Perhaps we have different codes. My NEC 502.145(B) refers to receptacles and attachment plugs, and is silent as to junction boxes and lights.
In any event, 502.145(B) seems deliberately vague, and appears to allow simple 'outdoor' "Bell" boxes and flip-covers for receptacles in Division 2 locations.
This would be consistant with 502.115(B), which only requires switches in Division 2 locations to be dusttight. 502.10(B)(4) calls for the junction boxes to be simply 'dusttight.'
Let's review this in terms of what is involved in testing a product for use in a Class 2 location. The testing has one primary requirement: that you be able to bury the item in the flammable dust, then operate it for an extended time, without anything becoming hot enough to ignite the dust.
Where there's no heat normally produced - as in a junction box - it's pretty hard to fail this test. Where great amounts of heat are produced - say, by a light bulb - the challenge is to keep the dust far enough away to prevent it from getting hot enough to ignite.
"Vaportight" may not appear in the code, but 'dusttight' does, regarding lights, in 502.130(B)(2). I submit that any design that will keep out vapors will also keep out any dust, however fine.
Please note that there is a tremendous amount of leeway for 'division 2' locations. Make it 'division 1' and a lot of your discretion goes away.
