The first time I ever needed a blowoff was with Notty.
It was a fairly high gravity cream ale. The morning after brewing, the airlock was acting like a sprinkler, spraying the room with a fine wort mist, and the better bottle was BULGING.
When I pulled the rubber plug out to put in the tube, the bottle EJACULATED foam, all the way to the ceiling. I thought that would leave a spot, but it didn't. More wort foam around the room.
Turned out for the best, I had a pint of that cream ale last night. It had some fusel issues early on, but time in the keg has smoothed it out just fine.