On Wed, 3 Aug 2016 20:59:36 -0000 (UTC), John McCoy
wrote:

wrote in :

On Tue, 2 Aug 2016 15:11:21 -0000 (UTC), John McCoy
wrote:

Depending on what your fumes are and their intensity, you
might need a fan rated for flammable vapors.

It would be _really_ unusual to have an air mixture above the
flammability (or explosive) limit. If the concentration in the room
were that high, the room would blow anyway. IMO, this is sorta like
the "ground your DC so you don't have a dust explosion" sort of thing.

Well, I don't know...what if he chose to build a spraybooth
type enclosure, to help ensure all the fumes go out the vent?
Seems like you could end up with a situation where the
concentration at the fan was pretty high.

A small, isolated booth, perhaps but anything room-sized should be no
problem. If it's high enough in the room to be a problem, he'd have a
problem. There are plenty of ignition sources around.

Probably not an issue, but worth taking a moment to think about.

A moment, sure. But overthinking problems is also a problem.