Air gaps in protective clothing during flash fire exposure
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Protective clothing is widely used in many industries and applications to provide protection against fire exposure. Exposure to fire can result in skin burn injuries that range from first-degree to third-degree burn injury depending on the exposure intensity and duration. Within the firefighting community, and especially the petroleum and petrochemical industries flash fire is one of the possible fire hazards for workers. Exposure to flash fire is usually of short duration (a few seconds) until the worker runs away from the fire location. The typical protective clothing system consists of a fire resistant fabric, the human skin, and an air gap between the fabric and skin. The protective performance of the clothing is evaluated based on the total energy transfer from the fabric to the skin through the air gap causing burn injury to the skin. Therefore the air gap between the protective clothing and skin plays an important role in determining the protection level provided by the clothing since the energy transfer through the air gap determines the amount of energy received by the skin. The more realistic the analysis of the air gap, the more reliable the evaluation of the protective performance of the clothing. This study introduces a more realistic analysis for the air gap between protective clothing and the skin compared to that found in the literature. More specifically, the study accounts for the combined conduction-radiation heat transfer through the air gap, which was treated as a thermal radiation participating medium with temperature dependent thermophysical properties. A finite volume model was developed to simulate the transient heat transfer in a single layer protective clothing system with radiation heat transfer. The model was employed to investigate the influence of the conduction-radiation heat transfer through the air gap on the overall heat transfer through the protective clothing system and hence on its protective performance. The influence of different protective clothing parameters on the combined conduction-radiation heat transfer through the air gap such as the air gap absorption coefficient, air gap width, fabric thickness, and fabric backside emissivity was studied. A comprehensive study of the influence of a periodic variation in the air gap width and associated inflow of cool air due to the motion of the person wearing the clothing on its protective performance was carried out. A wide range of variation in the frequency and amplitude of the fabric periodic movement was considered to capture different scenarios for the wearer’s motion. Finally, a finite volume model was developed to simulate the transient heat transfer in multiple layers firefighters’ protective clothing. The model considered the combined conduction-radiation heat transfer in the air gaps entrapped between the clothing layers, which were treated as thermal radiation participating media. The influence of each air gap on the overall performance of the clothing was investigated as well. The improved air gap model is a significant improvement for modeling heat transfer in protective clothing. It was used to obtain a more detailed knowledge of the theoretical performance of such clothing, e.g. it was found that reducing the fabric backside emissivity was more effective in improving the clothing protective performance than increasing the fabric thickness. It was also observed that the motion of the person wearing the clothing has a significant effect on the performance of the clothing: an increase in the frequency of the fabric movement improves the protection provided by the clothing, primarily due to the more frequent inflow of cool air, while an increase in the amplitude of the fabric movement reduces the protection provided by the clothing by concentrating the exposure on the skin. Finally, the air gaps entrapped between the clothing layers in firefighters’ protective clothing were found to improve the clothing performance, and the influence of the air gap between the moisture barrier and the thermal liner is greater than that of the air gap between the outer shell and the moisture barrier.
DegreeDoctor of Philosophy (Ph.D.)
SupervisorBergstrom, Donald J.
CommitteeOosthuizen, Patrick; Sumner, David; Evitts, Richard W.; Torvi, David; Simonson, Carey; Bugg, James D.