I have a rather large garage, accommodates two full size vehicles, a moderately sized shop and the usual mower in summer, chainsaws, fuel cans, etc. My question is how big is your garage, how well ventilated is it? I smoke in mine when working and have never had a whiff of fuel unless I've fueled something up. If you are concerned I'm sure there are vapor detectors you could install.
Admittedly I'm not a fire investigator but, my experience with garage fires as a cop was that most were started by vehicle problems, poor storage of flammable materials, etc. Correct me if necessary "ashdigger", but, thousands smoke in their garages as a matter of routine while storing fuel, solvents, etc. What's the percentage of garage fires idnited by smoking? As compared to faulty wiring, vehicle fires, storage of rags impregnated with solvents (spontaneous combustion?), etc? Just curious.