The vast majority of AC fans do not have brushes - the load curve of a fan is almost ideal for the torque curve of an induction motor. Any fan with a shaded pole motor will not have any internal sparks. A fan with a capacitor start motor, or any other motor with a seperate switch starting winding, will produce an internal spark once during start-up. These use a centrifical switch to open the contacts to the starting winding once rpms reach a level where the run winding can take over.
Capacitor start motors are only used in larger fans and blowers - your $9.99 ace hardware box fan will have a shaded pole motor, and is not likely to be able to ignore any fumes. Even a motor with starter contacts will only spark once, within about a half second of turning on. Keep in mind your power switch just sparked too.
Blowing air in is much harder than sucking air out, in terms of not screwing up your painting.
I have a large (probably 28", 1hp motor) fan in the garage, that exhausts out the back of the building. It's a capacitor start motor, with the possibility of igniting fumes. However, it does such an effective job keeping the air fresh, that it'd be really hard to get to the LEL. (hrmm, I have a flammable gas monitor... I should try using it during painting)
--Bushytails