Dangerous problem, need advice.

[Brad Schmid]

My dad just called me to ask a question about a dust collection system. He's a retired licensed electrician. Having worked in the utilities industry for 40+ years, he's very skilled in this area, but he was recently contacted by a local Sawmill to help solve a problem with their dust collection system. It is his first dealings with dust collection, and I certainly don't know the best path to take given the size of the system in question.

Details:
The system runs off a diesel engine, it has a 30" impeller. All pipe on the suction side is steel and grounded, however, the exhaust side is 12" schedule 40 PVC suspended between 2 buildings for approximately 60 feet before blowing into a giant hopper.

The sawmill recently increased the speed of the impeller, and this thing must be moving some SERIOUS air and dust/chips. They contacted my dad to consult when after increasing the impeller speed, they started hearing an unusual noise. He went and took a look, and knew immediately, the "unusual" noise was static building and discharging on the PVC exhaust side of the blower. He said it's so bad, it sounds like a .22 caliber pistol, and had them shut it down right away until a grounding solution is found.

So question is, can anybody recommend a good way to ground 60 feet of 12" schedule 40 PVC? Can it be wrapped with wire? Does it need to have a conductor through the interior of the pipe?

Thanks in advance.
Brad

[Larry Cooke]

Brad,

I'm not sure this will help, I'm sure it would but considering the pipe is in place that may pose a challenge. Look at Bill Pentz's site reegarding static electricity. Here's the link:

http://billpentz.com/woodworking/cyclone/Ducting.cfm#Static%20Electricity

I suspect that this would work, but I've not had any experience personally.

Larry

[tod evans]

brad, the least expensive, quickest way to fix the system right is to install 12" diameter 1/8" wall steel pipe and ditch the pvc.....02 tod

[Jim Becker]

brad, the least expensive, quickest way to fix the system right is to install 12" diameter 1/8" wall steel pipe and ditch the pvc.....02 tod

Agreed. This is an industrial application, not a home shop. They should be using metal.

[Dev Emch]

RIP IT OUT!

Many have written that its O.K. to use PVC and other plastic pipe such a polyethene etc for DC systems. Well as kids, we often took a comb and rubbed it in out hands and then zapped the little sister or brother with a static discharge. That or you hold the tip of your cat's tail in one hand and pet the cat vigoursly with the other. You can feel static charges moving through the cat and see and feel the tip of his tail twitch as the electricity get to your hand. At any rate, you never got the same effect by rubbing a stick of steel in your hands. So when your moving a bunch of chips and air through a plastic comb, look out out!!!!!!

You can wrap wire around the tube but realisticly, your now assuming that the PVC can conduct that juice. Last I checked, PVC behaved more as an insulator than a conductor. You can run some copper wire on the inside of the tube and this would work better electrically but now your running the chance of getting snags and plugs. Thanks, but no thanks.

The best solution is replace that run of pipe with good ole honest of goodenss DC pipe and be done with it before you get a CLASS ONE, DIV ONE explosion on your hands!!!!

[Cliff Rohrabacher]

I've seen people run multi strand or solid copper wire throughout the entire length and grounded that. Ya gotta figure a way to anchor the wire or the chunky crap in the flow will tear it out.

Ive seen one installation with lots of metal screws shoved through the PVC from outside sticking into the air flow with a grounding wire to each but I don't think it's all that evvective.

The only other alternative is to re fit with metal pipe.

It's also not too craxy to install a few sections of Steel piping and ground them when the material passed through them the static will exit leaving the sustem free it'll build as it approached the next grounded steel segment .

It may be possible to calsulate the maximum air flow areas and just ground them on the theory that there needs to be a critical level of static before a discharge can happen -- not the best idea on an industrial system.

Additionally it's possible to inject moisture in the form od an atomized venturi spray which will facilitate grounding as well as discourage static.

[Brad Schmid]

Well Guys,

I promise you, both my dad and I agree that it should be replaced by all metal ducting. However, it's not as simple as it sounds... I probably should have included this info before, but here goes...

This mill is an Amish owned and run establishment. They are not governed by the rules and regulations we all take for granted and consider mandatory. As a matter of fact, these folks rarely consider safety a primary concern. There is no government agency to force anything in this situation. Therefore, he is simply trying to advise these folks (as a friend) in the right direction. He is not under employment, or taking any kind of compensation for this, nor is there any liability. He's already been trying to sell them on replacing the ducting and doing it right. If they refuse to do it this way, there is little he (or anyone) can do. Bottom line is, he's hoping there's some viable solution out there so if they do refuse to do it right, it can be grounded and someone doesn't get killed.

Larry - thanks for the link to Bill's site. I forgot about it. I just read the solution by Brent Dugan which seemed to work in that situation... We're not sure it would hold up under these conditions though.

See, sometimes regulatory agencies are good!

[tod evans]

brad, if they won`t ditch the pvc have `em run copper waterline at the top of the duct, drill small holes every so often, cap the end and pump`er full of water. be sure the copper is grounded..02 tod

[Rick Christopherson]

I have stayed out of these discussions for years because I am tired of the home-shop arguments. However, this isn't a home shop. This is a situation where you already know you have a static ignition source, and large enough dust flow to experience LEL concentrations. When those two conditions finally happen at the same instant, it will be a problem.

One of the largest manufacturers of dust collection equipment in the country has asked for permission to reprint my article on static electricity for distribution to their clients, so I would imagine that your dad's client would benefit from it too.

You cannot ground a PVC system. Any document that tells you otherwise has flawed mathematics (you know the document I'm talking about).

If these people do not want to replace the simple run of PVC with metal, then I suggest walking away, or your father could find himself liable for only partially working on the system.

http://waterfront-woods.home.att.net

[Thad McCulloch]

Can you find thin wall metal pipe that will fit just inside the PVC, if they don't want to do it right and replace the PVC with the proper metal ductwork? Presumably the PVC would support thin wall metal pipe and keep it from collapsing from the pressure differential, yet be relatively cheap to buy compared to proper heavy wall stuff.

[Michael Adelong]

Brad,

Given that no one is concerned with the regulations, safety, or as Rick said, the fact that they have plenty of static and suspended matter in the same place, your Dad should refer them to a mason. The only solution is to build a concrete structure around it to contain the remnants of the hopper and exhaust duct when they explode. :eek:

Build the wall on the shop side twice as thick.

Michael

[Paul Turner]

Your Father should ask them how they feel about fire in a sawmill.

[Bill Lewis]

your father should advise them that they are generating electricity. Doesn't that go against their beliefs? ;)

The simple fact is they asked for your father's advise, if he told them the pipe should be changed out to metal, he has done his part and should walk away. I really don't understand why they are outside of the "law" on this one, they are not in a foreign country. I can't even believe it has anything to do with religious freedom, even churches have to meet code.

There is one government agency that can "force the situation", the local fire marshall or an equivalant.

[Brad Schmid]

Thanks Guys,

I anticipated this topic might stir quite a discussion, but in the end, I think we got the answer. I think the simple answer is, it is not possible to effectively ground this type of system, and that's good enough for us. We'll pass the information on and hope they do the right thing. Thanks for everyone's contribution.
Cheers.