I'm sorry but I don't see what the Kräusen has to do with you inadvertently setting a spunding pressure of 40 PSI or thereabouts and the fermenter then blowing up before that pressure is reached.
I'm sorry, but I don't see how on earth you think I'd be so stupid so as to set a spunding valve to 40 psi. Can you give me a clue as to why you'd think that?