Home Engineering Thermal Protective Clothing for Firefighters
Clothing comfort (physiological) evaluation
As mentioned before, clothing can provide physiological comfort to its wearers by properly transmitting the metabolic heat and sweat-vapor from wearers’ bodies to their ambient environment [306-311]. Various fabric attributes are important for the physiological comfort provided by any clothing; these attributes are: thermal resistance; evaporative resistance; air permeability; and water (liquid sweat) wickability/absorptivity (rate of water wicking and absorbency, and total water absorbent capacity) [375-378]. Although fabrics’ air permeability and/or water wickability/absorptivity can be important attributes for the physiological comfort provided by regular clothing, these are not as important for the physiological comfort provided by thermal protective clothing. This is because an air-permeable and/ or water absorbent fabric may lower the thermal protective performance of the clothing under various thermal exposures (eg, radiant heat, hot liquids), which can be detrimental for wearers (firefighters) [24,29,75,76]. Thus, thermal resistance and evaporative resistance are the two key fabric attributes for the physiological comfort provided by protective clothing. Furthermore, a combined attribute of the thermal and evaporative resistance of a thermal protective fabric, called the THL capacity of the fabric, can be important for the physiological comfort provided by the clothing [31,379-381]. In this context, the thermal resistance of a fabric can be defined as the resistance provided by the fabric to the flow of dry metabolic heat from wearers’ bodies to the nearby environment; the evaporative resistance of a fabric is the resistance provided by the fabric to the flow of sweat-vapor from wearers’ bodies to the nearby environment; and THL is the total amount of metabolic heat transferred through a fabric by the combined dry and evaporative heat exchanges [377,382]. A fabric with a low thermal/evaporative resistance and a high THL value generates lower heat stress for wearers, resulting in higher physiological comfort. Related research at the Hohenstein Institute in Germany has established an association between rain suit fabrics’ intrinsic evaporative resistances and the comfort perceptions of human subjects wearing the suit under different environmental conditions and level of activity. This is shown in Table 5.3. Similarly, the European standard EN 469 suggested that the intrinsic fabric evaporative resistance of firefighters’ protective clothing should not be >30 m2 Pa/W for providing an effective physiological comfort to firefighters. Additionally, the NFPA 1971:2007 standard suggested that the THL of the fabric used in thermal protective clothing should be at least 205 W/m2 in order to provide physiological comfort to working firefighters.
Table 5.3 Association between intrinsic fabric evaporative resistances and clothing comfort perception
Overall, it can be inferred that a thorough understanding of thermal resistance, evaporative resistance, and/or THL is essential to properly evaluate clothing’s (physiological) comfort . The following section discusses in detail the evaluation/calculation and assessment of thermal resistance, evaporative resistance, and/or the THL of fabric and clothing (Sections 5.3.1 and 5.3.2). Some researchers have directly evaluated the physiological comfort provided by clothing using human subjects [383,384]; therefore, the evaluation of clothing comfort through human trials is thoroughly discussed in Section 5.3.3.
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