I once painted a car in -5C weather in a garage with no ventilation with a 55 gallon barrel stove in it, I used Acrylic Urethane mixed 50/50 with hardener. It was so cold my compressor water separator kept freezing up and I had to eventually remove it to continue, the fog created by the gun was so thick I had to hold my breath in between shots because the mask kept getting clogged. I made 12 coats in 12 hours and it took an ounce of fisheye remover in each mixed gallon to keep the paint from "eyeing". I had stoked the stove to try and get it warm but once I started painting I just let it go out.
There was never an explosion but I was very worried about it at the time, the paint took a week to flash to the point where it was dry enough to touch and the car looked like it had been dipped, truly spectacular!
I would never do it again because of the serious danger of explosion but the weather turned bad in two days before I could shoot the car and my father and law was adamant it be painted NOW!
I learned some things that day, painting when its cold out is a PITA but it sure levels out nice.