Dust and Static

[sbarton22]

Last night, in my guild's monthly meeting, we had a presentation on shop safety, particularly fire safety.

One of the big topics was dust and static electricity. We spoke about grounding collection, combustible steel wool, and all manner of dangers. The one question I forgot to ask was once you create static electricity, say from dust collection, does it every go away? Are you in danger of starting a static fire only when you are collecting dust, just for the next 24 hours, or for weeks on end?

[PaulMarcel]

Used to be that it would last there until I walked by then it would bolt out to my leg in a masochistic form of auto-electrolysis.

The charge stays there like it does on one plate of a capacitor with the other 'plate' being ground. The drain time on the charge is a function of the 'electrolyte' between the plates, that being air, humidity, and likely plastic hose. So it will drain over time. You know those spray products for static on clothes? They just greatly change the electrolytic effect between the charge and the other plate. Atomized water is pretty effective. This is all making a lot of generalizations and simplifications, but that's the idea.

What I did to stop the electrolysis and bring back my hairy legs was to make a snip in the outside plastic of the flexible hose and push a bare ground wire in there around the metal in the hose (the slinky). Found a screw on the DC (which is grounded) used to hold the Y connector in place and tucked the wire under the screw. No more static shocks. I did this for the static shock (and clingy sawdust) aspect; I don't buy the whole auto-ignition stuff.

[PaulC]

I think this has been beaten to death. All I can say is the Mythbusters tried to create a dust explosion and failed. (they did blow up dust, but with a road flare.) I think there has never been a documented case of an explosion caused by dust in a home shop. Everyone knows someone who knows someone who heard about someone....well you get the idea.

Plus....someone still needs to explain to me how you can ground an insulator if you are using PVC.

[nateswoodworks]

I think this has been beaten to death. All I can say is the Mythbusters tried to create a dust explosion and failed. (they did blow up dust, but with a road flare.) I think there has never been a documented case of an explosion caused by dust in a home shop. Everyone knows someone who knows someone who heard about someone....well you get the idea.

Plus....someone still needs to explain to me how you can ground an insulator if you are using PVC.

You are right (as far as I know) that ther hasn't been a documented case but some people like to cross all their T's and dot their I's. I did my DC 12 or 13 yrs ago and it was a lot harder to find info back then to prove one way or the other so to make myself feel better I ran copper wire through all my pvc and attached it to my DC which is grounded as well as my RAS. As far as grounding an insulator-you aren't grounding the pvc itself, the conductor (the wire running through the pipe) allows the static charge to flow to a ground immediately dissipating. Knowing what I do now about the static in the PVC I wouldn't be nervious like I was then but I personally still do it the same just because I don't want to be the first to document a case!!! As far as S Barton's question about how long the static electricity stays, you can find several experiments if you search the web that helps figure that out. I think when winter rolls it's nasty head my kids and I will do a few and let you know what we find out.

Nate

[Rapid Roger]

There are such things as "dust explosions". It used to be fairly common in grain elevators in the Midwest. It does take ALLOT of dust in the air and a spark to ignite it.

Our safety friend "OSHA" has done allot to cut this problem back these days using "dust collectors" on grain elevators and requiring regular electrical inspections. If you have ever seen a grain elevator running when they are turning wheat (before they had the dust collection systems) you would know how much dust in the air it really takes! And of course a good sized spark from say a hot, dry, worn out bearing or a short in an electrical wire.

If you ever get that much dust in the air in your home work shop, you wont be able to see your saw blade from more than two feet away. And if your running old, worn out, dry bearings on any of your machinery, you should be shot! If you have a short or bare wire causing a spark that large, you will probably burn your shop down before the dust explodes.

My grand father and my father worked in grain elevators for years and although they both helped with clean up from dust explosions in other elevators, they were lucky enough not to have one in the storage facility that they worked in. I am 67 years old and I can remember as a teenager the total fear of the "big bangs" that we all had in those days.

Rog

[Beechwood Chip]

Dust explosions: yes

Fires caused by an ember or worn out bearing or a short in an electrical wire in a hobby woodworker dust collector: yes

Dust explosions caused by static electricity in a hobby woodworker dust collector: I'd say no

Fires caused by static electricity in a hobby woodworker dust collector: I'd say no

I wouldn't worry about static. However, I wouldn't use a dust collector with a grinding wheel, angle grinder, etc. There's a chance that a spark or hot shard will get deposited into a nice pile of sawdust.