Heat release measurements for non‐flaming barrier fabrics using thermopile and oxygen consumption techniques

Abstract

Two standard methods of measuring the heat release have been used for barrier fabrics comprising flame-retardant cellulosic fibres and selected reactive intumescent components. These methods are based on the principles of (i) direct measurement of the convective and radiant heat liberated using a mass loss calorimeter fitted with thermopiles, and (ii) oxygen consumption using a cone calorimeter. The results obtained from these two methods are different, which is contrary to work published by other researchers. The barrier fabrics used for the present study do not undergo flaming combustion; instead they char immediately and then oxidize slowly when subjected to heat fluxes in the range 25-75 kW m -2 . Furthermore, heat release rate (HRR) measurements from thermopile sensors are only slightly dependent on the presence, absence or type of intumescent present, unlike oxygen consumption HRR measurements and, indeed, earlier values determined using the Ohio State University apparatus. Cone calorimetry determines the reduced HRR values associated with the burning behaviour of these char-promoting samples, whereas with thermopiles embedded above the heater, the sensors will be influenced by radiative heat from the charred fabric samples. The latter will be less affected by the intumescent character as results suggest, because thermopile responses are determined by the black body radiative characteristics of the chars. These initial studies, therefore, have demonstrated that heat release rate measurements for very effective char-forming samples using either technique require careful interpretation because of the non-convective flame burning character of char combustion. In subsequent experiments, shielding of thermopiles from direct radiation is recommended.