Static electricity with dust collector

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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

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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.

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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: