Static electricity with dust collector

I have made a dust pre-separator to go between my table saw and my 2hp dust collector. After a short run cutting MDF and Masonite, I was amazed at the amount of static electricity on the hoses at the top of the pre-separator when I went to see the results. The dust had actually left tracks on the inside walls of the plastic drum, possibly from static?

My concern is the potential for a spark from the static electricity, and the fine dust flowing around, leading to a fire or possibly an explosion.

Can anyone advise if there is a problem, and how should it be overcome, please?

regards,
Jill

I really have no idea but earthed metal bands around the ends of your pipes may reduce the charge.

http://www.carbatec.com.au/dust-extr...ding-kit_c1855

Run copper wire along or around your hoses and drum back to an earth point on the extractor. this way the static will not build up and cause any sparks. The likes of Carbatec sell kits to earth extractor systems.

There you go Funky's all over it.

Jill, there will not be a fire or explosion from the dust collector. You may get zapped but that is about it.

Fire in a DC is most likely from cutting a nail or sucking in a cigarette butt.

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Originally Posted by Groggy

Jill, there will not be a fire or explosion from the dust collector. You may get zapped but that is about it.

Fire in a DC is most likely from cutting a nail or sucking in a cigarette butt.

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I agree, this one is way over hyped and IMHO those kits are designed to sell a product rather than make any sort of significant contribution to safety.

My guess is that there are dozens of greater risks and precautions that we could take in our sheds than worrying about that one.

For example how many of us have a fire extinguisher and fire alarm in our sheds?

It's all a myth, till someone gets hurt. Do yourself and your peace of mind a favour and earth it. Could be cheaper to buy a roll/part roll of bare copper from an auto electrician or motor winder. Either way, just do it.

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Originally Posted by Enfield Guy

It's all a myth, till someone gets hurt. Do yourself and your peace of mind a favour and earth it. Could be cheaper to buy a roll/part roll of bare copper from an auto electrician or motor winder. Either way, just do it.

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It IS a myth. The only danger from static electricity is getting shocked and forgetting where the blade is.

I ask anyone to find and post a single verifiable occurrence of a dust explosion from a normal domestic-style wood dust extractor; it simply does not happen. It is not worth investing money in these things unless your sole purpose is to avoid a jolt from static.

I just stripped back some 10amp tps and did a few big coils around the flexes, couple of cable ties hold it in place and back to the dusty no more nasty little bites.

Terrible photo but you can just see the wire and cable ties in this shot.

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Originally Posted by Groggy

Jill, there will not be a fire or explosion from the dust collector. You may get zapped but that is about it.

Fire in a DC is most likely from cutting a nail or sucking in a cigarette butt.

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I don't think there is risk of fire from static. But we had a fire in the dust pipes at knox woodworker's cos someone cut a bit of hard wood on a band saw. Saw dust from that was hot enough to set a bit of saw dust in the pipes alight. It must have smoldered away for a few hours till it started to burn properly and a next door neighbour saw he smoke coming from under the door and got in and put the fire out before the whole place was set alight. (Dusty prolly wasn't on at the time. Or not working that well, cos there was a build up of dust in the pipes near the saw to set alight. ) (Forgot to say the fire didn't get goin gtill an hour or so after everyone had gone home. Just luck the guys in the studioo next door were around for a while.)

I am very interested in this topic as I want to get a cyclone for my shed vac and I have been getting a bit worried (paranoid??) about the static electricity issue. I'm relieved that you say static is not a problem, although I was reminded about petrol tankers which are filled at the refinery from the bottom rather than from the top. Apparently, there is a risk of static from the petrol falling from the top of the tank to the bottom (when empty) and the risk of a big bang. I would be quite happy to not bother earthing my cyclone vac (when I pull my finger out) but I don't want to catch fire either. :no:

Here are a couple of really interesting articles on static and fires in dust collectiuon in the home workshop, exploding some of the myths.

Grounding PVC and Other Dust Collection Myths

The Principles of Static Electricity in a Dust Collection System

Interesting that all the static buildup is supposed to be inside the hose and the plastic drum, with the dust laden air whizzing past these surfaces (remember charging up the plastic ruler or plastic rod in static electricity experiments at school?).

So why is there so much static outside? The hairs on my arm just stand on end when near the hoses and the pre-separator . Admittedly I have 4.5m of hose that is all charged up internally

I am going to run a wire with cable ties just to stop getting zapped when I touch these things, and earth it to the frame of the shed with a portable lead with alligator clips on each end

regards,
Jill

All ducts do it, if you look at some air conditioning grilles and see dirt all over them it doesn't mean the filters in the a/c are dirty or you have dirty air coming down the duct it is the static created at the grille as the air passes over it attracts any airborn dust and it sticks to to the surface.
I haven't had a zap since I put my copper wire on, its far more pleasant using my dusty these days.

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Originally Posted by JillB

So why is there so much static outside?

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It's all the same charge on the duct, (the opposite charge is carried along in the air/dust) and like charges repel so they like to be as far apart as possible so they head for the outside of the container hence they appear on the outside.

The reason that the risk of fire inside a home shop DC is very low is that the amount of charge made inside the ducting is small and over a long enough period so it has plenty of time of time to move to outside the ducting. In commercial/industrial DCs the charge generation is much greater and the ducting is much thicker. Some also use sheets of a wear plastic to line deflection areas inside the ducting, if these wear plates are not earthed or mounted correctly they can build us a charge and discharge to the ducting inside the dust flow and whammo.

Thanks Claw, willl be fitting the bare wire this weekend. But I still don't understand why the static on the outside of the hose :(

regards,
Jill

I had a dust explosion once, they are not easy to ignite. I was sanding my floors and decided to run a ventilation system, I lit the open fire in the room (big roaring fire) and opened the windows a little:doh:. It worked reasonably well and I poured the dust on the fire to get rid of it on tipping the last of about the 6th bag the room caught fire flames everywhere the windows shook and I had burnt eyebrows and hair:C felt rather stupid afterwards.:no:

I think the static is formed on the inside of the hose but the whole flex becomes staticly charged by earthing the length of the flex it doesn't allow the charge to build up. Like when you scuff your feet on nylon carpet in an air conditioned room (dry air/ lack of moisture in the air makes it worse, air conditioning removes moisture like a fridge) and then zap someone on the nose:zap: (great fun:roflmao:) if you had an earth strap/wire on connected to an earth point it just wouldn't build up.
That is the other thing, normaly with moderate relative humidity say 30% plus you may not get an explosion but if the conditions were right you might, who knows could be 1/100000 chance. Ifyou get low humidity like we had in Newcastle the other day which I measured in my workshop at 18% and if you had a hot day say 35C or up and some the static in your flex will be a lot worse than normal, add some nice fine dust and :blowup:
The bush as we know goes up with spontanious combustion, hell, throw in a nice big 1000 volt plus static zap.
All government dust extraction systems have always had to have earthing systems and having worked in wheat silos etc static is a big concern.

Hmmmmm. Petrol tankers, wheat silos and commercial/ government installs all do it. Low humidity and high temps. Might not be so expensive and time consuming after all, to err on the side of caution.

My greatest expense was about 8 cable ties.

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Originally Posted by Enfield Guy

Hmmmmm. Petrol tankers, wheat silos and commercial/ government installs all do it. Low humidity and high temps. Might not be so expensive and time consuming after all, to err on the side of caution.

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This logic is just wrong, sorry. With petrol tankers you are talking about highly flammable fumes and with silos you are talking different materials and larger volumes. Government and commercial installations deal with much higher volumes and flows. I understand the caution (always a good thing) but it is not required. There has never been a verified instance of it happening.

I'll say again, use it to help stop the static from zapping you but if you buy a kit to avoid a dust explosion you are wasting your money. An equivalent amount would be much more wisely spent on a smoke detector as fires DO occur.

I found that spraying a line of zinc paint down the length of the pipe did the trick.
No mucking about attaching wires. :thyel:

The answer to "beer is good" with the petrol tanker is not static but another effect pressure. Falling fron the top or if it was one big tank without baffles there is a chance that a bubble of fumes could be compressed enough to ignite like happens in a diesel engine.

I used to work for a transport company and we carried petrol as well many other liquids. It was always poured in from the top it would take too long to load through a 100mm pipe at the bottom, not to mention the spillage when you disconected. This is 35 tonne in 5 compartments. A static line was conected to earth the tanker.

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Originally Posted by Groggy

I'll say again, use it to help stop the static from zapping you but if you buy a kit to avoid a dust explosion you are wasting your money. An equivalent amount would be much more wisely spent on a smoke detector as fires DO occur.

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As well as a detector how about a fire extinguisher?

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Originally Posted by BobL

As well as a detector how about a fire extinguisher?

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I don't think I would use an extinguisher on a dust collector as the pressure would blow the burning dust all over the place and maybe make it worse. I'd use water after killing the power - any firies out there can say what would work best for a dust collector fire?

Hi JillB,
What Enfield Guy said is what I also think.Don't be fooled by those who believe in myths. It is a fact, but it will only Explode.
The easiest way to stop all this is to use Metal pipes, what I mean is
Household Downpipe, then you don't have to Earth anything to my knowledge.
Where do you get it ?, at the local tip, or recycle dump. Probably a fraction of the cost of buying plastic pipe, & maybe you might be able to use plastic joints, but then that separates the metal.
You can cut short pieces off, cut & split the band to use as a join, & pop rivet them together.
The Plastic must be earthed to a spike in the ground.
So how do I know this, easy, I was Employed by The State Electricity Commission of Victoria for 33 yrs.
Had I said I worked for them, there would be a barrage of comments.
Well that's my bit, & let us all know how it worked out.
Regards,
issatree.

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Originally Posted by Groggy

I don't think I would use an extinguisher on a dust collector as the pressure would blow the burning dust all over the place and maybe make it worse. I'd use water after killing the power - any firies out there can say what would work best for a dust collector fire?

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I wasn't referring to the 1:100000 chance of fire in a DC but the much greater risk of fire in a shed from other causes which is what we should really be worrying about.

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Originally Posted by BobL

I wasn't referring to the 1:100000 chance of fire in a DC but the much greater risk of fire in a shed from other causes which is what we should really be worrying about.

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Agreed :2tsup:

Unfortunately i have experience with dust explosions as part of my history in the food industry and particularly flour milling. What is critical is the concentration of dust. It is a small range but if you are in that range any spark is good enough. The fact that it doesnt happen in home workshops (that we know of) if probably due to an excess of dust. It seems wise to ground equipment but as has been stated it is not expensive or a big deal.

and in case you dont believe it can happen...

[ame="http://www.youtube.com/watch?v=zKMPC2l80NU"]YouTube - Flour Dust Explosion[/ame]

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Originally Posted by Sebastiaan56

Unfortunately i have experience with dust explosions as part of my history in the food industry and particularly flour milling. What is critical is the concentration of dust. It is a small range but if you are in that range any spark is good enough. The fact that it doesnt happen in home workshops (that we know of) if probably due to an excess of dust. It seems wise to ground equipment but as has been stated it is not expensive or a big deal.

and in case you dont believe it can happen...

YouTube - Flour Dust Explosion

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It can happen but the video shows an open flame.... I really believe you would be hard pressed to find an explosion occurring due to a spark. Open flame sure but not a spark. Also, isn't flour smaller in particle size anyway?

Interesting subject, However I would be more concerned about my lungs to be honest than an explosion. Got to be worried about all the air born particles the dust extraction doesn't pick up (shoots out)

Harlan

On the last job I was making I was using old recycled Blue Gum roof beams, the dust that came off when I was using the thicknesser was equally as fine as flower. First it came through the filter bag and then it blocked the filter bag and started to ooz out around the sides as the pressure buit up. Cleaned and emptied etc but my whole workshop was full of fine floating powder. Even if it was only a flash it wouldn't have been pretty not to mention the paint, thinners, turps, metho, chain saw fuel etc. Me I'll keep my little bit of copper wire on thank you, just in case.

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Originally Posted by Claw Hama

On the last job I was making I was using old recycled Blue Gum roof beams, the dust that came off when I was using the thicknesser was equally as fine as flower. First it came through the filter bag and then it blocked the filter bag and started to ooz out around the sides as the pressure buit up. Cleaned and emptied etc but my whole workshop was full of fine floating powder. Even if it was only a flash it wouldn't have been pretty not to mention the paint, thinners, turps, metho, chain saw fuel etc. Me I'll keep my little bit of copper wire on thank you, just in case.

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The chances of an explosion in this situation are extremely low. For a start the thicknesser motor would have been constant sparking :oo:, so why don't a lot more sheds blow up? Because the particle size distribution and concentration requirements for a wood dust explosion are very narrow. Even air-petrol explosions are more difficult to create than people think - think of how hard it is to start a flooded engine or one that has a partially blocked carby or injection system. Flour - air explosions are easier to create to create in a paper bag because purely by chance the particle size distribution and concentration of the flour dust inside a shaken bag are about right for an explosion.

A far greater personal risk from wood dust than any explosion over the longer term is constantly breathing this stuff in and is why the best place for a DC is not inside the workshop.

Explosions do occur in home workshops but they nearly always are preceded by a fire which your copper wire does nothing towards averting. So it makes far more sense to put $ towards the greatest risk reduction strategies ie the fire. One major risk in home workshops is fire. Once again I ask how many of us have a fire extinguisher and smoke detector in our shed?

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Originally Posted by Sebastiaan56

Unfortunately i have experience with dust explosions as part of my history in the food industry and particularly flour milling. What is critical is the concentration of dust. It is a small range but if you are in that range any spark is good enough. The fact that it doesnt happen in home workshops (that we know of) if probably due to an excess of dust. It seems wise to ground equipment but as has been stated it is not expensive or a big deal.

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It's not just concentration but particle size distribution. The flour example is not comparable to wood dust in workshops - see my previous post. Power tools make heaps of sparks made yet the incidence of workshop explosion is very low and most explosions are cause by fires not sparks. Instead of focussing on grounding and explosions we should be focussing on spotting fire hazards and making sure our fire alarms and extinguishers.

Somebody - please - post a link to a genuine dust explosion in a home workshop dust collector or let this go. Given the tens of thousands of woodworkers around the world using dust collectors there should be many recorded instances with pictures. Just like the cut off fingers, fires, electrocutions and hair caught in drill presses. Why can't we find them? The simple reason is that it is an exceptionally rare event - if it has ever happened at all.

I agree with BobL, spend the money on another safety issue that is much more likely to occur.

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Originally Posted by BobL

The chances of an explosion in this situation are extremely low. For a start the thicknesser motor would have been constant sparking :oo: (My thicknesser has a fully enclosed motor) , so why don't a lot more sheds blow up? Because the particle size distribution and concentration requirements for a wood dust explosion are very narrow(But imposible ?). Even air-petrol explosions are more difficult to create than people think - think of how hard it is to start a flooded engine or one that has a partially blocked carby or injection system. Flour - air explosions are easier to create to create in a paper bag because purely by chance the particle size distribution and concentration of the flour dust inside a shaken bag are about right for an explosion.( Which I believe would have been getting close to in my workspace on this project, cosistancy very similar to flower)

A far greater personal risk from wood dust than any explosion over the longer term is constantly breathing this stuff in and is why the best place for a DC is not inside the workshop. (Always were P2 masks if there is any dust around)

Explosions do occur in home workshops but they nearly always are preceded by a fire which your copper wire does nothing towards averting. So it makes far more sense to put $ towards the greatest risk reduction strategies ie the fire. One major risk in home workshops is fire. Once again I ask how many of us have a fire extinguisher and smoke detector in our shed?

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Hi Bob (I agree, I know the risk of dust explosion are very slim but why run the risk for the sake of maybe $5 and 10 min of time? I have 2 fire extinguishers one inside the workshop door (1kg)and one outside (3.5kg) and a hose within 3m. While the risk is minimal, there is a risk.)

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Originally Posted by Claw Hama

Hi Bob (I agree, I know the risk of dust explosion are very slim but why run the risk for the sake of maybe $5 and 10 min of time?

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Sure, but making any sort of deal about minimal risk factors get newbies very nervous and in the hullabaloo of the concern they lose sight of greater risk factors such as fire.

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I have 2 fire extinguishers one inside the workshop door (1kg)and one outside (3.5kg) and a hose within 3m. While the risk is minimal, there is a risk.)

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Sounds good. So you are well prepared with extinguishers, but a cold hard analysis of where best to spend the next $5 and 10 minutes would still be a fire alarm and many other things beforehand over grounding a DC. Better machinery guards, better PPE, better procedures, better tool racks, covers over blades, foot pedal safety switches on machinery, better storage of flammables etc would all rate as far more risk reducing than grounding a DC.

Mainly I spent the $5 and 10 min so I wouldn't get zapped every time I moved or brushed against the flex.

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Originally Posted by Claw Hama

Mainly I spent the $5 and 10 min so I wouldn't get zapped every time I moved or brushed against the flex.

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Yep - that is a good enough reason to do it!