[QUOTE=brassbanjo;7046453]Yes, it does need to be Oxygen (or Oxygen rich) for there to be a serious risk of combustion, (unless you are atomising a specific combustible fuel like diesel in an engine) the only risk with 3 in 1 in a compressed air pump is possible contamination.
Compressed air is just that it is atmospheric air compressed, and the atmosphere is 78% Nitrogen & less than 21% Oxygen, so the inert N2 acts as a "damper" to the O2 content.
I clearly stated "high pressure &/or pure Oxygen" with the Oxygen underlined.
Oxygen and Compressed Air are two hugely different things and have markedly different characteristics under pressure, while pure Oxygen is volatile even at atmospheric pressure.