Aluminum scuba cylinders in oxygen-enriched and oxygen service – I’ve heard about fires and explosions occurring in tanks that were supposedly cleaned for oxygen. How could that happen?

There are two main possibilities. First, the cylinder might well have been properly cleaned and tested, but subsequently became contaminated in a way that was not detected before the fire occurred. Sometimes other elements of the oxygen filling or containment system become contaminated, and they, in turn, contaminate the cylinder; sometimes a valve is improperly installed into the cylinder or an improper lubricant is used; sometimes contamination occurs during use—the possibilities are numerous. Or, second, the cylinder was not cleaned and tested properly in the first place, and a contaminant was still present to serve as fuel for the fire. One thing is certain: An oxygen-fed fire cannot start without oxygen, an ignition source and a contaminant—so contamination must have been present.