Originally Posted by piston broke again
I thought the basic rule was that on a moustache/goatie, all the build up of grease, wax etc in a pure oxygen environment from the mask, is more likely to support combustion. Hence the reason why cabin crew, prior to administering medicinal oxygen to passengers, would advise the pax to wipe their mouths with a sterile gauze before placing the mask over their face.
That is not the rule for oxygen administered in the cabin as it is far from pure.
It is a different story though for PBE use where the oxygen content is pure.
Anyway moustaches are permitted, probably because the mask seal will not be touching the mo.