I've taken some dumb risks over the years, and fortunately never exploded.
When I painted in my parents garage growing up, all I had for heat was a barrel stove, and ventilation consisted of a garage door opened with a box fan. The fact that I painted in a fume filled garage with little ventilation and the health effects concerns me even more then the fact I was painting near an open flame. The garage was not insulated real well. It would be cold, but once painting the fumes would get the fire really roaring and finally would get warm inside. A friend in school also painted out at his uncles farm and it had a wood stove for heat.
I now only have a torpedo heater, but put less overspray in the air with a efficient hvlp guns, and have a much bigger fan for ventilation. I shut it down when painting, and allow garage to clear out well before thinking of firing up the torpedo heater again.
I have heard of shops burning down. One was down the road from where I use to work. Not sure what happened, but this shop actually had a wood stove for heat.
Another one recently burnt down, but was due to some rags or something starting on fire after everyone had left. With all the paint supplys in the building, it made a good explosion. I would expect that more fires are started due to flammables catching fire then exploding while painting.
It would probably require doing something stupid to blow yourself up, with a high concentration of fumes built up along with a open flame, or something causing a spark, but really only would take once to lose a bunch of property, or worst end a life. Thats why saftey is allways stressed and why shops are required explosion proof lights, fans, non sparking equiptment, no open flames, ect. and we advise to think about saftey first, no open flames, and have heat source in a separate room and vent into the paint area.