Engineering Variables to Replace the Concept of ‘Noncombustibility’

Abstract

The concept of noncombustibility evolved in the early days of building codes, before quantitative methods of measuring and assessing components of fire hazard were available. ‘Noncombustible’ lacks a technical definition of general scope, but in the US codes, which are the primary focus of this study, it is defined as a material which meets the criteria of the ASTM E136 test. The hazard variables underlying the noncombustibility concept are examined in this study. In view of today’s state of the art, it is shown that noncombustibility requirements, in most cases, constitute a misapplication of fire safety principles and that their use should be discontinued, in preference of using variables that express quantitative fire safety principles. Heat release rate (HRR) is the primary variable which correctly establishes the relevant hazard. In recent years, some regulations have been promulgated which use bench-scale HRR test results directly for this purpose. The ultimate hazard to be addressed, however, is the full-scale HRR behavior. When the hazard involves fires which may spread over surface linings, however, the full-scale HRR is not simply directly scaled to the bench-scale HRR. To quantify this hazard properly, additional properties of the material which govern the flame spread behavior need to be considered. A simple, easy-to-use method for this purpose are described, which is based solely on data obtainable from the Cone Calorimeter (ASTM E1354; ISO 5660) test. Validation of the concept against room-scale data is provided and is shown to be successful.