The maxcap for a canbomb is 7000 power. The canister ruptures at 145908kpa and beyond, and gains a three percent chance to rupture at 127669.5 kpa. the canister starts losing health at 1273.15K, so once the gas enters the canister, you need to act fast. The min pressure for the canister to boom is 7000kPa and the min temp is 100000K. Just fill the plasma tank you attach the canister to at 1013.25kPa with plasma. The ideal mix is 127669 kPa and 1865532844 Kelvin. There's higher but risking the 3% chance for a few extra decimals of power isn't worth it. Also to note: You can use any gasmix for the canister.

If you wish to use oxygen to make bigger bombs, beware that it is worth 1/6 of plasma. To effectively use oxygen you will need a tank transfer valve to lots of oxy in. The ideal mix for only explosions is 673.16 Kelvin and 12.6725 moles (1013.25kPa) of plasma, if you're going only for an explosiom. If you want to add some fire then go 673.15 or below, with some oxygen if it's in a oxygenless environment. The min temp for anything to happen is 373.15 Kelvin.