Static electricity with dust collector

OH here we go again.........this one pops its head up every few years.

No body yet has be able to produce one single example of a dust explosion in a small scale workshop due to static electricity or plastic ducts......none ... not one.....and this same issue has been beaten to death in every single woodwork forum on the net.

NOT one single case.

And there are very good proven reasons why not..and they are detailed in the links posted.

Even mythbusters had a go at a similar issue.

there are however plenty of people ( including manufacturers of steel duct systems) who are prepared to beat this one up for all they are worth.

metalic down spout is entirely unsuitable for dust extraction porposes....it is simply not strong enough and will collapse.
I have read a story about a bloke that went to great effort to build an extraction system built on metalic down spout......all went well......till the closed all the blast gates with the blower running........the whole lot collapsed.........sucked in:D

It can be argued however that placing foreign metalic earths particularly point sources like bolts and wires in and on ducts increases the small ( none, not one example) risks that exist.....among other risks.

Any static suppression efforts will simply be for the sake of comfort.

Consider also connecting anything to the electrical earthing system is electricains work and there are very specific rules about this.

as to why the static is on the outside of the duct........insulation resistance and high static voltages..........static voltages ( while largely harmless) are very high voltages....thousands of volts.........the plastics used have limited and finite insulation properties and there is no discharge path....no current flows.....so the charge builds up on the outside of the pipe.


the same issue exists in your home vacume cleaner, built in home vacume systems and a number of other situations.

now if you want something to worry about.....worry about your dust bag......is it smouldering while you sleep........did that nail you hit throw a spark into your dust bag........you have been cutting a heap of green timber......has it heated up enough to start smouldering among all the realy dry shavings ( remember the self igniting piles of grass clippings)..........so you were pushing that blunt blade thru that hardwood.......did it create embers and are they in your dust bag.

If you are worried enough to earth your ducting you should be emptying your dust bag every day.

there are many cases where dust bags have caught fire and burned down the workshop.

remember..... not one single case has been produced where static has caused a fire or explosion in small workshop dust systems....... not one.


cheers

Watch out for hearing aids, my father was helping me with some thicknessing he got a little to close to the vertical duct and zapped his hearing aid ...dead.
Luckily his new $1000+ whizz bang hearing aid was in getting fixed(typical that)and it was only an old spare that got zapped!

I think Soundman's post about sums it up. It takes more heat to ignite wood dust then flour particles. I once tried to deliberately create a small scale wood dust "explosion" and it took more effort than i thought. I heard about the phenomenon, so i wanted to have a go at it myself. Plastic jar, bit of wood dust from an orbital sander bag, spark plug, old petrol motor with magneto, vigorously shake the jar and crank up the motor to create sparks. Nothing happened. The mix ratio with air must be just right and i think you rather need really hot particle-like sparks (angle grinder disc sparks or sparks from a nail head inandvertantly being sanded down by a belt sander) instead of "electrical" sparks.

Smouldering in a dust bag is a much greater risk. I've witnessed a belt sander bag been set alight after an unseen nail had been sanded down together with the surrounding wood. There's first a scorching smell and then smoke and all of a sudden there are flames, probably because of the machine's hot air. It really helps when the bag pores are clogged a bit and the machine has been active for a while, so the dust laden air entering the bag is already heated up. With a properly "breathing" bag and a good airflow, the air is colder and the intenser flow will blow out any beginning flames.

By the way Soundman: i really enjoyed your speaker cone repair post. I wish i would have had your experience and knowledge written down in such a story a few years back, when i had a go myself!

As for static shocks, one particular shop vac hose often surprised me with that. I was fed up and took a length of bare copper wire with a clamp soldered at either end. The wire was bound along the hose by rubber bands at every 10 cms, with one clamp gripping the sanding machine's metal frame and the other clamp gripping a large metal object somewhere in the shed. No more shocks from the hose. I stole the idea from fuel tanker trucks (the ones used for airfield or gasoline station logistics) which have hoses with an added earth wire. First they connect the earth wire, than the hose and with the static voltage drained off, there's hardly any chance of sparks igniting fuel fumes.

Many shop vac hoses are now antistatic or very slightly conductive, so they drain off static automatically. Festo was one of the first brands to offer such solutions, since they are a great name in sanding technology and thorough dust handling (automotive and furniture industry, professional painters, interior decorating industries, etc.).

greetings

gerhard

Not all wood dusts should be treated equally. MDF dust ignites and can cause explosions at 200 deg C.

I am a professional hazardous area consultant (and a wood worker in the bit of spare time I have) and have investigation many sites where "incidents" have occurred - from factories to school woodworking facilities.

Best to treat this as a potential hazard people.

As to Mythbusters, their methods are hardly rigorous and I would not put my life or that of others on the line on the basis of their tom foolery.

If anyone wants to know more about actual issues with combustible dusts (wood and others) see my site - www.epeeconsulting.net

Happy crafting!

Paul, please post a documented case of where an explosion has occurred in a standard style HOME dust collector system and been caused by static discharge when cutting normal materials (not bags of flour :rolleyes: ). Despite looking over many years, and asking those who say it is dangerous to post proofs, nobody has been able to.

There are often people who state this is dangerous, and encourage all sorts of "solutions" - some expensive - when there is no proven threat. Home dust extraction systems simply have not been proven to be susceptible to dust explosions. Fires yes, and if money is to be spent then a fire extinguisher would be a good investment.

The biggest proven threat so far is getting 'zapped'.

Quote:

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Originally Posted by PaulSpresser

Not all wood dusts should be treated equally. MDF dust ignites and can cause explosions at 200 deg C.

I am a professional hazardous area consultant (and a wood worker in the bit of spare time I have) and have investigation many sites where "incidents" have occurred - from factories to school woodworking facilities.

Best to treat this as a potential hazard people.

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The key word is "can". MSDS also use the term "can" or "may" to cover their backsides. According to one MSDS a minimum of 0.04 g/L of suspended wood is needed to create to an explosion. In a 200 L DC this is only 8g of suspended wood dust
BUT
What they don't say is that a specific particle size distribution is needed to initiate an explosion. For example wood chips from a TS or BS won't count.

A far greater risk from MDF dust is the formaldehyde which led to me losing my sense of smell for weeks from using it and beer tasted like soap - now that is a real risk worth considering.

Having some experience in hazardous areas through the chemical industry, and recently having run through a course in management of hazardous areas through my work, dust is a hazard to be cautious of. The rule of thumb from the expert was if you could see it, then you could have a problem.

Having recently been involved in the investigation of a fire caused by static I am well familar with the risk static poses. I looked for minimum ignition energies on the internet to give an idea as to how this compares with what I know.

Here is a useful link to compare the minimum surface temperatures required for wood dust ignition. You will see that the temperatures required to cause ignition are significant. There is a correlation between the ignition temperatures and static measured in V, but not sure what it is. I know that 2000V is a recommended upper level for the most flammable vapours. You can feel a 2000V spark, but only just. Visible sparking is much higher 10000v+.

I think whilst ignition of wood dust in a dust collector is unlikely, the consequences of a dust ignition can be severe. There is also the nuisance factor of static - like everything sticks to it on the inside and outside.

For the sake of a bit of copper wire you could eliminate the nuisance factor and also any potential (extremely unlikely) dust hazards.

Cheers,

Tom

It has been well argued that if metal is placed within a duct.....it may in fact increase the risk of ignition.

On a more ammusing note......I was sucking up gritt from sandblasting bits inside my aluminium boat......I had been vacuming for quite some time....when I touched both the hull and the vacume hose at the same time...

CRRRACK....OUCH

I copped a realy healthy across chest static discharge....and belive me the crack was loud.

This was over a week ago..so I'm not likley to keel over suddenly.

But someone with an unhealthy heart might not have been so lucky.

now I was using my small cyclone and about 5 meters of standard 32mm vac hose and anout 2m of 50mmdust extraction hose......my cyclone is bonded to the mains earth.

this static was generated completly within the vac hose

I'm I going to go out and wind wire arround my vac hose.....nup don't think so.....

cheers

I posted this a while back and received no comments, so I will post again.

I used plastic water pipe to duct my garage and also had a lot of static build up on the pipes and received a lot of shocks.

The cure:-
I simply sprayed a line of "Gal Metal" anti corrosive paint along the length of the PVC and problem solved. (this is the silver coloured paint not the red)
(The Galmet spray was left over from some brackets I was making at the time.)

I didn't need to earth the line of spray and yet it still dissipated the static charge effectively! :2tsup:

HTH

Petrol fumes or a wet cell battery may have made that a far more exciting experience than a little zap:U

Thats a good trick , might borrow that one

Quote:

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Originally Posted by robbo266317

I posted this a while back and received no comments, so I will post again.

I used plastic water pipe to duct my garage and also had a lot of static build up on the pipes and received a lot of shocks.

The cure:-
I simply sprayed a line of "Gal Metal" anti corrosive paint along the length of the PVC and problem solved. (this is the silver coloured paint not the red)
(The Galmet spray was left over from some brackets I was making at the time.)

I didn't need to earth the line of spray and yet it still dissipated the static charge effectively! :2tsup:

HTH

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Maybe it acted like a sprayed line of metal down the duct. :shrug: At least it doesn't get tangled. :D (Not actually earthed? :think: Weird. Maybe static charge can collect at one end so to speak, and you just have to spread it out again. :hmm:

Galmet is zinc rich paint so it is earthing through the zinc even a lead/carbon pencil will do the same thing. Years ago it was always fun to put a pencil mark on your mates spark plug on his car, the plug would play up under load.

Quote:

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Originally Posted by Claw Hama

Galmet is zinc rich paint so it is earthing through the zinc even a lead/carbon pencil will do the same thing. Years ago it was always fun to put a pencil mark on your mates spark plug on his car, the plug would play up under load.

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The main reason it works is that static charge cannot build up on a conductor. However, I don't know by what mechanism it gets dissipated? :?

I was also getting zapped by my "cyclone" - a 20 litre bucket with a funnel on the bottom - so I sprayed a ring around it and then up over the top like a handle, no more zaps.

Even if the galmet doesn't go back to metal it may touch or get close enough to the ground to earth out.

Quote:

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Originally Posted by robbo266317

The main reason it works is that static charge cannot build up on a conductor. However, I don't know by what mechanism it gets dissipated? :?

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Static is often stored on conductors like the aluminium spheres in a van der graaf? generator. I have no idea how it is dissipated either but it sounds like a great idea.

Any conductive material like the zinc paint will allow the charge to equalise and disipate.

Even some detergents will do the job short term.....try spraying your vac pipes with spray & wipe......it does not last long but it works

the conductive / leaky path allows the built up charge to disipate to "some where else".......it does not matter where, anywhere that is not at a raised static potential.

This same leaky path will also prevent static from accumulating to start with

If the charge is allowed to move...it ceases to be a static charge.

In electronics, we have been controlling static for decades. Introduction of metals such as zinc and carbon into and onto plastics and introduction of detergents into and onto plastics are very effective.

Quite a lot of this problem could be avoided if manufacturers of dust extraction hose simply put some carbon or metal into the plastics used to make the hose.

Most domestic vac hose ( that does not have wire in it) is either black, grey or silver.
There may still be static accumulated but it is controlled.

as for the PVC pipes many of us use......hell yeh a squirt of zinc spray is a great idea..........wish I'd thaught of it myself......I have Duragal on the shelf ( great stuff):2tsup:

but remember there are metal objects that will act as accumulators of static energy......the give away is a metal object that is in an insulated situation.

Like our Vandegraf generator.. the metal ball is connected to the brushes that run on the belt....the ball is suspended on good quality insulators....it is the brushes that develop the static.

In my metal cyclone....I recon it is the PVC entry pipe that generates the static... the particles become charged passing thru the pipe........ transfer that charge to the cyclone body on contact.

When i first tested this cyclone hanging from bungy off a ladder.....it was drawing 6 inch sparks off the ladder frame.

back to my CRRACK experience......I recon it was the PVC conduit wand I was using that generated the charge.......the garnett grit I was sucking up is an excelent static material...... resuit big charge.

If I would have been using the vac hose direct or a metal wand....I do not believe there would have been as much charge accumulated

I know this is a long rambling post but I hope it explains a few things.

cheers

To save the re-hash , read these
https://www.woodworkforums.com/f200/e...ghlight=static
https://www.woodworkforums.com/f18/pv...ghlight=static
:2tsup: