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Replies
NICE !
think I will go vacuum my shop now.
roc
Give me six hours to chop down a tree and I will spend the first four sharpening the axe. Abraham Lincoln ( 54° shaves )
I'm not sure I get it. Is there something to be learned from this about shop dust collection? Or is this just a cool clip?
>what is to be learned<Some say it is hard to ignite a saw dust cloud and the possibilities of an explosion are very remote. There was a discussion here a few weeks back pretty much debunking the danger from static electric spark ignition inside a dust collector any way. Heck I don't know . . . but it is interesting to see what happens when the cloud finally gets touched off. A good electrical fire at the wrong time in a shop that does not have any dust collection would certainly be bad news. A person could be blown to kingdom come before they could get the electrical fire put out. etc.http://en.wikipedia.org/wiki/Dust_explosionrocGive me six hours to chop down a tree and I will spend the first four sharpening the axe. Abraham Lincoln ( 54° shaves )
I missed the discussion that debunked the possibility of an explosion in a dust collector. Having led two teams to rebuild a safer dust collection system after industrial explosions from grain dust and herbicide, I can assure you that most dust can explode and burn even if it is from a typically nonflammable material. The YouTube video was non-dairy creamer exploding. The ignition source in both my projects was static electricity accumulation from materials rubbing inside the system. Proper grounding eliminates this possibility. I just read where on manufacturer of a trash can cyclone collector recommended looping a length of copper wire and inserting it into the chamber and running it to earth ground — akin to a lightning rod.Greg
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Greg ,Sounds like you have experience with it. I don't.First a DISCLAIMER: OK no body put their shop/house at risk on my word here. I have almost no experience with this because I mostly make big, safe, curls from a hand plane or hand saw or chisel.The thread I was thinking that I feel debunks the HOME SHOP dust explosion DUE TO STATIC IGNITION SOURCE is this one:http://forums.taunton.com/fw-knots/messages?msg=43844.1I give Forestgirl all the credit for info; see her "this article" link ( I just remember reading some of it )
Here is an excerpt:begin quote:Before getting started on what may at first sound very scary, I would like to point out that I have read more than a dozen research papers on this topic recently. The thing I am most struck by is how hard these guys have to work to get dust explosions in the lab. It is not hard to get ignition if one makes a very carefully controlled, nonmoving cloud with just the right dust mix, and introduces a spark from a very carefully designed sparking mechanism. But no one seems to be able in lab sized experiments to get electrostatic discharge ignition of even very highly combustible dusts in remotely realistic situations, and they do try. Is is possible? I presume so, but it is extremely difficult. The issue, in a nut shell, is that with a charged conductor the charge is free to move, and thus the charges throughout the conductor can can join forces to make a strong spark. But, because charge on an insulator is not free to move, discharges only occur from a small area, leaving the majority of the charge behind. For this reason discharges from insulators are not as energetic as those from conductors. Glor (1988) points out in a physics journal that while there are often multiple possible ignition sources, electrostatic discharge is often given as the ignition source for dust explosions even when there is no real evidence, simply because it is hard to know what really happened.
Also, there has never, to my knowledge, been a documented case of an explosion problem with PVC in the home shop or a case of an explosion in a filter bag in a home shop. A friend of mine who is a professional cabinet maker asked his fire inspector what he thought about the hazard of PVC ducts, and the fire inspector said he was far more concerned about people keeping lighter fluid under the kitchen sink.End quoteAS FOR THE COMPUTER KEY BOARD cleaning ( I brought up in that pervious thread ):Since that thread one day I got all brave and using my GROUNDED Fein shop vac. I turn off the computer and with the suction reducing vent on the hose handle open I just vacuum the junk out of my keyboards including my MacBook Air and have had no problem. If I were cleaning a chassis on a computer tower with the covers off I might consider the canned air suggestion ( why don't people just use an air hose from a tank or compressor rather than those cans ? I have seen people using cans with the air compressor hose right next to them on the wall ! )For the key board, especially the Mac Air, the compressed air would just blow the junk around inside the keyboard/computer and not remove it. Thats why I vac the key boards.For what it is all worth there it is.rocGive me six hours to chop down a tree and I will spend the first four sharpening the axe. Abraham Lincoln ( 54° shaves )Edited 4/14/2009 3:24 pm by rocEdited 4/14/2009 3:25 pm by roc
Edited 4/14/2009 3:27 pm by roc
They also ignited that explosion with a`flare. I believe earlier in the episode they did the same thing with sawdust, but again used a flare (I may be thinking of another episode.)So...keep flares out of your ducting.Oh...and i don't imagine grounding is all that bad an idea either, just more safety like a riving knife or a push-block. So why not do it?my 2 cents worth.Paul
It's just a cool clip.
I'm not sure I get it. Is there something to be learned from this about shop dust collection? Or is this just a cool clip?
I would say both! Dust of almost anything on Earth that will burn can do that.. And even if not an explosion.. FIRE... Moist wood or other generates heat! AS IN FIRE.
I empty the bags often.
As to if it was REAL.. Ask ANYBODY that works in or near a grain silo....
The key statement in the video is: the "mass of the creamer in relation to the volume of air is crucial".
In other words,in a shop environment, the concentration of sawdust in the air would need to be at a point where you would not be able to see and maybe could not even live.
As far as I know, there has never been a fire or explosion in a small, shop dust collector.
One comment about this is that the Mythbuster crew didn't actually produce a dust explosion - just a rapidly burning fire. Spectacular though it was (had to watch that a couple of times - very cool, and probably illegal in 42 of 50 states).
A true dust explosion is considerably more serious - the combustion propagates faster than the speed of sound, leading to a detonation and a blast wave that flattens anything anywhere close.
The key part is that the mixture of combustibles and air must be above the LEL (lower explosion limit) and lower than the UEL (upper explosion limit). Below the LEL, there's not enough fuel to continue the ignition process throughout the cloud of dust. Above the UEL, there's too much fuel and not enough oxygen to propagate an explosion.
Where exactly the LEL and UEL are sensitively depends on the combustibility of the fuel, the humidity of the air, the particle size, and the air density (temperature). Wood dust is most certainly capable of generating a devastating explosion - there are pictures on the internet of whole 19th century sawmills that were completely leveled by such an accident. More recently, the West Pharmaceutical plant in NC suffered a rubber dust explosion - that killed a dozen people, completely leveled the plant and broke windows up to a mile away.
It's unlikely that an explosion could propagate in a woodshop DC system because there's not enough dust and too much air when running continously. But vacumming up a large amount very fine sanding dust could easily trigger such an event. Having seen first-hand what a detonation can do, I wouldn't want to find out.
We have a fairly large cabinet shop operation here where I live (maybe 200k sq. ft counting the offices and finish room space). Some of the DC lines are 36" dia. All are some type of spiral-wired duct, and a detector system detects fire/smoke and activates a sprinkler system if smoke/fire is detected (that's a lot of detects in one sentence!).Engineer for the DC system designed this. Shop has been in operation for several years now, no problems as of yet that I am aware of. Not sure if this means anything other than someone seems to think it's important.Rich
QUOTE: "In other words,in a shop environment, the concentration of sawdust in the air would need to be at a point where you would not be able to see and maybe could not even live."
You're misunderstanding the conditions necessary for an explosion: It's the concentration within the collector or the pipes or any area, enclosed or not.
You must have the right concentration of particulate, an oxygen source (often air), and an ignition source (often static discharge). Take away any one of those factors, and the system becomes safe.
Probably the easiest way to keep a dust collector safe is to prevent static build-up with a good earth ground at every component.Greg
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I just thought the fireball was cool.
The fireball may have been cool. But these kids could have been in the running for a Darwin Award. The pressure wave of an explosion travels in excess of 700 miles per hour. They were a little close to their experiment — they were chlorinating their gene pool!Greg
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Sometimes ya get lucky, sometimes ya don't.
I'm sure the MythBusters insurance company cringes at some of the stuff they do.
"Probably the easiest way to keep a dust collector safe is to prevent static build-up with a good earth ground at every component."Contempt prior to investigation is guaranteed to keep you in ignorance as well as give your imagination free reign.The "best" way (not to mention the easiest way) to keep a dust collector safe is pinpointed in the article that Forestgirl recommended.It has nothing to do with grounding.
Edited 4/15/2009 2:52 am by Jammersix
"Contempt prior to investigation is guaranteed to keep you in ignorance as well as give your imagination free reign."Jammersix. I don't claim to be the ultimate expert in this area. But I have been the lead project engineer on two dust explosions. In both of these, the expert investigative teams that were brought in agreed that static discharge within the system provided the ignition source. Our solution was to ground every component. Twenty years later, and never another explosion. Maybe some could still claim we were all ignorant and just got lucky.Forrest Girl's article under recommendation #2 quotes this:"If you wish to protect yourself from the electrostatic discharge hazard in filter bags the easiest thing is to use a metal cyclone with a metal bin, and ground everything metal."Now we have two ignorant people with free reign imaginations giving the same advise.Greg
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One thing that gets overlooked is that the likelihood of explosion is EXTREMELY sensitive to the particle size of the combustible material. The majority of the "dust" that woodworkers create would more accurately be called "chips," which typically don't have a high enough surface area/volume ratio to sustain an explosion.
On the other hand, if your method of work creates lots of fine, flour-like dust...
-Steve
Fortunately I have never been involved in a dust explosion. However please, all, remember that static is not the only possible igniter. In grain milling and conveying systems you can get an explosion from a piece of gravel or a loose nut impacting the mill rollers or some other fast moving component.I know of one brewery which had suffered several mill explosions over the years. Damage was minimal because these systems are carefully designed to cope. They discovered the cause when they installed a new system. The old one screened malt through sieves. The new one used a vibrating plate as a destoner. They were "recovering" about a sackful of gravel from 6 tons of malt. (I witnessed this personally).I leave it to your imagination how the interview with their main supplier went.Back to woodworking: electric motors spark. A lot.
> loose nuts <There arrrrre allot of nuts where I live . . . I am going to keep an eye out. ThanksrocGive me six hours to chop down a tree and I will spend the first four sharpening the axe. Abraham Lincoln ( 54° shaves )
steve,
"...fine, flour-like dust..."
as in random orbit sanding or sweeping the shop?
eef
Sanding, yes, although the total quantity of dust is usually small, so that limits the risk. Sweeping up the shop, probably not, unless you're very vigorous about it.
-Steve
For an organization that try to promote respect for the planet - what does this say?
Not much
Don
The fireball was cool. OK? That's all. Were you this uptight when you were young?
Throw a handful of sawdust in the air and then flick your lighter into it . . .Voila, a fire ball. It may not be an explosion, but it would not be pleasant to have a room full of dust and air go up like that.I have done this little experiment many times to show people what can happen. It might depend on the dry California air and resinous softwood dust, but it is not difficult to get a flaming result.
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