Author Topic: Can a fresh mulch pile self ignite?  (Read 728 times)

EddieF

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Can a fresh mulch pile self ignite?
« on: October 11, 2021, 12:14:34 PM »
  This morning i saw my fresh brazil pepper tree mulch pile (mostly leaves) steam when i pushed top off with steel rake.  I pushed it to make room for more. 
Bought electric chipper, love it, not loving steaming pile.
I'm going out now to buy another 50' garden hose to leave there for wetting it.

Ed
« Last Edit: October 11, 2021, 04:20:55 PM by EddieF »

spaugh

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Re: Can a fresh mulch pile self ignite?
« Reply #1 on: October 11, 2021, 12:55:24 PM »
Its not going to ignite.  Its normal for mulch piles to warm up and compost as the organic matter starts to break down.  Pure tree trimmings are not potent enough to self combust.   If you had a pile of horse manure and kept it really well turned and got it cooking really hot it can ignite but even that is very difficult to achieve. 

If it makes you feel better, i get dump truck loads of mulch delivered and thry always steam for a month or 2.  Its totally normal and nothing to worry about.
Brad Spaugh

roblack

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Re: Can a fresh mulch pile self ignite?
« Reply #2 on: October 11, 2021, 01:47:39 PM »
Freaked me out first time I saw it.

Had just moved in, and chopped down most of the large trees surrounding the property to make room.

Yard went from looking like a jungle to looking like a war zone.

...smoldering piles of mulch and trimmings added to the effect.

It is not smoke. There is not much risk of fire. You would probably have a tough time igniting that pile without help.

EddieF

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Re: Can a fresh mulch pile self ignite?
« Reply #3 on: October 11, 2021, 04:20:13 PM »
Spaugh & Roblack, whew- thank you.  I'll continue piling it up.
Bought the rubber hose, needed it to water settle dirt, foliar feed & drench palms in that far corner anyway.  It'll get used.
Ed

slopat

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Re: Can a fresh mulch pile self ignite?
« Reply #4 on: October 11, 2021, 04:31:28 PM »

Composting piles/rows of waste at the calpoly dairy!

It does look like a ww1 zone in books and movies.



https://cafes.calpoly.edu/cal-poly-compost


roblack

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Re: Can a fresh mulch pile self ignite?
« Reply #5 on: October 11, 2021, 05:28:27 PM »

Composting piles/rows of waste at the calpoly dairy!

It does look like a ww1 zone in books and movies.



https://cafes.calpoly.edu/cal-poly-compost

Wrong war, but...

"I love the smell of (smoldering mulch) in the morning"

zands

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Re: Can a fresh mulch pile self ignite?
« Reply #6 on: October 11, 2021, 10:36:13 PM »
That steam is good. It shows that things are cooking and breaking down into eventually humus and compost.
Do not breath in that steam! It can be full of mold as in toxic mold.

Daintree

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Re: Can a fresh mulch pile self ignite?
« Reply #7 on: October 12, 2021, 03:47:04 PM »
I don't know about mulch, but wet hay or straw bales CAN self-ignite.  Speaking from personal experience.

Carolyn

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Re: Can a fresh mulch pile self ignite?
« Reply #8 on: October 12, 2021, 08:38:19 PM »
You inspired me to do some research Carolyn, so I did a trusty Google search.

Holy Cow! Seems mulch does spontaneously combust.

Wonder if anyone has tried this as a fire making tek on Naked and Afraid?

https://www.turfscapeohio.com/blog/prevent-common-mulch-fire

slopat

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Re: Can a fresh mulch pile self ignite?
« Reply #9 on: October 13, 2021, 12:16:03 AM »
Silage gone bad??

Btw: Around most of California,  it's best to keep mulch and decorative bark a distance away from the home. Last year, a friend's neighborhood yards lit up... strong dry Santa Ana winds and embers from nearby grass fire. Fortunately the stucco and tile roofs were resistant enough for CDF and local fire dept to put down.

They have river rock and pavers now. Melted waste cans and toasted ornamentals next to the house is a scary sight! A wind tunnel between the houses effectively fanning some major heat.

Jamesther

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Re: Can a fresh mulch pile self ignite?
« Reply #10 on: October 13, 2021, 02:28:09 PM »
Buy a compost thermometer. Reotemp makes good ones.

pineislander

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Re: Can a fresh mulch pile self ignite?
« Reply #11 on: October 14, 2021, 09:10:14 AM »
Yes, can definitely spontaneously combust. I had 2000 cubic yards brought in and it was the dry season so I wet it down very well, spent a whole day with a firehose. The problem is usually worse in taller piles. A nearby mulch/compost operator has continual fires because their site space is small and they pile up too high.
https://www.youtube.com/watch?v=lPhuKld5o8s
 
The more professional composting operations will use long windrows for this reason.

Usually a 10 ft tall pile with average to moist moisture content will be able to reject the heat formed by decomposition, getting taller than that is the problem.
https://www.biocycle.net/fire-prevention-at-composting-mulch-facilities/

Mike T

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Re: Can a fresh mulch pile self ignite?
« Reply #12 on: October 17, 2021, 07:34:36 AM »
Just yes

spaugh

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Re: Can a fresh mulch pile self ignite?
« Reply #13 on: October 17, 2021, 03:22:10 PM »
Surely this would be happening at least occasionally if it were really a problem yet Ive never heard of a mulch pile catching fire around here.  Theres mulch piles all over town that the tree trimmers leave out at parks and schools.  Wildfires are a real problem here yet ive never heard of one starting because of a mulch pile.  We have single digit humidity and crazy winds that would surely exacerbate the problem if it existed,

When I first moved in to this house we started using a LOT of mulch and experimented with composting.  I actually tried to get mulch piles to get hotter and speed up the decomposition process.  I have a long thermometer that gets inserted into compost heaps.  I used to put perferated septic pipes into the mulch piles to draw air into the center of the piles.  Also experimwnted with adding 50lb bags of 46-0-0 urea mixed into the piles.  I would add grass clippings, horse manure, urea, hosed the piles to keep the humidity correct so they would cook as fast as possible.  Never did the temperature get close to catching fire. 

In the end I decided making big compost piles was not worthwhile and have since shifted to burying scrap material or chipping in place etc and not composting anything.  Even our chicken manure we dont bother composting.  I use everything fresh and let it decay in place.  Never had any fires start.

Im not saying its impossible but seems the problem is overstated for single truckload of green waste.
« Last Edit: October 17, 2021, 03:26:34 PM by spaugh »
Brad Spaugh

roblack

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Re: Can a fresh mulch pile self ignite?
« Reply #14 on: October 17, 2021, 03:33:22 PM »
...but remember to "duck and cover" whenever the mulch fires come your way!

=)

spaugh

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Re: Can a fresh mulch pile self ignite?
« Reply #15 on: October 17, 2021, 04:22:17 PM »
Stop drop and roll ::)
Brad Spaugh

pineislander

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Re: Can a fresh mulch pile self ignite?
« Reply #16 on: October 17, 2021, 05:00:18 PM »
Surely this would be happening at least occasionally if it were really a problem yet Ive never heard of a mulch pile catching fire around here.  Theres mulch piles all over town that the tree trimmers leave out at parks and schools.  Wildfires are a real problem here yet ive never heard of one starting because of a mulch pile. 
Im not saying its impossible but seems the problem is overstated for single truckload of green waste.

Maybe you didn't see this one.
https://www.latimes.com/california/story/2021-02-18/wind-driven-mulch-fire-breaks-out-in-ontario

I guess it wasn't clear. The main problem comes when a pile is loo large. The thermodynamics doesn't work once these piles get too large. Some of the danger comes from fermentation which produces alcohol. The alcohol has a low enough flash point and when hot alcohol vapor hits good air flow it can sponateneously combust.

What needs to happen to keep them safe is large enough surface area to radiate the heat generated so that temperature doesn't get too high deep inside, or keep moisture levels high enough that the water content absorbs the heat and vents off. In a smaller pile the surface area compared to the total mass is enough to reject the heat safely. But, if made too large, the temperature deep within the core is insulated from the outer part allowing heat to rise too much. At that point, what usually happens is that a "chimney effect" forms a duct between the core, and exit point for air flow up high, and an air inlet lower down.
At that point, a flashover can happen.

Bottom line, keep pile small, the sweet spot seems to be ten feet(3-4 meters).

spaugh

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Re: Can a fresh mulch pile self ignite?
« Reply #17 on: October 17, 2021, 05:07:11 PM »
I didnt see that its not close to me but thats a green waste center with huge piles like you are saying.  My point is only thats is very difficult for the average homeowner to get a truckload of mulch to ignite.  The recycling places have those giant piles and are moving it around with big machinery and keeping it well turned and its all inoculated with the right microbes etc to be able to get that hot. 

My neighbor has a horse boarding ranch with over 100 horses.  They take out big rig loads of horse crap every week.  Many years ago he let his piles get too large and one of them caught on fire. 

I tried really hard to get some piles to get that hot.  I really wanted to see how hot it could go.  If it caught fire I would have been happy, it just wasnt happening no matter how hard i tried to make it happen. 
Brad Spaugh

EddieF

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Re: Can a fresh mulch pile self ignite?
« Reply #18 on: October 17, 2021, 07:53:50 PM »
So far so good for mine.  I do push the top of pile daily as i dump more to keep making room for more.
Didn't see any steam today.  Weird that it becomes very light grey color.  Almost looks ash color.  My stuff is very green, meaning not dry old leaves, suppose that makes difference why it gets hot vs dry stuff?

pineislander

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Re: Can a fresh mulch pile self ignite?
« Reply #19 on: October 18, 2021, 07:57:38 AM »
So far so good for mine.  I do push the top of pile daily as i dump more to keep making room for more.
Didn't see any steam today.  Weird that it becomes very light grey color.  Almost looks ash color.  My stuff is very green, meaning not dry old leaves, suppose that makes difference why it gets hot vs dry stuff?
The light gray and low steaming is telling you the pile is dry. I am told they may be actinomycete bacteria which thrive in hot conditions. It is hard to get water into a large pile they tend to shed water like a thatch roof. It will penetrate so far then begin to run sideways. The pros use a turning machine which sprays water to replenish moisture as it moves along the windrow.
https://ozturners.com.au/product/ct-compost-turners/

If you want to wet a large pile the best solutuion is to install micro sprinklers along the top and run water slowly so it has time to soak in. Over the course of a Florida summer rainy season this happens but some material may still remain dry inside if it is aligned to shed water.
 
Be careful if there is a lot of free flying white dust in dry mulch. I have become ill after moving dusty compost all day using a front end loader. Some days I would haul 100 or more bucket loads then spread with rake and fork. My lungs felt heavy and I began to have headache and cough. I had to resort to an N-95 rubber cartridge style dust respirator.
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