Effect of backing board on the heat release rate of wood

Abstract

Cone calorimeter tests of wood with three different backings showed that the backing did not affect time to ignition, initial peak heat release rate (HRR), and total heat release, at four different imposed heat fluxes. However, use of dense backing board for the Steiner tunnel test eliminated the second peak in the HRR profile and prolonged the intervening period of simultaneous flaming and glowing combustion, as evidenced by a gradual increase in the heat of combustion with time. Gypsum backing board had an intermediate effect on the HRR profile. The volatile and glowing effective heats of combustion were separately invariant with time for at least two wood specimens, southern yellow pine and redwood, regardless of the backing and imposed heat flux. This observation was used to reconstruct separate HRR profiles (and mass loss rate) for flaming and glowing. An analytical thermal wave solution for the temperature profile was fitted to thermocouple data for exposed and protected sides of southern yellow pine, resulting in reasonable thermal properties. The char front position, as identified with char temperature on the thermal wave profile, was converted to flame heat release (FHR) by multiplying it with the volatile heat of combustion, the mass fraction of volatile gases, the initial specimen mass, and the inverse of specimen thickness. Differentiation of FHR resulted in a flame HRR somewhat in agreement with the post-peak decreasing HRR data. Predicted thermal wave depth reached specimen thickness (25.3 mm) at 230 s, at which point (1) temperatures began to rise for the protected side of the specimen, (2) HRR data started to level out, and (3) HRR profiles began to diverge as a result of backing board variations. These results will influence testing protocols for cone calorimeter and modeling techniques for fire growth. 

Citation

Dietenberger, Mark. 1999. Effect of backing board on the heat release rate of wood. In: Proceedings of the International Conference on Fire Safety. Columbus, OH. Sissonville, WV: Product Safety Corporation. 28: 62-73.