Something like that happend to me about a month and a half ago, went to work, and the fermentation was going like crazy but there asn´t a blowoff yet, soon as I got to my job my girlfriend/wife called and told me that "the thingy in the beer is bubling out and dripping" She didn´t knew how to habdle hit so I ask her to leave like that and 8 hours after that I got home, cleaned the mess and replace de airlock for a blow off tube, beer was allrigth, actually one of my best. I think if the fermentation it´s very active it´s constantly pushing co2 outside, so the chances of getting an infection are small, my concern it will be that if you don´t have much headspace maybe a lot of the active yeast gets out of your fermentor and that´s a shame but not critical, at least in IMHO.
PS: If it´s just bubbles (it can bubble a little specially if you put star san in your airlock) I wont be to concernd, if happens to me i just change the airlock but that´s maybe because I´m lazy.