Re: Oxygen is not flammable
"Speak for yourself. Divers frequently use between 80% and 100% O2."
No they don't you can't use pure oxygen underwater due to oxygen toxicity. Even enriched oxygen products limit the depth you can dive - standard compressed air (the standard recreational scuba kit) only allows you to dive 40-50m but you'd risk nitrogen narcosis at that depth anyway..
The only time you have high purity oxygen in diving is for post-dive medical treatment for decompression sickness (which wouldn't be frequent) or submersible which is mixing its own gas ratios (once again, not common).
High purity oxygen is commonly used in medical situations though - without much risk. People have even been seen to smoke while attached to nasal oxygen supply.
"Which is why you generally use a maximum of 70% oxygen for bottled breathing gas"
Medical oxygen is usually a minimum of 90% and a maximum of 96% pure oxygen.