Wet shavings Cumbustible?

[Denny Nebgen]

Another question. Hadn't thought of this or given it any concern and I have turned several wet bowls before. But, tonight it crossed my mind that all these wet shavings might be combustible ? Is that the case or am I looking for zebras on the plains of Kansas?

My MO is to rough turn a wet blank, put it into a box with the wet chips all around it and fold up the box lid, mark what's in it and set it aside for several months. What is the chance that these chips could ignite?

[Jeffrey J Smith]

I'm more than happy to be proven false, but I doubt there's a problem - never heard of chips spontaneously combusting (if that's what you're asking about). Seems like most of the moisture is from water held within the cell structure. Unless you're turning something incredibly pitchy I think that mold is more of a problem than fire in the situation you describe.

[Denny Nebgen]

I'm more than happy to be proven false, but I doubt there's a problem - never heard of chips spontaneously combusting (if that's what you're asking about). Seems like most of the moisture is from water held within the cell structure. Unless you're turning something incredibly pitchy I think that mold is more of a problem than fire in the situation you describe.


Thank you for the reply. I haven't had an issue but, it crossed my mind yesterday and i thought if it was an issue someone on here would know.

[John K Jordan]

Thank you for the reply. I haven't had an issue but, it crossed my mind yesterday and i thought if it was an issue someone on here would know.

I've never heard of a case but from what I've read it may be possible for wet shavings/chips to create enough heat to spontaneously combust but more likely if the quantity is huge. Perhaps read what I found with a google search:
https://www.imcontrol.com.au/white-papers/woodchip-stockpile-combust/

Things like large piles of hay, grass, and compost have often gotten hot enough to combust. Barns have burned to the ground from putting up hay bailed before it was dry enough. I got some bales like that once that started to heat - got to almost 200F inside as measured with a thermocouple probe.

When turning big piles of manure/hay compost I've often see smoke and ash from hot spots! My piles might be 12' wide and 6' high.

I personally don't think a small quantity of shavings could generate enough heat to combust. It might be interesting to monitor the temperature of one of your drying boxes occasionally with a remote thermal meter. I use this one around the shop:

https://smile.amazon.com/gp/product/B0089N2ZH6
I bought this much cheaper one for a friend and it works well:
https://smile.amazon.com/gp/product/B013X0NQT0

Or uses a thermocouple. I use this:
https://smile.amazon.com/gp/product/B001EUB6BM
https://smile.amazon.com/gp/product/B005OXQUOI

JKJ

[Reed Gray]

Wet shavings on the floor are no problem. Like John said, bigger compost piles can generate enough heat, through decomposing, that things can combust. If you are going to build a mound of shavings, do it outside, and away from the shop. There is a yard waste recycling center that I drive by frequently, and they always have machines turning over their compost piles. The piles are smoking and/or steaming when they are turned over.

Personally I worry more about forgetting a rag that has oil finish on it. Always take them outside and spread out flat on the gravel. Some take them directly to the wood stove. I did have a rag with walnut oil in it combust once. I had experimented with lots of variations, but since the oil dries so slowly, it generally doesn't combust. I did set one outside on a black plastic bag of shavings in mid summer sun, and that triggered a reaction. Take care, always!

robo hippy

[John K Jordan]

...

Personally I worry more about forgetting a rag that has oil finish on it. Always take them outside and spread out flat on the gravel. Some take them directly to the wood stove. I did have a rag with walnut oil in it combust once. I had experimented with lots of variations, but since the oil dries so slowly, it generally doesn't combust. ...


I've read just spreading them out on gravel or concrete outside is not enough. The recommendation is to weight down the corners so the wind can't blow the rag into a wad up against something that can burn.

I've quit using cloth to apply oil finishes to woodturnings. I use small pieces of paper towel (usually 2x3") which dry quickly or get thrown in the burn barrel.

JKJ

[Eugene Dixon]

If the shavings aren't compressed tightly, i.e., they can breathe, there is no issue. Hay bales, silage, compost, etc., are compressed from weight (or baler springs) and the thermal transfer to air is throttled. "Keep 'em loose, they won't smoke." just made that one up.

Like John, I've restacked a few hay bales because of internal heating - usually the hay was baled and stacked while still a little green.

Nothing like the sight of steam and smell rolling out of the silage pit when digging out a load to feed the cows. Like firewood, it would warm you twice.

[Alan Rutherford]

Years (and years and years) ago I and other Boy Scouts visited a sawmill and were climbing around on a mountain of sawdust. Someone stuck a pole like a broomstick into the pile as far as he could and when he pulled it out, the end was hot. I believe it was hot enough to notice, not too hot to hold onto. I wouldn't worry about combustion in a box but, as mentioned, I'd worry about mold.

[Denny Nebgen]

Thank you everyone. I won't be too concerned then.

[Rich Aldrich]

At work, we have large pile of sawdust that we burn in our boilers. Since we stopped driving on it with the end loader, we haven't had a spontaneous combustion issue. Its the compression that causes the issue - as others have said.

[Michael Edelman]

What generates heat in wet hay, we’d sawdust, and compost piles is bacterial and chemical decomposition. If the bale or pile is loose enough for air to circulate, then the heat can escape via convection. If it’s packed tight, heat builds up and combustion can occur.

What happens in linseed oil soaked rags is similar. The polymerization of the oil generates heat, and if the rages are spread out, the heat will dissipate. If they’re stuffed in a wastebasket, air can’t circulate, and heat will build up. As the heat increases, the polymerization reaction speeds up, and eventually it reaches ignition temperature.