How much pressure does it take to start an underwater gas fire?

It’s recommended for underwater use of acetylene torches that you set the oxygen pressure to 90 psi, so that it creates an air bubble which allows the fire to get started. This made me wonder… do you physically need this much pressure, or would a lesser amount suffice?

Also, does this apply to all underwater gas fires, such as oxygen-hydrogen, that if the oxygen pressure is below 90 psi, it won’t light?

I am curious about the minimum pressure necessary, to start a gas fire underwater.