Ok, calling all electrician-heads here….this is an honest to god true problem and I’ve never heard such a thing as this before..this is no joke….it’s not construction related but is a true electrician question.
I run a small special FX business on the side. I’m currently doing indoor pyrotechnics and smoke/fog effects using CO2 for the stage production Wizard of Oz. The wizards unit was made out of P-board, that 2″ thick foam board with foiled surfaces like Celotex has. To do my CO2 FX I have two holes in the P-board that accept a 3″ PVC 90degree elbow. One end of the elbow has a 2′ long 3″ straight PVC pipe that goes to the back of the wizards unit. My guy stand behind the unit and spray CO2 from extinguishers into the PVC where the 90 elbow then directs it upwards to create billowing smoky columns.
Twice tonight during rehearsal my guys got shocked. We’re talking 110volt shocks, that type. At first I thoiught my electric panel I use to fire my pyrotechnics had a ground fault leaking to the P-board. But in the one scene I had no power on my panel, so it wasn’t that. In one instance of this shock as he sprayed CO2 continuously the horn at the end of the hose the CO2 comes out of started to glow blue..then bluer….then bluer until it sparked like a very powerful static spark.
It seems that somehow the CO2 is inducing a very powerful static charge. He said it shocked him so bad his whole arm felt tingled. Anyone ever hear such a strange bizarre anomoly such as this??? My next question is….how to fix it….I have the front of the wizards unit loaded with explosives for the special FX. Though all my devices are insulated from the P-board by wood, insulated connecting terminals or cardboard, I’m worried enough juice will be induced to prematurely fire my devices. How can I fix this to prevent the static buildup???any ideas????
I thoiught of taping a bare ground wire all over the place along the backside of the unit so that it contacts the P-board and then running the other end over to the faceplate screw of a grounded outlet to try and make the charge follow the ground.
Thoughts, opinion??? And no, don’t tell me to go ask the Wizard…..remember he turned out to be a fake who knew nothing.
Rich
Replies
I would thing that the flow of CO2 over the nozzle (plastic?) could induce a static charge to the extinguisher and operator. Maybe try a drain wire from the extinguiser to building ground? Keep the charge from building up in the first place.
Probably not much -- something like a 22 gauge should be all you need to drain the charge as it builds up.
Edited 7/23/2003 11:36:33 AM ET by ProBozo
actually.....you're right. The folks at the CO2 place today said it's common for CO2 to build up static charge (never knew that obviously). They tell their guys to wear rubber gloves. Thinking along the same lines I did tie a 22ga wire to the P-board unit and plan to tape it all around the CO2 area to try and drain the charge prior to it building up.....you confirmed my thinking.
I remember a thread not too long ago here about PVC pipe being used for a dryer vent and there was a big concern about static electricity....can't find it though. If I recall the poster wanted to maybe use PVC pipe to extend a dryer vent out past his deck, and was entusiastically advised to use a ground wire to dissipate the static generated by the PVC.
Mike
Spiral wrap the PVC with bare copper and run it to a earth ground. Can you get away withcovering at least one side of the P2 with wire mesh, ie chicken wire, and run that to ground. Ground the nozzle of the fire extingusher. Tape the wires to the surface with conductive foil tape. Foil tape has some gorilla stickum.
I agree with the above. My experience is with static shocks x shot blasting cabinet. The media (walnut shells or glass beads) would build up a charge and zap the crap out of you.
When we added a 22 gage wire with one of those velcro grounding-strap things that you wrap around your wrist when soldering delicate elecronic circuits the problem went almost totally away.
I think that running a bunch of ground straps from each of your plastic parts exposed to the CO2 flow (PVC pipe - on the inside, the fire-extinguisher nozzle - near the tip, and the operator's arm), each run independantly to a dependable ground point would solve the problem.
Norm
Static electricity is a "differential problem".
The charge is generated by the friction of the CO2 againts insulating elements, the pvc pipe and maybe the nozzle.
You really don't need to "ground" it as much as giving a method for the charge to bled off.
While a wire around the outside of the pipe will help you can still get a large charge.
Run a bare wire inside the pipe. Connect one end to the foil and the other end to the CO2 tank.
There are special conductive plastics used in computers to bleed off static. It just takes a little conductivity. If there were pipes made of that stuff, it should work. Are the pipes used for central vacuum systems made conductive like that?
-- J.S.
John
I suspect that if you do enough research and have enough money you can find some conductive plastic pipes. Might be used in explosive locations, but they probably use metal.
Central vac use a "special" PVC pipe. What is special is size and wall thickness. As far as I can tell it the plastic is the same as ordinary PVC pipe.
There is just not enough velocity in a central vac system to build up that much static.
Now workshop dust collection systems do have enough velocity to build up static. Some people do wrap the outside of the pipe with wire to help bleed off the charge. But that is so that user does not get zaped if they are near the pipe. And in that use a inside wire will cause clogs.
Woohoo, Mylar foil pipe! I gotta go patent that and make my first $1,000,000.
I'd probably make that on my first order.
Mike
Yur late but I still want the million.
Oh well. I guess I'll go cancel the order for that new Ferrari.
Mike
Any two dry insulators will generate a static charge when they rub or flow past each other. A ballon on your hair (do this at a party and then stick the ballon on the ceiling). Plastic comb and silk clothe (in physics class). Gasoline into a plastic container (why the container should always be on the ground and not in the truck bed. Also why pilots ground their planes and gas nozzles while refueling). And CO2 and PVC. Both are insulators and one has a greater affinity for electrons. So as the CO2 carries them away (or adds them) to the PVC, the PVC builds up a greater and greater charge until it is large enough to arc to something or somebody.
Metallic paint with a ground wire is one solution. Grounded metal ducted a better one. In lieu of metallic paint, a grid of wires would work better than a single wire. Like the chicken wire someone suggested. Roll it tight, insert and let it expand to the ID of the pipe. And then ground it to a an electrical ground or water pipe.
Or time the discharges to a dramatic moment in the performance and charge extra for the effect.
David Thomas Overlooking Cook Inlet in Kenai, Alaska
Ground your guys with the extinguishers?????
I worked for a brief time at Key Industries. You may have seen the work coats or insulated overalls.
One of my jobs was that I trimmed and measured the lining that we used for the insulation. The lining with the nylon face, most of it, would knock the crap outa me on a regular basis. Like every two minutes.
I finally got a length of small chain and put it around my ankle so that it just touched the floor.
No more shocks!