Ignition characteristics of various fire indicators subjected to radiant heat fluxes: Fid-Bau Portal

Ignition characteristics of various fire indicators subjected to radiant heat fluxes

Mowrer, F.W.

Various combustible materials are specified in a number of fire test standards for heatproducing consumer products to serve as indicators of the potential for ignition as a result of contact with or exposure to hot surfaces. A series of 142 Cone Calorimeter tests and 122 LIFT Apparatus tests have been conducted with ten ordinary household combustible materials to evaluate their ignition characteristics under unpiloted radiant exposure conditions. The combustible materials were relatively thin household materials that might be located near, and ignited by, an adjacent heat-producing appliance. The potential for ignition by direct contact with a hot surface was not evaluated as part of this investigation. Minimum heat fluxes for unpiloted ignition of the ten test materials were determined by bracketing the incident heat fluxes where ignition was and was not observed. In general, it was found that there was an inverse relationship between the surface density of a material and the minimum heat flux for ignition, with the heavier materials igniting at the lowest heat fluxes. Minimum heat fluxes in the range of 12 to 15 kW/m2 were observed for materials with surface densities in the range of 0.27 to 0.37 kg/m2. Of the materials tested, cotton canvas seemed to exhibit the lowest minimum heat flux for ignition and among the most consistent results, suggesting that it would be a suitable candidate to serve as a fire indicator. Alternatively, a measured heat flux of approximately 10 kW/m2 might be used as a conservative indication of incipient ignition, based on the experimental data acquired to tested materials or for materials with substrates, before deciding upon a specific heat flux to be associated with incipient ignition of different fire indicators.While the primary purpose of this work was to determine the minimum heat fluxes for unpiloted ignition of the ten ordinary house hold combustible materials, additional data was acquired in an effort to characterize the ignition characteristics of the materials. Thermally thin and thermally thick theories of heating and ignition were applied to the experimental data. While neither theory is clearly correct or surperior to the other, both therories are consistent with the experimental data and can be used to derive useful effective material properties related to ignition characteristics. Additional data and more detailed numerical analysis would be useful to further explore and characterize the material and ignitionproperties of the then household combustibles evaluated in this investigation.