Im in another “heated” debate about PVC in dust collection and it’s potential for a fire hazard. I still firmly believe that the static shock could not create a fire because it is not the voltage or amperage that will ignite the sawdust, it is the heat of the electricity. The static shock could not be hot enough to start a fire… am i right? now it is a known fact that it will discharge and make you say ouch, but i want more information on weither is will make your shop go boom… can i get a few more opinions? i plan to do a podcast on this soon hopefully.
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Myth busters could not get a real spark when they tried to generate one!
I would add a "ground" wire just to stop me getting zapped by surprise! I don't think there is enough power to start anything, maybe if you have some Gas vapour in just the right mix.
or fine saw dust....
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i had a friend tie a piece of pvc on a insulation blower hose,so he could get way back in the low part. that thing would shoot a lighting bolt about 12-16" long about every minute.
it was cool to watch,but i didn't want to get hit with it.
don't know if you could start a fire or not.
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Same experience here with PVC and an insulation vacuum. If you want to see just how much static moving all those small particles around can generate, use PVC to suck up blown FG! Sounded like a gunshot when the pipe discharged...Personally, after my experience with the insulation vacuum, I'd never use PVC for dust collection. Z
static shock could not create a fire because it is not the voltage or amperage that will ignite the sawdust, it is the heat of the electricity.
Uh, Andy--a couple of thoughts come to mind.
1. Lightning is static electricity.
Electricity doesn't generate heat unless it is forced through a poor conductor. Send a bazillion watts thru a superconductor and it'll barely get warm. But air--thru which lightning propagates--is a piss-poor conductor, so it gets hotter than the Dickens in the wake of a lightning bolt.
That rapid heating causes the air mass to expand almost instantaneously, leaving a semi-vaccuum in its wake. When that air cools again--and it doesn't take long--the two air masses on each side of that pathway slam back together violently, and the resulting bang is heard as thunder.
2. Dust explosions--like sawdust, flour, grain-elevator dust, etc.--happen because there is an explosive mixture of extremely fine particles suspended in air.
Every combustible 'fluid'--which in this sense of the word includes dust-air mixtures as well as liquid vapour mixtures--has an upper explosive limit (UEL) and a lower explosive limit (LEL). Have too much combustible fuel and too little air, the 'fluid' is above the UEL and it won't blow up. Have too much air and not enough fuel and the mixture falls below the LEL and likewise won't explode.
The other salient point about dust explosions is that the particles that burn in the initial flash are so incredibly minute. They have mass measured in nano-grams, and thus it doesn't take a heck of a lotta calories to ignite one: Even a very small 'lightning bolt' will do it. And once one particle is burning, it lights off the next couple of particles over, and they in turn light off the next dozen or so and so on and so forth...all in the space of a hot NY nanosecond. This is the chain reaction which fire engineers now recognise as the 'fourth leg' of the classic fire triangle that we all learned about back in science class a hundred years ago....
Dinosaur
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foolish men call Justice....
yeah... but the heat caused by the electricity from a PVC pipe is not hot enough to ignite those mixtures. hey, if i get one confirmed story that shows ELC (electrostatic discharge) from a PVC pipe, i will look the other wayhttp://www.cocoboloboy.webs.com
If you're looking for confirmed incidents, I suggest you check the NFPA database. I'm not a professional firefighter; I'm just a (retired) Merchant Marine deck officer with the required shipboard fire-fighting course under my belt.
Dinosaur
How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....
You ever heard of a grain dust explosion?
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Check this link out. It comes from a manufacturer of a dust collection system that is one of the best according to my research. http://home.comcast.net/~rodec/woodworking/articles/DC_myths.html
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Andy,
There are dozens of threads discussing this issue over on Knots. From I could discover (from people who seem to have A LOT more free time then me) is that while you will get significant static build up, the dust density in in the pipe is insufficient get an explosion. When you think about, it makes sense. At say 650 CFM you would need an incredably large amount of dust to ignite. Silo's don't have anywhere near this kind of air movement.
Just my 2 cents