Exploding Sawdust

[etat]

One time I  was helping my uncle sand a hardwood floor.  He had a great big belt type floor sander.  We were stripping the floor, I'm not sure if it had shellac, or varnish on it.  After a while the dust bag started filling up and he asked me to empty it.  I took it out back.  It was cold weather and earlier we had built a small trash fire.   The wind was slightly blowing.  About the time I started dusting that bag out on the fire it exploded.  Like pouring gasoline on a fire.   Or vodka, but that's another story. Burnt most of the hair on my beard, mustache, and eyebrows.  And the hair on my arms.  Luckily I was falling back so quick I didn't get seriously burnt.  He got mad about the bag I burnt up.  Told me I shoulda known better.  After that I did.

[Corley5]

I had something similar happen.  When I was nearing completion of my house I swept up a bunch of sawdust and shavings from the table saw, skilsaw, jointer, etc. and put them in a plastic garbage like you'd find in your kitchen and took it out back where I was burning scraps.  I tipped the can up over the fire and whoa!!! .  The flash fire/explosion ripped the can out of my hands and it actually flew up into the air a bit.  Didn't burn me but scared me a bit and I ya I probably new better too but :

[L. Wakefield]

   OK, this is a major safety thing. Who else has any information? The first poster made it sound like there was something new or old on the sawduat acting as an accelerant. The second makes me not so sure- as if finely divided sawdust suspended in air is enough of a setup for a blowup of the type you describe.

   If the situation was properly controlled, this might actually be a useful way to enhance combustion or increase energy gained. I can see it now- the car that runs on carbureted sawdust..  :D :D  lw

[Minnesota_boy]

This really is old tech, this exploding sawdust.  We just tend to forget about how it reacts.  Grain storage elevators have to watch and control dust to avoid explosions.  Coal fired power plants use finely powdered coal blown into the combustion chamber with the air needed to combust.  Shucks, Otto Diesel made his first engine to run on powdered coal.

[L. Wakefield]

   I'd heard about the grain dust as a hazard, but I missed the early techno on powdered solid fuels.

   I would assume they abandoned that because it is easier to spray a liquid fuel than the solid. Also I'm guessing that engines were big things- and the coal fired plants natch are big..but..so..what I've heard of sawdust as a fuel is mostly forming it into little blox. Do you know if anyone has looked into a useful app of the explosive tendency of the dust?

   Also any webrefs on either Otto, or the coal plants, would be cool. I'll also try to find something meself. Thanks for writing back..  lw

[Minnesota_boy]

Whoops, wrong Diesel.  Rudolf Diesel invented the diesel engine.  I'm sure that Otto did something too.  :-/  I'm having trouble finding the references online to his using coal dust, just that one of his early engines blew up and nearly killed him.  I think that one was fueled with the coal dust.

I've found several references to his work online, but sprechen Sie Deutsch?  ??? ???  Here's one that is in English.  http://inventors.about.com/gi/dynamic/offsite.htm?site=http://www.dieselpage.com/tipshis.htm

[Minnesota_boy]

Here's a nice animation of how a coal fired power plant works.

http://www.eskom.co.za/story/coalpower.html

[L. Wakefield]

Whoops, wrong Diesel.  Rudolf Diesel invented the diesel engine.  I'm sure that Otto did something too.  :-/  I'm having trouble finding the references online to his using coal dust, just that one of his early engines blew up and nearly killed him.  I think that one was fueled with the coal dust.

I've found several references to his work online, but sprechen Sie Deutsch?  ??? ???  Here's one that is in English.  http://inventors.about.com/gi/dynamic/offsite.htm?site=http://www.dieselpage.com/tipshis.htm

   I do a bit of German- technical German is a mite harder for me. The vocab is much more specialized, and it's not like in the Czech, where the techno is the only part I can make out because it's all anglicized- like 'mathematicky' and terms like that.  lw

[L. Wakefield]

   Very cool websites- thank you.

   Lots of those coal fired plants in WV- the one in St. Mary's was fun to drive by because you could see into the base of the nearer of the 2 colling towers to where the hot water was being sprayed out to be cooled. The plant sucked water out of the Ohio for the initial boiling phase but had to cool it before any discharge (or more likely re-use)- they wouldn't want to cook the fish in the river (those fish had enough things worng with them).

   The 'bump' of rising air over the towers was also fun to fly through- like an invisible frost heave.  lw

[Corley5]

The dust and chips that I speak were pure wood.  They were extremely dry as they came from dry lumber and had been dried even more from the wood heat in the house.  Add flame or a spark to a really dry combustible and it will ;D

[L. Wakefield]

   My husband had also experienced the same type of reaction- said it was with *really fine* sawdust.

   Honestly, guys, you're getting to me. I feel an experiment coming on..lw

[Minnesota_boy]

L. Wakefield,
Wear your safety goggles, hair covering and less flamable clothes.  Before Nomex was invented, wildland firefighting was done in cotton or wool, I think.  These clothes are not as easy to catch on fire as polyester or nylon.  Be careful!

[L. Wakefield]

   heh heh heh- I've got a full set of turnout gear... used to be on the fd, now am chief of rescue but still use turnout gear on 10-55s.

   What we did with the gunpowder experiments was to work up from a ridiculous margin of safety. First one goes pifft. Second one goes pop. Third one goes boom. And everyone is smiling at a safe distance and if you're on the back 40 the neighbors don't mind.

   I wish I'd been there when Colonel wotsisname did the original gunpowder research- you know, when they developed the various progressive burning powders.. I borrowed a book on it one time and he must have loved doing the work. It sounds like they did make a few mistakes from time to time.
  
   'Dust in the wind'- an updraft would be safest, but it sounds like most of the inadvertant experiments have been on the order of dumping the sawdust out over an already cooking fire.
I value my a** a bit too much to go overboard on volume first time on that one.

   Oh, it's got me smiling remembering the first time one of the kids took apart one of those morning glories to try to figure out how it does what it does. They were really good boys that I actually knew what they were doing and didn't find out later by the cops coming or fingers being blown off.  
  
   I'm trying to picture the heat, air, and particulates. 'Just a pinch' and work up from there. Granny's kitchen.  lw

[Minnesota_boy]

Good!  Put on that turnout gear and pull down the face shield on the helmet.  Might not be needed when you start out with the small quantities, but some of these experiments have a "critical mass" when things can go so wrong.

[Minnesota_boy]

Bald people with one eyebrow look soooo funny.   :D :'(

[etat]

I actually wouldn't have thought anybody would want to try to duplicate this on purpose!  I was thinking more along the line, be carefull putting sawdust on a fire!  

[L. Wakefield]

   Dunno that I want to duplicate the full 9yd outtacontrol takeyoureyebrowsoff boom thing- but- it's just teasing me. I want to know how it works and if it's got any use. I don't want to involve the wood stove or the interior of the house- sigh- time to think about a burn permit and a bonfire.

   Does the sawdust need to be dry? I would certainly think so- and then I'm willing to bet there will be a quantitative difference between hardwood, softwood, and type of sap. Particle size has got to be an important variable.

   I have a lot more experience with volatized sap. Conifers in full summer when it's very dry can put off enoughflammable vapors that a fire can result in them exploding and a really bad crown fire. I don't want to get too up close and personal with that but it's fun with Christmas tree branches. You can see how it was only a short hop from that to my steaming the Christmas tree to get the oil.  lw

[Tom]

White dynamite is what the furnace tenders at the pulp mill called it.  They accumulated sawdust from the wood shop and stored it next to the boiler room for when they needed hot fire 'right now'.  Then they would throw a shovel full of sawdust into the air stream of the furnace and there would be instant heat.  Enough of it to back them up a step or two and enough to raise the temperature of the boiler to keep the plant running.  Put enough air around a sawdust particle and it just flashes.

[Corley5]

My exploding sawdust was mostly hardwood- sugar maple, black cherry, ash with a little red pine thrown in.  The big factor in making it explosive is the dryness.

[Buzz-sawyer]

Hi LW
Here is a link to a discussion bout the same topic(in this case the danger of explosive dust and its power)
I think the sawdust vortex furnaces might interest you to ....amazing though one sack of flour can do so much incredible rearanging of nearby matter!

Dave ,m it is a fact that dust is ,"ALL SURFACE AREA" any dust is extremely explosive, does that mean you will definitely have an explosion of course not does it mean it is a possibility YES...

a half a sack of flour ,air born with an ignition source could easily level ranch home....
ever see the results of a flour mill explosion.....on the news?
It takes 3 things for combustion/explosion.... dust in the air ignition source and air...
hook up that blower!
Don

[Ianab]

Have come across this effect a few times, and it's pretty safe to experiment throwing a handfull of dry sawdust on a rubbish fire. But stand back cos it will probably make a little fireball. As others have said, the effect gets bigger fast  
A bucketfull will remove your eyebrows and as Buzz says, a sackfull in an enclosed place would be a major explosion.
Had an incident at work here where a customer emptied waste photocopier toner onto a rubbish fire. This is made of very fine plastic powder and carbon black   Results looked a lot worse than they actually were because of the carbon black, but it took a while for the kids eyebrows to grow back.

Be safe out there

Ian

[L. Wakefield]

   Buzz sawyer, your link was missing. (I mean that in a nice way. Some days my link is not only missing, but I suspect I am the missing link..)

   I did the 'pinch' of material test, using cedar shavings that were very dry (supposedly)- grinding them as fine as I could- the results were sparkly but not impressive. Then I tried a pinch of flour and the reaction was more complete and brisk. I think particle size is critical. I bet sanding would give a finer material to start.

   Thanks, Ian, for the quantitative estimates.

   I cannot IMAGINE the copier powder reaction- that stuff is ultrafine.

   Buzzsawyer- I do want to read about the sawdust vortex furnaces- that sounds like the application I was wondering about. I'm not a bit surprised if someone already thought of it, tried it, and it worked. The commercial breakpoint would be in the handling and the costs of preparation as compared to burning the rregular stuff as it comes from the tree- or the pelleted sawdust .  I will do a web search on sawdust vortex furnaces but if you have a link that wouild be kewl to read.  lw

[L. Wakefield]

   OK, yes there is plenty online. www.shirleyassociation.com/history_of_drummond.htm is kinda cute, if only a peripheral mention of it. Talks about 1400*C temperatures and corrosive exhaust gases.

www.eabioenergy-task32.com/overview/largescale.html gets more specific, and
www.fwc.com/publications/tech_papers/powgen/pdfs/DesignIssuesforCoFiringBiomass.pdf
really gets down to it, showing BTUs for wood dust as compared to some of the coal dusts (check out the names for the coal dust..) and implies that while the btu is less, the corrosive components to be removed from exhaust gases are also less. Getting low on coal dust? Bleed in a little sawdust.

   I don't think they'll be making one that will run my car, somehow. There were a few sites talking about H2 production from wood via pyrolysis- I guess that could go into a fuel cell.  lw

[L. Wakefield]

   That 2nd link should be
www.ieabioenergy-task32.com/overview/largescale.html  

   lw

[Duane_Moore]

 :-[ found a no-no- was working on a hot rod today on the brakes, grandson showed up to help.....4yrs old.... anyway he spilled the brake fluid. so I kinda wiped it up before Grandma caught up. then Grandma cleaned it up good..... she got the Beach out...no-no-no-....do not mix bleach and brake fluid as we found out....Smoke and lots of it... I mean Lots...  won't do that one again.... Duh---Duane :-[

[L. Wakefield]

   Bleach and brake fluid!!?? Who knew? Now I gotta finger that one out.. lw

[PatrickG]

  Bleach and brake fluid... There are lots of "home" chemicals that are generally safe to use but can be dangerous when mixed.  Bleach can give off chlorine gas when mixed with the wrong stuff.  I choose to not elaborate here but trust me there are lots of wrong combinations.

See also: "Anarchist's Cookbook"

Now then back to the topic... dust explosions.  A Jr. Highschool science demonstration to illustrate the danger of dust goes like this...

Required materials:

1. A closed container, don't use a compression lid (paint can style) as it will explode too violently. A large metal can with friction fit lid like you see for potato chips and such is good.
1.1  OK you can use a 5 gal can with a compression lid but for goodness sakes do it outside away from windows and anytihing that a flying lid might damage.  After you understand the process, ask yourself how you will safely get the large compression lid on the can withought risk.  Some folks have hust layed a piece of plywood over the can.  Beware exploding seams!

2. a few feet (3-10) of flexible tubing (plastic, rubber, I don't recommend garden hose or large diameter tubing if you detonate by blowing by mouth)
2.1  You can use a shop air hose instead of blowing by mouth.

3. a candle

4. A few teaspoons of plain white wheat flour or extremely fine sanding dust.

Assembly directions:  Punch a hole in the bottom of the can near one side not near the center (About half the diameter of the large end of the funel from the sidewall.) It should be a snug fit to the tubing. Insert the tubing through the hole and insert the small end of the funnel into the tubing.  You want a tight fit between funnel and tube. With a little fussing you can make the tube fit tightly to the hole in the can and to the funnel.

Place a couple teaspoons of regular flour (not Bisquick or other baking mix but plain white flour OR alternatively sanding dust from sanding wood) into the funnel.

Place the can on a table or workbench or better yet on a chair located outside.  

A. Put on your hearing protection

(The rest of these instructions are to be performed in rapid succession.)

B. Place a lighted candle inside the can on the side opposite the funnel.

C. Place the lid securely on the can without bumping the can much or allowing your head to be over the top of the can.

D. Hunker down with your head under the chair (or whatever is supporting the can)

E. Blow sharply into the tube.

Expected results:  Relatively violent explosion that may rupture the side seam of the metal can and will likely shoot the lid to quite a height.

This used to be a relatively common demonstration of a dust explosion.  Of course, coal dust, fine sawdust, or whatever burnable substance can be substituted.  The finer the fuel dust the more violent the explosion. Finer fuel gives more surface area in contact with atmospheric oxygen and a faster burn rate per unit weight of fuel.

When I was in the USAF a Senior Master Sgt special ordered "Electrical Safety Shoes" for everyone in the Training Devices Section" flight simulators and such.  We worked around dangerous voltages.  Everyone was trying on their new safety shoes but I read the labels and instructions in the shoe box first.  There were instructions on how to measure the conductivity of the shoes to ensure they were operable.  Another sticker went on say how they met bureau of mines specification such and such.  Well my little light came on to a dim glow as I realized that THESE ELECTRICAL SAFETY SHOES were built for the purpose of grounding the wearer to prevent the build up of static charges that could set off an explosion in a mine, grain elevator, spray booth, flour mill, gun powder or explosives plant or wherever explosive or highly combustable products were handled.  

Unfortunately we needed shoes to insulate us from ground not directly connect us to it.  These shoes could have got one of us killed.  I did a slightly unprofessional thing like shouting. "Sgt. Mc Bride, you idiot, you're going to get us killed" as I threw the shoes about 50 ft in his direction.  To save face at base supply he refused to return the shoes.  He told veryone to take them home and wear them to work on their cars or something where the steel toes would make you safe.

 8) 8)   Pat    8) 8)

[Buzz-sawyer]

LW
You remind me of me.....with all the curiosity and experimentation.....have you studied wood gasification...that will run your car!!!! people were doin it 60 years ago .....

[L. Wakefield]

   no, I haven't seen that- I've seen propane cars. Is it like that- gasify, collect in a tank etc- or do ya load a few chunksa wood inta the hopper and drive off?  lw

[L. Wakefield]

snip

2. a few feet (3-10) of flexible tubing (plastic, rubber, I don't recommend garden hose or large diameter tubing if you detonate by blowing by mouth)
2.1  You can use a shop air hose instead of blowing by mouth.

snip

 

   I'm a mite skeered of that one- whatever you do, don't inhale!   :D :D :D

[Hunter]

One of my good friends works at a mill in Maine.
He is in the bagger house, bagging the shavings.
They have to be super catuios about the dust. all of there wood is dried and they get all the by products in there room. they have massive air movers and absolutly no open flames.
 One guy did try to light a cigerette and the forman punched him in the mouth and asked him if he was wanting to kill them.
Needless to say, they have very strict rules and they dont take it lightly.
Hunter

[james]

its also refered to as a fuel-air explosive used by the military and for demolition

[sawguy21]

Just about any fine dust suspended in the air is a recipe for a ka-boom. A co-worker was using corn starch in a media blasting cabinet. I heard a loud WHOOOMP and ran over to see him standing there, his gloved hands inside the cabinet and his eyes and mouth the size of hubcaps. He had bumped the light in the cabinet
Reminds me of Halloween when us kids bought calcium carbide at the local machine shop until they figgered out what we were doing with it but that's another story.

[ksu_chainsaw]

Thats the reason that grain elevators explode too.  When I was woking on them to repair them, we couldnt use a torch on the larger elevators because of the exlposion risk, and we had to wet down everything around the area we were working.  Seveal years ago, an elevator in the Witchita area exploded from a buildup of too much grain dust.

Charles

[Ianab]

Not that I've been experimenting or anything...
but a cupfull of that really fine sawdust from the belt sander dust bag should only be thrown on the rubbish fire from a safe distance upwind... :D

Disclaimer... If You or any of your dumb buddys try this and loose your eyebrows... dont blame us

Another version is Milk Powder.. Dairy factory up north of here lost part of it's roof after a flash fire in stray powder.

[sawguy21]

Careful of them Darwin Awards. Don't want one.