I have a picture somewhere that was taken by factory techs at USD a number of years ago... It was a cofee can filled with HP seats that had indications of incomplete combustion.. A recreational nitrox mix shouldnt be enough to maintain an o2 fire, but its surely enough to aid the combustion of contaminates in a high pressure enviroment.. AN o2 fire needs an ignition source and a fuel. Most HP seats are made out of an o2 compatible material so they themselves usually dont burn, but the contaminate can/does ignite.. I have seen regs that worked 100% flawlessly but on inspection of the seat showed the tell tale discoloration of an ignition.. The easiest way to avoid this potential is to always pressurize very slowly and then even incompatibkle materials hold up well.. The localized heat by adiabatic compression can be significant, and as the o2 content goes up do does the heat generated..
