Recently I mentioned to @bar I had come across a form on wood work where there was a discussion of using an exhaust fan and long runs of PVC to vent to the out doors while wood working indoors. This in some cases had caused fire and explosions. The wood chips would outgas from the wood working, the air forced through the PVC caused large amounts of static electricity. Potential plus sparks, not so good. The solution was to run a ground wire through the PVC. 2 cents of free advice. I came across it while researching the best way to vent my laser cutter. This was using a conventional saw and a big industrial fan.
This is a wives tale. Urban legend. No documented case exists where wood dust collected via PVC (or any other plastic tubing) has resulted in a fire or explosion ignited by static discharge. If such a case exists, please share it.
Wood doesn’t “outgas” as there are no volatile organic compounds within, so I think you’re referring to the dust itself. The concentration of wood dust required for combustion is very high and only exists in collection systems at the storage point which is, in almost all cases, grounded.
Long lesson short: If you’re using a shop vac or other dust collector, static is not of concern.
TheRifleSpiral is correct, I have a home wood shop and most of my dust collection runs are PVC. Most manufacturers of dust collectors recommend PVC as a viable solution for dust collection, It is probably the most efficient piping for this application. There should be no need to worry about PVC piping for your collection runs.
I can find evidence for both sides if this on the web -
“Wood dust, when it goes up in an enclosed area, is just as explosive as gasoline fumes,” - Jamison Scott
I’m not saying you are going to encounter a problem for certain, however even the nay sayers seem to preface it by saying this is a myth … But I’m not an expert so there is a chance. You get to choose what is right for you.
@Bee I remember reading about that mill fire when I was doing some research after my OSHA training. Wood dust most certainly is explosive, and is very much a danger for us woodworkers.
It is a good idea to ground your dust collection system. Commercially available hoses generally have a copper ground wire that should be secured to some form of a ground. I have not worked with PVC for dust collector piping, so I can’t speak to it. I do know that we generally use zinc-plated steel ducting to connect hoses to the main collector.
I have coined a phrase here I think may be my Maslow bummer sticker. “Be safe while having fun.”
I respect peoples right to do what they do the way they do it. I just want to share information, what you do with it is up to you.
When my dad worked in shop as a welder they used to fill balloons with acetylene and light the attached string and let them go. The building they worked in was a cinderblock space with a roll up door in the back and glass front with a glass door. Someone made a ballon with a shorter string. When it went off the shock wave blew through the building and relived it of the plate glass front.
At some point I may build a test unit to see what can be produced with ESD and wood dust in a safe controlled set of conditions. However that same time, expense and effort could be spent making a couch.
I appreciate you all and your opinions even when they don’t agree with mine, especially when they don’t because it will probably lead to more learning on my side.
This is a bit of a hornets nest online. But I agree with @TheRiflesSpiral that in many posts and forums that I have explored, no one has been able to find documentation of static discharge from a PVC dust collection system causing an explosion. No doubt, wood dust is very explosive, in fact nearly any moderately flammable substance dispersed in fine particles is explosive.
I would also argue that running a single wire down PVC does very little. PVC is an extremely poor conductor of charge, so a ground wire only discharges the material within about an inch, if this is really a concern to you, you need to wrap around the tube as you go.
I have a rather extensive dust collection system using 4 inch pvc piping for many years now. And a central vacuum in my home using 2 inch piping and neither are grounded. I actually have some issues cleaning the dust off the outside of the dust collection system because it is so difficult to discharge the static.
All of that said, I realize that proposed solution is easy and cheap, so do it if that is what you want, but this is far from the most dangerous aspect of this project.
Absolutely. Just like a grain bins or other fine dry material storage and collection systems, in the right concentration with the right ignition source, wood dust is explosive.
In a dust collection system, neither the concentrations (in the ducting) nor the ignition sources are appropriate for combustion.
Correct. All the specifications for electrically isolated convey of materials provide for a minimum allowable discharge and for this reason, it’s almost always necessary (with plastic tubing) to have a spiral with a relatively tight pitch.
Dust collection is an important topic; the health concerns are real when exposure level and frequency are high or if you have an already compromised respiratory or circulatory system. It’s important enough that barriers to installing effective dust collection should be reduced as much and as often as possible and this (widespread) notion that you’ll blow your shop up if you don’t wire your ducts to ground isn’t helpful.
Again, if someone can show me a single example of the spark from a static discharge igniting the dust in the ducting of a dust collection system, I’ll redact all statements above and champion any and all static elimination methods necessary.
EDIT: I should add; don’t let me talk you out of adding a ground wire if you feel it’s necessary. We all should take the precautions that we feel are necessary for our safety. By all means, if you have the desire and means to do so, you’re certainly not making yourself less safe.
Sorry, I was not advocating to avoid using a dust collection system if you have no method for grounding the system. Dust collection is probably one of the most important safety mechanisms to use with any CNC router. I was simply noting that in manufacturing we have grounded hoses at every machine.
I can’t find the copper wound ones, but a hose like this one from Rockler is very similar to what we use. Although in industry 4" diameter hoses are much more common.
If anyone is concerned with static discharge and PVC, either wind your pipes in grounding wire using a grounding kit like this, or use galvanized steel ducts instead.
I have not had any issues with static discharge in a dust collection system. I did a quick google search just to make sure I’m not missing anything apparent. I did not clarify very well in my previous post that I was referring more to dust build-up being dangerous than dust in a collection system. In any of these industrial accidents that we’re referring to, the build-up is what actually triggers the mill fires and explosions. If anything, this should be a testament to how important dust collection is.
Sorry about the confusion, I did not write my previous post very well.
I think we could outsource this to the Myth Busters. They like to blow up things and have experience. And if it doesn’t blow up, they help a little to make it happen. Does anyone have their email?
Grain elevators explode from dust every now and then
I hope to be installing a dust collection system soon (but nothing in this project moves as fast as I want). If you consider adding a ground wire to pvc pipe, what’s the cheapest effective (not collapsing when all the blast gates are closed) way of installing the overhead ducting, guessing about 50 feet, U shaped, and around 10 +/- machines. A CV 1800 is currently the top of the short list so a pretty serious sucker
Good example. Mine’s around 25 years old and hasn’t blown up yet, nor have any of my plastic shop vacs. The vac line cleaner might have blown up a few times while fishing socks out of elbows, but that’s a different type of explosion. Fish tapes work…
I would argue that is actually pretty fun. One of the many perks of living in the great state of Nevada is that I can drive 15 minutes and be on public land (almost 85% of Nevada is public land). As a kid we used to go out into the desert with my dad and find stuff to blow up (cars, refrigerators, cabinets, TVs etc. etc.). We used a binary explosive mixed on-site and detonated with a blasting cap and a car battery (and a very long wire). It was great fun. One thing I vividly remember blowing up was a couch. It was actually pretty incredible, it smelled worse than you would imagine but it was awesome to watch!
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Does a router really make dust? It’s more like chips, and the larger the particles, the higher the energy required to get them to explode. I would thing a drum sander or a bandsaw would be more of a problem, but they don’t produce enough of it to saturate the pipes i would guess.
if you have the rpm too high, with too many cutting surfaces on the bit, and are
moving the router too slowly, you get dust, not chips (and/or burned surfaces
and bits)
given the limits of the router rpm (fairly high) and the router speed (currently
35 ipm) and common 2-flute bits, most people are creating dust rather than
chips.
Depends on where the difference between dust and chips is, i’m no expert and just deducing here. But i would guess that the smaller your dust gets, more kinetic energy is used to remove less material. And that kinetic energy is exchanged for heat. If you cut a board into chips of 1 mm long, or you cut it into particles of 0.1 mm you’re putting 10 times more energy into the wood, and sooner or later you’ll reach the limit of how much energy can be dissipater in the chip and the board will burn.
I don’t know if this holds true for wood, but in metal the vast majority of the deformation energy goes into the chip.
