blew top off fermenter! should I toss batch?

Got home this evening and the plastic lid to my primary fermenter had blown off. Actually, it just snapped off, I guess the pressure got to be to much for the air lock and it snapped the seal. It was still covering the top of the fermenter bucket. There was some foam on the wall next to the fermenter but other than that, not much mess. I just snapped it back on, cleaned and refilled the air lock and put a garbage bag over it (vented for the air lock).
My question is -- does this mean the batch is now infected with bacteria, since the lid was loose for several hours and exposed to room air? Guess I`ll find out in a few days, if the venting activity doesn`t stop and/or a nasty sludge develops in the secondary. Hate to throw what would have been a perfectly good batch of Belgian Pale Ale...

Often times, when I`m brewing with a 5 gal primary (usually use a 6 gal), I will leave the lid loose for the first 48 hours because this primary doesn`t allow for a whole lot of head space. All of my batches have turned out fine so far. The yeast is producing CO2 that will protect your wort. After about 48 hours though I snap the lid on and let it finish and try to not expose the wort to air again through the rest of the brewing process.

yeast, some friends and I were awoken by an explosion. The lid blew off the bucket; the rubber seal in the lid went its own way also. Ironically, there was very little mess.
Anyway, don`t worry about infection. The CO2 being produced at this stage will prevent any airborn yeasties from entering the bucket.