Effects of various factors on performance of thermal protective clothing

Protective clothing, specifically, thermal protective clothing, is primarily used to provide protection to wearers (eg, firefighters, oil and gas industry workers) from various types of thermal exposures (eg, flame, radiant heat, hot surfaces, molten metal substances, steam, and hot liquids). Generally, fire-retardant/resistant fiber-based fabrics are tailored into thermal protective clothing to cover the complex geometry of wearers’ bodies; consequently, many factors related to textile (eg, fabric, garment) engineering affect the thermal insulation characteristics of the protective clothing [19,38,305,502]. In this regard, the porous (hygroscopic) nature of a fabric (shown in Fig. 7.1) demonstrates that the structure of the fabric comprises two phases: (1) a gaseous phase, consisting of water vapor and/or dry air, and (2) a solid phase, consisting of fiber/yarn (as well as bound water, if hygroscopic). These phases individually contribute to the transfer of thermal energy through the fabrics. The gaseous still- or dead-air phase transfers comparatively less thermal energy than the solid fiber/yarn phase because the thermal conductivity of the dead air is much lower than the fiber/yarn. The dead air in the gaseous phase is mainly trapped by the solid phase, and this solid phase comprises different types of fibers or yarn depending upon the approach (woven or nonwoven) used at the time of engineering the fabric. Overall, it can be hypothesized that the fiber and/or yarn properties, along with the fabric properties, contribute to trap the dead air in the gaseous phase of the (woven or nonwoven) fabrics. Therefore, they control the thermal energy transfer through the gaseous phase of the fabrics, which in turn affects the thermal insulation characteristics of the fabrics [307,393,503,504]. These properties also control the thermal energy transfer through the solid phase of the fabrics, thus affecting the thermal insulation characteristics of the fabrics. Additionally, a two-dimensional (2D) flat fabric is converted into threedimensional (3D) protective clothing through the process of garment engineering; therefore, various features of the clothing regulate the microclimates that exist in between the clothing and wearers’ bodies. This microclimate is an air layer that controls the thermal energy transfer through clothing, thereby affecting its thermal insulation characteristics [22-24,76,302,505]. In summary, various factors associated with textile engineering, such as fiber properties, yarn properties, fabric properties, and clothing features, along with the developed microclimate, significantly affect the thermal insulation characteristics of fabric/clothing. These thermal insulation characteristics are strongly associated with the protective and comfort performances of clothing. If a factor enhances the thermal insulation characteristics of fabrics/cloth- ing, the transfer of thermal energy (in the form of heat) through fabric becomes low

Thermal Protective Clothing for Firefighters. http://dx.doi.org/10.1016/B978-0-08-101285-7.00007-1

© 2017 Elsevier Ltd. All rights reserved.

under a thermal exposure, and the thermal protective performance of clothing increases. However, the transfer of metabolic heat from wearers’ bodies to their ambient environment becomes disrupted (causing heat stress) due to the enhancement of thermal insulation, resulting in a decrease in the comfort performance of the clothing. Keeping this thermal protective and comfort performance in mind, many researchers have studied the impact of individual factors on the thermal insulation characteristics of fabrics/clothing. In the following sections, their findings are discussed. This discussion will develop an understanding of the engineering of thermal insulation from fiber, yarn, fabric, and clothing. This understanding will be useful in helping to achieve the best possible clothing performance for the protection and comfort of wearers.

Hygroscopic porous nature of fabrics

Fig. 7.1 Hygroscopic porous nature of fabrics.

Adapted from G. Song,

P. Chitrphiromsri, D. Ding, Int. J. Occup. Saf. Ergon.

14 (1) (2008) 89-106.

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