From the Tasmanian data that Garland found, and your workshop size:

Your shop, at 35' x 40' x 12', is 475000 litres. At 20 mg/L, you will need 9 kg of dust (20 lb) to fill your shop with an explosive mixture.

But, for an explosion, you only need to have an explosive mixture in a small part of the workshop - say 4 oz of dust kicked up into the worn-out brushes of the motor in the saw table. That should be enough to blow your windows out and burst your ear-drums!

I have used a borrowed Festo dust extractor for all the work with power tools that I have done on my Shearwater Baidarka. I have used a domestic vacuum cleaner for all the work with hand tools. This has been more for health and comfort than for fire or explosion. The biggest benefit comes soon: a spotlessly clean workshop will ensure a blemish-free last coat of epoxy and an inclusion-free coat of varnish on the boat. These are all worthwhile reasons to beg, borrow, steal or even buy dust extraction.

Andrew

: I work in a shop which is 35 x 40 feet. I have built numerous cedar strip
: canoes etc. etc. I have started building hardwood strip hull & ribbed
: kayaks with treated canvas top, but I'm getting in trouble with WHMIS
: because of the dust. I have been doing this kind of work for over 25
: years.

: I believe in an open door policy which is an 8 x 10 garage door on each end
: of my shop. When I am ripping hardwood both doors are wide open to get rid
: of the dust. I have asked & asked but nobody can give me the parts per
: million before sawdust becomes explosive with the flow through ventilation
: that I have. Why is this not safe?

: Parts per million (what would it look like?) I have no idea, I would like
: some information because I cannot afford a dust extraction system.

: Thank you. Jake