Dangers of Dust/ Vapour Combustion?

[Steve Aiken]

Where would you find more information about the dangers of combustion of dust or vapors in the workshop? A simple Google search wasn't much help.

I have a natural gas furnace in the workshop which has a constant-on pilot light. I would think that the concentration of dust would have to be extremely thick before an explosion would ignite, but I do want to be safe.

Steve

[Steven Wilson]

I have a natural gas furnace in the workshop which has a constant-on pilot light. I would think that the concentration of dust would have to be extremely thick before an explosion would ignite, but I do want to be safe You would need a fairly high dust concentration to light it, the bigger problem are vapors from contact cement and finishes. The vapors tend to collect in low spots, usually about the same height as pilot lights. For more info you should still Google but you might want to be a bit more creative in your search. Some of the state OSHA's have publications that address this and are searchable on line. IIRC, California and Oregon OSHA's have a fair amount of information online.

[Chris Barnett]

Information should be available in ASHRAE if not in a national fire code. Flour fines in the air will explode violently (do a search on flour mill explosions in the USA) so dust from lumber cutting operations could also be extremely hazardous if not controlled. [American Society of Heating, Refrigerating, and Air-Conditioning Engineers].
But thats OK, I only did this kind of work as a degreed mechanical engineer for over thirty years. Surely the guys who guess that it is not a problem and that the flour example is too extreme, should know so much more.
The ASHRAE Fundamentals volume on air contaminants gives the ignition temperature of dust cloud 430 C, mimimum spark energy 20 mj, minimum explosive concentration .040 oz/cuft and the pressure rise in psi per second average 850 and 1200 max. [thats an explosion dude]. Cracked wheat [flour] has about the same ignition temp of 470, 160 spark energy [safer] and about the same minimum explosive concentration .060 [slightly safer, and about the same pressure rise. It takes technical expertise to understand the numbers, so that is why I initially left them out and simply said it is dangerous. The Applications volume provides details on dust extraction systems, if anyone is interested. No more words of wisdom from here. Oh, btw, on a different post, the rectangular ducts are less efficient since the laminar flow boundary layer is disturbed by high velocities which is the reason round ducts having uniform velocity profiles, are more efficient in extracting airborn pollutants, than square corners which have poor velocity. A calculation of the Reynolds numbers determines if the flow is laminar or turbulent. But I digress...sorry. Oh, I partially wrote a different chapter in ASHRAE than the one quoted since my specific expertise is not dust contaminants, but nuclear. Bye.

[Cecil Arnold]

Both the above observations are correct. The main danger is from heavier than air vapors reaching an ignition source (the pilot) and causing a flash fire. So far as the dust hazard, it is a hazard but not one that you should be overly concerned by. The comparison to flour dust (or most other grain/milling operations) is extreme. Dust hazards generally are dependent on the particulant size. You may recall from high school science class that the more finely divided something is the more easily it will burn (or explode which is almost the same thing if you look at the definitions of each). An example of this is steel. You can't burn a steel beam with a cigarette lighter, however you can readily burn steel wool with one. The dust from most woodworking operations, cutting, plaining, routing, should not present too much of a hazard. If, however, you are sanding a great deal your level of hazard increases as the particle size decreases. Were I you I would be concerned about the flammable liquids much more than the dust.

[Rob Littleton]

Just to throw in my 2c. FWIW.

I have NO chemistry background or any knowledge what so ever about this subject to be involved in this conversation intelligently. BUT, I did see (I think it was episode 23) of Myth Busters on the Discovery Channel and they emulated a house, filled with several "combustable" materials, flour and sawdust I remeber being a couple of them. They threw in electrical problems and even open flames to see if the theory of explosion was likely. It was proven that this is possibly a myth.

Interesting show.

regards

[Chris Barnett]

At 1:32 P.M. The Sacramento City Fire Department responded to a water-flow alarm at Lifetime Doors at 8280 Elder Creek Rd. The alarm had been set off by the sprinkler system in the sawdust hopper that had been activated by a sawdust fire. As Engine and Truck 10 arrived onscene one of the employees "dumped" the smoldering contents of the hopper. This created an explosive mixture of dust resulting in a large explosion and fireball. The explosion knocked the employee off an 8-foot catwalk. He suffered 1st and 2nd degree burns to the face and hands. A coworker immediately turned on a "house-line" and wet the injured employee down, possibly reducing the seriousness of his injuries. The injured employee was treated and transported by Medic 10. After the explosion there was a large amount of sawdust smoldering that required extensive overhaul. The hoppers were 3-stories tall and all of the sawdust had to be spread out and wet down. Overhaul was completed at approximately 6:00 PM. Due to the amount of work involved, two additional engine companies were requested for manpower. Initial units responding were Engine 10, Truck 10, Medic 10, and Sac Metro Engine 53. Additional units were City Engine 56 and Sac Metro E50. Investigators could not rule out a malfunctioning auger in the upper reaches of the hopper as the initial cause of the fire. The following pictures depict overhaul operations at this incident. For further information please contact the Public Information Officer (916) 765-7590. [from the web.....happened on 5/4/2002, I suppose the operator had not seen that episode of Myth Busters, huh]
Do a search on sawdust and explosion or flour and explosion; there is so much more fantasy to whet your imagination. Was even a situation wherein insurance would not cover damages if normal precautionary actions could have forseen a danger and prevented a dust explosion. Television is almost like the web, only worse. Published documents by world respected professional socities are just bad novels I suppose.
Revised to indicate in italics what was obtained from the web. The same could be obtained by visiting the Sacremento library and getting it there from the web. I was near there....had I known I could have stopped.The balance is my feeble attempt at being facetious. My first post was attempt to respond to the person's question and agree with his concern; I did not tell him it was not a problem but provided several sources where he could obtain the answers. The detailed information is proof that sawdust explosions are real.

[Rob Littleton]

At 1:32 P.M. The Sacramento City Fire Department responded to a water-flow alarm at Lifetime Doors at 8280 Elder Creek Rd. The alarm had been set off by the sprinkler system in the sawdust hopper that had been activated by a sawdust fire. As Engine and Truck 10 arrived onscene one of the employees "dumped" the smoldering contents of the hopper. This created an explosive mixture of dust resulting in a large explosion and fireball. The explosion knocked the employee off an 8-foot catwalk. He suffered 1st and 2nd degree burns to the face and hands. A coworker immediately turned on a "house-line" and wet the injured employee down, possibly reducing the seriousness of his injuries. The injured employee was treated and transported by Medic 10. After the explosion there was a large amount of sawdust smoldering that required extensive overhaul. The hoppers were 3-stories tall and all of the sawdust had to be spread out and wet down. Overhaul was completed at approximately 6:00 PM. Due to the amount of work involved, two additional engine companies were requested for manpower. Initial units responding were Engine 10, Truck 10, Medic 10, and Sac Metro Engine 53. Additional units were City Engine 56 and Sac Metro E50. Investigators could not rule out a malfunctioning auger in the upper reaches of the hopper as the initial cause of the fire. The following pictures depict overhaul operations at this incident. For further information please contact the Public Information Officer (916) 765-7590. [happened on 5/4/2002, I suppose the operator had not seen that episode of Myth Busters, huh]
Do a search on sawdust and explosion or flour and explosion; there is so much more fantasy to whet your imagination. Was even a situation wherein insurance would not cover damages if normal precautionary actions could have forseen a danger and prevented a dust explosion. Television is almost like the web, only worse. Published documents by world respected professional socities are just bad novels I suppose.

Television is almost like the web, only worse. Published documents by world respected professional socities are just bad novels I suppose. Did you get this info from the Web???????

[Bryan Nuss]

I have built two board plants (one OSB and one strawboard). The OSB plant consisted of a gutting of an old particle board plant and reinstallation of new OSB machinery. This old plant had sawdust everywhere ... on top of steel beams, in between the walls and the siding, and in all the old bins and baghouses. I won't tell you the number of fires we had during construction, but none were really serious .... only called out the fire department twice!

Sawdust or chips in a pile or in a bin will burn or smoulder, but will not explode. Even a handful of sawdust thrown into the air will explode if exposed to an acetylene torch flame .... I personally have seen explode in a whoosh! in fireballs about 3 ft. in diameter. I have enormous respect for sawdust.

Having said all that, the chance of a dust explosion in a woodworking shop is remote, given the absence of open flames and a really heavy dust-laden atmosphere. However, the smaller the dust particles and given enough of them, the greater the risk of explosion. A spark could do it under the right circumstances.

I wonder how many of us really check the pan at the bottom of the filter on our cyclones for smouldering dust at the end of every day.

[Lee Schierer]

While there is no doubt that sawdust in the right concentrations might be explosive. As I understand it the dust has to be thick enough that you can see it in the air, or not see it since it obscures vision. Personally, I would be more worried about the hazard to my lungs long before the dust got thick enough to pose a hazard from explosion.

My shop has both dust collection and air filtration and when I do lots of sanding, I wear a high quality dust mask (not a paper throw away type).

[John Hart]

My Brother-In-Law is a service guy for the East Ohio Gas Company and it's funny that he was just talking about this on Easter. He's been called to several exploding houses and each time it was the result of people storing open containers of flammable liquid in their hot water heater closets. He also pointed out that my furnace being so close to my wood shop wouldn't cause an explosion but if I didn't keep it clean, I run the risk of higher gas consumption and higher bills.

[Steve Aiken]

Thanks to everyone for the replies.

So I did a little research on the web. Out of a couple hours of searching, I found only a couple of helpful websites: http://www.chemeng.ed.ac.uk/~emju49/SP2001/webpage/
http://www.warren-group.com/articles/grainpartI.html

Maybe I wasn't looking in the right places, but I couldn't find any useful information on ASHRAE or National Fire Code. I'm not about to spend mega-bucks to buy a copy.

If I'm understanding this correctly, there is a very real danger of suspended wood dust explosions. However, most of these explosions seem to take place in industrial settings where the dust concentrations are VERY high. There is danger of explosion where the concentration of suspended dust is 1 to 2 grams per cubic foot (I'm assuming that is equivalent to Chris' reference to .040 ounce/cubic foot). The websites describe this level of concentration like this:
"In a dust cloud containing .020 ounces per cubic foot of dust., a human being would not be able to see beyond about three feet. A concentration of .020 ounces per cubic foot is below the minimum explosive limit for most grain dusts. Obviously, concentrations of dust above the minimum explosive limit usually do not occur in occupied areas. However, these concentrations frequently exist in bucket elevators, conveyor housings, bins, silos, and other such structures where grain is moved around. "
and
"As a general rule of thumb it is said that if a 25W bulb can be seen through 2m of the dust cloud then the dust concentration is below 40g/m<SUP>3</SUP>. A cloud of this concentration is unlikely to be in the workplace, and should only be found in process vessels."

I'm thinking it will be Ok to place the new cyclone dust collector beside the furnace, but I will take precautions to avoid stirring up clouds of dust when it's time to clean the filter.

I was going to clean up all the dust on horizontal shop surfaces with compressed air. Methinks after doing the reading I will use the shopvac instead.

I'm also thinking that if-and-when I have to replace the furnace or hot water tank, I'll shop around for direct-vent units. If combustion air is drawn directly from outdoors, that would eliminate the risk of combustion/ explostion.

Steve

[Steve Aiken]

Now about the solvent vapours.

I generally have stayed with water-based stains and finishes, and I don't do spraying indoors. I have applied some oil-based stains in the basement shop. I usually open the basement window during application. Should I 'cease-and-desist'?

I was going to apply solvent-based contact cement in the basement, but after seeing the warnings, I'm thinking maybe I should keep this out of the shop.

What about if I apply the solvent-based contact cement in the main-floor kitchen with windows open and a large fan exhausting the fumes? I'd keep the basement door closed to keep the fumes from flowing into the basement.

Steve

[John Hart]

Yep..definitely a shopvac instead of shop-air. I do this as well, because of the furnace and the fact that one of my computers is in the wood shop.

It sounds like you're safe

[John Hart]

I spent nearly ten years as an engineer at an aerospace company working with fuels and fuel equipment and electronics and that sort of thing. During that time, I spent a bunch of time dealing with vapors and ignition....If you remember the exploding Flight 800, I helped with that investigation...but anyway, one of the most interesting things I learned was that of Hardhats that Miners wore in the olden days. The hat lamp was a small flame. They couldn't use glass in front, because the flame had to breathe and they couldn't leave it open because the lamp would ignite the atmosphere in the mine.

The solution was a fine meshed screen. The screen allowed the saturated air to go through, but the flame was only capable of igniting the gases within the flame chamber. The micro-miniature explosions were occuring all the time, but because of a phenomenon known as "surface tension", the explosion never extends beyond the hat.

'Course then...sometimes a miner would accidentally break the screen and...uh....boom.

Probably not the risk you want to take for your family. Perhaps adequate ventilation and maybe an inexpensive vapor reader alarm thing from Home Depot.

[Bill Lewis]

I just had a thought regarding this subject.
That is, what defines saw "dust". Think about it. Most of the stuff we generate with our wood machines on hard wood materials isn't saw dust at all, or at least the greater portion of it really can't be considered dust. They are really chips or shavings. The particle size of these chips and shavings is just not small enough to remain suspended in air. However, there is a component of dust created but the concentration is too low to create a potentially explosive environment. This portion of dust that can support an explosion might be best referred to as "saw vapor".
So in general, we as hobbiest woodworkers, may have somewhat of a misconception about how we think about sawdust. I'm just trying to put add some perspective to the concept. I hope I am making some sense in my ramblings.

[Lee Schierer]

Now about the solvent vapours.


What about if I apply the solvent-based contact cement in the main-floor kitchen with windows open and a large fan exhausting the fumes? I'd keep the basement door closed to keep the fumes from flowing into the basement.

Steve
Just be careful that your fan doesn't pull air in the exhaust for the furnace or the hot water heater. If you have a fan blowing air out of a room, you will need and opeing several times larger to let air in to prevent producing a small vacuum in the house which might suck combustion products back into the room. Just remember you can't draw air out of or push air into a closed space with a fan.

[Tom Kelley]

Steve,
I have the same problem in my garage/workshop. I have a natural gas heater on the wall but I only put the pilot light on when I'm actually heating the room. I have had clouds of dust in the air and I'm still here in one piece. However since I don't like breathing in all that dust and worry about blowing up the house I just ordered a Delta air cleaner that I am going to hang from the ceiling. It should help keep the air a lot cleaner. As for vapors I would avoid spraying solvent based products with the raw flame going.

Tom Kelley