A question of static...

[Finger Dicer]

This for all those that have some form of DC system in their workshops.

As some of you may already know I was by chance able to procure a DC. I did some checking and its an 850cfm model, with 100mm ducting outlets.

I have obtained free of charge a pile of good condition pvc pipe to use for the basis of a more serious dc system.

Now I had read either here or somewheres else that Static buildup could be a problem.

So the question is: Has anyone experienced this, and to what degree, and did you find a method that was reliable at dissapating the charge?

[fletty]

Some recent (American Woodworking) magazine articles have advised both how to fix the problem AND that it doesn't happen! Logic says that it could be an issue and the 'pro' article suggests wrapping a run of copper wire along and around the tube, joining the lengths of wire together and connecting one end to a suitable earth ... not your power lead!
My Jet dust collecter has the metal sheathed dust filter connected to plastic fittings and hence is not earthed. If I don't connect the earthing alligator clip lead to the metal sheath I can get quite a belt off the static charge.
I've also seen metallic "sticky tape" which could be wrapped around and along the pipes and this should be equally effective.
Sounds like a good bargain and I'm about to replace my fixed lengths of corrugated flexible dust hose with 100mm poly pipe as well,
Fletty

[ozwinner]

There is a thread on here somewhere all about it.

I remember reading that wrapping wire around the outside is useless, for the static to travel from the inside to the outside of the pipe, a voltage of 50,000v is needed to breach the pvc wall, or something in them there figures.
Do a search.

Al :)

[vsquizz]

Oh the ole static build up in the DC...read all about it:

http://www.woodworkforums.ubeaut.com.au/showthread.php?p=133695#post133695

or of course you could save yourself a lot of time and just believe Al. I read all the technical reports for hours and its pretty much a myth.

Cheers

[PAH1]

Oh the ole static build up in the DC...read all about it:

http://www.woodworkforums.ubeaut.com.au/showthread.php?p=133695#post133695

or of course you could save yourself a lot of time and just believe Al. I read all the technical reports for hours and its pretty much a myth.

Cheers

Not really, fine dust is extremely explosive and I mean really explosive- it just doesnt frequently get the right conditions to blow. It is actually a major pain in industrial design eg an icing sugar factory blew up when I was a teenager, also I think it was a cardboard factory in europe as well. This has been reported in the media and I have seen the follow up reports, so I am not talking about urban myth status here. Just about any material when divided fine enough is explosive and less than 10micron dust collected by a DC is plenty fine enough.

Static from DC pipes may be able to generate enough to get it going, but it is unlikely, the cure is simple, cheap, not really that hard to do and would prevent it from happening.

A dust fire is more likely to be caused by heat build up from something else, but a static caused one is still a possibility.

Sorry Al but no voltage is needed at all to move things from the inside to the outside. First principle physics, like charges repel each other, the closer you are the more the repeling effect. To lessen the repeling effect the charges on any object move to the face that has the greatest surface area ie the outside. Putting a wire on the outside is the most effective way to do it. The figures that you quoted are for carrying a current through the material which is a completely different kettle of fish.

[Groggy]

A dust fire is more likely to be caused by heat build up from something else, but a static caused one is still a possibility.
Well, not to put too fine a point on it, I have never seen anyone able to produce a reference to a domestic dust collection system igniting due to static. In fact, I can't recall a light commercial unit either. I have even looked myself a few times with no success.

Most ignite through nails being cut and sparks going down the chute. One I recall sucked the fumes from an open cleaning solvent can through the TS and eventually the motor ignited it, blew the cr*p out of the DC (and probably the operator too).

Still, if you can find a reference....

cheers.

[PAH1]

Most ignite through nails being cut and sparks going down the chute. One I recall sucked the fumes from an open cleaning solvent can through the TS and eventually the motor ignited it, blew the cr*p out of the DC (and probably the operator too).

Still, if you can find a reference....

cheers.

I will look sometime but I doubt that it would be able to be found as the reporting for domestic things is less stringent than commercial. I am really trying to say do not think that it is all bulldust and that it can be completely ignored, dust generated during sanding is flamable and explosive-only under the right conditions. A van de Graf generator can generate voltages in excess of 1million volts simply using static electricity-almost zero current but that is another story. I agree with you about those other incidents as things like that are far more likely to cause problems.

[Groggy]

A few years ago I read through the US reports from Fire reports which are well documented and found none. Also hazard reports from school WW shops (now mostly closed in the US) revealed none in small to mid size systems.

I agree it MAY happen, but to my mind there is more risk the static will zap someone and make them jump into a moving blade (I got zapped on the ear once - not funny).

[rev]

Sounds like a challenge for MYTHBUSTERS!:D

[chrisp]

One reference I read (but cannot remember where) suggested that static in domestic dust collectors using PVC piping is more of a nuisance than a hazard. The reference suggested grounding both inside and outside of the pipe. The method suggested was to place a ground conductor in each length of pipe and attach it to a screw that goes through the pipe wall. When the system (i.e. pipes) are connected together, run an external ground wire on the outside and attach it to each of the screws that connect to the internal grounds.

I cannot remember what type of material was suggested for the internal conductor, but it occurred to me that foil tape would probably work well. With a bit of thought it should be possible to stick foil tape to the inside of the pipe, place a screw through the foil and pipe, and use this as the internal conductor.

Chris

[vsquizz]

Like Al said, this topic has been really really done well before with excellent links to all sorts of experts, investigations reports etc You can read and make up your mind yourself but PVC or not it wont happen unless you intoduce an ignition source to the system and even then its quite diffricult. A number of DC's have burnt after shutdown because of hot stuff in the bag.

I strongly recommend a search before everybody runs out and pulls their ducting apart.

Cheers

[Harry72]

Sounds like a challenge for MYTHBUSTERS!:D Yes thats what I thinks...

[echnidna]

If you have ever seen wood flour ignite you would take every precaution possible.
It goes up like a can of petrol

[Woodlice]

Ever seen a can of petrol "go up"? Ive played soccer with a can of petrol on fire... My understanding is that Petrol needs to vaporise for it to be explosive. Such as the dust in a grain silo (or case in point, the sanding dust in a DC.) Here/read about them exploding all the time.

When a substance is volatile it is heat alone that causes it to explode. Usually a spark or naked flame is not even necessary.

J!

[Harry72]

Just went to the MYTHBUSTERS site and found,
Saw dust, in dust collector, in PVC pipe leading to dust collector from static
Its been mentioned many times.

[numbat]

Here are some links you might find useful.

The Bill Penz site http://billpentz.com/woodworking/cyclone/Ducting.cfm#PVC%20Confusion has a section on static electricity and seems to recommned PVC. Here is a link on earthing (grounding) PVC pipe http://mywebpages.comcast.net/rodec/woodworking/articles/DC_myths.html

More links:

http://www.woodweb.com/knowledge_base/PVC_piping.html
http://www.woodmagazine.com/wood/story.jhtml?storyid=/templatedata/wood/story/data/357.xml&catref=wd18
http://www.airhand.com/dust-control.asp

Here is a link on working with PVC http://billpentz.com/woodworking/pvc.html

Good luck

Cheers

[Eastie]

Taking a stab in the dark here but lets just say there are at least 5,000# commercial cabinet makers, another 5,000# timber yards, and 1000# saw mills in Australia. (I've disregarded the wood working machine shop in each secondary college and the few in Tafe's,..........).

Lets say the professional ones operate the DC 4# hours a day, 5# days a week 50# weeks a year. That's 1000# hours operation each p/a, with a total of 11,000,000# hours total operation in Australia. Keeping it simple, lets say that each workshop has only 1 dust extractor.

In my travels I've seen somewhere between 150 and 250 cabinet shops and a few saw mills, and I'd say that less that 10% have static control systems associated with dust extraction.

So, given these highly accurate figures, only 1,100# dust extraction systems operate with protection. I'd do the sums on the other 9,900# without static dust protection, but the figures would only be accurate for such a short ammount of time given that these things are reportedly exploding into balls of flame every other day of the week..... :rolleyes:

(#actual numbers may vary to the ones I've plucked out of my backside)

[outback]

By reading Easties post it is obvious he has put a lot of time into researching it. I believe everything he says, and conclude my shed will explode into a ball of flames tomorrow.


If we all worry about what is possible we'd be too scared to fart because it's possible our head will cave in. Worry about probability.

It is probable I'm gonna have a beer now.

[ozwinner]

If you have ever seen wood flour ignite you would take every precaution possible.
It goes up like a can of petrol
Flour makes me choke when I sniff it, petrol on the other hand..........:rolleyes:

Al :D

[PAH1]

I was thinking about this thread on the weekend and going back through the reasons arguments etc. Although wood dust is explosive it has to be in the right condition ie oxygen available etc and then you need ignition. Ignition is far more likely from other sources sparks from grinding, bad motor etc. However I think I have come up with an argument that sort of kills the idea.

The dust is on the inside of the piping, any static discharge will be from the outside to another object. The chance of a static discharge reaching the inside of the pipe, to get at the dust in it, is zero. You may be able to ignite the stuff on the outside but not that which is inside, this is for the same reason that I told al you did not need any voltage to move the static from the inside to the outside of the pipe.

[Lucas]

G'day All
i work in the Petroleum industry and work around fuel and fuel vapour every day
As you could imagine static spark is or could be a big problem in my field
We have a serious check list to go through be for starting work

One of the major worries is static
We are made aware of the dangers and causes of static
I can only wear natural fibre clothes
only skin showing is hand and face ( gloves and safety glasses are worn 50% of time) and a bump hat

NO phones, lighters, torches (unless approved cost 100 plus), power tools, petrol engined equipment, laser equipment etc

i have read in this post MYTHBUSTERS something about it
MYTHBUSTERS also said some stuff about moblie phones wont cause a static spark
well its not the phone that does its the movement of the person .... more the manmade fibre clothes that 95% of us wear
and you get a static spark due to this

just like all fuel nozzles are earthed from the spout to the dispenser/ pump to stop static spark cause by the negitively charge static meeting the positively charged static


Most people think it **** but just ask the guy i work with every day where and why he's court fire twice .... once blown out of a turret and the other a fuel can court fire due to being rested on a milk crete and not the ground

i see it like this
how much would enough wire to run inside the PVC pipe cost?
is it worth the risk?

As i have to keep reminding myself every day ..... ONE FLASH AND YOUR ASH

[ozwinner]

All I think about when buying petrol is.

Cash gone in a flash.

Al :D

[vsquizz]

i see it like this
how much would enough wire to run inside the PVC pipe cost?
is it worth the risk?

Just as likely to introduce an ignition source to a flammable environment than it is to remove it (it doesn't exist in the first place) from a practically zero conductive medium in the first place.

Cheers

[soundman]

From my understanding of the issue,
reasons why it wont happen.
1/The amount of energy and the type of discharge inside the duct it too low to produce a spark suitable to ignite wood dust.
2/ The dust generaly found in woodworking dust extraction in small shops is not fine enough to be explosive. ( its mostly big lumps not true dust)
3/ The air fuel ratio is unlikley to be correct to support combustion.
4/ the volume of the duct is unlikely to contain sufficient fuel (even if a correct mixture is achieved and a suitable ignition source is present) to present a "danger".
5/Nobody can produce a single case of a situation wher an explosion has happened in a small to medium scale system & this discussion is all over the place, magazines ,buliten boards.....

Drawing paralels in the petrolium, mining or milling industries just aren't valid because the fuels, circumstances and scale of the problem is completely different.
If any one can point out 1 thats ONE single case of an explosion in a small to medium scale woodworking shop proven to be due to static discharge idniting woodworking dust inside a duct chough it up or stop theorising.

cheers chaps :D