Grounding DC

[Marc Prudhomme]

I have been reading conflicting reports about grounding your hoses of your DC units because of the possibility of static shock igniting your wood dust.Has this ever happened to anyone?I have a Delta 1.5 HP,1200 cfm DC and the 4" hose is not grounded.Should I,and what is the best way to do this.Pics would be nice if anyone has them.
Marc

[Greg Funk]

I have never heard of a documented case of static electricity causing a fire or explosion in a home based dust collection system.

[Marc Prudhomme]

Uhhhhhhhhhhh Explosion??? Can that happen?
I have never heard of a documented case of static electricity causing a fire or explosion in a home based dust collection system.

[Rob Bodenschatz]

Uhhhhhhhhhhh Explosion??? Can that happen?

See? Now you scared him. Nice work.

[Greg Heppeard]

I've seen the video of that, but I must admit, I've never even seen a fire caused by it. My insurance company didn't even know of it when I mentioned it to them. I'm begining to think the video must have been done with a dust collector that had been running for a long time with a big hole in the bag to completely fill the room with dust. If that were the case, I don't think you could breathe in there anyway. Just MHO.

[Chris Padilla]

Forget about grounding it. Even if you do attempt to ground it, it isn't very easy to do a good job with it. Will you get shocked and feel the build up? Yes, you probably will. Is it enough to ignite wood dust? Nothing I've seen convinces me it will.

[Jon Bonham]

The guy at the store tried to scare me into buying a $20 grounding kit today. I told him about the "Shark Bite Principle." This is the principle I use when I examine risk. I don't know anybody that's been bitten by a shark, nor do I know anybody that knows anybody that's been bitten by a shark. Now, I have heard about it happening and seen it on TV. So, if something is less common than a shark bite, it's a non factor.

[Lee Koepke]

Forget about grounding it. Even if you do attempt to ground it, it isn't very easy to do a good job with it. Will you get shocked and feel the build up? Yes, you probably will. Is it enough to ignite wood dust? Nothing I've seen convinces me it will.
and in addition, you would have to make sure all of your connections were continuous and no breaks in your fittings, etc .... I would think its pretty involved to make sure. I dunno, just thinking outloud.

[chris yount]

I work at a company that grinds rubber,among other things.The dust collectors are huge as sometimes 300-500 pounds of overstock maybe removed from one piece.There have been 3-4 fires in the dc in my time there, almost all caused by sparks from metal being ground mixing with the dust or extreme heat from the grinder wheel when trying to remove too much stock at once.I do not think the dust generated by small shop sized equipment would be enough to ignite or enough heat build up could be generated either.

[Jim Becker]

The static in a small home woodworking shop is a nuisance to your person, but not a danger for any kind of explosion. As far as I know, there are zero documented cased of that ever happening. So grounding is a personal decision to avoid getting zapped when you reach out and fondle your duct work...

[Greg Funk]

Uhhhhhhhhhhh Explosion??? Can that happen?
It hasn't happened in home systems. Not enough dust or sparks are too small. Sometimes happens in grain elevators with lots of dust or in commercial operations.

[Tim Marks]

If it was possible, then you think a clearvue cyclone would have blown up by now. Not gonna happen.

[Chuck Lenz]

Theres been so much talk and debate over the issue that instead of listening to it over and over and worrying about it, I bought some 4" steel flex hose and built a sheet metal port for the tablesaw. It's all metal now, no grounding wires. http://i25.photobucket.com/albums/c89/Woodchuck_/100_0059_2-1.jpg

[M Toupin]

http://mywebpages.comcast.net/rodec/woodworking/articles/DC_myths.html

Mike

[Greg Just]

This is a topic for Myth Busters! I bought a grounding kit and never installed it.

[Steve Clardy]

None of my flex or pvc is grounded

[Jason Roehl]

This is a topic for Myth Busters! I bought a grounding kit and never installed it.

They already did an episode on it. They couldn't make it happen.

Just like one of my other pet peeves...gas stations banning cell phones out of ignorance.

[Darrin Vanden Bosch]

Just because noone seems to have knowledge of it happening to anyone they know doesn't mean it can't happen.Who here smokes while filling up their car at the gas pump, do they know anyone that has blown up a gas station? For $10 or $20 why take a chance, lets face it, truth is stanger than fiction.

Darrin

[Jason Roehl]

The point is, that the Mythbusters crew TRIED to make it happen, even creating optimal fuel-air ratios and then using the cellphone (remotely, of course), and they couldn't make it happen. Cigarettes are different--those have open hot embers capable of igniting gas vapors...

[Greg Cole]

Guess I am the only one who will say yes so far, I grounded my ducting. Each machine is grounded along with each run of duct work including a self tapping screw (with ground wire attached to it) in the wyes & tees to act as an electrode. $10 bucks and an hour was worth it......
Wanna know the real reasons? I've got 2 decent ones.... my little dude (he's 6) & dog. They both are in the shop alot with me and both used to get shocked occasionally. It's a distraction to have a kid beller or a dog yipe like it got run over when you are in the shop. I cut off the tip of my pinky all by very self, wouldn't want to have had that happen b/c my little dude yelled from getting a little zap..... those kind of disctractions can be bad news.

Cheers,
Greg

[Sam Yerardi]

As an electrical engineer, I tried to find the statistics on home dust explosions, etc. So far I haven't found any. However, as one can assume, that doesn't mean there aren't any or it hasn't happened. The fact remains that dust and an ignition source is a very big issue for industry. Myth Busters was mentioned and it is one of my favorite shows. Even if they couldn't make it happen, the concept of an explosion from dust exposed to an iginition source such as a static spark is well documented and a very real danger. As far as for the home, I'm inclined to believe that it is another danger in your shop just as a table saw would be. The likelihood of an explosion I believe is extremely rare, and a lot of the efforts taken electrically to 'prevent' it from happening most of the time aren't as effective as one would think. The NFPA essentially recommends ducting that is electrically conductive inside as well as outside. Grounding and bonding on the outside of ducts helps protect the user from static sparks upon touching, etc. but does nothing for what's going on inside the duct.

My personal feelings are (and I have absolutely no data to back this up) the reason we don't hear a lot about home shop explosions due to dust is that it is extremely rare if non-existent. It is an established fact that the position of a spark in relation to where the dust is also has bearing which may also help explain why we don't see it happening enough to hear about it. Humidity, etc. also have an effect as well. I have no plans for extra grounding protection in my shop. Having said that, I would research any ideas that I was going to implement to make sure I'm not making a rare situation more likely to happen. For example, if I were to create a network of PVC piping throughout my shop and I was creating a lot of dust, I would at least consider what measures I could take.

[Lee Schierer]

I put in 4" pvc duct work in my shop for the DC. In the first week or so that it was there I noticed some sawdust sticking to the outside of the pipe and the hair on your arm would stand up if you put your arm near the pipes. After that the static charge gradually went away, the dust fell off the outside of the pipe. I've never been zapped by my DC and I have my saw, router table and planer all connected. I also regularly sweep sawdust off the floor using a plastic hose with no static.

When I redid the system last year, none of the pipes seemed to have retained any charge. Just last week my granddaughter swept the floor and any other sawdust she could find and reach with the hose in the entire shop and never once got zapped.

[Ken Fitzgerald]

I've read a lot about this. I don't know that there is any material documenting a case where static electricity started a fire in any HOBBIEST or HOME shop DC. A smoldering fire cause by a metal spark getting into the system...maybe but not caused by static electricity

Static electricity......relative humidity has a significant effect on it. Wearing everyday work clothes.....I get shocked regularly.....year round getting in and out of my van....Getting shocked by static caused by air traveling through the pipes in your DC is going to be a factor of your local relative humidity. I bought metal pipe. Why?.....our average moisture is 12" annually. Last year we only got a little over 7".....my dryer climate is going to make it more likely to have it occur...getting shocked that is. I don't find it pleasant and I'm jumpier than I used to be. The last thing I need is to be unexpectedly jerking/jumping due to a static discharge with woodworking machinery turning blades etc around me at the time.

If the relative humidy where you are located is high, you probably will never have a problem. If the relative humity is low....it's your call. I called for metal pipe and won't worry about it.:D

[Jason Beam]

M Toupin's got the best source. You can NOT ground an insulator, period. Physics won't let it. Simple.

I'm with Ken - if I have to think about trying to ground something that can't be grounded, I'm switching to something that doesn't have the issue to begin with. Metal duct work instantly puts this crazy topic to bed. Can't ground plastic. CAN NOT DO IT. To those who disagree, feel free to do so - take all the measures you want. I'll stick with physics. :)

[Lee Schierer]

I Wearing everyday work clothes.....I get shocked regularly.....year round getting in and out of my van....
If the relative humidy where you are located is high, you probably will never have a problem. If the relative humity is low....it's your call. I called for metal pipe and won't worry about it.:D

Years ago when in the older cars with vinyl seats my moter and sisters used to get shocked regularly geting out of the car. My dad bought a piece of conductive rubber that he connected to the frame of the car and arranged it so it would touch the ground when the car was stopped. This grounding strap stopped the zapping from day one. I had a similar experience with a car I owned and did the same thing. These instances happened a number of years ago, so I don't know if the autoparts stores still carry conductive rubber strips.

As far as humidity and zapping, right now the relative humidity in my shop is about 35% I still don't have static problems

[glenn bradley]

I have been reading conflicting reports about grounding your hoses of your DC units because of the possibility of static shock igniting your wood dust.Has this ever happened to anyone?I have a Delta 1.5 HP,1200 cfm DC and the 4" hose is not grounded.Should I,and what is the best way to do this.Pics would be nice if anyone has them.
Marc

This battle will rage on as long as folks insist that a friend of a friend's brother-in-law's cousin saw a video from Japan where some Spanish cabinet shop exploded due to an un-grounded DC duct.

The only way scientists were able to create a wood dust environment dense enough for a problem to arise was to create one in a lab as no other environment would support it. The atmosphere created would have killed anything that breathes long before it went boom.

IMHO.

[Sam Yerardi]

glenn

Good point. I liked that one. I'll have to remember the Japanese video. :)

[Lee Schierer]

glenn

Good point. I liked that one. I'll have to remember the Japanese video. :)

I think my BIL's friend saw that movie....:D

[glenn bradley]

I think my BIL's friend saw that movie....:D

:D:D:D:D:D

[Ken Fitzgerald]

I didn't see the movie.......and with video special effects the way they are today ....I wouldn't believe it anyway......


BTW....I dont' know either of your BILs.....:D

[Tom Veatch]

...The only way scientists were able to create a wood dust environment dense enough for a problem to arise was to create one in a lab as no other environment would support it. The atmosphere created would have killed anything that breathes long before it went boom.


In the fairly limited research I've done on this subject, it appears that the dust concentration necessary to support a flame front (without which there is NO sustained combustion or explosion) is such that the visibility in that environment is less than a meter. From that, I conclude that an explosion in the shop itself is virtually impossible given that any reasonable person would stop work and air the place out long before that much airborne dust would accumulate.

However, in the dust collector ducting and bin, that sort of environment is quite possible. However, my readings on the subject indicates that the energy density to be expected in a static discharge is insufficient to initiate the flame front. There is a far higher probability of ignition from metallic sparks than from static discharges.

The controversy will continue as long as that brother-in-law's cousin continues to watch Japanese videos. My ductwork is PVC. It is not grounded. My shop has not yet achieved Low Earth Orbit, nor do I expect it to. If grounding the ductwork (or attempting to) gives one peace of mind, please do so. However, if it isn't grounded, the odds of survival greatly exceeds the odds faced at the casino's crap table, and in my estimation, even exceeds the odds of surviving the next trip to the grocery store.

Just my opinion formed from the research alluded to previously. No, I can't cite references since they have long been forgotten.

[Greg Heppeard]

http://www.youtube.com/watch?v=uLjQ0nGvH2g

http://www.risktech.se/intro.htm

found these with google

[Jason Roehl]

Greg, those are pretty neat, except, again, they represent conditions pretty much never found in a non-industrial situation. I know they occur in industrial situations as my father was plant manager (or reported to him, it's been a while) at a plant that had a dust explosion of some sort. They took a few days to find a 200-lb manhole cover that was over 150 yards away.

The video with the handful of dust thrown into the flame has two conditions not found together in the home shop together--high dust concentration and open flame. The high dust concentration would occur in the dust collector, but the flame wouldn't be there (and static discharge isn't near powerful enough to ignite the dust). Open flame might be present outside the DC, but it would take a major malfunction of something to put enough dust in the air to create the explosion in conjunction with the flame.

The aluminum dust explosion was interesting!

[Greg Heppeard]

Greg, those are pretty neat, except, again, they represent conditions pretty much never found in a non-industrial situation.

The video with the handful of dust thrown into the flame has two conditions not found together in the home shop together--high dust concentration and open flame. The high dust concentration would occur in the dust collector, but the flame wouldn't be there (and static discharge isn't near powerful enough to ignite the dust). Open flame might be present outside the DC, but it would take a major malfunction of something to put enough dust in the air to create the explosion in conjunction with the flame.

I totally agree. I think it would take one big metalic spark inside the dust collector to explode. It could start a fire tho...but I don't think from static electricity.

[Steven Wilson]

Jason, the one situation that can occur is as a secondary deflageration hazard. Say you have a lot of dust built up on your pipes (PVC is more suceptable to this than metal) and for some reason you have a disruption in your piping (for example a fire starts in your DC collection bin from a sucked up screw). The dust on your pipes is forced back into the air (at a fairly high concentration) and you have an ignition source. That cloud can ignite. Prevention is simple, vacum your horizontal pipe runs quarterly or so. There is a fairly recent OSHA instruction on this that you may care to read http://www.osha.gov/OshDoc/Directive_pdf/CPL_03-00-006.pdf

[Marc Prudhomme]

I dont think that I will be worrying about it much.It seems pretty remote that it could happen.Thanks for all the imput.
marc, (cool videos)

[Ken Fitzgerald]

Marc.....I agree the probability of something happening is remote.

[John Thompson]

I read everything I could for weeks when I installed a cyclone. It pretty much all pointed the the fact that an explosion has only a long statistical odds of happening, so I didn't ground. But.. I do run my Cyclone continuoulsy for an hour or more on occsasion and it did zap me several times with the slightest touch.

So.. I grounded it from cyclone all the way to the machine. Did I eliminate the chance of an explosion? Probably not as that was no concern to me to start with. But it did eliminate the zap so I can move freely around without the side thought of avoiding touching it.

It was worth the $20 necessary for the material to do it IMO, as I am in the shop almost every day.

Sarge..

[Cody Colston]

My cyclone barrel and the dust inside caught on fire. It was pretty dramatic, too.

I went to dump it on my burn pile. The only problem was the pile was burning at the time. WHOOSH!!!!! That dust will burn rather rapidly if dumped onto an open flame. :eek:

I know, it was a stupid thing to do but I just had a brain fart. I singed the hairs off my arms but at least the cardboard barrel survived. Just another day in the life of a newbie woodworker. :p

Oh yeah, I remember seeing a picture someone posted on one of the WW forums that showed a lightning-strike-looking streak down the inside of one of those plastic cyclones. Evidently the static build-up was pretty severe.

[Steve knight]

The static from the dust effects my cnc router. I ran grounding wire and no communication problems. so static can effect a few things (G)

[Rich Engelhardt]

Hello,
Years of working with computer and electronic equipment have made me very "static aware".
I'd be far more concerned about the possible static damage to electronic components in the tools, than a fire hazard.

Matter of fact, reading through any number of posts here where the electronics suddenly and unexpectedly "went out", I have to wonder if static wasn't the culprit.

Some of the comments - such as "it worked fine last time I used it, then when I took it out to use it again, it wouldn't work" as almost "classic".


The last thing I need is to be unexpectedly jerking/jumping due to a static discharge with woodworking machinery turning blades etc around me at the time.

That bears repeating!
Back some 35 years or so ago when airless paint sprayers were introduced by the Gray Company - later renamed Graco - hoses weren't made conductive. They went to using braided metal in the hoses to shunt away static. It was only partially for fear of a spark setting off the paint fumes.
The main reason though was, as the Graco rep put it, "The 50,000 volts would hurt you, the 50 foot fall off the scaffold is what will".

Jason,

Can't ground plastic. CAN NOT DO IT. To those who disagree, feel free to do so - take all the measures you want.
Much of the plastic in use today is conductive.
Carbon powder is added to make it conductive.
Ohm out the plastics on computer parts, radios, your keyboard, etc.

True - plain plastic is an insulator. The problem is, not all plastic anymore is nonconductive.

[Ray Moser]

On the old Badger Pond web site there was a link to an article by a college professor. He pretty well disproved the notion that there were explosion problems with home wood shops. I though I had saved the link but alas it is gone.:(

[Eddie Darby]

Two words made into one, about whether or not a DC can explode:

MythBusters

If anyone can do it, these people can!

[Mike Seals]

The static from the dust effects my cnc router. I ran grounding wire and no communication problems. so static can effect a few things (G)

I've been in the electronics side of the world for 30 plus years. Static electricity is a killer for equipment such as your controller. Lots of newer equipment has these tiny components in there. I don't think the static is enough to cause a fire in a DC home system, but I always ground my equipment for static to protect any of the devices in the shop.

I don't think I'll get in a wreck today, but I'll still wear my seat belt.

[Jim Becker]

On the old Badger Pond web site there was a link to an article by a college professor. He pretty well disproved the notion that there were explosion problems with home wood shops. I though I had saved the link but alas it is gone.:(

See post 14 in this thread for a link to Dr. Rod Cole's article.

[Marc Prudhomme]

#13.....................................

[Jim Becker]

#14 for me, Marc...do you have someone on "ignore"?? :)

[Marc Prudhomme]

No I do not.Thats weird.......
#14 for me, Marc...do you have someone on "ignore"?? :)

[Ken Fitzgerald]

Static and lack of humidity are killers in electronics.

I've been involved in two incidents where I came in on a CT scanner site. The site had been in for a month or a couple of months unable to successfully scan patients. Both of these sites were on the edge of or in the desert/arid part of the US. You could sit at the control console...tap your foot and draw an arc to the keyboard with your hand. You could run diagnostic programs on various subassemblies in the system and never get the same failure twice.

In both cases I had hospital maintenance bring in a sling pshychometer(sp?) used for the wet bulb / dry bulb method of measuring humidity. We measured the humidity and the humidity measured less than 10% at the time. In both cases..one in TX and one in central WA we put cheap room humidifiers in the computer rooms and put a grounded floor pad under the operators chair and the problems were resolved. Raising the humidity up to a level above 20% resolved the issues and the equipment performed as advertised and designed with no further measures. AT both places once we knew that raising the humidity resolved the static electricity issues within the equipment, both hospitals brought HVAC designers back in to design and install industrial humidifiers in their HVAC systems.

I've worked for 2 different large medical equipment manufacturers in the last 31 years....both have the same environmental requirements that customers have to maintain....temperature and humidity of 40-50% non-condensing.

I know of one case locally where the customer didn't put in a conductive floor in a scan room. We went through many times the normal amounts of signal amplifiers in this MR scanner. We were finally able to isolate the cause to the floor material used in the magnet room. The technologists would walk across the floor to place a patient on the table....touching the table the technologist would get a shock and the surface coil rf amps in the area of patient table would get zapped and destroyed. It's hard to resurface a floor in the immediate area of a 1.5 Tesla magnet. Resolution....they put conductive pads down on each side of the patient table and grounded the pads to the magnet of the MR scanner.

I don't, however, think static will be a fire or explosion issue in the home DC realm when using PVC or metal. I used metal because I don't want to be shocked.....just me.....