Alan,
Alternately Wood chippers produce dust and if a piece of wood has a nail there may be sparking.
Followed by .............BOOM
There must be more to this. Sawdust or chipper dust is not any where near fine enough to make an explosive atmosphere. You have to have a sanding type operation to get that type of dust. Also in general if you hold your arm out in front of you and can still see your hand, you do not have enough dust for an explosion.
Don
