The time weighted average threshold limit value for "Wood dust, certain hardwoods such as beech and oak" is one mg/cubic meter. And for "Soft wood" is 5 mg/M^3. No listings are given in PPM, but there is a conversion formula.

ppm = (mg/M^3) * 24.45 / (mole weight of the substance). I know not what the mole weight of sawdust is.

This, I believe, is the exposure limit not the explosive level. The explosive level would be much higher.

If you want to check, buy the book "Industrial Ventilation, a Manual of Recommended Practice", put out by the AGGIH. Mine is the 22nd edition, I believe the current is the 24th edition.

: Rehd is correct, the dust would be too uncomfortable to breath. I dont know
: the PPM, nor do I think it is in the "dust collection bible",
: but I'll look tomorrow for you. In any event, explosion is not the risk in
: the general shop. In a dust collector, explosions are common where high
: dust loads and static electricity are combined, or where some nitwit puts
: his cigarette out in the DC intake. Or hooks the DC system up to a metal
: grinder. These are normally industrial applications, there is not a single
: documented case of DC explosion in a home shop from static electricity,
: even where PVC pipe is used. If you want to know more on the subject,
: there has been a great deal of discussion on the wood magazine board,
: www.woodmagazine.com . Go to the tool D-group and search for DC, or
: static.

: The risk you are running is from breathing the particles of certain woods.
: Cedar, for example, is a known carcinogen. Redwood, too. For more on that,
: contact your local OSHA or equivilant safety agency, and get the allowable
: PPM concentration of sawdust for a furniture shop. It's the 10-micron and
: down ones that are particularly nasty, as they do not settle out of the
: air nor can you see them. You are probably in fair shape with the doors
: open, and pretty good shape with the doors open and fans blowing. Of
: course, good dust collection at source is the best policy, but until
: recently it has not been feasible for a home shop. And even now, there is
: an awful lot of crap out there. Talk to me, or read the WOOD board if you
: are looking at installing DC. It's what we do at Benz Air, and my boss is
: one of the best in the country. I've learned a lot by osmosis...