Factors for Consideration in a Test for Cigarette Ignition Propensity on Soft Furnishings

Abstract

The outcome of a cigarette ignition propensity mock-up test is largely determined by the characteristics of the fabric/substrate and to a lesser extent by the characteristics of representative cigarettes. The effects of the im portant cigarette variables on ignition propensity are reflected in two measur able cigarette characteristics-Mass Burn Rate (MBR) and Linear Burn Rate (LBR). MBR is related to the instantaneous heat flux and LBR is a measure of the rate of movement of the cigarette firecone on the substrate. MBR and LBR are coupled but do not vary colinearly within cigarette sets that encompass wide parameter ranges. The cigarettes' relative ignition propensity rankings can be dominated either by MBR or LBR. The substrate fabric's characteristics dictate largely which burn rate controls the ranking. Dense fabrics of appre ciable thermal conductivity, such as the cotton ducks used in NIST test method development, are good heat sinks and rank cigarettes according to their extin guishability (viz. MBR). Moderate to heavy weight, less dense fabrics of higher air permeability and lower thermal conductivity are poorer heat sinks, and tend to not extinguish cigarettes but rather rank them according to the rate of pristine substrate involvement (viz. LBR). Moderate air flows impinging on cigarettes have a differential effect on the burn rate of cigarettes of different construction and thus can change the relative ignition propensity rankings of cigarettes. An investigation of the properties of 113 cellulosic upholstery fabrics which were ignitable by test cigarettes has shown that the ignition- determining properties of the duck fabrics lie on the outer fringe of the charac teristics ranges of upholstery fabrics. The interaction between the majority of upholstery fabrics and cigarettes is not predominated by the extinction mechanism. Hence, the duck furniture mock-up test is a poor predictor of cigarette ignition propensity ranking on real furniture.