PVC and Dust Collection a way to find out without blowing up your shop

[Thomas Syrotchen]

I've seen the arguments on both sides like many others and I both sound logical are backed with facts. I do see a way to settle the debate. Mythbusters love to blow things up and what a better way to prevent a fire than to settle the debate. There is a couple of threads on their website for PVC and dust collection, one specifically addresses PVC in a home shop but both threads have little support. If enough interest is shown, we might just get them to test the myth and settle the debate. I'd be more than happy to put up a link but I'm not sure if it would violate the rules.

[David Hostetler]

Okay now THAT would be cool! I'd watch that one.

[Kevin Hartnett]

What's the issue? Being new to all this woodworking stuff, I guess I'm not familiar with the problem. Is there something about PVC and Dust Collection I'm missing? Please enlighten.

Thanks,

Kevin

[Mike Wilkins]

That would really be a nice way to find out for sure. But Fine Woodworking had an article about PVC piping in one of their annual Tools and Shops issues that debunked the static electricity issue. The author pointed out the fact that PVC is an insulator and would not support static at all. But it would not be a bad idea to add the wiring to eliminate static anyway.

[Prashun Patel]

What's the issue? Being new to all this woodworking stuff, I guess I'm not familiar with the problem. Is there something about PVC and Dust Collection I'm missing? Please enlighten.

Thanks,

Kevin

Swirling dust generates a lot of static electricity. Metal ducts provide a ground path for discharging. But in a 'plastic' system, if the charge should ignite the dust, there could be a big explosion.

[David Hostetler]

FWIW, my DC is currently hose from machine to machine, as I am in the beginning on a major shop remodel, and do not want to run the pipe until the wiring is complete (and insulation is in, and walls are back up etc...). I already have, and will be using S&D PVC, I already have a grounding wire kit, which I found out was nothing more than a bag with a short spool of 12ga bare solid copper wire, and a fist full of wire nuts. I got even cheaper and grabbed a 50ft roll of 12ga bare solid copper wire, and a large bag of wire nuts (about 3X what you get in the kit, for the same $$), and am ready to run the ground wire along with the PVC in the up and coming system..

[Narayan Nayar]

I'm fairly sure they've already done this one, and if I remember correctly, they couldn't get sawdust to ignite.

Ah, yes, wikipedia backs me up:

http://en.wikipedia.org/wiki/List_of...ecial_episodes

[Curt Harms]

I had a wire running in an old 4" line--I guess it sorta worked but was a bit of a pain. I now have 6" line without grounding and find little or no evidence of static electricity. I think dust would cling to the outside of the DC line if there were static. I've seen where people wrap bare wire around shank of a screw then drive the screw thru the pipe so the tip just sticks into the airstream. I've read about this, haven't tried it and haven't felt the need. Fasten the bare wire to the dust collector and/or perhaps water pipe.

[Brad Wood]

I made the mistake of dumping my shop vac onto a burning burn pile

I realized I had made a mistake microseconds before the flame flash, and microseconds after being fully committed to the "dump"... one of those slow motion "ooooohhhhh nnoooooooo" moments where you know you did something stupid but can't do anything about it

So ... wood flour will for sure flash burn, and I suppose if it is in a confined space it would explode rather than just burn. The real question is if a spark of static electricity in a small DC system can set off the event.

It sounds like Mythbusters dabbled in it a little, but who knows. I'd say it is "possible"... so why not take the cheap precaution of grounding the pipe. Better safe than sorry.

[John Schreiber]

Rather than have Mythbusters set up an artificial test, how about we have thousands of small shop woodworkers use their equipment on a regular basis and see what happens?

Oh, wait. We've already done that and we've learned that there is no danger.

Darn, I wanted to see an explosion.

[Jim O'Dell]

I'm fairly sure they've already done this one, and if I remember correctly, they couldn't get sawdust to ignite.

Ah, yes, wikipedia backs me up:

http://en.wikipedia.org/wiki/List_of...ecial_episodes

That was what I remembered too, though I've not seen an episode that did the test. Thanks for finding the link! I can only say that I have all PVC on my ClearVue cyclone, which itself is PTEG plastic, and no problems. And I've mostly cut MDF in the last 2 years. Yes, when I get close to the pipe, I can feel the hairs on my arm stand up. But if I touch the pipe, there is no shock.
I think the big difference in a small shop as opposed to a commercial shop is 1 person can not produce enough dust to get to the saturation point needed to get the explosion. Grain elevators are notorious for this problem.

Now, I did redo my main run so it was visable from the shop on the recomendation of Bill Pentz. If a fire did start, if the plastic pipe was in the attic, you wouldn't know until too late. Bill said that in the case of ducting that is out of sight, metal is the safe thing to do. Jim.

[Thom Sturgill]

I'm still at the 'move the flex hose' stage as I'm in a temporary shop. When I do build, I intend to use SD PVC depending on price vs metal ducting. I think the engineering consensus is that home systems don't move enough dust to cause a problem.

Just to be safe, I will run some of the metal duct tape inside the pipes, letting it wrap around the end and along the outside about 4-5". Interconnect the pipes and couplings such that the circuit is complete and ground ONE end. Probably not cost as much as a commercial grounding kit and should do a better job.

I think this has also been discussed here.

[Steve Sawyer]

I ran S&D PVC for my system. At first, it did build up static - enough so that I got an annoying poke whenever I turned the DC unit off. Within a couple of weeks, that problem disappeared, I'm guessing because a fine layer of dust had collected on the inside of the PVC pipes, eliminating most of the friction between the dust particles and the plastic.

My conclusion (without going to the Myth Busters) is that it's a complete non-issue, and just a good way for vendors of grounding kits to make a few $$.

[glenn bradley]

Why does this myth continue? Its like the story of the baby alligator that got flushed down the john, or the couple that drove back from lover's lane only to find a bloody hook stuck in the car door. ;-)

[Tom Hargrove]

If wood dust mixes with air in the proper ratio, and an ignition source enters the picture, ignition will occur. If all of the dust ignites at the same time, we call it an explosion. If the dust ignites gradually, we call it a fire. Energy is being released in either situation, and it will happen in plastic ducts, metal ducts, in a vacuum cleaner or in the atmosphere of your shop if the ratio is correct and an ignition source is present.

The critical question is whether the static electricity that builds up in a plastic duct system will build enough to generate a spark (the ignition source) when the dust/air ratio is correct.

When I worked in woodworking for a living, we had two fires (not explosions) in our dust system. Both occurred from sparks that were generated in a machine that was outside of, but hooked up the dust control system.

This topic has been examined many times here, and on other forums. IIRC, there are no documented cases of static electricity causing an explosion in a PVC dust control system that was filled with wood dust. It is theoretically possible, but I don't think anyone has actually witnessed it happen.

If we worked with aluminum dust, I would be more concerned, since there are documented cases of static igniting aluminum powder.