An Evaluation of Polymers as Ignition Sources During Particle Impact in Oxygen

When contaminant particles are present in oxygen systems they can be entrained in the flowing oxygen and collide with system components causing ignition and burning. This particle impact ignition mechanism has been the cause of many fires in oxygen systems and has been systematically studied in the laboratory. For the laboratory studies, materials for particles and targets are generally classified into three groups: metals, oxides (inert), and polymers. Of the three groups, metallic particles and targets have been tested most frequently. Oxide (inert) particles and targets have been studied occasionally. Polymers, however, have not been systematically studied either as particles or as targets.

In this work, four polymer materials commonly used in oxygen systems, Teflon (PTFE), Vespel SP-21, Kel-F 81, and Viton A, were evaluated as particles which were impacted against 316 stainless steel targets. Small particles, with major dimensions of approximately 250 micrometers (μm), were tested in quantities of one and five at subsonic and supersonic velocities. Single larger particles, with major dimensions of approximately 1000 and 2000 micrometers, were tested at subsonic and supersonic velocities. The oxygen pressure was maintained at 27.6 MPa (4000 psia) and the temperature was varied between 21 and 93 ‡C (20 and 200 ‡F). No ignitions of the target material occurred in any of the test series, which indicates that at least for these polymer materials and test sample configurations, particle impact ignition is unlikely. The limitations and applications of these tests results to actual oxygen systems is discussed.