Static Electricity Dangers You Might Not Expect

When I built my shop (shed), I installed pvc pipe under the slab to get rid of exhaust gases, ya know kinda like they have in the big shops, flex hose, sucker fan, etc. I've been told that the static electricity generated in the plastic pipe can ignite the vapors. I also did this in the wood shop for getting rid of dust, chips, and was told to install nails through the pipe, connect them with copper wire and attach to ground via ground rod. Not doing this has burnt down some sheds, I understand.

Seeing as how I can't drive nails thro the pipe under the slab, maybe I could just snake a wire thro the pipe and connect to ground.

I would like to run my stationaries indoors this winter, but don't want to burn it down.

Your comments please????????
"My Montana Gold"
Rick
ricandkath@qwest.net

I have no particular experience with exhaust gases in PVC but, I'll share a story with you that may shed some light.

A couple of years ago on a dry winter evening, I was sandblasting with my cabinet blaster. The parts were small and to prevent them from blowing everywhere, I thought it would be a good idea to place them in a small one gallon plastic bucket. I cranked up the blaster and blasted into the bucket about 5 seconds, when a "lightening bolt" came from the inside of the bucket to my upper arm. The arc was over one foot long! It nearly knocked me out of the blast cabinet and hurt like hell.

All I can figure is the inside of the bucket acted like a big capacitor, storing the charge until sufficient to bridge the gap to my arm. I WILL NEVER BLAST INTO A PLASTIC BUCKET AGAIN!

Reading the Empire blast cabinet literature they speak of the air/abrasive hose as being a static conductive rubber hose to prevent shock. This would indicate your concerns are warranted.

That said, lets assume the exhaust gasses WILL generate static electricity and sparks. Your suggestion of "just snake a wire thru the pipe and connect to ground" sounds like a good one.

One other preventive effort, would be to add the sucker fan you mentioned at the beginning. A small fan would keep exhaust gas (latent with unburned fuel) concentrations low enough to keep below spontaneous combustion levels. In other words, "slip" lots of air by in the pipe to keep exhaust gas concentrations low.

And lastly, perhaps just pouring some water in the pipe will provide enough humidity to prevent the risk of static buildup.

Good luck,
Curt Holland
Gastonia, NC

For what it's worth, there was a big to do about filling gas cans in the backs of pick up trucks with the box liners when I was in the service station business. The information was that the box liner rubbing and flexing against the box caused a build up of static electricity which could arc while fillint the plastic gas cans.

Duncan

Seems to me if the pipe is underground it would be grounded and would not build up static electricty. The recomendations for filling plastic cans is to remove them from the truck and place them on the ground. My dust collection pvc has a wire running through it and hooked to a ground. J.B. Castagnos
Belle Rose, La.

The outside of the pipe will be grounded, but the inside, the pipe itself being an insulator, will not be grounded.

Gene Waugh
Elgin, Illinois USA

Since plastic pipe is an insulator, it separates the inside of the pipe from the outside............studies have shown that underground plastic pipe can build up a static charge from being uncovered. Companies will use a wet rag or other grounding device to eliminate the surface charge. The charge on the inside is a result of the particulate matter flowing through the pipe and rubbing against the inside wall (rub a wool sweater over a plastic rod and then ground the rod-real pretty arcs!) Generally, the static charges build up the greatest at restrictions or other changes in the flow pattern like elbows, change in pipe diameter, etc. So, to be safe, a ground needs to be on the interior of the pipe, and if exposed, the exterior as well if flammable gases may be in the pipe. I have seen three men get burned when static electricity ignited natural gas coming out of the end of 3 feet of exposed plastic pipe-pressure was approximately 5 psig. Just my 2 cents worth. Hope it helps.

Seeing as how the pipe is an insulator, only the outside of it will be grounded. The inside of the pipe can still build up static electricity.

Static sparks on the outside of a plastic gasoline container could ignite vapors, so placing it on a grounded surface provides a measure of prevention. The vapors on the inside of the container are probably too rich to ignite. (Just like choking and flooding a gasoline engine--won't run if too rich.)

FWIW, even though I have a metal bead blasting cabinet, under certain conditions it has give me some pretty nasty shocks. I realize this could be prevented by standing on a metal plate connected to the cabinet and wearing shoes with conductive soles; however, the rubber mat I use is a whole lot kinder to my feet.

Orrin

FYI: In Montana you cannot legally fill a gas container in the back of your truck. You have to remove it and put it on the ground. I could probably reference a situation where a gas station pump caught fire and it got ugly. Townsend, Montana is the example.

I have liked the demo's at Home Depot on sawdust removal..ya know those cute little tubes (plastic) that run to all your saws, sanders, planers, and the like. Very handsome. Well I was over at my son's and saw he had put nails thro his pvc every foot or so and connected them with copper wire and then to ground. I asked him what the hell was going on, and he said he's read in a woodworking magazine that static electricity in these tubes/pipes had caught the sawdust on fire and burnt down the shed. Case closed........

It was suggested to me when I built this shop that PVC would decay, melt, the electrolysis thing, and various other variables would fail the PVC. Never once was static electricity mentioned. I should have known as I've got bit occassionally with my shop vac and sandblaster, but I'm 56 and I know everything, yea right. "Hell, I ain't gonna live long enough for it to fail, and if it does, it should leave a hole in the concrete and will still work, right, right." No problem!!!

The suggessted idea of putting excessive air thro the pipe I like. Only when the fuel/air ratio is correct, will the mixture ignite. Like that one. I'm brand new to stationaries and have cranked on them a time or two hoping the fuel/air mixture would get right. The propane leak I've heard about, and it is a definite factor.

Ok, I'm blabberring so will cool my jets with this: That damn google.com just amazes me, just like the SEL does: I cranked it up and found this.

http://home.att.net/~waterfront-woods/Articles/Electricity/static.htm

Will shut up with this: being in aviation for 32 years, static electricity is big sh%it. If you ever get dowsed with fuel, GET TO WATER AND GET A SHOWER NOW, IF POSSIBLE HAVE SOMEONE FOLLOW YOU WITH AN EXTINGUISHER, DO NOT REMOVE YOUR CLOTHES!! BIG TIME STATIC ELECTRICITY..DELUGE YOURSELF WITH CLOTHES ON..AND THEN IN THE SHOWER REMOVE YOUR CLOTHES.!!!!

Thanks for the info and help..I'm not quite sure if the link has the answer for me, but will snake a bare copper wire down my pipes and wait for the outcome

again thanks
"My Montana Gold"
Rick
ricandkath@qwest.net
"Remembering when we used to put a spark plug in the exhaust pipe to make it backfire"

A coupla other static stories..... A tractor with rubber tires doing belt work with a rubber and canvas belt can become a big Van De Graf generator. We always hung a chain from the drawbar to the ground. I didn't do this once and got my big dumass zorched when I went to get on it. Tears as big as horse turds, it really hurt.

The other thing is.... If you have a cabinet sandblaster, make sure the ground wire going to the gun is intact. We have one at work and one at home and I have zorched myself with them as well. If I didn't have a big gut to ground myself, I would probably have electrocuted myself...;-)
Joe