Desktop version

Home arrow Engineering arrow Thermal Protective Clothing for Firefighters

Source

Analytical models

In flame, radiant heat, and hot surface exposures, heat transfer mainly occurs through fabrics; whereas, mass transfer predominates in molten substance, hot liquids, and steam exposures [76,84-86,267]. During the heat transfer, thermal energy diffuses from regions of high temperature to regions of low temperature. While in mass transfer, thermal energy diffuses along the molecular-concentration/pressure gradients in various forms (eg, hot liquids, vaporized water molecules).

Behavior of the imposed thermal energy in flame, radiant heat, and hot surface exposures: In radiant heat and flame exposures, the thermal energy imposed on the fabric of clothing (in the form of heat) divides into three parts: reflected/emitted, absorbed, and/or transmitted (Fig. 6.1). Convection is the prime mode of thermal energy transfer during the close or engulfed flame exposure [25,76]. This thermal energy majorly transmits (instead of being reflected or absorbed) through fabric in the radiant heat exposure, in comparison to the flame exposure [35]. Here, it is also worth mentioning that a significant amount of absorbed energy may transmit again

Thermal Protective Clothing for Firefighters. http://dx.doi.org/10.1016/B978-0-08-101285-7.00006-X

© 2017 Elsevier Ltd. All rights reserved.

through the fabrics during and/or after the radiant heat and flame exposures. Altogether, it seems that reflectivity/emissivity, absorptivity, and transmissivity are the prime fabric parameters that can affect the transfer of thermal energy through fabric and can affect the thermal protective performance of clothing [76,167,353]. In hot surface exposure, imposed thermal energy (in the form of heat) is mainly transported through conduction (Fig. 6.2). Here, the compressed configuration of the fabric

Behavior of thermal energy (a — reflected/emitted thermal energy, b — absorbed and transmitted thermal energy, c — transmitted thermal energy) in radiant heat and flame exposures

Fig. 6.1 Behavior of thermal energy (a — reflected/emitted thermal energy, b — absorbed and transmitted thermal energy, c — transmitted thermal energy) in radiant heat and flame exposures.

Behavior of thermal energy (a — absorbed thermal energy, b — transmitted thermal energy) in hot surface exposures

Fig. 6.2 Behavior of thermal energy (a — absorbed thermal energy, b — transmitted thermal energy) in hot surface exposures.

changes the thermal properties of the fabric; eventually, most of the thermal energy is absorbed and/or transmitted through the fabric and lowers the thermal protective performance of the fabric-based clothing.

Behavior of imposed thermal energy in molten substances, hot liquids, and steam exposures: In molten substances, hot liquids, and steam exposures, thermal energy is imposed on the fabric of clothing in the form of mass drops/jets [76,110,353,358]. This causes a significant amount of mass transfer through a permeable fabric or a multilayered (shell fabric + moisture barrier+thermal liner) composite fabric with a permeable outer layer (shell fabric), which ultimately lowers the thermal protective performance of the fabric/clothing (Fig. 6.3). On the other hand, if thermal energy is imposed on an impermeable fabric or a multilayered (moisture barrier+ shell fabric + thermal liner) composite fabric with an impermeable outer layer (moisture barrier), much of the thermal energy deflects on the fabric’s outer layer, and a negligible amount of mass transfer occurs through the fabric (Fig. 6.4). This situation enhances the thermal protective performance of the fabric/clothing. Additionally, the pressure applied by the mass drops/jets compresses the fabric (permeable or impermeable) against firefighters’ bodies, and results in the transmission of thermal energy through fabric in the form of conductive heat (Figs. 6.3 and 6.4). This transmitted thermal energy may lower the thermal protective performance of the fabric/clothing.

Behavior of thermal energy on a permeable fabric or a multilayered composite fabric with a permeable outer layer (shell fabric) in molten substances, hot liquids, and steam exposures

Fig. 6.3 Behavior of thermal energy on a permeable fabric or a multilayered composite fabric with a permeable outer layer (shell fabric) in molten substances, hot liquids, and steam exposures.

Behavior of thermal energy on an impermeable fabric or a multilayered composite fabric with an impermeable outer layer (moisture barrier) in molten substances, hot liquids, and steam exposures

Fig. 6.4 Behavior of thermal energy on an impermeable fabric or a multilayered composite fabric with an impermeable outer layer (moisture barrier) in molten substances, hot liquids, and steam exposures.

 
Source
Found a mistake? Please highlight the word and press Shift + Enter  
< Prev   CONTENTS   Next >

Related topics