Static electricity through Dust Extraction--- advice PLEASE

[Mark.R]

Could anyone please advise me wether I need to be concerned about the static electricity caused by dust extraction. My set up is based on 110mm underground piping with all junctions in the ducting made from the same. I saw in Axminsters catalogue their earthing set for dust extractors, but dont know if this is required for aluminium ducting only, or wether the fire risk caused by the static electricity, is just as risky or worse with ducting made from underground ducting??

Could any of you please advise?? I dont want a fire!

Thanks

Mark.r

 

[9fingers]

I have an extensive all plastic 110mm system and never had a problem.

Even if the sawdust does become charged electrostatically then it still can't cause a spark until it meets something of a radically different charge.

My collection bin is metal and I've never had a static shock off it.

IMHO - not worth worrying about.

Bob

 

[Shadowfax]

Don't worry about it. It is not possible to satisfactorily earth plastic piping for a start and secondly you do not have a set-up anywhere big enough or fast enough to generate the kind of static that might cause a dust explosion.
In over thirty years of fire fighting and fire safety work I have never seen anything like the sort of thing that concerns you.
I have 110mm ducting too and it is fine.
For a dust explosion or a fire you would need masses of very fine dust like flour, in a cloud near an ignition source. You won't get it inside a pipe like ours.
A glowing ember inside the pipe might cause a fire but that could happen anywhere.
My advice:- keep things as clean as possible and enjoy your woodwork.
Best wishes.

SF

 

[Digit]

Without a source of ignition Mark you don't get fires, you get explosions.
For that you need a good static charge and the precise air/dust/ particle size.
If you are using an industrial size sanding machine you might have a problem, but chips and shavings? No!

Roy.

 

[ivan]

Static can build up on plastic pipes, and some people used to suggest running an earth drain inside the pipe (outisde is no use at all) Even inside is of doubtful effect as pvc is such a good insulator. Soil pipe is fairly commonly used, (although I think HSE would like you to use earthed steel in a commercial workshop). More likely is a spark from a screw or whatever hitting the fan. The HSE website has some info that suggests a dust stream is actually quite difficult to set alight with sparks(thank goodness) but the photos there (worth a look!) of a 6m plume of flame from a small extractor resulting from a "sucessful" ignition promped me to make sure I had a way of turning mine off from any point in the workshop, just in case!

 

[Digit]

Actually the greater risk would probably come from localised concentrations of airborne dust particles IMO. That's not to diminish in any manner the reults of any dust explosion but the risk is probably over stated.
During WW2 an awful lot of cash was expended in attempting to make a coal dust bomb that would go bang to order.

Roy.

 

[Shadowfax]

You need a source of ignition for an explosion too. Whether that is electrical or an open spark or flame without it, and the exact combination of material and oxygen, nothing will happen.
In my opinion it is not worth the worry. Like I said, I have seen dust explosions and I have seen fires started by the smallest of sparks but never in a domestic workshop situation. They have all been large scale.

 

[Digit]

And as I understand it the right mixture of air, dust and particle size is critical. Near enough is not enough.

Roy.

 

[Shadowfax]

the right mixture of air, dust and particle size is critical. Near enough is not enough.

Roy.

Absolutely! Or at least these things must all be present within a limited range between upper and lower levels of flammability depending on what is actually involved in the impending fire or explosion.

In the end if you put enough wet stuff on the red stuff it all goes out - with luck and a lot of skill and daring!!

SF

 

[Digit]

The worst explosion in a domestic situation I have experienced was from the fumes produced by smouldering MDF. The dog apparently turned the ceramic hob on that was protected from impacts by a sheet of MDF.
The resulting explosion tore the roof of the caravan off, blew the windows out and wrecked one side.
The glass from one window travelled about 20 ft.
The dog survived I might add, but it's popularity rating reached an all time low!

Roy.

 

[Shadowfax]

I always tell people that every fire/incident can usually be traced to something stupid that a person did. The dog was not wholly to blame because cooker tops whould only have cooking utensils placed on them. Certainly not pieces of man-made board. Hot MDF...............stone me!

SF

 

[Digit]

The dog was not wholly to blame

That's why the dog still has two of everything it was born with!
But for stupidity check out the nuclear reactor in America where the maintenance man went looking for a problem with a candle, he set fire the wiring insulation, which then spread down conduits etc etc.
You would think state of the art installations could provide something a little safer than a candle!

Roy.

 

[Shadowfax]

Sounds about right! Don't they provide hand lamps for that sort of thing over there?
Kind of confirms my theory, really!

SF

 

[Digit]

The best/worst I ever heard of was during WW2 during the development of self sealing fuel tanks for the Wellington bomber. Having made one they fired bullets into it, Great! So they moved in closer and repeated the experiment. Great! Till one genius was so impressed he stood on top of it let fly with a Bren gun.
The rest is history!

Roy.

 

[9fingers]

The best/worst I ever heard of was during WW2 during the development of self sealing fuel tanks for the Wellington bomber. Having made one they fired bullets into it, Great! So they moved in closer and repeated the experiment. Great! Till one genius was so impressed he stood on top of it let fly with a Bren gun.
The rest is history!

Roy.

Just goes to reinforce the theory of natural selection! :lol: :lol:

 

[Shadowfax]

It only takes one muppet!
I thought the idea of a Bren gun was to allow effective shooting from a short distance. Right on top eh?
Priceless!

SF

 

[ivan]

Just bear in mind, that in none of these amusing anecdotes was the source of ignition being blasted with air travelling at over 100 mph. It's been prooved that spark ingnition in small extractors is extremely unlikely, but is never the less possible. Any ignition melts a hole in the bag and the air blast shoots out a plume of flame about 6m long, together with incandescent sawdust. (see the pictures I mentioned)

It seemd a reasonable compromise to me, to use soil pipe, but make sure I had a way to turn the thing off from anywhere in the workshop. Some people use an across-the-workshop wire rigged up to a pull cord shower switch (mounted on the wall) or a radio/remote operated socket for the extractor (make sure the remote's always in your pocket....)

 

[PaulO]

The dog survived I might add, but it's popularity rating reached an all time low!

Roy.

Surely the dog would receive a medal for destroying a caravan? One less to clutter up the A303 / M5

 

[Digit]

It was a static van, there's 1000s of 'em round here.

Roy.