http://home.comcast.net/~rodec/woodworking/articles/DC_myths.html
John 2pt0
The Chemical Safety Board has a long technical report on dust explosions; csb.gov
And the ACGIH publishes an industrial ventilation manual, with info on vent design and energy losses in narrow or rough pipes.
Thurman Wenzl
http://tbwenzl.wordpress.com/
http://www.flickr.com/photos/tbwenzl
Jon:
I would suggest that, if we plan to mount the DC such that the input is above the light fixtures ,
we consider a two stage approach.
1) mount the DC to a back board as mentioned I the manual
2) mount this assembly inside a tower built from 4x4's, which assembly would be strapped to the roof support.
This would allow the DC to be at any height within reason, and would allow secure mounting without putting holes
in the roof support.
John S.