Combustion of plastics

The use of synthetic polymers in everyday life has grown considerably over the last forty years. These materials possess mechanical, thermal and electrical properties that are highly attractive for a wide range of applications (housing, transport, clothing, manufacture of various objects, etc.). Compared with more traditional materials such as steel or non-ferrous metals, however, plastics present a major drawback linked to the risks of ignition and combustion. A number of dramatic fires involving plastics have unfortunately confirmed these risks, and raised awareness of the need for regulations specifying the conditions of use of these materials. The groups charged with drawing up the rules were faced with the problem of choosing the conditions for testing materials and the criteria for assessing risk. A compromise had to be found between the ease with which tests could be carried out, the accuracy of the measurements made and the representative nature of a real fire situation. A better understanding of the processes involved in the development of a fire proved necessary to guide these choices and increase their reliability.

In response to these needs, fire research programs were launched in the 1960s in the USA, Great Britain and Japan, and in the 1970s in France. Three main lines of investigation were considered in these programs:

• large-scale testing;

• development of predictive codes;

• laboratory studies.

Combined efforts in these three areas have led to significant progress in our knowledge of the conditions under which a fire develops in a residential-type room (compartment fires). Large-scale tests and numerical simulations have made it possible to identify the predominant phenomena and to specify the range of variation of characteristic variables. But these direct studies of the overall phenomenon also revealed the extreme complexity of the close coupling between heat and matter flows. One of the key objectives of the laboratory experiments was therefore to isolate the predominant processes so that they could be studied under controlled conditions. At the same time, specific models have been developed and validated by comparison with experimental measurements. Global calculation codes benefit from the progress made in these specific models, thanks to a better description of physico-chemical processes and, consequently, improved reliability.

Knowledge of the combustion mechanisms of plastics has therefore progressed considerably over the last twenty years. It is now possible to predict, with reasonable accuracy, the behavior of typical materials placed in well-defined configurations. It has to be said, however,...