Ignitiion Mechanism in Oxygen Systems

Hydrocarbons are not acceptable in pure (or high-concentration) oxygen storage and piping systems, regardless of the presence of any ignition system. Once outside the high-oxygen containment zone, mixing with fuel and combustion are acceptable. You seem to be confusing two separate system, or two separate zones of an overall system.

Any condition or no condition.

It is not allowed, ever.

You might Google LEL and UEL for a better understanding of flammability.

The NFPA codes on liquefied and pressurized systems address the mentioned condition. As an example, carbon inclusion in welded aluminum tanks were determined to be the cause of an explosion when carrying Lox. The spill containment pad for a liquefied oxygen system may not be asphalt. Check the codes and related NFPA references for more examples.

This is the closest answer that addresses the original poster without stating the section, paragraph or quoting the whole section.

When we oxygen clean an assembly, we have to check for residual oils and greases before the units can be assembled.

I must admit it is some time since i last looked at this phenomenon but the wisdom at that time could not answer your question. There were several theories at that time but nothing was able to be proven. The upshot is NEVER put grease or oil on a fitting or valve etc. where high concentrations of oxygen will be present. An explosion will most likely happen.

BTW one of the theories was that small particles in the gas strike the oil and ignite it that way. Others said it was friction as the gas squeezed past. Some asserted that it only needed the oxygen to be put under pressure.

So, do you really need to know the mechanism? Will it be enough to accept the knowledge learnt from many a disaster? I hope so.

Jim