On a cold evening many years ago, I sprayed two coats of primer on a Beetle in my friends repair shop, I wore wear a decent mask but other than leaving the overhead door open an few inches there was no decent ventilation . We had just finished and a heavy primer grey cloud hung in the shop, as we walked into the office for a beer the oil fired hot air furnace decided to come on, that was followed by a somewhat muffled " Boom " that rattled the shop the air was suddenly crystal clean .........we were lucky.