An increasing number of composite cylinders are being used every year to store and transport compressed gases. These cylinders are very efficient, since a large quantity of gas can be transported at a relative low total weight compared to the traditional steel and aluminum cylinders. The most efficient composite cylinders are the cylinders that have plastic liners. The main applications are where the weight savings are important, such as cylinders for self-contained breathing apparatus (SCBA) used by firemen. In this paper, we describe an accident which occurred in France. A fireman was killed by the explosion of such a cylinder during use; the accident was attributed to the violent reaction of the oxygen (contained in the compressed air) with the plastic liner. In the paper, the ignition mechanisms are investigated and recommendations are provided to avoid any repetitions of such an accident.