Re: my install of the transom in 27 deg weather
At the exit opening of a torpedo heater, the temp is hotter than 200. Don't believe it, place your hand right at the opening of one that's been running a while and see how long it last. Not much different than an open flame. All it takes is some fumes to run across the front of the heater.
That's where good ventilation comes in. As long as you have a lot of ventilation, the fumes get dispersed enough that it makes it very hard to ignite. There's still a chance, but it's reduced somewhat.
Realistically he's more likely to ignite the polyester resin in his hull than the fumes from the epoxy. In order to get the fumes to a high enough concentration to ignite at the exit to the heater, he'd have to put a tub of uncatalyzed resin on a hot plate and bring it to near boiling, then plug the air holes in the boat to let it build up. He'd also be having trouble breathing and nausea before that happened.
If it did somehow build up enough to ignite, it would flash over once then go out... it's not like gasoline or something where the heat would liberate more fuel, the only fuel would come from the hot plate. So it would flash over, probably burning him briefly (like burning arm hair off in a camp fire) and maybe injuring him if he was inhaling at the time (assuming the nausea from the fumes didn't make him get out of the boat). Then the CO2 and other combustion products would hang in the air for a bit, and the cycle would start again.
Epoxy is really, really non flammable... the greatest danger from it is becoming sensitive to the hardener and getting eczema or similar problems.
The greatest danger to him in this case is knocking the heater over without noticing or letting it heat a section of polyester resin to an ignition point... once the hull ignites you'd best just get out of the boat, putting it out will be very difficult.
I'm impressed with the dedication it takes to do this in the cold outdoors... for my first season's work I at least had a garage to do this in, with a heater...
Erik