# Dust Collector Combustion from Static... Myth or Reality?



## steliart (Jan 15, 2011)

I have been reading all this time all warnings about static build up in soil pipes ducting of dust collection systems and about grounding and so on.
But I have found no evidence of such a danger no where. On the contrary experts on this subject (not metal ducting companies) say that this is highly unlikely to happen in ducting systems with 8" pipes or smaller.

Static combustion occurred in the big dust collection systems like the farmers cyclones. Personally I believe it's more of a marketing sales myth for use metal ducting instead of the less expensive soil pipes.

From what I red from professionals who are in this line of business, there was never a recorded incident n the US of static dust combustion in 8" or less in ungrounded soil ducting pipes. 
There is a much higher danger for combustion from your workshop's floor dust sweep. If your collector picks up some small metal things like nails etc. those MAY hit the metallic fan and trigger a spark that can result to fire. So ducting has nothing to do with this.

I would like to here what you have to say on this safety subject.

Is this a myth, and who's myth is it?
or
Are there facts suggesting that this did really happen, and so the experts are misleading us?
What did you use or what would you use for dust collection ducting system in your shop, metal or PVC pipes?


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## RobertT (Oct 14, 2010)

Didn't the Myth Busters bust this one. But youll still here a lot of people say better put a ground wire on that pipe.


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## dbhost (Jul 20, 2009)

The fire protection people I have talked to that have researched the issue say it's baseless. You CAN ground your PVC pipe DC ducting if you wish, but there is little benefit. The risks of static discharge combustion in a home workshop dust collection system are so small, that you would have more benefit trying to protect your shop from an engine falling off of a passing jetliner…

There are those, and it's no small number, that swear that you MUST ground your DC ducting, and I am not going to argue against that, mostly because grounding it will give them a good feeling about what they are doing, and it's relatively cheap. But I won't bother unless a reputable expert in the field can show me studies and case examples of this actually being a problem and not urban myth…


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## Johnny_Yuma (Nov 29, 2009)

It's funny how myths can grow legs.

Your dust collection is the least dangerous tool in the shop!

BUT, if it makes you feel better to ground the ducting then go ahead. Just make sure to ground the INSIDE of the ducting!


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## steliart (Jan 15, 2011)

The reason I brought this subject back again is because someone just asked me about static combustion protection from building my mini cyclone dust collection bucket. 
What sales marketing promos do to us… sigh


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## FatherHooligan (Mar 27, 2008)

Hmmm, I'm under a major flight path, how much will I have to beef up the roof trusses to deflect a falling engine LOL!

I was wondering if the Mythbusters had busted this; good to hear they have. I can see where you may want to ground your DC and pipes to avoid an unpleasant shock, but I don't believe you can start a fire in the ducting just from static. I think this was covered some time ago in another thread. Search "grounding dust collection" or something similar and you will see lots of discussion.


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## Knothead62 (Apr 17, 2010)

I have an Oneida DD. I did run a wire from a bolt in the lid, soldered a washer on the wire and let it drag the concrete floor. I think it is more to keep stuff from sticking to the sides of the bucket than a fire prevention. JMHO.


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## Jeff28078 (Aug 27, 2009)

I'd ground it just so I didn't get a static shock every now and then.


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## woodspark (May 8, 2010)

I have 4 " PVC pipes on my DC systems. No grounding. I'm not worried.


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## Gator (May 2, 2008)

Could your insurance company use the fact that you did not have one as a "loop hole" to get out of covering you in the event of a fire by saying you did not take precautions or follow safety procedures when installing your system?


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## steliart (Jan 15, 2011)

Yes this is true.
Sometimes you can get static shock on your TS for example and especially with metal ducting. But not combustion please… Problem easily solved with a piece of any wire grounded externally and not internally, even some metal tape would do the job. Our bicycles build static and it can give you a shock sometimes, that's why we tape the steering, we don't wire the bike to the ground. I remember many years ago cars used to have this thing hanging from the rear touching the ground for protection from… lightning!!! another fine sales marketing example.

Don't know anything about insurance policies in US but with the same logic I have not follow any safety procedure when building my house against meteors.


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## DaveRI (Jan 23, 2011)

Great topic for me as I bought a used dust collection system but, have yet to complete my shop. I was wondering what I had to do to prevent fire and I had even heard explosions from dust duct static discharge and subsequent fires. Thanks guys, for putting that one to rest for me.


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## SCOTSMAN (Aug 1, 2008)

I don't think it's a serious fire risk but you can get a nasty sharp dunt from static which will throw you.So play safe actually plastic soil pipe is worse than metal ducting but this plastic can also be ground.Alistair


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## dkirtley (Mar 11, 2010)

Dust collection? What is this dust collection of which you speak? We would hear more of it!.

Seriously, this just comes from the world of grain elevators and grain mills that have much finer particulates which can go off with just a spark in quite spectacular explosions (as in no survivors).

Whether there are enough small particles in your dust collection to combust is probably not even close. Now, here is a good reason to think about grounding them: The electronics on your power tools may not take kindly to extraneous static charges flowing through them. Most are pretty robust but there are some that are more delicate. Also, getting zapped with a stray static charge can make you flinch at an inopportune time when your attention should be focused elsewhere. Not a good idea around power tools.


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## TopamaxSurvivor (May 2, 2008)

I do not know about Mythbusters, but an aquaintance of mine proved a static charge did not have enough power (heat) to ignite black powder. Black powder will fire my flintlock but I doubt if wood dust will ;-)) You be the judge.


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## HorizontalMike (Jun 3, 2010)

Regardless of which side of this debate you are on, NOW is the time to at least check that you have several (more than ONE) *fire extinguishers* in your shop and that they are properly charged. I personally have three 2lb. units spread out in the shop with one at the entrance door.

While the DC static spark may not be a danger, sparks from cut nails in a TS and sparks from a dis-functioning and over heated router can and do (as evidenced in recent weeks on LJs threads). And these sparks could potentially be sucked into your DC. Just saying…


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## dkirtley (Mar 11, 2010)

CessnaPilotBarry:

You just run a conductor down the inside. The down side of it is that it adds places for chips to hang. Actually strip of a/c ducting foil tape would probably do just fine.


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## steliart (Jan 15, 2011)

I also agree with Mike, whatever you do a fire extiguisher is a MAST.

I am still reading alot of different opinions. 
OK combustion is out of the question but static can still give you a shock i.e. while working on the TS and might made you do a movement that could be very dangerous.
So what is the vertict? Do we ground all the PVC pipes or just the one on the TS and how do we do that to discharge the static.
Thanks


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## Gregn (Mar 26, 2010)

The danger of this happening in the small workshop is very minuscule compared to large shops. The grounding of PVC pipes in my opinion is for personal comfort to aid in preventing static shocks to the user. At least this is why I run a copper wire around my PVC, and I don't run a wire on the inside of the PVC as the purpose is for just personal comfort.


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## dkirtley (Mar 11, 2010)

Yes, the pipe is an insulator. The idea is to have a better conductor available to attract the static charge should the charge build up in the air *near* the pvc. This charge is built up in this case by the friction on the pipe by air and debris. This type of grounding is an insurance policy. My clothes dryer should never have a current flowing through the case, but I still have the outlet grounded. This is the whole idea behind having grounded appliances and tools and lightning protection. In a perfect world, these ground wires should never carry a current. I also really like GFCI breakers and plugs as well even though I have never tripped one. Having worked as a licensed electrician, I have seen enough of the bad things that electricity can do. It is easily the most lethal thing that we deal with on a regular basis. No fear of it here, just a really big healthy respect.


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## dbray45 (Oct 19, 2010)

When I did HVAC I had a job working for an apartment management company. They refinished wood floors using a floor sander. It was understood that the bag would be emptied when going to lunch. One day they did not. I was two building down when the explosion occured. The inspector showed where the building above rose about 2" off the foundation and that it was caused by spontaneous combustion. The only thing that kept the building in place was that the gas had been turned off in the entire building before the sanding was done.

Humidity and sawdust can be an interesting combination. I treat it like it can explode. Those people were lucky, it exploded only a few minutes before they returned. Had they come back earlier, people could have died.


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## TopamaxSurvivor (May 2, 2008)

*How would we ground an insulator?* All insulators have conductive properties at some level although they may be extremely high. I believe the grounding of the PVC would limit its static producing ability and draw off any static created.

*Humidity and sawdust can be an interesting combination. I treat it like it can explode.* That is a good practice to follow. In the fired dept we used to say if it grows it blows!!!!


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## dbray45 (Oct 19, 2010)

It is not that the PCV conducts or not, it more that the air movement and sawdust create the equivelance of something between a Vandegraff generator and a Leyden jar. The rapid movement of the air and sawdust creates the static charge and the PVC's properties help to store the charge until there is enough charge to span the gap. From time to time I take the DC hose off the tool(s) and use it to vacumn the top of the saw or the floor. The resulting charge that I get can give you pretty good jolt in less than a minute.

A small spark may not do much but a spark that can span a few inches may not be as forgiving. I wouldn't be wearing a pace maker. I treat this with a great deal of respect.

What does it cost to be careful????


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## LeeBarker (Aug 6, 2010)

My .02. I have relatively short runs, but some PVC in the mix. Some metal. When I got it all operational, periodically I would hear a SNAP while I was, say, running the edge sander. I got curious. Turned the lights off and replicated. Wow. The arc was down near the floor where sawdust, the finest kind, can accumulate. I immediately ran a wire from a bolt that holds the motor to the concrete (a wooden platform between the two) to a lug on the 55 gallon drum. No more arcs, no more snaps.

Did I have an explosion? No. A fire? No. Could I have? Yes, and it would have been irresponsible of me to know what was happening and not do the fix.

There are plenty of hypes out there which are generally connected to selling something. But when someone like dbray tells the story it has different weight for me.

And for the record, I think floor sweeps are incredibly stupid accessories to a dust collection system, particularly when the debris goes directly through the impeller.

I have fire extinguishers at both doors, checked annually.

Kindly,

Lee


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## dbray45 (Oct 19, 2010)

Thank you for the kind words

It was sobering to see the sliding glass door panel in pieces about 25 yards away from the building. It was one of those "Thank God nobody was hurt events".


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## steliart (Jan 15, 2011)

From what we see here we can say that there is defenetly need for grounding but for a different equal serious reason. 
It seems to me now that the hole subject was badly presented and with the wrong reason of why we should ground. For me it's clear now why it was missrepresented.

Anyway the posibility is there and is real… so grounding is the second MAST together with extiguisher/s in easy access points.


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## TheDane (May 15, 2008)

Does anybody use a computer in their shop? If you do, grounding your dust collection system just makes sense.

I don't think the fire risk is very high with an ungrounded system, but I have been in the electronics and computer industries since 1966, and I know what ESD (electrostatic discharge) can do to solid state electronics.

Integrated circuits are made from semiconductor materials (e.g. silicon) and insulating materials (e.g. silicon dioxide). These materials can suffer permanent damage when subjected to high voltages that result from ESD.

-Gerry


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## dbray45 (Oct 19, 2010)

At that point, all is gone-shall we say "toast" to the old


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## TheDane (May 15, 2008)

Yup … one good spark, and your data, your hard drive, your mother board, etc. could be gone forever!

-Gerry


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## steliart (Jan 15, 2011)

GROUND - GROUND - GROUND


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## Bertha (Jan 10, 2011)

I grounded mine because it cost less than $5 & made me feel 5% better.


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## steliart (Jan 15, 2011)

Who ever wants can read an interesting article in this link

http://home.comcast.net/~rodec/woodworking/articles/DC_myths.html#intro theory theory


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## dbray45 (Oct 19, 2010)

As I stated earlier, the event that I was a part of was deemed to be from spontaneous combustion, not electrostatic discharge - two very different events. That being said, there are different types and qualities of sawdust:

1. ) Chips and particulates from planers, jointers, table saws and the like - these are course particules that if a constant flame were introducted would generate a really good fire very rapidly

2. ) Sanding raw wood - material is much finer and as a result has the potential of getting explosive under the propoer conditions depending upon humidity, MC of the wood, etc…

3. ) Sanding various finishes new and especially old finishes - THIS IS NOT WOOD, many finishes, especially old finishes are not fire safe in any sense of the the word. Creating a fine dust can and could be explosive, making copper into a very fine dust can be extremely explosive.

4.) No sawdust or very little - Someone is finishing a piece with laquer or shellac and the dust collector is on and a static discharge occurs and there is fine dust in the air

Unless you have a seperate DC for #s 2 and 3, you are introducing a variable that all these studies and nythbusters do not incorporate into the equation(s). As science projects I made spark gaps and Tesla coils (I was a strange kid), and it isn't hard to light a piece of paper on fire - it may take a couple of times but it will ignite. When you use flash paper - the same characteristics as a fine dust of a combination of wood, varnish, shellac, and or laquer; the result is a whole lot different.

I have not seen any studies with all of the variables that I state because there are too many to make a clean conclusion nor does it matter to me one way or another. One of the main reasons that I participate in these discussions is that I look at some things a little differently, I don't take things at face value. If there are circumstances that could pose a serious threat to someone because they are not aware of the potential situation in front of them, and I can help them not to get hurt, I would like the opportunity to do so. Everyone out there will do what they want and need to do - have no problem with that - but if we are experts at what we do and others are asking us questions, lets be real - there could be a real problem. It is in my oppinion better to ground than not.


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## steliart (Jan 15, 2011)

This article is in one of the books I have - The New Best of Fine Woodworking - Small Woodworking Shops.
I present the article here as it is in the book, you can also find this online with its title as a PDF file in this Link.

http://www.sacramentoareawoodworkers.com/Articles/DustCollectionandPVCPipeDangersDebunked.pdf

*The Conclusions are YOURS*

*PVC PIPE DANGERS DEBUNKED*
by Rod Cole

Home-shop dust-collection systems have become increasingly popular, but their safety has been hotly
debated. The primary issue is whether PVC pipe is safe for use as ductwork. Many claim that sparks in
PVC pipe due to static electricity may ignite the dust cloud in the pipe.
The specter of a giant fireball consuming a shop and home is repeatedly raised. Others claim you can
ground PVC, thus ensuring its safety.
Two years ago I had to decide for myself: PVC or metal ducts for my basement shop. Being both an
avid woodworker and a scientist, I made a concerted effort to understand the issues. Fortunately, I have
the resources of the library at the Massachusetts Institute of Technology (MIT) and a professor just
down the hall who's an expert in the physics of lightning.
I studied static discharge from insulators, as well as the more general topic of dust ignition. I found that
it's extremely unlikely for a home-shop-sized system to have a dust cloud explosion. Commercial-sized
systems have had dust-cloud explosions, but different phenomena come into play in larger systems, and
4-in.-dia. PVC is too small for use in such systems, where the airflow is much greater than in a home
shop.

*Sparks are unlikely in 4-in.-dia. PVC pipe*

In my research I turned to the Journal of Electrostatics, a publication that covers the effects and
interactions of static electricity, particularly in commercial applications. This journal has published a
number of studies on the combustibility of dust clouds by electrostatic sparks. The researchers were
able to determine some of the conditions necessary to create sparks and ignite a dust cloud.
Sparks can be caused by a variety of conditions-one of which is static electricity. However, sparks are
unlikely inside a standard 4-in.-dia. PVC pipe that would be used in a home shop, and more importantly,
any such sparks are extremely unlikely to be strong enough to cause an ignition. I can't say it is truly
impossible, but it is very close to impossible, and I do not know of a single instance. The difference between metal and PVC is that one is a conductor (metal) and the other is an insulator (PVC). A
conductor allows electrical charges to flow freely. If any excess charge is not given a path to ground, it
can arc, creating a spark that in certain conditions can ignite a flammable substance such as dust.
Grounding provides a path for this excess charge to flow harmlessly to the earth, which is why dust collection
systems in all commercial shops are required by code to be grounded. However, an insulator
is a very poor conductor of electricity. While it's possible to get a static shock from the outside of a PVC
pipe, it is highly unlikely for sparks to occur inside.

*Dust collectors with 3 hp or less pose little danger*

I published my findings on my web site. Rob Witter, a representative at Oneida Air Systems Inc., which
makes dust-collection systems, said he largely agreed with my research. "We as a company have been
trying to trim away at these misunderstandings for years," he said. He added that plastic pipe will
"probably never cause a problem" in a home shop. Finally, he pointed out that the National Fire
Protection Association (NFPA) puts no regulations on dust-collection systems of 1,500 cu. ft. per minute
(cfm) or less.
All of this discussion applies to home-shop-scale systems. Larger systems, complete with ducts and
filters that move more than 1,500 cfm, require at least 3 hp and are not found in most home shops.
Larger systems need larger ducts, and with that you have to begin to worry about more complicated
forms of static sparks.

*The real hazards*

In a home shop, the dust-collection fire hazards you need to worry about are not in the ductwork but in
the collection bag or bin itself. A fire may be caused by a spark, which can occur when a piece of metal
is sucked into the ductwork and strikes another piece of metal, or by embers from a pinched blade. The
spark or ember settles into the dust pile to smolder, erupting into a full-blown fire hours later, often after
the shop has been shut down and no one is there to respond. For this reason, my most important
recommendation is to empty the collected dust every day or at least keep it in a closed metal container.
As you can see from the photo of my shop, I ended up plumbing it using 4-in.-dia. PVC pipes and did
not ground them. I feel perfectly safe using them this way.

*Real small-shops fire hazards*

*1.* Buildup of dust in machines. Hot metal that finds its way to the dust that collects at the base of a saw could start a fire there or be sucked up into the dust collection system.

*2.* Cutting a nail. Not only does this damage a blade, but it can also send a very hot piece of metal into your saw cabinet.

*3.* Metal in the dust pile. When cleaning shop, it's easy to sweep up screws, washers and nails. Dust from the floor should be sifted by hand, before it's introduced into a dust-collection system.

*4.* Sparks in the bag. Metal sucked into the dust collector's fan blade may cause a spark and ignite sawdust in the filter bag.


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## jusfine (May 22, 2010)

Installled my DC system (3 HP Oneida) this past summer, did not ground it.
No static electricity on any of the ducts (mine are all run under the floor - shop is in the loft of the barn).

Engineer who designed the runs said it was not an issue.


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## Scsmith42 (Jan 26, 2011)

I did some research on this topic when I set up my current shop. What I learned was this.

In order to have an explosion in a dust colletion system, three things have to be present.

1 - particles small enough to spontaneously combust. About the only thing in a woodshop would be the wide belt sander.
2 - a relative humidity level conducive to creating the static required.
3 - a high enough flow velocity in the ductwork to create the amount of static required. The number that I was told was 1500 feet per minute.

Most home shops will not meet these three criteria.


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## shipwright (Sep 27, 2010)

I can't believe I haven't seen this link here yet: http://home.comcast.net/~rodec/woodworking/articles/DC_myths.html When I was building my new shop I asked myself the same question, until I read this. It's the best article I've seen on the topic and has come up on LJ's forums before.

My system is large and all PVC (underfloor where I don't get shocks from it). I have no problems and I'm not worried.


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## dbray45 (Oct 19, 2010)

Read the material, know the theories, electric etc…

Here is the disconnect - the articles are only dealing with wood dust and not other sanded materials (finishes, etc…) and the potential of fumes. The articles only discusses "PVC only" ducted environments versus metal environments.

I have a hybrid of metal and plastic where I must cross the "plastic bridge" that in essence creates a capacitor within the sections and the electrostatic discharge can be significant.

I agree that if you are running an all PVC installation, you should not have problems - but - if you have a combination of metal, plastic, and/or wire wrapped plastic, the metal components should be grounded to each other, the tools, the DC, and ground.

If you are running a 5' section of PVC, you should not generate an arch with enough heat to create ignition, 4-8" could be very different and if there are fumes or other particulates involved, the concentration of dust to air mixtures may not be the same.


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## LeeBarker (Aug 6, 2010)

AHA!

My system is most certainly a little of this and a little of that, metal and PVC. It has evolved over years.

Thank you David, again! This explains why I was getting those very disturbing arcs. I didn't feel erudite enough to argue with all the cut-and-dried you-don't-need-to-ground final statements, yet I knew that, without the grounding I installed, I had significant cause for a very serious event.

Thank you.

I hope your words can be widely distributed on this subject. I suspect there are many systems that are a daisy chain of available materials that could benefit from some simple grounding.

Kindly,

Lee


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## northwoodsman (Feb 22, 2008)

As a couple people have stated, one of the most liklely causes for a fire in your DC or DC system is cutting through a scew, nail or staple and causing a spark to ignite the fine dust or even large particles. If you have a steel impeller in your DC system, picking up a nail, screw or staple off of the floor could also cause a fire. Chances are that it will smolder for several hours before flames occur. This is one of the reasons that I like to vacuum my shop in the morning before I begin for the day instead of at night before I finish. When I finish for the day I sweep, put away tools, and organize and in the morning I suck up the sawdust.


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## HorizontalMike (Jun 3, 2010)

northwoodsman and actually everyone,...

Do you leave all the chips/dust in the cabinet of your TS?,...your BS?,... your router?, etc. all UNTIL MORNING? Or do you gather it all up, bag it, and place it outside away from other combustibles the evening before? I guess we all should be thinking about having a routine to minimize the fire hazards in our shops before/after AND during use.


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## dbray45 (Oct 19, 2010)

Lee - thank you for the kind words 
The problems arise because we build our environments as we can afford them or grow. There are not too many people that go and install a whole new system with everything by the numbers. As we piece things along, the problems rarely show themselves for a very long time and even then, when something happens are the correct reasons identified? Theories are wonderful and explain specific situations, components, events, etc. I do not work with maple only and do not only use my tablesaw, I use a number of different woods, tools, and finishes. I do not have a finishing room and although I try not to turn on the dust collector after I finish something, if it is the first coat I can (it is the seal coat any way), it happens. If the finish is shellac or laquer, any spark scares the cr*P out of me. And yes, I do plug my RO sander into the DC.

Mike - As a rule, I empty my DC bag when it gets 3/4 full - UNLESS I hit a nail or something metalic hits the impeller. If this happens, everything stops, the bag is taken outside and the contents are put into a plastic bag OUTSIDE. It is then sealed in the far corner of my yard until trash day - just in case.

My TS is a hybrid, the jointer is a table top version and its chips fall into the trash can.

Explaining to my wife why our house burned to the ground is not an option that I welcome.


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## AaronK (Nov 30, 2008)

just using a shop vac sometimes i get a nasty static electricity shock every few minutes. I'm thinking of using a grounding wire around the hose.


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## dbray45 (Oct 19, 2010)

I would call the manufacturer an see what they have to say. You could be missing something that should be there. Tell them you have a family member that has a pace maker and you are worried that this could be a problem if they were to use it. Woodworking is good therapy They should send you something to correct it.


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## dbray45 (Oct 19, 2010)

Paul - you are an exception to many things, your system I would expect, IS built by the numbers. Probably 30% better than it needs to be. Mine is pieced together because I have no room, everything is very mobile and flexible.


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## HorizontalMike (Jun 3, 2010)

dbray45,
I also started emptying the DC and TS cabinet BEFORE using my Sanding Disc on the TS. Boy! You shoulda' seen the first time I mounted that thing on the TS! The disc was slightly over-sized and rubbing against my riving knife/splitter holder and throwing sparks like a motorized grinder! Had to grind down the outside perimeter of the disc in place(using an old broken metal file) in order to eventually stop the spray of sparks. Needless to say I DID NOT run the DC at the time!

After following the threads about the TS and router fires in recent weeks, I went out and purchased three 2lb extinguishers for the shop. My thoughts on this is that it would cost less to afford and replace a 2lb'r than a larger 5lb'r, that and the 2lb'rs were on sale at Ace for just $16 apiece. They were even the gauged/rechargeable type.


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## dbray45 (Oct 19, 2010)

My recommendation, sanding discs can do a lot. If you have a closed cabinet saw and you have the space, are going to use this option a lot, go get a $120.00 Craftsman TS or something like it, that has an open bottom. This makes a really nice appliance where you can monitor what goes on. If you find a nail, piece of barbed wire, or piece of maple syrup spigot (yes I have gotten this) you have a way to monitor and deal with the sparks.

If you cannot put in a dedicated saw and you can put a metal trash can as a pre-stage chip dust collector, do this and empty it before and after you use the sander on the TS.

Dust collectors are great but it doesn't take a lot for the rules to change.

If you ever have a fire in a wood shop, use the fire extinguishers to get out, let the fire dept put it out. If a fire department is too far away or you live in the fringe areas, put in a sprinker system, then use the extinguishers to get out and let the sprinklers do their job. I was a nozzleman on my ship in the Navy during fire events, and even with the proper equipment, this kind of fire is a whole lot more than serious. Any shop can be replaced, people cannot.

The reason I take the bag outside to empty it if I hit something nmetalic? If there is an active spark in the bag, if undisturbed may smolder. Once you shake things up to empty the bag, you add air and dust to the equation, that can react quickly. Doing this outside makes it impossible for it to react in your shop.


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## Pop (Aug 6, 2007)

This discussion is sorta like the Sawstop debate. We all have our ideas and from them we will never part. I did a presentation several years ago for my woodworking club on shop design & construction. I researched this. Here's what I came up with. Meth Busters couldn't get it to go boom. Flour mills DO go boom. 4 inch pipe is not big enough to go boom. There is a paper from a guy at MIT who really researched this with the help of another MIT professor who had a PHD in static electricity. They said "1 in a million". I talked with a dust collector engineer who said "OK! What if you just happen to be the "1" in the million? My solution. Braided copper wire is cheap. I know it's probably not going to go boom, but why take a chance. I'm going to ground mind. Another hint. If static collects it will be on the "outside" of the plastic pipe not on the inside. It's created on the inside but dissipates to the outside. Your ground should be looped around the outside of your pipe & grounded to both your machines and dust collector.

PS: Shipwright has the address of my MIT guy. http://home.comcast.net/~rodec/woodworking/articles/DC_myths.html

Pop


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## dbray45 (Oct 19, 2010)

Electricity flows on the outside of the surface, that is to say, does not penetrate the surface - say, the inside of a wire.

The study in the link is an all plastic versus an all metal ducted environment. This being the case, I agree with the study.

It would be interesting to ask the MIT folks or mythbusters about a hybrid environment where there is a mix of plastic and metal AND adding a variety of sanded finishes into the mix. The problems in doing this, if their results change, there could easily be a change in building and fire codes and a serious change in insurance rates. It could be one of those, "Be careful what you ask for," situations. This is why I would recommend to anyone that if you have any metal elements, ground them to the quipment and to the DC. What is it going to hurt? Since plastic does not conduct electricity but will create the effect as a capacitor if there are metal components salted into the system and hold a charge, adding a strip of metalic tape to the outside of the plastic connecting the metal parts might reduce the potental of a good shock if not fire.

If you have a pacemaker, I would look into making sure that your dust collector and equipment are properly grounded to a common ground and to have either all plastic or an all metal duct work just from the potential of static discharge.

It really isn't whether anyone is exactly right or wrong, there are so many variables that there is no definitive answer, it is being safe, don't you agree?


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## Pop (Aug 6, 2007)

Yes dbray45. I feel it's much better to err on the side of caution.

Pop


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