Let me give you the obvious answer first. Three weeks ago I brewed a new batch of lager. I pulled enough water off the mash for my boil, then put a sanitized one gallon glass jug under the tap to collect everything else that ran off to save for a starter. After it was full, I capped it and put it in my lagering fridge with my two glass carboys.
This morning, at 6:04 a.m., I was awakened by an earth-shattering explosive sound. I jumped up, checked outside for airplane parts, car accidents, a fight between the Bloods and Crips, but found nothing and went back to sleep. When I next got up, I was greeted by a HORRIFIC stench, and upon further investigating, a wet floor in front of my lagering fridge. I opened the door to find glass and beer spray everywhere. The bad news, that one gallon jug was under massive pressure and exploded with vengeance. The good news is, my two carboys somehow survived - and the remaining glass mess was contained to the fridge.
I just spent two hours cleaning out the fridge and replacing the remaining beer. At some point before I go to sleep I'll need to mop the floor, and the basement floor underneath.
Lesson learned, the mash phase doesn't get hot enough to kill off nasties. I'm just thankful that the lesson wasn't as expensive or messy as it could have been.