Effects of oxygen availability on the combustion behaviour of materials in a controlled atmosphere cone calorimeter

The reaction-to-fire of materials is commonly studied with bench scale experiments conducted under controlled test conditions. Two bench-scale instruments commonly used for this purpose are the cone calorimeter and the fire propagation apparatus. Research performed with these test apparatuses on the burning behaviour of polymeric materials has demonstrated the significant effect on the results of test variables such as pressure, irradiance, flow velocity, etc. In spite of the fairly large number of studies, little is known concerning the effect of oxygen vitiation and reduced ventilation on the burning behaviour of polymeric materials. Recent work in a controlled oxygen environment raises the question of interpretation and accuracy of the results. This paper reports the results of a study to evaluate the effect of oxygen vitiation and reduced ventilation on the burning behaviour of materials in a controlled atmosphere cone calorimeter. The study was performed on a typical thermoplastic material, i.e., a black poly(methyl)methacrylate. The dependence of the results on the experimental fire conditions is presented and discussed. The experiments show that the inlet airflow rate is a major factor to consider when studying the burning behaviour of polymeric materials in an enclosure. It strongly affects the available amount of oxygen that can react and may lead to a misinterpretation of the results when the effects of oxygen are studied.