Volume 6, Issue 10 (November 2009)
Identification and Quantification of Combustion Products Released by Non-Metallic Materials Used for Medical Oxygen Equipment
Non-metallic materials (plastics, elastomers, and lubricants) are known to be the most critical ones in terms of safety in high pressure oxygen distribution systems. When proper oxygen system design guidelines are not followed, the risk of accidental ignition in service arises and has been known for many years. It has been observed that if sufficient mass was available when ignited, concentrations of species could arise in a level that could be considered toxic. This is a concern in particular for those non-metallic parts containing halogens. This risk shall especially be addressed for medical equipment and for any high pressure breathing gas system. International standards (ISO 15001 or EIGA 73/08) recommend how to address this toxicity risk. They give specific recommendations such as minimising non-metallic materials in design of equipment and use of non-metallic materials whose thermal decomposition and/or combustion in oxygen produce less toxic products (with lethal concentration LC50>5,000 ppm). They also present a list of theoretical potential combustion products but no quantitative values of real combustion by-products from which a toxicity risk assessment can be achieved. Then, in order to evaluate the toxicity risk for medical oxygen and breathing gas applications, it is necessary not only to identify but to quantify compounds generated by combustion. In this paper, an analytical procedure used to identify and quantify the released products will be described. The target is to analyze these compounds with the shortest delay after combustion promoted by adiabatic compression with oxygen at 200 bars (20,000 kPa). The analysis of combustion by-products must be done in the few minutes following the combustion. Therefore direct analytical techniques, like Fourier transformed infrared spectrometry and mass spectrometry, were used to identify and quantify the generated species and sample extraction was taken on the closest emission point to the combustion on the installation. All such precautions were intended for avoiding modification or subsequent reaction of compounds due to sample preparation steps or delays in analysis. Comparisons were made for several plastics materials and elastomers. The list of quantified combustion by-products will be presented for polytetrafluoroethylene and polychlorotrifluoroethylene. The quantification data obtained during this study is proposed for use in a toxicity risk assessment. Then a global risk evaluation can be done including this toxicity risk assessment and an ignition risk assessment. Based on this global risk evaluation, practical recommendations could be provided.