clothing, gloves and boots). Furthermore, many items of protective clothing have to be watertight, and the ensuing moisture barrier will reduce the transfer of sweat to the environment. Therefore the protective function of protective clothing is only achieved with a certain discomfort for the wearer, and the best balance between protection and comfort has to be found for every type of protective clothing, depending on the foreseen metabolic heat production and climatic conditions.
This contradiction is probably the most obvious for heat protective clothing, as it should prevent the external heat from flowing towards the body, but on the other hand allow the metabolic heat to escape to the atmosphere. Working at higher temperatures quickly leads to heat stress and stress-related heart attacks are frequently reported: in the United States, about 50% of the lethal accidents of firefighters on duty are due to heat stress (Washburn et al. 1999, LeBlanc and Fahy 2004). But even at moderate temperatures, the burden of increased weight and reduced permeability of this type of clothing can lead to heat stress. The results can, however, greatly vary depending on the set parameters: measurements at low temperatures and/or low relative humidity (22 0C and 20% to 45% RH (Reischl and Stransky 1980); 20 0C and 50% RH (Bartels and Umbach 1997); 45/65 0C and 15% RH (Sköldström and Holmer 1983), 22 0C and 56% RH (Ftaiti et al. 2001)) resulted in great differences in the skin and core temperature increases for different jacket types (PVC, Neoprene or leather vs. breathable materials). As soon as the temperature or the humidity of the environment approaches the conditions near the skin, the differences become smaller. (Schopper-Jochum et al. 1997) stated that the increase of body core temperature in an environment of 30 0C and 50% RH was independent of the jacket type. Griefahn et al. (1996) and Rossi (2003) did not find any significant differences between different types of protective clothing (breathable vs. non breathable) during exercises at higher temperatures either.
The weight of the equipment represents an additional load for the firefighter. An equipment set of 24 kg, for instance, reduces the performance of the wearer by 25% (Louhevaara et al. 1995). The size of the clothing and the number of textile layers (Teitlebaum and Goldman 1972, Lotens 1983) also increase the energy consumption of the wearer and thus the required heat loss to maintain thermal comfort. With chemical protective clothing and other types of impermeable clothing, the comfort problems are mainly caused by the lack of water vapour permeability, as the protection against chemicals often imply that the materials used are totally liquid- and sometimes also vapour-tight. Different studies report heat stress as the primary limitation of use duration of chemical protective clothing (Santee and Wenger 1988, Veghte 1988, Ilmarinen et al. 2000, Töpfer and Stoll 2001). Problems of body dehydration can also occur, as the sweat production cannot be easily compensated due to the wearing of a gas mask or self-contained breathing apparatus (Melin et al. 1999). Therefore, new developments of such clothing often aim at increasing the thermophysiological comfort (Amos and Hansen 1997, Reneau et al. 1999), primarily by improving the water vapour permeability (Wilkinson et al. 1997). For totally impermeable protective clothing, technical aids like ice-, liquid-, or air-cooling can help to reduce the thermal strain of wearing such equipment. However, the additional weight causes additional metabolic heat production and lowers the benefits of such systems (Glitz and von Restorff 1999).
Foul weather and cold protective clothing often contains a waterproof, moisture permeable barrier. This barrier ensures the water tightness, but at the same time still hinders the free flow of part of the water vapour produced by the body to the environment, as even the most breathable membrane or coating adds a resistance to the vapour flow. If the outside temperature is low, there is a certain risk of water condensation within the clothing layers when the water vapour pressure increases beyond saturation. The presence of condensation can then change the thermal and moisture transport properties of the clothing (Rossi et al. 2004b, Fukazawa et al. 2003, Finn et al. 2000).
Ballistic protective clothing also has to be a compromise between comfort and protection. Because of weight and bulkiness problems, the users sometimes refuse to wear these garments continuously. Furthermore, ballistic protective clothing using aramid-based panels has a significantly lower ballistic resistance when water enters the structure. For this reason, the panels have to be packed into impermeable outer shells, which have unfavourable consequences on the clothing physiology of the garment (Reifler et al. 2003).
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