Specimen heat fluxes for bench-scale heat release rate testing

When a specimen is testd for its heat release rate (HRR) behaviour using a bench‐scale such as ISO 5660 or equivalent, one very important test condition is not pre‐standaridized and must be set: the heat flux to be imposed on the specimen by the heater. The heat flux cannot be ligitimately standardized, since the value appropriately to be used will differ according to purpose or application. The present paper sets forth the considerations which should govern the correct choice of heat flux. A discussion is given of minimum ignitiability level; statistical variability at low heat fluxes; the ranges of heat fluxes associated with small actual ignition sources; the heat fluxes associated with fires away from the ignition sources, all the way up to fully‐involved room fires; the application of the product; and the needs associated with mathematical modeling of room fires. Correlational approaches are also illustrated and contrasted to physics‐based ones. Finally, the empirical nature of the present situation is emphasized. Judged from first principles, it would appear that successful prediction of room fire results from bench‐scale test data would require both the testing at a large number of different heat fluxes and the use of algorithms to permit time‐dependent interpolation. Such algorithms have been proposed; however, some very successful predictions are noted with much simpler techniques.