# Why does sawdust burn so poorly? **URL:** \ **Category:** Factual Questions\ **Created:** [March 18, 2012, 3:18pm UTC](https://boards.straightdope.com/t/why-does-sawdust-burn-so-poorly/616137 "2012-03-18T15:18:59Z")\ **Posts on this page:** 17\ **Page:** 1
**Author:** ![Vicullum](https://avatars.discourse-cdn.com/v4/letter/v/6de8d8/32.png) [@Vicullum](https://boards.straightdope.com/u/Vicullum)\ **Post date:** [March 18, 2012, 3:18pm UTC](https://boards.straightdope.com/t/why-does-sawdust-burn-so-poorly/616137/1 "2012-03-18T15:18:59Z")
Take a log and set if afire and you get a nice flame. Break it down into kindling first, and it’ll burn even faster. Reduce it to sawdust, however, and at best you get a weak, smoldering flame. Why? (I realize sawdust can create an explosion when mixed with air and ignited, but I’m talking about when it just sits in a pile.) ---
**Author:** ![Ca3799](https://avatars.discourse-cdn.com/v4/letter/c/9f8e36/32.png) [@Ca3799](https://boards.straightdope.com/u/Ca3799)\ **Post date:** [March 18, 2012, 3:30pm UTC](https://boards.straightdope.com/t/why-does-sawdust-burn-so-poorly/616137/2 "2012-03-18T15:30:35Z")
I would think that the saw dust doesn’t allow the proper mix of fuel and oxygen. You need three things for a fire- oxygen, fuel and heat. The dust does not allow for good airflow. I bet if you poked tunnels in the dust, it would burn slightly better. ---
**Author:** ![am77494](https://avatars.discourse-cdn.com/v4/letter/a/d2c977/32.png) [@am77494](https://boards.straightdope.com/u/am77494)\ **Post date:** [March 18, 2012, 4:09pm UTC](https://boards.straightdope.com/t/why-does-sawdust-burn-so-poorly/616137/3 "2012-03-18T16:09:06Z")
My wag is that sawdust is a good insulator (all that trapped air) and prevents the heat from getting inside to the bulk. Also, as posted above, it prevents air circulation. ---
**Author:** ![billfish678](https://avatars.discourse-cdn.com/v4/letter/b/7bcc69/32.png) [@billfish678](https://boards.straightdope.com/u/billfish678)\ **Post date:** [March 18, 2012, 4:10pm UTC](https://boards.straightdope.com/t/why-does-sawdust-burn-so-poorly/616137/4 "2012-03-18T16:10:56Z")
Perhaps all that trapped air in there is causing the pile to act like an insulator? Good question though because at first glance you’d think sawdust would burn quite well. Darnit, beaten by 5 seconds! ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [March 18, 2012, 4:25pm UTC](https://boards.straightdope.com/t/why-does-sawdust-burn-so-poorly/616137/5 "2012-03-18T16:25:59Z")
I think it has to do with particle size. If you look at a how a piece of wood burns, the fibers tend to curl, and pull away from each other, which exposes unburned wood to the air. When sawdust burns, the outside chars, and the tiny particles pack so close together that the unburned dust beneath them never gets any air. ---
**Author:** ![Reply](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/reply/32/15952_2.png) [@Reply](https://boards.straightdope.com/u/Reply)\ **Post date:** [March 18, 2012, 4:32pm UTC](https://boards.straightdope.com/t/why-does-sawdust-burn-so-poorly/616137/6 "2012-03-18T16:32:06Z")
> [@Vicullum](#): > > I realize sawdust can create an explosion when mixed with air and ignited Homemade fuel-air explosives? They didn’t teach us THAT in woodshop. ---
**Author:** ![drachillix](https://avatars.discourse-cdn.com/v4/letter/d/48db29/32.png) [@drachillix](https://boards.straightdope.com/u/drachillix)\ **Post date:** [March 18, 2012, 4:40pm UTC](https://boards.straightdope.com/t/why-does-sawdust-burn-so-poorly/616137/7 "2012-03-18T16:40:54Z")
My combustion chem class was a long time ago but I will give it a stab. Sawdust IIRC tends not to burn due to lack of airflow (too rich to burn). It can also trap alot of heat and have a fire smolder in it for weeks or even months waiting for the right conditions to flare up. However, given the right conditions sawdust (or almost any particulate matter) can make for some wicked fires and explosions. > **[Dust explosion](https://en.wikipedia.org/wiki/Dust_explosion)** > > A dust explosion is the rapid combustion of fine particles suspended in the air within an enclosed location. Dust explosions can occur where any dispersed powdered combustible material is present in high-enough concentrations in the atmosphere or other oxidizing gaseous medium, such as pure oxygen. In cases when fuel plays the role of a combustible material, the explosion is known as a fuel-air explosion. > Dust explosions are a frequent hazard in coal mines, grain elevators, and other industrial ... With the right dispersion of material and an ignition source you effectively get > **[Thermobaric weapon](https://en.wikipedia.org/wiki/Thermobaric_weapon)** > > A thermobaric weapon, also called an aerosol bomb, or a vacuum bomb, is a type of explosive that uses oxygen from the surrounding air to generate a high-temperature explosion. The fuel–air explosive is one of the best-known types of thermobaric weapons. > Thermobaric weapons are almost 100% fuel and as a result are significantly more energetic than conventional explosives of equal weight. The fuel is often elemental. Many types of thermobaric weapons can be fitted to hand-held launchers, and ca... ---
**Author:** ![johnpost](https://avatars.discourse-cdn.com/v4/letter/j/f17d59/32.png) [@johnpost](https://boards.straightdope.com/u/johnpost)\ **Post date:** [March 18, 2012, 4:57pm UTC](https://boards.straightdope.com/t/why-does-sawdust-burn-so-poorly/616137/8 "2012-03-18T16:57:47Z")
pellets, which can be made by compressing sawdust, burn well. i agree it’s air and airflow. ---
**Author:** ![Reply](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/reply/32/15952_2.png) [@Reply](https://boards.straightdope.com/u/Reply)\ **Post date:** [March 18, 2012, 5:24pm UTC](https://boards.straightdope.com/t/why-does-sawdust-burn-so-poorly/616137/9 "2012-03-18T17:24:10Z")
nm ---
**Author:** ![aceplace57](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/aceplace57/32/3500_2.png) [@aceplace57](https://boards.straightdope.com/u/aceplace57)\ **Post date:** [March 18, 2012, 6:15pm UTC](https://boards.straightdope.com/t/why-does-sawdust-burn-so-poorly/616137/10 "2012-03-18T18:15:22Z")
Pellet stoves are really popular in rural areas. Pellet fuel is cheaper than propane or electric. A great use for very fine sawdust that would have been thrown out. As the OP noted a pile of sawdust doesn’t burn well. It needs to be compressed into a log or pellet. > [@](#): > > Pellet fuel is a renewable, clean-burning and cost stable home heating alternative currently used throughout North America. > Our pellet fuel is made from clean sawdust, much of which comes from our own lumber operations in the heart of the Appalachian Region of the United States in West Virginia. > > Why Choose Hamer’s Hot Ones? The dust is compressed into pellets that produce clean, reliable heat with low emissions and an extremely small amount of ash. > **[Hamer Pellet Fuel](https://hamerpellet.com/)** ---
**Author:** ![IAmNotSpartacus](https://avatars.discourse-cdn.com/v4/letter/i/cc9497/32.png) [@IAmNotSpartacus](https://boards.straightdope.com/u/IAmNotSpartacus)\ **Post date:** [March 18, 2012, 6:21pm UTC](https://boards.straightdope.com/t/why-does-sawdust-burn-so-poorly/616137/11 "2012-03-18T18:21:14Z")
And yet curiously enough, the chief ingredient in firelogs is sawdust, either compacted by itself or compacted with paraffin. ---
**Author:** ![JBDivmstr](https://avatars.discourse-cdn.com/v4/letter/j/b4bc9f/32.png) [@JBDivmstr](https://boards.straightdope.com/u/JBDivmstr)\ **Post date:** [March 18, 2012, 7:08pm UTC](https://boards.straightdope.com/t/why-does-sawdust-burn-so-poorly/616137/12 "2012-03-18T19:08:58Z")
> [@Vicullum](#): > > … > (I realize sawdust can create an explosion when mixed with air and ignited, but I’m talking about when it just sits in a pile.) > [@Reply](#): > > Homemade fuel-air explosives? They didn’t teach us THAT in woodshop. It has to a **very** dry and _ **very fine** _ sawdust (besides having the proper air/sawdust ratio) in order to react explosively. ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [March 18, 2012, 7:21pm UTC](https://boards.straightdope.com/t/why-does-sawdust-burn-so-poorly/616137/13 "2012-03-18T19:21:16Z")
Yeah, it’s all about the fuel/air ratio. Sawdust of the right grain size and packed at the right density is incredibly flammable. In pellets and fake logs it’s actually compacted to reduce the flammability and create a slower burn. ---
**Author:** ![Lynn\_Bodoni](https://avatars.discourse-cdn.com/v4/letter/l/e47c2d/32.png) [@Lynn\_Bodoni](https://boards.straightdope.com/u/Lynn_Bodoni)\ **Post date:** [March 18, 2012, 7:30pm UTC](https://boards.straightdope.com/t/why-does-sawdust-burn-so-poorly/616137/14 "2012-03-18T19:30:35Z")
> [@Reply](#): > > Homemade fuel-air explosives? They didn’t teach us THAT in woodshop. Hell, they never taught us any of the really useful stuff in school. For instance, I took 5 years of Spanish in middle and high school. I move over to Spain, and I find that I desperately need to inform someone that he’s the product of a union between a syphilitic goat and a dimwitted dog. However, despite getting excellent marks in my Spanish vocabulary tests, I am unable to express myself adequately. Now, if you’ll excuse me, I have to dig up some sawdust and do some practical science experiments. ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [March 18, 2012, 7:36pm UTC](https://boards.straightdope.com/t/why-does-sawdust-burn-so-poorly/616137/15 "2012-03-18T19:36:49Z")
> [@Lynn\_Bodoni](#): > > Hell, they never taught us any of the really useful stuff in school. > > For instance, I took 5 years of Spanish in middle and high school. I move over to Spain, and I find that I desperately need to inform someone that he’s the product of a union between a syphilitic goat and a dimwitted dog. However, despite getting excellent marks in my Spanish vocabulary tests, I am unable to express myself adequately. > > Now, if you’ll excuse me, I have to dig up some sawdust and do some practical science experiments. An easy one is to fill about 2 inches of a soda straw or similar tube with very fine sawdust. Blow hard through the straw and direct the bloom of sawdust at a flame about 2 feet away. Then repeat using coffee creamer powder for a better effect. ---
**Author:** ![yabob](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/yabob/32/2821_2.png) [@yabob](https://boards.straightdope.com/u/yabob)\ **Post date:** [March 18, 2012, 9:40pm UTC](https://boards.straightdope.com/t/why-does-sawdust-burn-so-poorly/616137/16 "2012-03-18T21:40:43Z")
The general topic is “dust explosion”. Basically anything which will burn can become explosive if dispersed into the air as fine particles. I remember being taught about this as a kid using flour - stick a candle in a coffee can with a small amount of flour and a tube to blow through. Generates a nice little “whoomp”, and blows the lid off the coffee can. The Mythbusters did, IIRC, 500 pounds of coffee creamer after confirming a youtube video of someone’s “sawdust cannon”. It was quite impressive. I’m actually moderately surprised that most people didn’t learn about this as kids. Wiki on dust explosions: [http://en.wikipedia.org/wiki/Dust\_explosion](http://en.wikipedia.org/wiki/Dust_explosion) ---
**Author:** ![Anaglyph](https://avatars.discourse-cdn.com/v4/letter/a/ed8c4c/32.png) [@Anaglyph](https://boards.straightdope.com/u/Anaglyph)\ **Post date:** [March 19, 2012, 1:27pm UTC](https://boards.straightdope.com/t/why-does-sawdust-burn-so-poorly/616137/17 "2012-03-19T13:27:26Z")
> [@Lynn\_Bodoni](#): > > Hell, they never taught us any of the really useful stuff in school. > > For instance, I took 5 years of Spanish in middle and high school. I move over to Spain, and I find that I desperately need to inform someone that he’s the product of a union between a syphilitic goat and a dimwitted dog. However, despite getting excellent marks in my Spanish vocabulary tests, I am unable to express myself adequately. [Have a look at this book to round out your language skills](http://www.amazon.com/Mierda-Spanish-Never-Taught-School/dp/0452264243/ref=sr_1_1?ie=UTF8&qid=1332163536&sr=8-1)