> Try putting a cigarette butt into the shop vac and see what happens...

No thanks. How 'bout you do it and give us a report...either before or after the trip to the hospital, whichever is more convenient for you. ;-)

> We desidn and sell industrial dust collection systems, so I have some
> background here. Sawdust is quite explosive in the right mixture.
> I would not recommend plastic ductwork although some will disagree.
> Why risk it? Also it is not as much a concern unless you are recycling
> the air. Certainly in most home shops with the bag type collectors
> (Penn State, Jet, Delta, etc...) i would recommend careful grounding
> and no smoking. With these reasonable precautions the risk is minimal.

I don't understand how the grounding cable can remove more than just the charge immediately surrounding it, as plastic is non-conductive. For example, isn't it the same as putting a grounded wire across your TV screen? Only the charge within the immediate vicinity of the wire will be removed, but the rest of the screen will be unaffected. Unless the piping is lined with a fine wire mesh, how can it work?

Anyway, like you implied, I wouldn't use plastic piping either. Go with metal, ground it, feel safer. Dust isn't to be messed with, either around flames/sparks or lungs. Stories of my father as a mischievous child setting off dust bombs (among other things) has also got me paranoid. Considering the dumb stunts he used to pull, I'm lucky to even exist!

While we're on the subject of insidious phenomena, I hope everyone is aware of spontaneous combustion. You know, crumpled up oily rags (eg. tung oil, linseed oil, etc.) casually tossed into the garbage pail, all of a sudden bursting into flames... For those that don't know about this, the cure is to drape the rags over something, preferably outdoors, to let the air get at them. Crumple them up, restrict air circulation, and the heat from the "drying" oil builds up enough to start a fire. Scary stuff, considering many people are completely unaware of this, and occasionally pay with their homes, or worse. BE CAREFUL!

Mike Spence