Cellulosic Insulation Material III. Effects of Heat Flow Geometry on Smolder Initiation

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Abstract
The variation with heat flow geometry of minimum heat source temperature which causes smolder initiation in cellulosic insulation has been examined for eight configurations. These configurations range from a wire-like source, to a flat planar source, to a corner formed by planar sources; they simulate such heat sources as electrical conductors and light fixtures and span the geometry range seen by insulation in practice. The ignition temperature for the same 20 cm deep insulation layer varies from 235°C (corner source) to 385°C (wire source). Other variables such as bulk density or the presence of smolder retardants have much less effect on ignition temperature. This behavior is rationalized in an approximate manner by simple heat generation/ heat flow arguments; it is predicted semi-quantitatively by a numerical model using reaction kinetics derived from thermal analysis. A smolder ignitability test for cellulosic insulations is suggested that simulates exposures to recessed light fixtures. The data here provide a correlation between results of such a test and ignition temperatures in other configurations.

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