"I realize you have to be careful, but I have sprayed with an open flame heater in the same building....and I didn't die"
Give it a chance, you may yet. I didn't fall off a 12 foot roof for the first 75 years of my life.......but I did 28 days ago and it hurt. I am slowly recovering, thank you. As for the unvented propane heater, turn it off when spraying. This from an old natural gas co. employee and retired Firefighter who has seen may unnecessary injuries and deaths. Even my "accident" could have been avoided.