Thermal degradation behavior of flame-resistant fabrics exposed to fires: effect of air gap type and thickness

The thermal degradation of flame-resistant fabrics reduces the protective ability of clothing and affects firefighters’ safety. Making clear the influence factors of fabric thermal degradation is important for predicting and prolonging the service life of fire-protection clothing. Experiments were conducted for open and sealed air gaps with different thicknesses under flame exposure. The degradation the of outer shell fabric was evaluated by observing the variation in fabric morphology, mass loss and tensile strength of specimens after heat exposure. The influence mechanism of the type and thickness of the air gap on thermal degradation was analyzed by the surface temperature curve and thermal stability of the fabric, as well as the microstructure of the fiber. The results indicated that the type and thickness of the air gap have a significant effect on thermal degradation, and a more serious negative effect was observed under the condition of an open air gap. After being exposed to heat fluxes of 30 and 50 kW/m ² for 40 s, the mass loss rates were 1.8% and 3.3% higher than those of the sealed air gap, and the tensile strength retention rates were 9.1% and 10.1% lower on average, respectively. Air gap type and thickness affected the heat storage and heat transfer efficiency in the fabric system by changing the heat transfer mode. The decomposition and fracture of the fabric were affected, which made the flame-resistant fabrics show different degrees of thermal degradation.