Anybody buy from Leichtung Workshops?

[K.-Benoit Evans]

"...I have read more than a dozen research papers on this topic recently. The thing I am most struck by is how hard these guys have to work to get dust explosions in the lab. It is not hard to get ignition if one makes a very carefully controlled, nonmoving cloud with just the right dust mix, and introduces a spark from a very carefully designed sparking mechanism. But no one seems to be able in lab sized experiments to get electrostatic discharge ignition of even very highly combustible dusts in remotely realistic situations, and they do try. Is is possible? I presume so, but it is extremely difficult."

"...there has never, to my knowledge, been a documented case of an explosion problem with PVC in the home shop or a case of an explosion in a filter bag in a home shop. A friend of mine who is a professional cabinet maker asked his fire inspector what he thought about the hazard of PVC ducts, and the fire inspector said he was far more concerned about people keeping lighter fluid under the kitchen sink. The fire inspector was intrigued and checked whatever registry of fire information he had available and came back and said he could not find one reference to a problem in a small shop with PVC ducts."

"In all the years that this has been debated on the Web, not one verifiable report has surfaced of an exploding home shop dust collector. I know full well that anecdotal evidence does not make good science, and just because I don't know of a problem caused by an electrical discharge in a home shop DC does not make it impossible. But, such evidence is certainly food for thought, and at least shows that such events, if they exist at all, are very rare."

Near the end of the report, there is an explanation of several common MYTHS (untrue, unfounded beliefs) about home workshop dust collection. That list (without the accompanying explanations) is as follows:

Myths--the following assertions are NOT true

1. PVC ducts are dangerous. FALSE

1. You can ground PVC. FALSE

2. The only thing of concern in a dust collector are the ducts. FALSE

1. The external ground wire works by reducing the static on the outside of the PVC. FALSE

2. The external wire must be bare. FALSE

1. Grounded screws can not help as they are too far apart. FALSE

2. Grounding works by removing charge from the dust. FALSE

1. Metal ducts keep the dust from charging. FALSE

2. Any spark will ignite the right dust mixture. FALSE

1. Grounding PVC works by removing charge at a point, and since charge must be uniformly distributed, it therefore removes charge everywhere. FALSE

2. Getting a discharge outside the ducts, say to your finger, means you also have discharges inside the ducts. FALSE The full report can be found at:

[Michael Baglio]

Hmm... I think I fukd up. Do I have to replace all the monofilament fishing line? That'll take longer than a winter in Luigiland.

How 'bout if I shoot 16-gauge brads through the fishing line into the PVC? That should improve the connectical disjointing of the charge buoyancy, right?

Michael

[Scott Cramer]

On 09 Dec 2003, Michael Baglio

What are you, a child? If you use differentially valented materials, i.e. nylon filament and brads, on humid days the moisture in the air will set up a battery-like effect, and the ions in the air will rust the top of your table saw down to the trunnions before you can grab the WD-40.

If I were you, I'd bring in a Feng-Shui master to make sure your ductwork isn't constricting the flow of positive energy through your personal space. You might want to get your chakras aligned as well, just to be on the safe side.

[Bob N]

Mike, as a benefit the brads should lower the impedance so you won't need to buy a preamp.

Bob

[B a r r y B u r k e J r .]

I've heard genuine wool thread, NOT cotton, will also work well. Don't forget to grease the connections with non-petroleum lube. I hear KY works well at a fair price. You could probably steal a tube when the doctor is out of the room during your next physical.

Barry

[George]

What makes you say that? It refers to a rash of explosions and fires caused by various spark sources throughout Canada and it does name static discharge as a source of ignition. If your concern is that sparking usually occurs to ground, grounding multiple points on a non-conductive (i.e., charge-holding) material would minimize its ability to hold a charge at all.

So, I guess you're saying that since no SPECIFIC idiot at a SPECIFIC address is named that one might as well "run with scissors" (I've never seen a documented case of THAT either...my assumption is that most of the Darwin Awards for that were already handed out about two generations ago)??? If you've ever seen a dust explosion of any sort, it results in a fireball and if caused by static discharge there would be no ignition source to be found (unlike embers, torches, cigarettes, etc)...as long as you don't live near me or my relatives or friends, do as you wish with the information and I truly DO wish you the best of luck.

[George]

Do you know who did the study and when??? You say it was published a "couple of year ago"...any idea of when the study occurred?

My experience was related to high static charges on G10, a printed circuit board material. Not too many raw materials are dangerous. THAT usually depends on one's design.

Since PVC doesn't conduct electricity, you cannot ground PVC. Since a static charge does not flow (definition of static), the distance from ground potential is what is important...I'd bond a wire to the PVC in multiple locations to ground to hold the static charge to a very low voltage. It is true that you would not eliminate static charge altogether by doing something like this.

Agreed. One should look at the entire system. I would hope that the manufacturers have already taken due care to make certain that the collector itself cannot become a source of ignition.

Depends on implementation. See #2 above.

Agreed.

Agreed...that was my suggestion

Agreed. We are only talking about a charge on the PVC. I do not know if the dust can even hold a charge (I tend to doubt it, however).

See #7 above. If the dust can charge, it'd be from the airflow and not the PVC. But, also, if the dust can charge, no individual particle could hold a charge sufficient to ignite the sawdust.

I have NO knowledge of what kind of spark is required for various dust mixtures.

Agreed. This is a rather weird idea for something that is non-conductive.

Agreed in principle, but due to the thickness of ductwork it is likely to be able to conduct through the thickness of the duct meaning that what is inside could experience sparking as well.

[George]

So, your system uses PVC ducts and you ran internal ground wires (which you have since removed)? I could see where that would cause you some grief. In the manufacture of electronic products, ESD protection is provided with much higher resistances. Many of the 3M products to reduce damage due to static use about 1,000,000 ohms to ground (or even 10,000,000 ohms). I've never put an ohmmeter to a piece of PVC (plus I'm sure it would vary by manufacturer as any impurities would change the resistance) but I'd investigate putting the ground wire on the outside...worst case you could even use small self-tapping screws to bring a ground from the outside to the inside and I wouldn't think that would cause the dust collection system to clog.

In spite of how the tone of our exchange may have sounded to you, I fall in the "better safe than sorry" camp...if you re-read my original posting on this, I merely stated that it was possible based on several factors. I don't think that it is highly likely for very many home woodworkers because most won't generate the concentration of dust nor the fineness.

[nospam]

the point is that despite lots of chicken little running around, there are no documented cases of home shop dust collection systems exploding from static electricity generated by plastic pipes. none. zip. zilch.

plenty of industrial woodshop and flour mill and so on dust collection explosions... mostly caused by things other than static from plastic pipes. IIRC, plastic pipes aren't allowed in industry for that very reason. they actually move enough dust with enough air for hot static discharge to be possible. they also have 24" pipe and 40 HP blowers sucking sawdust from dozens to hundreds of machines simultaneously.

my measly 2HP dust collector and 40 feet of 4" plastic pipe isn't gonna blow. nope. Bridger

[nospam]

here's the updated link.

[George]

You obviously, have not played with this equipment! When I was in high school, I did connect a Van de Graff generator to a doorknob (teenage pranks) and after seeing that I could zap an unsuspecting victim with about a 7" "lightning bolt" (ESD) decided to add licopodium powder to the prank. It IS impressive and it DOES ignite and is reminiscent of flash powder of years gone by. For those unfamiliar with licopodium powder, it is about the same fineness as flour and would represent a fine dust explosion or ignition.

As for permanent harm, a Van de Graff generator doesn't generate sufficient static charge for that, though lightning does.

[Jeff Gorman]

"George" wrote

: Like I said in my previous post, an ESD-caused sawdust fire or explosion : would be most likely with a high concentration of FINE (very fine) sawdust, : like from sanding, rather than what your table saw or planer generates.

Edited from a 1977 posting to rec.ww. I fear that I no longer have details of the actual source.

'.........................................................an OSHA required data sheet..... lists the safety requirements of hazardous material. It states therein that the Least Explosion Level (LEL) for wood dust is 40 grams per cubic meter of air.

If there are 453.5 grams in a pound and 35.31 cubic feet in a cubic meter then this calculates out to 0.0025 pounds per cubuc foot of air.

If you have a typical 1-1/2 horsepower dust collection unit and nothing else connected to it you can probably draw 1100 cfm according to the manufacturers rating. So, at 0.0025 pounds per cubic foot of air, you are going to need to sand off 2.75 pounds of wood per minute to reach the minimum dust explosion level in your ductwork.

How does that relate to in the real world? The book says red oak has a density of 43 to 63 pounds per cubic foot. If we use 53 pounds as the average and divide 2.75 pounds by 53 pounds per cubic foot we get 0.052 cubic feet of oak to reach LEL in our ductwork. If we were sanding a red oak 4" x 4" on the sander, we would have to sand away .468 feet of 4x4 per minute or a little over 5-1/2 inches if 4x4 oak per minute to reach LEL. Unless you have the Tim Allen memorial sander in your shop, I don't think that a home size workshop can produce enough dust to get to the minimum explosive level.

Now, When you start moving thousands of pounds per minute of wood dust through a dust collection system, you can relate it to a grain elevator.'

Jeff G

-- Jeff Gorman, West Yorkshire, UK Email address is username@ISP username is amgron ISP is clara.co.uk Website

[B a r r y B u r k e J r .]

"Recently, firefighters were trying to remove smouldering sawdust from the hopper of a dust collector when an explosion blew burning materials out of the equipment. Six firefighters and eight workers suffered serious burns and cuts. The explosion happened 36 minutes after the fire apparatus arrived."

Read the first sentence.

Barry

[B a r r y B u r k e J r .]

I work in the electronics biz (telco), and we do all kinds of things to contain ESD. For an entirely different reason. Reasons for that resistance include SLOWLY discharging the static electricity.

So do I, which is why I originally installed ground wires. When I replumbed after a shop rearrange, I removed the existing internal wires, and thought about driving screws in from the outside. After using it ungrounded for a while, I saw no reason to bother to ground it.

Barry

[George]

Not to mention worker safety (in case of other fault conditions), otherwise the assembly labor would likely be barefoot on copper ground plates to save $3 ICs... For production, one of the nicer solutions is ionizers.

[Renata]

[John Sellers]

need to buy a preamp.

I knew there were pickers here.

John Sellers

[Michael Baglio]

Oh, hell yes. Bob and I met on rec.music.makers.guitar.acoustic. Great group of folks, have annual get togethers, good newsgroup to check out.

Michael

[mscottgruber]

I have ordered tools from for my husband and he was happy with them.

[Trenbidia]

I did - a long time ago. The company has been sold to Woodworkers Supply in Casper. I've also ordered from them, but again, it was a long time ago. Used to stop and browse their store any time we drove through Casper.

So any old reviews you see about Leichtung no longer apply. But I never had any problems with Woodworkers Supply. But it may have changed hands as well - I don't know.