All this talk about "adiabatic" is straight out of some diving textbook. Ditto the carbon monoxide stuff, ,mostly bull but with just enough truth to scare the bejeebus out of some divers. The textbooks' authors got it from gahd knows where, some general physics book or egghead at NASA. The idea that merely turning on HP gas and "slamming" the first stage, or that normal flow rates inside the tank will cause combustion is simply wrong. It is true that HP oxygen may cause some combustibles like heavy silicone, magnesium or titanium to ignite. However, all the usual conditions for flammability must be met; fuel, oxygen and local heating. Unless it has been lubed with silicone, a brass valve does not contain enough combustible to ignite. There may be some local heating of the valve but during PP filling the oxygen being pumped into the SCUBA tank is usually decanted, and cold, causing the valve internals to cool, not heat. A scuba tank does not reach flammability conditions of heat and fuel because of the large surface area, volume and lack of fuel. A few milligrams of compressor oil will simply oxidize and become very difficult to ignite. The conditions would not be met to produce CO. That is junk science and won't hunt. Moreover, should it ever occur, a flare inside a dirty tank, the byproducts of a flash burn would be detectable as soon as the diver checked his air. Byproducts would be soot and CO2. All this stuff would carry odors associated with common smoke. A hyperfilter is nice but not necessary for the conscientious. In this context it means that the compressor operator uses a filtration system with either commercial components or well designed DIY components. These include a condensator to remove most moisture and oil and a final filter which include dessicant, activated charcoal and a micronic disk or cylinder. When water, oil and particulates are suppressed, the air inside the tank will be "oxygen" clean enough to be safe without an expensive hyperfilter. Over time, some water and oil may accumulate but yearly cleanings will take care of that. If the hyperfilters live up to the claims, then inspections but not yearly cleanings should be the rule. However, in the real world, if the tank is being presented to a dive shop it would appear that the shop operator would have difficulty ascertaining who what and when occurred over the intervening year and would insist on cleaning before PP filling with oxygen. That is understandable.
