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_MythBusters_special_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 :eek:

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_MythBusters_special_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.

[Jason Beam]

Peace of mind?

What if I told you that casually draping a wire over an insulator wouldn't discharge any more static electricity than that near where the wire actually was touching?

PVC can't conduct electricity too well. Neither does air. So ... you stick a wire on your PVC and it sure does discharge the static electricity - but ONLY the the static that can reach it. Since neither PVC nor air conducts electricity so good, the static that's on the REST of that PVC pipe is still there. Can't reach the wire. So, i guess you could wrap the whole thing in wire mesh ... that might increase the amount discharged.

Peace of mind is knowing it's safe, not hoping the trick worked. False security is not peace of mind.

Static discharge found in PVC duct work has been shown not to be strong enough to serve as an ignition for wood flour. It just can't discharge strongly enough to really set a blaze going. It pretty much ends the debate, right there, IMHO.

Nevermind how concentrated the air has to be if it IS ignited. :)

[Brian Kent]

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. ;-)

And when they opened the door what did they find on the end of that hook, swinging from the car door? The alligator!:eek:

[Ken Fitzgerald]

And when they opened the door what did they find on the end of that hook, swinging from the car door? The alligator!:eek:

Brian...you were there?:confused::rolleyes:

[Chris Padilla]

FYI, it is VERY difficult to ground plastic...adding a wire or tape or whatever is practically useless and ineffective...one would need to add it to the point of..."gee, why don't I just get a METAL pipe!"

When I first installed my PVC duciting system, I would get shocks. Now a couple years later, I no longer get any shocks. This could be a time thing that when the pipes gets sufficiently dirty, the dust moving through the pipe no longer rubs directly against the plastic...it rubs against other dust hence no electrons get moved to the plastic.

[Ken Fitzgerald]

Chris will verify this:


PVC is an insulator. Check you wiring used in your home...a PVC wrapper is quite common.

Grounding an insulator only works at the point of contact and a very very short distance....Fractions of a millimeter around the point of contact.

You would have to ground it by encasing it inside and out and then ground the casing.

In the end,

though it's been discussed here many, many times over the last few years not one person has been able to provide documented evidence of a DC fire in a home hobby shop investigated and the cause found to be static electricity.

Frankly, while a lot of things are "possible"....and a home hobby shop Dc and static causing a fire is "possible" it isn't very probable based on historical evidence and some scientific research.

I have metal because I live in a very arid climate and I don't enjoy static shock but I wouldn't hesitate to use PVC.

[Dan Friedrichs]

There's a table saw accident every 9 minutes in the US, and people still think that causing the first DC explosion ever heard of is a concern worth worrying about?

[Mark Bosse]

There are four different environments to consider, one "known" factor, and one "unknown" factor to look at in the entire situation:

(1) The environments are (at least) in the machine itself, inside the ducting, inside the dust collector chamber (cyclone, bagger, etc.), and last, most importantly, the air volume of the shop.

(2) The two factors (at least) are the lower and upper explosive limits of the dust air mixture. This varies hugely with particle size, species, air movement and temprature, etc. Yup - there are both upper and lower limits for dust to form an explosion. Too much dust, no explosion

(3) The last part (which is uncontrolled by us shop dewellers) is ignition source. Using any sort of non-conducting ducting has as much to do with this factor as with any other.

See - you can get an enormous explosion outside your duct work when the air mass of the shop falls between the lower and upper explosive limits of whatever you have in the air mass. Your plastic duct then provides the ignition source (static discharge).

There are people out there who do this work. Some of then write great books that are cheap and written in english so we can understand them. I like one by Sandor (not even going to try to spell his last name - you guys know who I mean).

This is no myth, with or without a truely fun but absolutely non-scientific TV show. If you rely on TV for shop design, will you leave at least one wall off your shop for the lighting and optic trolleis? Maybe you could fake one of those "Canadian winter window panes" we see so often on wookworking shows.

Don't burn down your shop. Get professional help. Most vendors provide it free.


Mark

[Ken Fitzgerald]

Mark,

Can you provide any documented cases where this has happened?

Anything is possible but IMHO this is highly improbable in the home hobbiest shop.

What I think is possible is that you are unduly trying to scare people without providing a shred of evidence of this theory that you are reporting.

Where is your evidence of even one case that was investigated by a professional fire investigator and their professional opinion was that static electricity in the DC started the fire?

Give us the evidence!

[Jason Beam]

Science has told me two things:

1) You can't ground an insulator.

2) Since an insulator does not conduct electricity, the static discharge is too small to ignite wood dust in the "butter zone" of explosivity.

Not a TV show. Not some guy who managed to get a book deal. Science.

My shop won't be burning down because of static discharge from PVC duct work. I am sure of this.

[Kenneth Hertzog]

I've had a more hair raising experience with my shop vac
cleaning up the floor than i've ever had with my dust collection system
and its PVC
ken

[Myk Rian]

I have a PVC ducted system. I wrapped ground wire around the pipes because I was tired of my hair standing on end when using the jointer and planer. There is no issue with the rest of the tools.

[Chris Padilla]

Science has told me two things:

1) You can't ground an insulator.

2) Since an insulator does not conduct electricity, the static discharge is too small to ignite wood dust in the "butter zone" of explosivity.

Not a TV show. Not some guy who managed to get a book deal. Science.

My shop won't be burning down because of static discharge from PVC duct work. I am sure of this.

Correct. The electrons in the atoms that make up plastic are very rigidly adhered to the atom...they cannot break free easily. In a conductor, the electrons are very loosely adhered to the atom and can break free extremely easily.

While insulators cannot conduct charge (very easily), they can HOLD charge that has been impinged upon them by friction. This friction is created by simply rubbing two materials against each other: like wood dust/chips against, oh I don't know, plastic. Even air blowing across a piece of plastic can cause charge to build up on the plastic.

There is a reason why it is called STATIC...it ain't moving. Electricity is the FLOW of charge and more commonly known as CURRENT. In fact, one could argue that when shocked by static electricity, it really isn't electricity in the first place because it only flows in certain cases...like when it come in contact with a material that is oppositely charged. Otherwise, STATIC electricity just sits there building up...highly localized...and it doesn't flow except under special conditions. This is why trying to "ground" plastic is tough unless you know precisely WHERE the static charge tends to build up.

In our dust/duct systems, I'd say it builds up pretty much EVERYWHERE along the pipe so you'd have to "ground" the pipe on every square inch in order to get all the static charge hanging around.

And as I said earlier, once the pipe gets a coating of wood dust built up on it, there is no longer friction between the wood dust and the plastic and hence, the build up of static charge no longer occurs or occurs at such a low level that even our sensistive digits can no longer detect it when it discharges through us.

[Mark Bosse]

Best thing for you guys who don't get it is to do an advanced google search on the controlled term "woodshop fire." You will find the examples you need.

For the other people, please look at the NFPA.org site. I think you will get a sense of how hard people work to understand fire prevention as well as the level of research those people are putting in.

On the static spark not being able to ignite an explosion question, it is temperature not amperage that is the problem. Because you can't "gound" an insulator (whatever that means), the voltage necessary for the break down in the air dielectric is higher. Hence, the ignition temperature is far exceeded in a static charge in dry air when initiated from an "ungrounded" insulator. What that means is that it is the ignition temperature that matters not how many electrons move. The drier the dielectric air, the higher the temperature.

I just don't understand why you guys are so defensive about doing some real homework on the leading cause of woodshop destruction. At this point I am wondering to what degree some of you are trying to sell unlisted products to home owners. Calling a markert "home owner" actually increases your responsibility both legally and finacially. You may want to hit LegalZoom or some other cheap source and get some idea how deep a hole you are in.

If any of these discussions on woodshop fire confuse you or you can't tell who has got it right, CALL YOUR INSURANCE AGENT. Please get some help. People really will help you out and it is cheap.

[Ken Fitzgerald]

Mark,

Provide the evidence......

You're the person making these wild accusations...provide the evidence.

[Gary Lange]

I looked in the places you quoted including the NFPA.org site and no matter what way I put the question in the search it had nothing on Woodshop fires. I googled "woodshop fire" and none indicated they were caused by a fire in the Dust Collection System.

[Jason Beam]

I just don't understand why you guys are so defensive about doing some real homework on the leading cause of woodshop destruction.

Now this myth is the leading cause of woodshop destruction?

I think you're using "fire" to support your argument when we're not talking about any and all fires. We're talking specifically about wood dust explosions caused by the discharge of static electricity built up on PVC dust collection duct work. Every word in that sentence is significant and to cast your insults with such a broad brush isn't going to get you any credibility.

Show me ONE. ONE documented woodworking shop explosion that was proven caused by static discharge built up on PVC dust collection duct work. Just one. You make the statements, back 'em up.

I don't disagree that fire prevention is key. But don't think for a second that you're safe just because you trailed a wire along your PVC pipe. You're safe because it's not a risk to begin with. If it were a legitimate risk, the wire wouldn't do much (if any) good. You'd have to completely coat the surface of the PVC pipe with conductive material to be sure to capture any errant static buildup. At that point, you might as well go with a conductive material to begin with, no?

To accuse any of us of advocating unsafe and harmful practices is purely a lack of comprehension. When you don't even appear to understand the concepts we're discussing, maybe you shouldn't be so quick to speak up.

We're simply saying that the risk isn't there and not to put so much stock in the popular "solution" without knowing the physics behind it.

[Dan Friedrichs]

I think everyone agrees that it's possible, it's just horribly improbable. You'd be better off worrying about a rabid skunk walking in your shop door and biting you in the leg.

One thing I particularly like about SMC is that many members here are very, very well educated people who are venerable experts in their fields. Several electrical engineers here have repeatedly explained that wrapping a wire around an insulator will remove very little of the static charge built up on it. Basic physics supports this.

[Edwood Ferrari]

I found this link a while back when I was planning my workshop as I too read all the worries of using PVC ducts. I am an electrical engineer so I understand electricity. This article put all my worries to rest

http://home.comcast.net/~rodec/woodworking/articles/DC_myths.html

Ed

[Frank Hagan]

Bill Pentz has a link on his site to this page: http://home.comcast.net/~rodec/woodworking/articles/DC_myths.html

Shorter Link Here (http://home.comcast.net/~rodec/woodworking/articles/DC_myths.html)

The author, Rod Cole, has a PhD in Mathamatics and a BS in Physics, and works at "MIT Lincoln Laboratory heading some research projects".

He mentions that the three areas of concern for fires are the dust bin, the dust bag, the ducts ... in that order. According to Uniform Building Code, Uniform Mechanical Code, and the National Fire Protection Association which (according to OSHA, 1997) all require that dust bins, dust bags, and cyclones be located outdoors. Nearly every homeowner shop in the country is in violation of these standards. The qualifier is that the standards seem to apply to systems delivering 1500 CFM or greater (in actual use, not on the marketing literature).

The article has references at the end, and seems well researched and explained to me. He does include non-scientific accounts of fire captains that cannot find any reference to dust duct fires in residential shops, but also searched for any reference himself.

I searched Google, and found plenty of references to shop fires, but none saying the ducting was involved. A couple said the fires were started by electrical shorts. If you really want to be safe, don't use electricity. :rolleyes:

In the absence of scientific evidence, or even one instance of the problem happening, I would be comfortable with PVC ducting.

[Chris Padilla]

On the static spark not being able to ignite an explosion question, it is temperature not amperage that is the problem. Because you can't "gound" an insulator (whatever that means), the voltage necessary for the break down in the air dielectric is higher. Hence, the ignition temperature is far exceeded in a static charge in dry air when initiated from an "ungrounded" insulator. What that means is that it is the ignition temperature that matters not how many electrons move. The drier the dielectric air, the higher the temperature.

Okay, bear with me here: Amperage is the flow of charge...which is in coulombs per second. When charge flows, it implies a potential difference from one point to another point...known as voltage. During a static discharge, you have a potential difference because there is a flow of charge (kind of a chicken or the egg thing but I digress...) and thus power can be calculated: P=iV. Power is in watts which is in Joules per second. Joules are a unit of energy. So, we have energy dissipation (or absorption) occuring over a period of time. This energy dissipation is what heats the air along the path of discharge. This is basically what lightning does only that has a lot more energy. It is the HEAT generated by this energy dissipation that "stings" one's finger when one is shocked. Yes, you are actually being slightly burned when you are shocked...or burned a lot when struck by lightning.

As to the breakdown of an air dielectric, it is only dependent upon what is in the air and the electric field across it. In other words, there needs to be another potential difference to allow current flow. That is fine...we may well have it with the plastic having a localized pool of charge built up from wood dust movin past it. But here is the trick, in order to have a discharge, there must be a potential difference...where is it? When your body rubs across a wool carpet, you can develop charge. You touch a doorknob...or rather...you come extremely close to touching the doorknob and you set of a discharge. Why? The doorknob is likely at a ground potential...and your finger is not (it could be at a higher or lower potential...only matters that it is different). I question where the potential difference is in a plastic pipe full of wood dust. WE only notice it when WE touch the pipe because WE are at a different potential. And even then, the discharge is OUTSIDE the pipe and not in it. What INSIDE a pipe full of moving wood dust causes a discharge? Wouldn't you think the wood dust and pipe to all be at the same potential?


I just don't understand why you guys are so defensive about doing some real homework on the leading cause of woodshop destruction. At this point I am wondering to what degree some of you are trying to sell unlisted products to home owners. Calling a markert "home owner" actually increases your responsibility both legally and finacially. You may want to hit LegalZoom or some other cheap source and get some idea how deep a hole you are in.

I apologize if we sound defensive but every once in a while someone like yourself comes along and starts informing us how we are going to more or less blow our shops up along with outselves. The plain truth is that there is no such evidence and many here have already pointed it out to you.

No one here is selling anything. No one here is making any money off of suggesting PVC as an alternative to metal for dust collection ducting. What you need to understand here is that most of us are HOBBYIST woodworkers and we simply don't generate enough wood dust for it to cause any sort of explosion from some mythical static discharge that has been shown time and again to not even be remotely powerful enough to ignite...assuming it goes off in the first place.


If any of these discussions on woodshop fire confuse you or you can't tell who has got it right, CALL YOUR INSURANCE AGENT. Please get some help. People really will help you out and it is cheap.

At this point, Mark, I question your motives and what it is you are trying to do. What do you do for a living? I am an electrical engineer (master's degree if it matters to you) and a hobbyist woodworker with a shop built cyclone dust collector using 6" PVC strung all over my garage working splendidly for about 4 years now. At the beginning, I got shocked from my PVC ducting...after 6 months of using the system, no more shocks.

[Steve knight]

my clearview has not blown up yet and I can make a lot of dust surfacing mdf on my cnc router. so there :D

[Rob Russell]

Folks,

Some of the rhetoric in this thread has crossed the line beyond what is acceptable at SMC. Personal and/or derogatory comments will not be tolerated.

Obviously, "DC explosions" is a topic that can degenerate into a "flame fest". Please keep your posts FACTUAL, not based on opinion.

Thanks,

Rob

[Chris Padilla]

I didn't have my table of Dielectric Strength in front of me last night when I wrote my mini novel above.

The dielectric strength of air is about 3 x 10^6 V/m (Volts per meter) or if we want to adjust the field to something more in line with the size of a 6" plastic pipe: 7.6 x 10^4 V/in (Volts per inch) or 76,000 V/in.

Now fill that air with something like wood dust and what happens. I would surmise that the dielectric breakdown of wood dust mixed with air (and at what ratio...no clue) would be higher than pure air since air is your basic dielectric (relative permittivity or dielectric constant of 1).

Wood is listed on my chart and while a dielectric constant is given (range of 2.5 - 8.0), the column with dielectric strength is blank.

[Nick Abbott]

After about 25 years of testing I can confidently say no worries here.

[Chris Padilla]

That is dedicated testing, Nick! Can you ellaborate a little bit?

[Frank Hagan]

I didn't have my table of Dielectric Strength in front of me last night when I wrote my mini novel above.

The dielectric strength of air is about 3 x 10^6 V/m (Volts per meter) or if we want to adjust the field to something more in line with the size of a 6" plastic pipe: 7.6 x 10^4 V/in (Volts per inch) or 76,000 V/in.

Now fill that air with something like wood dust and what happens. I would surmise that the dielectric breakdown of wood dust mixed with air (and at what ratio...no clue) would be higher than pure air since air is your basic dielectric (relative permittivity or dielectric constant of 1).

Wood is listed on my chart and while a dielectric constant is given (range of 2.5 - 8.0), the column with dielectric strength is blank.

The link I gave above has a section on just how hard it is for researchers to get wood dust to explode in a lab setting. The author concludes it would probably never happen in a home shop setting, except perhaps in the dust bin or filter bag.

[Ken Fitzgerald]

Frank,

I'd spent a couple of hour looking for that article here. It's been posted before.

What I like about it is..it points out the significant difference between "possibility" and "probability".

Excellent study IMHO.

Thanks again for posting the link. I have it saved on my home computer now for future reference.

This subject ....urban legend...internet rumor comes up way too often.

[Frank Hagan]

Frank,

I'd spent a couple of hour looking for that article here. It's been posted before.

What I like about it is..it points out the significant difference between "possibility" and "probability".

Excellent study IMHO.

Thanks again for posting the link. I have it saved on my home computer now for future reference.

This subject ....urban legend...internet rumor comes up way too often.


I think he did a good job of analysis, and also did well with making it easy to understand. Now if we could get him to work for the IRS ...

[Chip Lindley]

Zactly! Dan! I can count the static dust explosions caused in home shops on NO fingers, assuming I cut both hands off in tablesaw accidents!! LOL

[Angie Orfanedes]

It seems to me that all we need to do is enclose our PVC ducting inside of metal duct and then ground the metal duct......:p

[Chris Padilla]

It seems to me that all we need to do is enclose our PVC ducting inside of metal duct and then ground the metal duct......:p

Precisely! :)

[Pete Shermet]

Grounding the PVC will prevent the static build up and possibly a large static discharge which would be most uncomfortable if you were the recipient, it will also prevent your pipes from accumulating "Hair" (build up of exterior dust.) They say it should not cause an explosion or fire. I'm going to use spiral pipe so I should not have to worry about it.
Regards
Pete

[Ken Fitzgerald]

Unless you ground every square inch,

You can't ground an insulator beyond the point of contact. That's why it's called an insulator. It won't conduct electricity and it won't conduct GROUND!

[Nick Abbott]

That is dedicated testing, Nick! Can you ellaborate a little bit?

Yes sir. I have used plastic pipe for dust collection in my shops for 25 years without a problem. That is a reliable enough test for me.

[Nick Abbott]

It seems to me that all we need to do is enclose our PVC ducting inside of metal duct and then ground the metal duct......:p

I think you nailed it! ;)

[Nick Abbott]

Grounding the PVC will prevent the static build up and possibly a large static discharge which would be most uncomfortable if you were the recipient, it will also prevent your pipes from accumulating "Hair" (build up of exterior dust.) They say it should not cause an explosion or fire. I'm going to use spiral pipe so I should not have to worry about it.
Regards
Pete

I have never grounded one inch of my PVC duct work.

[Rick Hutcheson]

Well I used 4" PVC pipe for my dust collection system. I ran a braided copper wire along the outside of the pipe and used a self tapping 1/2" sheet metal screw into the side of the pipe about every 10", then wrapped the wire around it. The tip of the screw was on the inside of the pipe and the head and wire on the outside of the pipe. This went to a ground and then was ran all the way to the machine and grounded to the machine.
I noticed over the years that if I had taken a wire off for some reason on a machine it caused problems. Not with explosions but another way. When I ran the shop vac to clean the shop or had the collector running for fine dust, I would get the static electric shocks when I tried to touch the machine. With the wire hooked up I never received those shocks.
So I run the wire for the static shocks not for the fear of a dust explosion.

[Chris Kennedy]

Okay -- it has been a long time since I studied electromagnetism, but here goes. The PVC ducting is building up a charge, which will dissipate either through a corona discharge or a spark discharge, and the fear is the latter.

But isn't this basically the same situation as lightning? So, if we have lightning rods in our shops (say, metal machinery that is grounded), shouldn't they work to dissipate the charge?

Cheers,

Chris

[Lee Schierer]

I've had pvc duct work in my shop for over 15 years. It no longer produces any static. It did produce a slight amount when the pipe was new from the store (actually came charged up) and the pipe even grew some hair in a few places, but that went away in a week or so.

Dust explosions take very very fine dust (called flour) and it has to be in fairly dense concentrations (basically too thick to see through). Neither of these conditions are likely to exist in a home shop unless the bag comes off your DC and you don't notice it for an hour or so while heavily sanding your latest project.

If you watched the mythbusters various dust explosion episodes the dust clouds they did ignite were completely opaque. I think most of us would have stopped working before the dust got that thick in our shop.

[Chris Padilla]

I think most of us would have stopped working before the dust got that thick in our shop.

...or choked to death from respiratory failure?! ;)

[Chris Padilla]

But isn't this basically the same situation as lightning? So, if we have lightning rods in our shops (say, metal machinery that is grounded), shouldn't they work to dissipate the charge?

Yes, static electricity is precisely what lightning is...one just has more energy associated with it.

The charge will be dissipated by grounded machinery but only LOCALLY or very close to the grounded metal. What about the charge build up that is 1 foot away? How is the charge to flow because it won't flow through the insulator. This is the whole concept of running a wire around your pipe...it'll grab any build-up and dissipate it...but it only works pretty much where the wire is and not much further from it...because charge doesn't flow on an insulator!

[Jason Raksnis]

It seems as tho people really think that a PVC system cant start a fire! It it produces spark then it can start a fire. Thats just simple science! I've had the not so much pleasure of being zapped quite badly a few times from a PVC system in a cabinet shop i work it. They were trying to cut corners and save some money and after enough people complained about it OSHA found their way in there and fined the owner and made him switch it out. Its also funny that people that use and say there is nothing wrong with pvc install a grounding kit "just to be on the safe side". Why spend ur money if theres nothing to be concerned about! JUST MY TWO SENSE!

[Frank Hagan]

It seems as tho people really think that a PVC system cant start a fire! It it produces spark then it can start a fire. Thats just simple science! I've had the not so much pleasure of being zapped quite badly a few times from a PVC system in a cabinet shop i work it. They were trying to cut corners and save some money and after enough people complained about it OSHA found their way in there and fined the owner and made him switch it out. Its also funny that people that use and say there is nothing wrong with pvc install a grounding kit "just to be on the safe side". Why spend ur money if theres nothing to be concerned about! JUST MY TWO SENSE!

I would think a commercial shop would have to adhere to the National Building Code, etc. that requires grounded metal ducting, the collector stored outside and all dust "storage" outside.

The issue is not whether there is a spark to ignite something, but whether there is anything to ignite. There isn't, until you get into the storage bin. There isn't enough dust in the pipe to ignite; too much air and not enough fuel. The real danger in a home shop is that we often have the storage bin inside the shop in violation of the NBC (if it applied to us, which it doesn't).

No one can criticize anyone for using plastic pipe if they have their dust bin inside the shop.

[Ken Fitzgerald]

It seems as tho people really think that a PVC system cant start a fire! It it produces spark then it can start a fire. Thats just simple science! I've had the not so much pleasure of being zapped quite badly a few times from a PVC system in a cabinet shop i work it. They were trying to cut corners and save some money and after enough people complained about it OSHA found their way in there and fined the owner and made him switch it out. Its also funny that people that use and say there is nothing wrong with pvc install a grounding kit "just to be on the safe side". Why spend ur money if theres nothing to be concerned about! JUST MY TWO SENSE!

Jason,

A lot of things are possible but not very probable. It is possible I could win the lottery but not very probable.

You want to check out the science? Check this out: http://home.comcast.net/~rodec/woodworking/articles/DC_myths.html

What OSHA might requre and what the NFPA requres is two different things. In reading the NFPA regulations, it appears to me that they only apply to industial/commercial operations...shops greater than 5,000 sq. ft. or DC systems capable of 1500 CFM or more.

There was a fire marshall either here or at another site I frequent. He did a study of reported DC fires in small hobby shops. IIRC, he found 2 cases where they were intially THOUGHT to be static related and were later found to be caused by different causes. One was just a motor caught on fire. The 2nd, it was determined the guy had been using his DC while grinding steel on his grinder. The investigator found that in his professional opinion, a steel spark had been sucked into the collector and layed there and smoldered for several hours before igniting a fire.

Nobody is saying it isn't possible Jason. What they are saying is there is no historical evidence of it happening and frankly if you take the time to read the above study, the science says the probability of it happening is extremely small.

BTW I installed metal as I live in an extremely arrid environment and don't enjoy getting shocked.

[Matt Hutchinson]

What a captivating thread. I am glad to hear what everyone has to say, and I have learned a lot.

So basically it's nearly impossible to create an environment in PVC that could lead to an explosion (mathematically extremely improbable), and it hasn't been produced in a lab yet. Additionally, simply by virtue of PVC being an insulator, and the relatively low air flow inside, there is NOT an environment that can cause an explosion.

Do think this is a fair and concise assessment? Or close enough?

Hutch

[Rod Sheridan]

Matt, I have only one experience with non metal ducting and it was with a length of 5" flex hose that ran from the ceiling to the hood on my planer.

I leaned forward to take the wood from the out feed end of the planer and had a nice arc jump from the hose to my head. Startling to say the least.

I now use metal flex, which is grounded through the metal duct work.

I know the static shock wouldn't be an electrical hazard, however I don't need any surprises when operating machinery.

Regards, Rod.

[Chris Padilla]

Matt,

I feel comfortable in saying your assessments are fair. Will YOU get shocked by PVC ducting on a DC system: most likely YES. Just as Rod stated above.... However, over time, as dust cakes on the inner walls of the pipe, the friction between the air/wood dust causing localized charge pools will decrease and the shocks become less and less....

[Eric Gustafson]

I have worked in the electronics industry for over 35 years. Static electricity damages components, although when I began my career we didn't know that. Plastic can be rendered static safe for components with the application of a electrically conductive coating. The simplest substance for this found in nearly any home, is fabric softener (diluted.) There is also a product called Static Guard. You spray it in your dryer to keep synthetics from clinging to themselves.

My Clearvue cyclone was only clear before the first time I used it. Then it became the color of mud. Not very clear! As an experiment, I sprayed some Static Guard inside. This was months ago, and the cyclone's plastic is clear as glass! Therefore, there is no longer any static build-up. I think you could treat the inside of your PVC pipes by spraying Static Guard or fabric softener while the DC is winding down. I would think it should wear off after awhile, but it doesn't seem to.

[Mike Gager]

mythbusters used coffee creamer to make an explosion but i dont remember saw dust


however here is a cool video of a sawdust explosion

http://www.youtube.com/watch?v=Va1sJF5_f-8

[Ken Fitzgerald]

I would suggest that nobody is using creamer or a road flare with their DC so it shouldn't be a problem.

[Anthony Whitesell]

Unless you ground every square inch,

You can't ground an insulator beyond the point of contact. That's why it's called an insulator. It won't conduct electricity and it won't conduct GROUND!

I don't generally chime in on these discussions, but I was recently reminded of something that is an aspect of directly related to this discussion.

I agree that a static discharge may cause wood dust to ignite. Whether it could, would, or can't I don't know. I'd like to set that aside for the moment and talk of the basic principles and physics of static electricity and insulators. This aspect is usually glossed over in these discussions.

Wood is for the most part and insulator and we all agree tha PVC is as well. When they rub together you get a build-up of static electricity. I think we all knew this part.

For those that have run or give into running that ground wire in or on the PVC ducting. Why does that work to dissipate a static charge? Because static electricity isn't completely static. Once you cover a surface in a charge, it will seek to provide equal potential across the entire surface (self-leveling if you will). If you then supply a single point (your finger or a screw) that is conductive to ground (or a lower potential) then you will get current flow and zapped. But not a second time because the charge is gone. If you attach the screw to the surface ahead of time and then try to build a charge, you won't be able to because you are providing a constant path to ground. Then charge that tries to build nearest the screw are shorted to ground and the higher charge furthest away will dissipate in the direction of the screw. It works alot like bucket with the hole in the bottom. If the hole is plugged and the bucket filled, then the water comes rushing out. If the hole is open and someone tries to fill the bucket, then there is less water near the hole and more further away. But never as much as there was when the plug was pulled on the full bucket.

Theoretically, a single point would be able to ground an entire PVC ducted system. But that is only if the connections between segments are equally as conductive and the charge builds and dissipates evenly. With all the seams, bends, and joints, I think we can agree that not going to be the case. Therefore, a ground wire should touch each segment in atleast one place. Whether you use a screw, duct tape, metal tape, or just run the bare wire inside and let it flop around. Inside or out it won't matter (there are two polarities to static electricity (one is on the inside of the pipe the other the outside). This is not saying the system is grounded and will always maintain a zero potential relative to ground. The grounding point provides a path to minimize and dissipate the static charge and keeps it below the level that will cause it to spark.

With that said, I still don't know if a spark will/would/could ignite wood dust moving at 400-1600 CFM. But knowing the physics behind and the requirements for dissipating a static charge, I'm going to be providing a ground path in my plastic ducted DC system.

[Ken Fitzgerald]

Anthony,

I might be wrong but I believe PVC is commonly used as a insulator on electrical wiring. You can't ground an insulator. It will neither conduct electricity or ground. Otherwise it wouldn't be an insulator. The ground wire will only work at the point of contact and maybe a extremely small distance around it.

[Dan Friedrichs]

Why does that work to dissipate a static charge? Because static electricity isn't completely static. Once you cover a surface in a charge, it will seek to provide equal potential across the entire surface (self-leveling if you will). If you then supply a single point (your finger or a screw) that is conductive to ground (or a lower potential) then you will get current flow and zapped. But not a second time because the charge is gone. If you attach the screw to the surface ahead of time and then try to build a charge, you won't be able to because you are providing a constant path to ground.

This is absolutely not true. There is no requirement that charge be uniform on an insulator (on a conductor, yes, but not an insulator!). This is easy to prove - go get a new piece of PVC pipe, rub it vigorously with a cat, touch one end while grounded, then go touch the other end. You'll get a zap both times.

The confusion emerges because people think that inserting grounded screws the length of the PVC pipe (or putting a grounded wire inside of it) completely removes the charge from the pipe. That's not true - it just decreases the electrostatic potential at which discharges occur. By allowing discharges to occur within the pipe, it's less likely that I'll get a strong zap by touching the pipe.

[Jimmy Coull]

PVC can cause static electrcity and that's a fact, but MIT did a study on the use of pvc on systems uner 3hp and found out that there is pretty much no chance of an explosion.

But my question to most of you is what do you use to collect your dust in, alot of people have cardboard drums or plastic bags. There is more of a chance of picking up a screw or small piece of metal in DC system, when that hits the metal impeller it can cause sparks or make the metal extremely hot as it lands on your saw dust, which can then start a fire.

this is just a little more info to keep the worry warts worrying.

Did you know that only female mosquitoes suck your blood, because they need it for having babies. But only the male mosquitoes make a buzzing sound as the females are quiet. So if you hear a buzzing while laying in bed don't worry because it's a male mosquito, but if you hear nothing at all.............;>)

Jimmy

[Dan Friedrichs]

PVC can cause static electrcity and that's a fact, but MIT did a study on the use of pvc on systems uner 3hp and found out that there is pretty much no chance of an explosion.


If you're referring to the source that I think you are, it wasn't MIT, but rather an employee of an MIT-affiliated laboratory who drew this conclusion. If we're not talking about the same thing, can you provide the source?

[Jim C Bradley]

Ken, you said it all. Give us evidence. Until then I shall continue using my SD-35 PVC dust collecting system. All of my joints are light friction fit so I can change the layout whenever I desire. I have no leakage that I can detect. I have no ground system.

Someplace out in electronic land I saw a very complete report by a person with all kinds of credentials who explained why we cannot get a spark explosion in a DC system. He had all of the data about air to dust ratios, the chemistry necessary to start the fire under DC conditions, etc. The article was in technical and explained in human terms. After reading it I just went PVC.

That is my 2 cents worth.

Enjoy,

Jim

[Ken Fitzgerald]

Jim,

Here's the link to the study they are discussing above: http://home.comcast.net/~rodec/woodworking/articles/DC_myths.html

[Bart Leetch]

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.


We already have for at least 10 years this topic has been kicked from pillar to post on most WW boards it hasn't happened & won't there isn't the right combination of oxygen, Heat, or fuel . This isn't like flour or grain mills the size of the duct is much smaller & so is the fan system.

Read this:

http://home.comcast.net/~rodec/woodworking/articles/DC_myths.html

Ok Ken your faster on the trigger then I am.

[George Bregar]

I love these threads. They're like the "best oil to use" threads on my BMW forum :D

I will be using PVC in my new shop. Either nothing will happen, or I will save the rest of you from disaster and go down in history posthumously. Win-win.

[Anthony Whitesell]

I'm going to say my last piece and then wander off.

From my physics textbook. "For any regular uniform shape (flat, spherical, cyclindrical, etc. not conical or T-shaped, or a bend) the static charge will find a uniform potential across the surface of the insulator." Or a hundred years of physics is being disproved. Keep in mind that this is a discussion on static electricity, for a static charge residing on the surface of the shape. If you momentarily apply a singluar discharge point, then the charge will dissipate from the immediate region and the remaining charge will redistribute across the surface. This only applies to regular surfaces. In the case of a 90 degree bend, there will actually be less charge build up at the inside corner due to the repulsitory nature of the static charge trying to maintain an even distribution (can have too many electrons in one place). And I never thought I would use all those years of classes in electromagnetics. :eek: Zero will the pipe ever be at zero potential with no charge on it? No. Will the charge be reduced? Yes, and most likely below the level at which a sudden discharge will occur.

What is being missed is that insulators build the charge on the outside of the body and don't pass current (easily) through the material. Where as a conductor easily passes current through the body of the material.

Ken you got me thinking even more. To take this train of thought one step further, all (modern) wires are covered by insulators. If the insulation/insulator can't be grounded, why don't we get zapped every time a cat rubs up against an extension cord?

Thank you for your time.

[Ken Fitzgerald]

Anthony,

IF you could ground an insulator......even for static....

explain, please, how you would ever build a static charge in the first place...........


Putting a ground onto an insulator just provides a path for static discharge, probably through the air.....

[Bart Leetch]

"Why don't we get zapped every time a cat rubs up against an extension cord?"

Just in fun...its the cat rubbing against the cord not we so why would WE get shocked?:eek::):D

[Anthony Whitesell]

I used the cat because (most of us) aren't furry. The cat rubs against the cord, we touch the cord, we would get zapped if the static charge wasn't dissipated.

[Anthony Whitesell]

Anthony,

IF you could ground an insulator......even for static....

explain, please, how you would ever build a static charge in the first place...........

BINGO! You can't build a charge on an insulator that has a way to dissipate the charge. If there isn't a path, then it builds a charge.


Putting a ground onto an insulator just provides a path for static discharge, probably through the air.....

You are correct. But remember that the charge that we are looking to dissipate doesn't reside IN the material, it resides ON the material. So through the air is a relative term. We are talking through 0.01" or less of air not 1 or 2 inches of air.

[Rod Sheridan]

I love these threads. They're like the "best oil to use" threads on my BMW forum :D
Win-win.

I love those as well, however riding an old airhead my oil choices are few:D

Regards, Rod.

[Edwood Ferrari]

I love this topic in a nerdy way.

Thought I would chime in from the point of a Semiconductor Engineer who often has to deal with static charge damage and prevention.

It turns out actually a charge induced in an insulator will not dissipate across the surface because the properties of an insulator impedes the flow of electrons from atom to atom. The charge will tend to stay put in the area where the charge was induced. Which coincidently is also why spot static energy fields can be built up so high in insulators. I'm sorry but it really is not possible to bleed off the charge over the entire surface of an insulator with a point ground. What you need is a conductor where in that case the charge is indeed distributed over the entire surface area thereby reducing the static energy field dramatically. There are anti static plastics that will conduct charge but I am afraid the cost would be more than metal ducting so not much help for us wood workers but it would be great.



Ed



I'm going to say my last piece and then wander off.

From my physics textbook. "For any regular uniform shape (flat, spherical, cyclindrical, etc. not conical or T-shaped, or a bend) the static charge will find a uniform potential across the surface of the insulator." Or a hundred years of physics is being disproved. Keep in mind that this is a discussion on static electricity, for a static charge residing on the surface of the shape. If you momentarily apply a singluar discharge point, then the charge will dissipate from the immediate region and the remaining charge will redistribute across the surface. This only applies to regular surfaces. In the case of a 90 degree bend, there will actually be less charge build up at the inside corner due to the repulsitory nature of the static charge trying to maintain an even distribution (can have too many electrons in one place). And I never thought I would use all those years of classes in electromagnetics. :eek: Zero will the pipe ever be at zero potential with no charge on it? No. Will the charge be reduced? Yes, and most likely below the level at which a sudden discharge will occur.

What is being missed is that insulators build the charge on the outside of the body and don't pass current (easily) through the material. Where as a conductor easily passes current through the body of the material.

Ken you got me thinking even more. To take this train of thought one step further, all (modern) wires are covered by insulators. If the insulation/insulator can't be grounded, why don't we get zapped every time a cat rubs up against an extension cord?

Thank you for your time.

[Chris Padilla]

What is being missed is that insulators build the charge on the outside of the body and don't pass current (easily) through the material. Where as a conductor easily passes current through the body of the material.

:D If the frequency of that flowing current is high enough, it won't pass through the conductor either: see skin effect. :D

The thing about the static build-up on insulators on our pipes is that it is largely unkown how it is distributed and what in the environment impacts that distribution (dirty pipe, greasy, metal, etc.). The charge may seek a uniform potential but we don't know exactly the shape of it or where it is necessarily.

My whole point in this matter is that just because WE, A HUMAN, get shocked by providing a path for current flow, doesn't mean that a shock will happen within the pipe...what could happen within the pipe to cause a path for current to flow thus heating the air thus igniting the sawdust??

[Ben Galluzzo]

mythbusters used coffee creamer to make an explosion but i dont remember saw dust


When I was 11 years old, I saw a demo at school of lighting fine particles with a candle. Well, I spent that summer over and over camping out and showing friends a similar setup using a 5 gallon potato chip can, a two foot hose, a candle, and a small cup of flour. I drilled a hole through the can and put the hose through so the end would sit in the cup of flour inside the can. Next I'd light the candle inside the can. Then I'd put the lid on the can. When you blew through the hose, the flour would dust up and be ignited by the candle and subsequently blow the lid off of the can. It's funny how many friends wouldn't believe you could light the flour like that.

[Frank Hagan]

I used the cat because (most of us) aren't furry. The cat rubs against the cord, we touch the cord, we would get zapped if the static charge wasn't dissipated.

Cats are magical. Everyone knows that.

[Dave Norris]

But one time I most definitely was the recipient of a static discharge from my Clearvue. The dust had clogged at the bottom of the cyclone (actually the bin was full). I walked over to the cyclone and gave it a good rap with my hand to clear the alleged clog. I got a serious bite from the static discharge. I wrapped a piece of wire around it and haven't had a problem since. Then again, I haven't rapped on the cyclone since either...

So maybe the question would be what parts of the system to ground? I know I use flexible pipe to go from the pvc to the woodworking machine. If I get to close the hairs on my arms stand up, and I occasionally get a bit of a zap from that as well.

[Thomas Syrotchen]

Well I wasn't really trying to start a debate on the possibility but was thinking that perhaps we could see the "Mythbusters" confirm or bust the possibility. A couple of thoughts, first as many have pointed out, grounding an insulator is not really productive in terms of reducing any risk. In fact, I've wondered if running a ground inside the pipe, or as other have suggested on other sites, putting a bunch of screws inside the pipe and then grounding the screw isn't really creating spark plugs. Its forcing one spot in the pipe to be at zero volts potential, and as the charge builds up in the insulator, will it eventually reach the point where it breaks the air gap and creates a spark. Instead of reducing risk, I think attempts to ground can only increase the risk.There is not doubt in my mind that static discharge from PVC pipe is capable of igniting sawdust. The NEC specifically addresses the requirement to ground DC systems to prevent static discharge and prohibits the use of PVC.

The best theories against the possibility I've seen really center around the dust particle size. I know its a heck of lot easier to start a fire with kindling than it is to light a tree. Since most hobbyist shops have machines that create large chips, its unlikely that static discharge would ignite the chip. If someone was running an abrasive planer, or large sander which generates a lot very fine dust and passed that thru a pvc pipe, I think the potential for fire would be far greater. I would guess that on occasion, a little bit of dust is ignited in a pvc pipe, but there is simply not enough fine dust in the system to sustain the fire and it burns itself out. The old fire triangle, no fuel no fire. However, the number of wood shops is dwindling and their equipment is hitting craigslist, and ebay. Grizzly and others have new machines at prices hobbyists are willing to pay, I begin to wonder if the potential risk will go from virtually zero to a plausible number once a few large sanders hit the home shops in greater numbers. However, I do wonder if a single sander would generate enough dust to sustain the fire in the PVC. Hence, the suggestion to let Mythbusters give it a shot.

For the record, I think the possibility regardless is very small, and I'll drive to work tommorow with a much higher probability of being hurt or killed.

[John Schreiber]

. . . The best theories against the possibility I've seen . . .
Theories are valuable and should be tested.

It has been tested through many years and thousands of users. No explosions have been documented. Plenty of those shops have belt sanders/drum sanders/disk sanders/hand sanders. Nothing.

Mythbusters is not the best place to test a woodshop environment. A woodshop environment is the best place to test this theory.

[Ken Fitzgerald]

The NEC specifically addresses the requirement to ground DC systems to prevent static discharge and prohibits the use of PVC.



For the record, I think the possibility regardless is very small, and I'll drive to work tommorow with a much higher probability of being hurt or killed.

IIRC the NEC addresses grounding DC systems that move a volume of air over a certain level or the shop is over 5,000 sq.ft. IIRC. That volume of air isn't exceeded in most small shop DCs.

[Adam Cavaliere]

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. ;-)

Its about as popular as the "Which Jointer should I buy" question!

[John Jackson]

The one part of the argument I never understood was that no matter what system you use, at the end of the line it ends up in a plastic bag at the bottom of the dust collector.

When on, the dust is continously swirling around and around on the inside of that plastic bag. It is also where most of the dust in the system has collected (most fuel).

So even if I have metal pipes, the dust is directed to a plastic bag that is made to swirl for hours on end.

Is this a different condition than inside a PVC pipe?

John

[Frank Hagan]

The one part of the argument I never understood was that no matter what system you use, at the end of the line it ends up in a plastic bag at the bottom of the dust collector.

When on, the dust is continously swirling around and around on the inside of that plastic bag. It is also where most of the dust in the system has collected (most fuel).

So even if I have metal pipes, the dust is directed to a plastic bag that is made to swirl for hours on end.

Is this a different condition than inside a PVC pipe?



When I did my Google search looking for dust collector fires, they were all in the motor or in the dust bin, and none were attributed to ducting. I have also heard people say they had a smoldering dust bin after picking up metal either with a floor sweep or by cutting into a hidden piece.

[David Christopher]

just buy some of that anti static spray and wipe the pipe.......it works

[Thomas Syrotchen]

Plastic bags will have different insulating and capacitive properties than the pvc pipe. I'm not sure about others but I've never been shocked touching the plactic bag, but your almost guaranteed to be shocked by pvc piping.

Two seperate issues regarding picking up metal and pvc ducting. Picking up metal is likely to cause sparks and generate heat as it contacts blades on the impeller right before it hits the collection bag. Its a good argument for a seperator prior to hitting the DC. Others install magnets.