Any contained flammable gas is a concern. an open drum with a little paint thinner and a spark goes whoosh. a closed drum and a spark causes death. It has to do with the dynamics of combustion under pressure. I don't care what the myth-busters say, if you want me to destroy your shop vac with 1 oz of lacquer thinner, it would be an easy thing to do.
A shop vac has a series wound motor ( with sparking brushes) that is cooled by the air (supposed to be) going through the machine.
A squirrel cage fan.blower with an external motor, either belt or direct driven should work just fine and be safe. It would also be a lot quieter and use much less power. W. W. Grainger has a 60CFM blower that we use for air supply to a small wood furnace, and many other uses that should be easily adaptable to something like this. In the north, greenhouses use a small, inexpensive blower to keep the layers of plastic separated. Possibly a source.
The fume level while you are working wouldn't be enough to 'blow', but if you forgot and let a bunch of solvent evaporate in the hood, then turned on the vac, it could get more exciting than you want to deal with. I guess it depends on how much risk you or your brother in law want to take.
Lights are the same. The best way to light a paint booth is by lights that shine through gasketed (fume proof) tough (Plexiglas) windows from outside the actual booth. The light switch is either explosion proof or in another room entirely.
Be a safe mad scientist.
jm
