Question

What will happen to a pressure cooker if you don't switch off it ?

Answer 1

Some cookers do not have a domed lid, so it is dangerously easy to fill the cooker almost to the underside of the lid. The contents can boil up, and in this case they appear to have done so just enough to block the pressure regulator pipe. The pressure then built up further until the safety plug blew out, which rapidly decompressed the contents.