Prevalence, causes, and prevention of oxygen fires

[rjack321]

It's not typically heat like you think, though it can be. It's often particles accelerated by the gas flow and striking the contamination.

"In the case of gas velocity, it is not the flow of gas that can cause ignition, but a particle that has been propelled by the gas and impacts the system with sufficient force to ignite. The heat generated may be sufficient to start a fire, depending on the material impacted. Friction from a component malfunctioning or operating poorly can generate heat. Friction between two materials generates fine particles, which may ignite from the heat generated."
http://www.airproducts.com/~/media/files/pdf/company/safetygram-33.pdf

For sure slow opening scuba valves with both a different seat design and material plus less torturous internal passages would be an improvement over what we have and do now. Contamination, materials, heat, and velocity issues all come to a head in the valve so its not surprising these are the nucleus of the majority of scuba related O2 incidents.