A brief background on thermal protective clothing for firefighters
In general, uncontrolled fires are likely to occur in three spaces: natural areas, structural buildings, and vehicles . These uncontrolled fires occur through ignition of a single, or combination of different, combustible materials and substances, such as wood, polymers, oil, gas, and so on. The burning of these substances rapidly spreads the fire from its source to the surrounding area through nearby combustible substances. Such uncontrolled fires are very devastating and may destroy property, human lives and, depending on location, millions of acres of forest. Sometimes, the aftereffects of such uncontrolled fires are worse than the actual fires, especially when a heavy rainfall occurs. This situation may cause landslides, ash flow, and flash flooding, which could cause additional property damage and affect the residential water supply .
Many fire extinguishers, namely water (H2O), foam, and carbon dioxide (CO2), are used to quench uncontrolled fires. The immediate application of such extinguishers could quickly suppress uncontrolled fires, and the proper application of fire extinguishers demands trained personnel . For this, firefighting training schools have been established. The prime job of firefighters is to immediately extinguish an uncontrolled fire at its source. Additionally, they need to rescue property and fire victims from the site of a fire. To accomplish these tasks, firefighters have to face thermal environments. These thermal environments can be categorized based on the intensity (routine, hazardous, and emergency) and type of exposures such as radiant heat, flame, hot surface, molten substances, hot liquids, and steam [10,11]. Firefighters work in thermal environments with varying intensities and exposures and statistics from the National Fire Protection Association (NFPA) have indicated that nearly 45,000 firefighter burn injuries and 100 firefighter fatalities occurred in the United States from 1981 to 2013 [12,13].
In order to mitigate firefighter burn injuries or fatalities, high-performance materials have been developed. Using these materials, various personal protective equipment (PPE), such as thermal protective clothing, footwear, and self contained breathing apparatus (SCBA) have been developed and are widely used in the industry. This PPE provides protection from burn injuries, inhaling harmful gases, and so on. Thermal protective clothing has been thoroughly tested to help reduce firefighters’ burn injuries and/or fatalities by protecting them from exposed thermal environments, as well as transmitting their metabolic heat and sweat-vapor to the ambient environment (Fig. 1.1) [5,14,15]. As one of the prime key components for clothing is textile fibers, a need has been identified for constant development of fire-retardant/resistant textile fibers to develop high-performance thermal protective clothing [4,16,17].
Fig. 1.1 The purpose of thermal protective clothing.
Fire-retardant fibers are developed through chemical treatment or modification of commonly used natural or synthetic textile fibers such as cotton, wool, polyester, and soon [4,16,17]. Initially, these chemically treated fire-retardant fibers (cotton or wool) were widely used; later, inherently fire-resistant fibers became very popular to provide better protection for firefighters. Different types of inherently fire-resistant synthetic fibers [eg, aramid (eg, Nomex, Kevlar), polyamide-imide (eg, Kermel), polyimide (eg, P84 from Lenzing), and polybenzimidazole (eg, PBI)] were invented in the last few decades [18,19]. The chemically treated, fire-retardant fibers are mostly used for the manufacturing of thermal protective clothing for firefighters who work with outdoor or vehicle fire hazards, whereas, the inherently fire-resistant fibers are used to manufacture the thermal protective clothing for firefighters who work in structural building fire hazards. It has been hypothesized that fire-retardant/resistant fiber-based fabrics developed through the application of innovative approaches and technologies may lead to the development of high-performance thermal protective clothing for better protection of firefighters [20,21].
It has been further observed that the currently existing fire-resistant/retardant fabrics comprise a wide range of thermal stability and insulation characteristics. Therefore, it becomes essential to evaluate the softening/melting temperature of fibers used in the fabrics, the flammability of these fibers/fabrics, and the thermal protective performance of these fabrics in the laboratory before employing them to manufacture the thermal protective clothing. To evaluate the performance of thermal protective fabrics as well as the manufactured clothing, many researchers conducted the laboratory tests (bench-scale or full-scale manikin) according to various standard methods established by different organizations, such as the ASTM (American Society for Testing and Materials), NFPA (National Fire Protection Association), ISO (International Organization for Standardization), CEN (European Committee for Standardization), and CGSB (Canadian General Standard Board) [22-25].
Conventionally, simple bench-scale tests were used to evaluate the thermal protective performance of a fabric under laboratory-simulated thermal exposures with varying intensities [22,26,27]. After World War II, the evaluation of thermal protective performance of clothing became a requirement in military operations. Therefore, in the last few decades, instrumented full-scale manikin tests and standards have been developed to evaluate the thermal protective performance of clothing, and these are now being widely used within scientific communities [15,23]. In both of these types of laboratory tests, it is challenging to accurately simulate thermal environments faced by firefighters. Furthermore, a group of researchers realized a need to understand the physiological behavior of firefighters when wearing thermal protective clothing, as thermal protective clothing exerts a significant heat stress to firefighters under thermal environments, causing a large percentage of firefighter fatalities [28-30]. Based on this factor, some research was conducted to study the physiological comfort provided by thermal protective fabrics and clothing in the laboratory through bench-scale tests, full-scale manikin tests, and human trials [31-33]. However, these studies mainly evaluated comfort in natural ambient environments, because it is challenging to set up an experiment that could evaluate the comfort under the thermal environments faced by firefighters.
In order to further understand the mechanism associated with thermal protective performance, a great deal of research has scientifically modeled the transfer of thermal energy (heat and/or mass) through firefighters’ protective clothing under a particular thermal environment [34-36]. Additionally, the transfer of metabolic heat and sweat-vapor through firefighters’ protective clothing are also analytically and numerically modeled to understand the mechanism associated with the comfort. These models are useful tools in identifying the factors affecting the performance and comfort of thermal protective clothing under a particular thermal environment. In this regard, it has been found that various factors (eg, fiber properties, yarn properties, fabric properties) affect the thermal protective performance and comfort of firefighters’ protective clothing [37,38]. Additionally, many extraordinary features associated with these factors may enhance thermal protective performance and comfort. For example, a hol- low/profiled fiber, a fiber with high surface to mass ratio, or a fabric with phase change material may demonstrate better thermal protective performance and comfort than conventional textile fiber/fabrics. To achieve these extraordinary features, new and upcoming technologies (eg, nanotechnology, intelligent and smart textiles) are being adopted along with conventional textile processing techniques (eg, spinning, weaving, finishing). These attempts have increased the breadth of knowledge on development of high-performance thermal protective clothing.