Pretty much everything inside the pressure cooker is a nucleation site, so if you could make the lid just disappear, the superheated contents would explode. Wa

Pretty much everything inside the pressure cooker is a nucleation site, so if you could make the lid just disappear, the superheated contents would explode. Water is only converted to steam while there's energy for it, so only a fraction of the water actually boils*. The risk is that it's a rapid process that propels a lot 100C water outside of the vessel. *) I haven't done the full calculation, but I'm pretty sure the upper bound is something like 10%, with 2-4% being the best most normal people could accomplish in a microwave.