chemical vs bottles varies by operator.
As far as I encountered, only B747 and A380 still use bottles (for the carriers I operated with)
Our 777 had chemical generators, 22mins duration as they did many cross-Himalayas flights.
A380 used gaseous system, with separate system for flight deck. If inadvertent activiation took place, replacing the pins into the valves at each PSU would cease oxygen flow, or it stopped automatically at 10,000' cabin alt.
Anyone else around when the 310L bottles were around with the full face mask attached? Ah, brings back memories of my first few flights...