Fire Safety Science Digital Archive

The Limited Oxygen Index test (LOI) is a small-scale test for characterising the flammability tendency of materials ignited with a small candle-like diffusion flame. It involves determination of the minimum oxygen volume concentration in an oxygen/nitrogen mixture required to just support the downward burning on a vertically mounted test specimen. Over the last decades, much effort has been devoted to developing correlations between the LOI of a material with its chemical or physical properties. However these correlations were deduced based mainly on empirical fitting, and as a result they cannot be related to the fundamental properties of the material. In this work, we present a novel approach based on simple extinction theory to predict the LOI of materials using their flammability properties measured in small-scale tests (i.e. TGA, DSC and the cone calorimeter). The present method is first applied to five polymers and the predicted LOI values in general agree with the measurements. Subsequently, the model is extended to examine the effects of the initial sample temperature and external heat flux on the LOI of a PMMA, in reasonable agreement with the experimental data.