Sawdust overheating?

[Silverfoxfintry]

This may seem a silly question, but. Our sawmill is now setup in its semi permanent position alongside the workshop.
In order to stop buildup the wet sawdust is ducted into a large collector.
When emptying the bags into a 1ton "builders bag" I noticed that the damp sawdust was warm.
I know that Hay and Straw can overheat and go on Fire. Can sawdust do the same?
Thanks.

Iain 

[SawyerTed]

The short answer is yes.  Sawdust can "go into a heat" just like green or wet hay, piles of manure, piles of mulch and even grass clippings do so.  It's part of the natural composting process.  Unattended, a pile of damp sawdust can get hot enough to catch fire.  

Glad you got to it before it got worse!

[mike_belben]

Throw some greens in there and itll really warm up.  


Grass and sawdust makes fast compost. 

[Southside]

Yup - the heat is a byproduct of sugar breakdown in the presence of oxygen by microbes.  Once the sugar is all gone or the oxygen supply is exhausted the heat will stop, which is why we plastic wrap green baleage and it does not catch fire.  Baleage is put up ideally between 45% and 65% moisture content - just about the same as green logs are.  The bales will heat up to about 100F for a short time then as soon as the oxygen is gone the bugs die and it cools off to ambient temp.  Wrapped properly the plastic does not allow any oxygen in.  Eventually the ph drops and we have a stable feed.

In your case you can't eliminate the oxygen supply so the bugs will keep breaking down the sugar and things will get hotter and hotter.  Conditions are right - poof!!   

Now eliminate the sugar because your logs are long dead, the moisture is low for the same reason, or the packing of sawdust into those bags that hold the heat and keep conditions right and green sawdust is not a threat.  

[KEC]

I worked at a sawmill back in the 1970's  and one of the lumber salesmen told about a mill that hauled their sawdust out behind the mill and just kept pushing it back, many feet deep. I guess that was common practice in some places. That pile of sawdust started burning and smoldered for a very long time; how long I don't remember.

[barbender]

There's a defunct wild rice processing plant just a few miles down the road. I worked there 20 some years ago. They had blown the rice hulls out into a swamp out back over the years. It was 10-15 feet deep, and it would occasionally start on fire deep underneath. The DNR would demand they put it out, so they would dig it up with an excavator and try to get it out. It was tough to get at because it was burning so far down. They would send me out with several hundred feet of hose and try to douse it with water, some of those burning chasms looked like Hell😬 Not a job  cared for, I was skittish of the ground caving in and falling into a fire underneath. 

[YellowHammer]

The key is to cycle the sawdust through the bin before it has time to compost. If you empty the bin and the sawdust is black, it's been there too long.  If it still looks like clean sawdust but is warm, well, empty it and dispose of it. 

[donbj]

I worked at a sawmill back in the 1970's  and one of the lumber salesmen told about a mill that hauled their sawdust out behind the mill and just kept pushing it back, many feet deep. I guess that was common practice in some places. That pile of sawdust started burning and smoldered for a very long time; how long I don't remember.

Exactly! I worked at a mill where all the yard clean up and waste was dumped in to a handy ravine. Every spring we were fighting that thing as it lit on fire

[WDH]

I have seen large sawdust piles that have burned and smoldered for many months at a time back in the early 1980's. 

[Don P]

A pile at a mill nearby burned all winter a few years ago, hard to put out.
There was a man, I think in France years ago that was heating his house by running hose in a compost pile as he built the pile. Then he piped it back to the house like an outside wood boiler.

[Silverfoxfintry]

I checked the bags yesterday and they have cooled down. 

Thank you all for the information.

Iain.

[curved-wood]

Lucky that the veneer machine didn't hit any forgotten metal tap ;D
I have seen some maple logs that were tapped many years before. Impossible to see any sign. The logger is not the most honest guy around ...he knew it, but didn't tell me. I was sleeping a bit on the switch and didn't ask myself why those top grade veneer logs were coming to my place especially from that logger. The logs were long enough that I was able to cut the part with the marks of the tapping and sell it with a premium. The rest of the log was clear and white

[curved-wood]

sorry my post went in the wrong place