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Design of thermal protective clothing

Although many innovative approaches have been applied to developing thermal protective clothing, they cannot provide adequate protection to firefighters from all types of thermal exposures, eg, radiant heat, flame, hot surfaces, molten metal substances, hot liquids, and steam. Furthermore, the presence of heavier and thicker thermal liners as well as water-impermeable and partially breathable moisture barriers in clothing causes a significant heat stress on firefighters’ bodies [28,29]. Hence, modern design philosophy demands the development of high-performance thermal protective clothing that can provide optimal protection as well as comfort to firefighters. Keeping this concern in mind, many researchers have developed new fabrics that can provide sufficient thermal protection along with reduced heat stress. For example, Hocke, Strauss, and Nocker [585] developed a nontextile thermal liner by using foamed silicon on a vapor-permeable moisture barrier, which can provide a better thermal protection to firefighters and also reduce their heat stress; Holme [586] macroencapsulated the nanoporous gels in viscose-based nonwoven fabric to produce a lightweight thermal liner that can provide adequate protection and comfort to firefighters; and Jin et al. [587] padded a needle-punched nonwoven thermal linear with 5% aerogels dispersed in acetone. As the aerogels are comprised of extremely fine nanopores with 99.8% air, they enhance the insulation features of the thermal linear under radiant heat and/or flame exposures [588]. Similarly, the application of nanoclay reinforced resin coating in thermal liners can enhance the insulation features. Dadi [589] also suggested that the application of lightweight nanofiber-based fabrics, nanofinishes on traditional fibers/fabrics, and/or phase change materials (PCM) to the manufacture of thermal protective clothing can provide a better protection for firefighters without compromising their heat stress [590,591]. Here, PCMs can be applied in either fiber spinning or chemical finishing (coating, lamination) processes. In this context, the thermal protective performance of firefighters’ clothing with or without PCM under radiant heat exposures were studied with a theoretical heat transfer model, and it was found that application of PCMs in firefighters’ clothing would provide equivalent performance with reduced garment thickness [592]. Similarly, the UK Defense Clothing and Textiles Agency demonstrated that the application of shape memory materials (SMMs) can also enhance the performance of thermal protective clothing. This is because SMMs (alloy, polymers) can change their current shape into a prescribed crystal structure shape depending upon the intensity of the thermal environments [593]. For example, an application of shape memory nickel-titanium alloy finishes to a multilayered fabric may widen the air gap between layers in the presence of thermal environments. This increased air gap can help to provide a better thermal protection for firefighters against extreme sources of radiant heat or flame [594]. In addition, shape memory polymers can be more compatible than shape memory alloys in a multilayered fabric; thus, the application process of shape memory polymers is much easier and more effective than that of shape memory alloys. Furthermore, a group of researchers suggested the development of high-performance fabrics that can passively control the firefighters’ burn injury and heat stress [591]. They recommended applying cooling resources (eg, ice, frozen gels) to thermal protective clothing, in order to actively alleviate heat stress caused by the clothing. Chitrphiromsri et al. [595] developed intelligent thermal protective clothing for firefighters. In this type of clothing, liquid water is injected into the outer surface of the thermal protective clothing, and the injection process is activated by temperature sensors embedded in the clothing. The applied water absorbs a large amount of thermal energy and evaporates in the presence of thermal environments. Hence, this mechanism can actively enhance the performance of the clothing and can provide greater burn injury protection to firefighters.

Additionally, the application of emerging technologies in thermal protective clothing can also passively control firefighters’ burn injuries and heat stress by monitoring their work situations [588,596]. For example, weaving of wires and sensors into the fabrics can provide firefighters information about the temperature and hazards they are encountering, and a fire officer can monitor each on-duty firefighter’s situation (eg, elapsed time, air pressure, remaining air time, ambient temperature, heat stress level). There are other benefits as well: integration of thermal sensors into the interior and exterior of thermal protective clothing can control the temperature near the firefighter, and the temperature inside the clothing and close to the body; incorporation of circularly polarized antenna (with a bandwidth of more than 180 MHz), two-way mobile, and two-way portable communication devices into thermal protective clothing can be a useful tool to monitor firefighters’ working situations; the addition of a gas detector into thermal protective clothing can monitor the presence of life threatening gasses in the ambient environment of firefighters; and the attachment of a personal alert safety system in the clothing can trigger an alarm when a firefighter experiences an extreme temperature, or has spent a long time at a lower temperature threshold.

Based on the previous discussion, it is clear that many developments have occurred in the manufacturing of high-performance thermal protective clothing that can provide optimal protection as well as comfort to firefighters. However, most of these developments are cost-inefficient, so are relegated to a laboratory setting and/or are only applied in highly specialized circumstances (eg, aerospace, military defense). It can be inferred that a cost-efficient and revolutionary application of the new standardized technology (eg, nanotechnology like nanofibers or nanofinishes, smart textiles technology like PCM or SMM, cooling devices) can contribute to the mass-production of the fabrics and clothing that are lighter, thinner and/or completely moisture/vapor-permeable [535,597]. As nanofibers are lighter than conventional macrofibers, it can be hypothesized that the use of nanofibers can reduce the weight and thickness of the clothing while maintaining the same level of performance. Additionally, the smart textiles can sense wearers’ physiological conditions, postures, and ambient environments. Thus, it is expected that application of smart textiles may be the most promising development for the manufacture of thermal protective clothing. This attempt may provide a greater protection to firefighters along with reduced heat stress [598]. Furthermore, firefighters are not only exposed to thermal hazards; they are also frequently exposed to various chemical hazards, especially hot smoke, toxic fumes, and gasses. An inhalation of hot smoke can burn firefighters’ lungs and impair their ability to exchange gasses during breathing; this situation results in hypoxia to firefighters, which is the major cause of their physical performance loss and fatalities. Additionally, firefighters might be exposed to various poisonous fumes and gasses (eg, carbon monoxide, hydrogen cyanide, nitrogen dioxide, sulfur dioxide, hydrogen chloride, and benzene), which are mainly produced by combustion of nitrogen-rich materials (natural textiles like wool and silk, polyurethane, polyacrylonitrile) in a structural fire. As 50% of firefighter fatalities occur because of the high lethal concentration of chemical hazards [599], it is recommended to design thermal protective clothing that can provide optimal protection from both thermal and chemical hazards.

Additionally, the terrorist attack in the United States on Sep. 11, 2001 created awareness that firefighters may be exposed to a combination of chemical, biological, radiological, nuclear, and explosive (CBRNE) hazards [584]. The 2007 version of the NFPA 1971 standard also suggested that firefighters’ protection issues should deal with chemical, biological, radiological, and nuclear (CBRN) hazards. As a consequence, a few efforts have been initiated to understand the customers/consumers’ expectations, preferences, and aversion; based on this understanding, a contemporary design philosophy needs to be adopted to invent firefighters’ clothing that can provide optimum protection from CBRN hazards along with thermal hazards [584]. It is also expected that this newly invented clothing should be ergonomically designed to provide sufficient comfort and mobility or dexterity to firefighters.

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