Sandwich Panel Performance in Full-scale and Bench-scale Fire Tests

Abstract

Fire hazard assessments must be primarily driven by life safety variables. Concern is often highly focused on toxicity issues, since fire deaths, in the majority of cases, are found (in whole or in part) to be due to toxic gas inhalation. Procedures have recently been published by ISO, wherein the toxicity assessment of fire products is focused primarily on bench-scale testing for toxic potency (the 'per-gram toxicity'). Yet hazards of products with regards to fire toxicity may be determined much more by their differences in burning rates than by any differences in toxic potency. Burning rates are not assessed in the pertinent standards (ISO 13344 and ISO TR 9122). For most product categories, techniques for predicting full-scale burning rates from bench-scale data are not yet in hand. Thus, today the best means of comparing actual, full-scale toxic fire hazards is the full-scale fire test, equipped with additional gas measuring instrumentation. Such an approach is not among the recommended methods of the international standards, yet it is the only one with innate validity. In the present work, a series of sandwich panel products were tested in a full-scale room configuration. Bench-scale comparison was made to the ISO 5660 Cone Calorimeter and the DIN 53436 tube furnace. The toxic gases were quantified in all cases by chemical analysis. The product which showed the best performance in the full-scale tests (rock wool insulated sandwich panel) did not achieve a good fire toxicity performance due to minimization of toxic potency. Instead, the successful performance was attributed wholly to reduction of burning rate. Bench-scale measurements of toxic potency were shown to lack relevance to reality in such cases where even the full-scale toxic potency is not a determining factor.

Recommendation of tests for assessing flame spread of materials in Hong Kong

“…Fur ther, in-depth stud ies on a wider range of prod ucts are rec om mended. The re sults should be com pared with BS 476: Part 7 [6] and the other gen er ally rec og nized rank ings [e. g. 34,[38][39][40] in or der to de velop the most suit able classi fi ca tion sys tem for the lo cal con struc tion in dus try.…”

Assessing smoke toxicity of burning combustibles by four expressions for fractional effective dose

“…Mathematically, if the exposure time is the same, then FED becomes the ratio of the average concentration of a gaseous toxicant to its LC 50 value. Assuming that the toxic effects are linearly additive, several equations were reported in the literature 9,13,15 on estimating FED in terms of the concentration of carbon monoxide [CO], and concentrations of other gases including hydrogen cyanide [HCN], hydrogen chloride [HCl], hydrogen bromide [HBr], nitrogen monoxide [NO], and nitrogen dioxide [NO 2 ]. Other toxic gases present in the smoke are not included because their concentration is either very low or their effects within the smoke plume of a burning composite are not considered important.…”

“…The N‐gas model has been proven accurate in calculating the toxicity of many combustible materials including a wide range of polymers. An expression for FED was reported 9,13,15 earlier as: …”

“…LC 50 is time‐dependent, and the value for each chemical species used is the average LC 50 over 30 minutes. For example, LC 50 for carbon monoxide was taken to be 5000 ppm in the above equation 9,13 . Toxic potency given by LC 50 for carbon monoxide is much greater than that for carbon dioxide, 9 for obvious reasons.…”

“…FED 1 was calculated using Equation (5) from the peak value of [CO] (denoted by pk[CO]) in the cone calorimeter test, matching with the current code requirement in Hong Kong, 4 by using this lower LC 50 value for [CO] at 5000 ppm 9,13 : …”