Single phase motors on compressors are also a good source of spark. They have a primary starting winding that is controlled with a centrifugal switch that lets off a pretty significant arc once the motor reaches about half speed.
Safest motors are 3-phase, no brushes, no contacts (except the motor starters). We just finished up a painting robot for Boeing, man what a huge expense for explosion proof everything! Each E-Stop button and housing was a grand
Positive ventilation is also best as far as keeping the dust down and the dirt and crap out. Pull through a filter and pressurize the painting area and if you do have an exhaust fan, make sure the fan feeding the area is running slightly more air than the fan taking the air away.
