Analysis of the Heat Transfer Characteristics of Fabrics in an Open Flame Exposure

摘要

The transfer of heat through protective fabrics was measured using a convective, open flame. The test material was exposed horizontally with respect to the flame which provided an exposure flux of 2 calories/square centimeter/second. An instrumented calorimeter was placed on the opposite side of the fabric to measure the heat transferred through the material. A burn protective index was calculated using the heat flux data and data concerning the tolerance of human tissue. Fabrics made with flame resistant cotton, rayon, and wool were tested along with fabrics of glass and ceramic fibers and fabrics from polyaramids, novolosids, modacrylic, and polybenzimidazoles. The heaviest fabrics had the highest thermal performance rating. The testing procedure used provided a continuous calorimetric trace which was useful in the analysis of the fabric heat absorption/transmission and in determining the mechanisms of degradation and ignition. Factors which appeared important in determining the performance of a given fabric included fabric thickness, density and construction along with the thermal conductivity and heat capacity of the fibers, the nature of the boundary layer formed at the fabric air interface, the extent of endothermic reactions occurring in the solid or vapor phase, combustion products formed and their thermal properties, and the moisture content of the fabric.