Originally Posted by Saccharomyces
At least you caught it in time. Most folks learn of their problem when NORAD calls them to inform them they are tracking their lid as a new piece of space junk.
There was a lot of pressure in that thing. When I yanked out the airlock, I got a big WHOOSH! as the CO2 escaped. I use US Plastics buckets, that have the segmented rim and a real neoprene 'O' ring inside the rim. Those lids actually seal, and they're not that easy to remove. Makes me wonder what would have given way if the pressure kept on building....
My first bucket was one of the generic "Ale Pail" type, and it doesn't really have a gas-tight seal at all, and pops off pretty easily. On June 3, '08 (a day I won't forget) I had an imperial stout in the basement that was just entering into the main phase of fermentation. That night, we got 7 inches of rain in about 3 hours, totally flooded the basement, and incidentally raised the temperatures down there considerably. I had been working getting all the stuff out of the basement, and was resting when I heard a BAM from the basement. Sure enough, lid had blown off the fermenter, beautiful brown foam everywhere. I cleaned and re-sanitized, put it back on, and had exactly the same experience about an hour later. So I just put the lid back on and put a Star San soaked sponge over the hole. That worked until it settled down. I bulk aged about 4 months and bottled as usual....and the beer was great. Always called it the "flood stout."