I just saw on the news here in Montreal that a dust collector exploded in a high school woodshop today.Ten students were injured and four were taken to hospital.According to the shop teacher the dust collector was well maintained and was not over full.
We keep reading about the possibility of fire and explosion from dust and dust collectors but how many of us really do everything we can to make sure our shops are safe?I’ll be spending the weekend going over my shop and doing maintenance on my machines and dust collection systems after hearing this.
The news didn’t say if anyone was seriously injured,or if any lives were at risk.We can only hope not.
I also hope that this doesn’t cause the closing of yet another school shop.High school wood shop was where I got my introduction to woodworking and I’m sure alot of you were the same.It would be a shame if the school board were to close the woodworking shop because of this.
Thanks for listening,
Brent
Replies
I would wait to see what an investigation determines was the cause of the explosion. It could quite possibly have been caused by some accidental misuse of the system or deliberate attempt to cause trouble. I could easily picture a student accidentally spilling some solvent for instance and using a hose connected to the DC system to clean up the mess.
DC explosions are extremely rare, I strongly suspect that the details of what happened will turn up some interesting facts. Hopefully the results of an investigation will be made public.
John W.
John,
It could have been caused by alot of things.The point is that it did happen.Kids were hurt and a shop program could be at risk because of it.The cause of it(besides rectifying it)is not really the main issue.
Brent
I think the cause is a main point, and would like to know what the investigation shows. Incomplete information results in wild generalizations, wasted time, and (possibly in this case) closed shop programs for no good reason.forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-)Another proud member of the "I Rocked With ToolDoc Club" .... :>)
I would be very surprised if the cause is something other than static or the vapor from some kind of solvent in addition to static discharge. There's not much else that would cause this kind of thing. If the ducting is sealed, sparks from a motor shouldn't be part of the equation.
"I cut this piece four times and it's still too short."
Reminds me of a rule I once heard:"for every complex problem there is usually a simple solution . . . . and it is usually wrong"I agree . . . it would be really easy to blame the poor old dust collectormark
Did a search for a "school explosion" and turned up one short news story about the incident. Seems that the shop teacher smelled smoke before the explosion, so it seems like there was a fire followed by an explosion, which makes the spark igniting airborne dust scenario less likely.
John W.
"The cause of it(besides rectifying it)is not really the main issue."
Rectifying it is too late, but finding the cause is the most important issue now by a long shot, allowing everyone to learn and prevent a re-occurance.
I agree with John, it will most probably be something external and unrelated to normal dust collection, very important to know though.
I'm eager to here the results of the investigation. Conventional Wisdom these days is that explosion in smaller, non-industrial DC systems are near-impossible.
I don't know how small this system was.Apparently it blew a hole in a cinder block wall and part of the ceiling.The views they showed from outside had all the windows blown out and most of the window frames also.
I bonded with my high-school chem teacher when he set off a substantial dust explosion (by intent) in class the first or second day.
Lots of static can build up in a vac system, especially in the winter when the rel hum is low. Just with my shop vac, taking up sawdust, I can create a pretty big ZAP! between me and a ground.
Sounds like you had the same chemistry teacher I did.He did the dust thing with some sort of mushroom spore
then he did the sodium in water thing with a taped beaker in a sink. The ceiling had burn marks...Mark
Measure it with a micrometer, mark it with chalk, cut it with an ax.
Little shop vacs aren't where explosions happen, but large cyclone type DCs can explode.
Dust is held in suspension in the swirling air and a spark can set it off. Where would a spark come from? Sparks from metal meeting impellers, sandpaper and sawblades are a common occurence.
Before I ever blame static for a DC explosion, I'd look at the many other, far more common source for sparks. There has never been a fire or explosion in my cyclone DC, but little, smouldering fires have occurred under the stationary belt sander after a metal fastener accidently touched the moving belt.
High school shops tend to have bigger DCs (at least the ones I've seen) and the likelihood of mischief in the school environment makes for greater chance for such a problem. Some of the shop teachers I've spoken to have great reservations about the type of equipment the district puts in their shops. They really don't get the opportunity to choose their own stuff. Most would prefer smaller DCs than the ones that are installed at the orders of others.
There's a lot of issues about those school shops. I don't know the answers. Too many people get a say in it that don't know what they're talking about. That's also true about who gets to say the program gets shut down.
What to do? It's way too political for the likes of me!
DonI'm not the man I used to be, but then I never was!
Not fightin' anybody here...
DC systems are near-impossible...
Not quite true.. I have seen a spark come of a common household vacuum that was about two inches (well, big spark) long... Dust and sparks do not get along!
I just have a small 11/2 or 2 HP dust collector (Jet I forget the HP).
Not sure how much it helps but I have a copper wire inside the full length of the hose and well grounded with a 6 foot long copper rod driven into the ground.. I still can feel some static on the plastic hose on a very dry day...
How much does 4 inch copper pipe cost?
I've seen >2 inch sparks just from shuffling across carpeting (this was in a 911 Emergency center; 'used to really do a number on the dispatching consoles I used to design).
Sparks are easy; the question is whether a small system can generate the volume and concentration of wood dust sufficient to trigger an explosion. Conventional wsidom says "no", but CW is one step up from rumour, and may be wrong. That's why the result of the investigation would be so interesting.
Seems I remember an article in one of the magazines, maybe a year or two ago, that explained why grounding wasn't really necessary because explosion in small-shop systems weren't going to happen. Anyone else remember that? I'll never find it, I'm sure!forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-)Another proud member of the "I Rocked With ToolDoc Club" .... :>)
I remember that article as well, Forestgirl. I'll try and find it. The basic gist was that the continuous level of dust/air concentration in a DC pipe required to enable a static shock to cause an explosion was so high it would be nearly impossible for a hobbiest shop to create. Large industrial applications could certainly produce the needed concentrations for an in-pipe explosion (e.g. those grain silo explosions everyone thinks off).
Fire is another story. Dust laying around can catch fire. This is why caution should be taken to investigate the dust bin or bag full of dust after each use.
Pipe explosions are on a totaly different level.
--Rob
Glad to hear I wasn't imagining that article! Or, it might have been a letter? Just don't remember.
I'm eager to get a DC going in my shop to avoid dust settling on top of fluorescent lights and such. I hear that debris can cause problems.forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-)Another proud member of the "I Rocked With ToolDoc Club" .... :>)
Jamie, here's the reference you want, I believe.
http://mywebpages.comcast.net/rodec/woodworking/articles/DC_myths.html
This the full article. It was excerpted in an article published in Fine Woodworking.
Howie.........
Edited 3/27/2005 2:48 pm ET by Howie
Thanks, Howie! forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-)Another proud member of the "I Rocked With ToolDoc Club" .... :>)
You guy beat me to it. If I remeber correctly, the author wrote it for his webpage before it even hit FWW.
I also remember that, after FWW published it, the Oneida people wrote a pretty strong letter to the editor in opposition. Something to the effect of, whether or not explosions can be caused in hobbyist systems, fires can still happen, and metal will contain fire while PVC will not.
The "smoldering sawdust pile" thing has me worried, and I know bits of metal can get sucked in the system sometimes when, say, cleaning the floor. That's a big reason I'm moving the DC to its own little shed outside.
BTW, you read about people "grounding" their PVC all the time. Note that, as a very good insulator, PCV cannot be grounded. Not unless you did something like coat the surface 100% wityh a conductive coating, that is. But any piece of PVC not in immediate contact with a grounded conductor can and will develop a static charge under appropriate circumstances.
I still think it's a good idea to run a wire down the pipe. This way, as static charges built up, they have only a short distance to discharge to a grounded conductor. The sparks will occur at lower voltages, and are less likely to discharge against human grounded conductors. ;)
The wood dust moving against the plastic pipe is the main cause of the static, followed by the dust itself in dry air. Ssame thing as a baloon rubbed on a sweater. The material makes a difference in how much static is generated.
"I cut this piece four times and it's still too short."
Sparks on the outside are easy to get. Sparks on the inside are more difficult. I would say impossible.
There are many spark detection and suppression systems available, that are installed in the ducting (not affordable probably for a home shop though.....definietly there and becoming more common in industry though).cabinetmaker/college woodworking instructor. Cape Breton, N.S
I remember seeing a post somewhere -- maybe even here -- from a guy who had a sawdust fire start in his shop vac. Fortunately he was able to drag it outside and not burn the building down. Apparantly the brushes were sparking and set off the dust.
-- J.S.
It would be very informative to know what caused such a large explosion. If only for the knowledge of how to avoid it in the future. I helped dismantle a collector system in a high school metal working shop. The kids used to hide behind the welding curtain and smoke. The duct work was full of cigarette butts, roaches, welding gloves, paper towels and other debris.
Beat it to fit / Paint it to match
In my first year teaching, general woodworking in a high school, I caught a young man smoking...inside of the dust collection system! The system was set up with an electrostatic collector (basically it fit against one wall with a small sheet metal access door). The static grid (collector) was open inside of the enclosure, a person could stand next to the collector plates and hide behind the door. Well suffice to say that after I explained the dangers of smoking, I then explained the possibility the large static discharge (if he completed the circuit). Well he never even went into that room again, but I don't know if I convinced him of the smoking dangers.
Donkey
"The duct work was full of cigarette butts, roaches, welding gloves, paper towels and other debris."
Hammer,
I've heard stories for years about how tenacious cockroaches are - and now to hear that they smoke and weld, too...
... simply amazing!
-Jazzdogg-
Whether you think you can, or you think you can't, you're right.
Dust explodes. A complete system should be well designed and dissipating static electricity has to be accounted for.
Since noone here has a shop that has a dust explosion, there is no need to worry.
You may not think it's worth worrying about, but if you have ever used an unbonded DC in winter when it's really dry, you'd be surprised at the shocks you can get after only a couple of minutes. Plastic ducts are a big problem with these. Metal ducts that are cleaned regularly are a great way to keep a static discharge from happening. Have you ever heard about grain silo explosions? The same situation occurs. Suspended dust in the air with an ignition source. Big time problems.
"I cut this piece four times and it's still too short."
You annot get a shock on the inside of the dust collector pipes.
You could get a spark from a screw or nail that is sucked up through the machine though.Tom
Douglasville, GA
I manage a shop at a university and I have definitely heard of dust collector fires. A nail or a screw meeting an impeller causing sparking and you can get $30,000 worth of damage real fast. It happened at the University of Minnesota where I have a friend that also manages a shop there. I think the liklihood of it happening with a two stage system is less likely because if the cyclone is working as it is supposed to the heavy stuff should get swirled out before it hits the impeller.
This is all just anecdotal so please don't take this as a challenge to anyone's theories. I really don't have any idea if dust system fires can be started via static and will have to defer to the experts.
I worked in a hardboard plant and, as Adrian pointed out, we had spark detectors, explosion sensors, smoke and fire detectors and all manner of suppression systems. We had several fires while I worked there but no explosions. The cause of the fires was invariably chunks of metal going through a blower, a hog, a chipper or something like that. Some sort of foreign object.
At a plywood mill I worked at, a flight came off a drag chain (the flight must have weighed 60lbs, went through a chipper, then a 100hp blower where it was flung 250 ft up a dust pipe (at about 20 degree up angle) to a Carter Day baghouse where it started a fire. Our worst fire involved smoldering sawdust that was disturbed, that scenario produced quite a strong blaze and had potential for explosion.
While I was at those plants none of our fires resulted in any injuries, just a whole lot of work shoveling out tons of wet sawdust by hand and some significant downtime.
Static will discharge wherever it can. If the air in the duct becomes conductive enough, static will definitely discharge.Immediately after I started using my DC this past winter, after cutting a few boards and sending some extra dust through, I put my hand on my saw and got a pretty good zap of static. My saw has no grounding issues. My DC has none, either. They were insulated by the vinyl tube that takes the dust from the saw and goes to the DC. I added a ground wire inside the tube (they way it is recommended in every manual on DC installation I have ever seen), with the insulation stripped back. Problem solved. There was no voltage potential between the saw and DC circuits before I added the ground and there is definitely none now.
"I cut this piece four times and it's still too short."
Hi Brent, yet another shop hazzard to think about. What a shame to hear of the school shop dust collector explosion. I use a central collector system based on 4" PVC sewer pipe but grounded all the pipe to each tool it supplies. All such systems should be grounded and the continuity checked from time to time. BobW
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