Hot compost...

[JimmyJames]

I was mildly miffed to see that one of my 2 compost heaps went up in flames sometime last week.  I arrived at the plot to see a pile of ash where the compost once was!

Is it more likely to have been caused by the heat within the pile, or by a passing vandal with a box of matches?

I find it hard to belive that it would have got hot enough to combust,  but if it was lit on purpose I cant see why they would have left the other pile untouched.

I have a bunch of pallets ready to make a compost area/bin out of, and Im glad i hadnt already made it - as it would have gone up in flames!

Does anyone have any experience of compost heaps going up in flames?
Should I have added water to it?

Thanks
J

[JimmyJames]

[SMP1704]

Well I wasn't going to mention anything, but.............since you posted first JJ

Last year when it was REALLY hot, first year on plot and placed my bins in full sun all day.  I have two daleks.  One was half full, when I lifted the lid and looked inside, I found all the contents where grey and ash like.

I took that as a sign that I needed to keep the bins a bit damper ::)  No problems this year. 

I'm surprised JJ that an open heap would spontaneously combust tho - perhaps it did have a bit of help?

[Robert_Brenchley]

I sometimes find dry ashy layers within our grass cutting mountain, but it's not due to combustion. If that was what had happened, the dalek would have gone up in smoke.

[jennym]

Have frequently had smouldering compost heaps here, yes they do spontaneously ignite, especially those with plenty of horse muck in.
As an aside, a neighbour, new to the area who'd always lived in a town, complained to the police when the huge heap of muck on the farm at the top of the hill a mile or so away started smouldering (as it does most years) and was most miffed when they told her they didn't see it as a problem.

[SMP1704]

I think the reason that the dalek didn't go up in flames is that there was not enough oxygen, so when the fuel had run out (leaves, etc) it stopped burning.  I think I was lucky not to have visted sooner and lifted to lid off then :o

I'm surprised that JJ's open heap went up unaided as it hasn't really been that hot over a sustained period of time.

When my neighbour's shed was torched, the two police officers tried to convince her that it was started by the bags of compo that she stored in there spontaneously combusting............. ???

[Robert_Brenchley]

If the contents of the dalek were hot enough to ignite, wouldn't the plastic have melted? that would then let the air in, and up it would go!

[SMP1704]

This is true Robert, but you only get flame with oxygen............Honestly I don't know.......

Any firemen/women/people want to help out????

[telboy]

JJ,
I'm somewhat surprised that a compost heap of any design would 'self ignite?
Temps. in the heat of the day do reach high temps. but not much higher than 60*?

[JimmyJames]

Thanks for your thoughts peeps, and sorry for my delayed reply!

I think I will keep an air of suspicion around the whole affair.  Will probably mention it to someone at the site in case there have been a spate of compost arson attacks!

:)

[Robert_Brenchley]

It's perfectly true that you only get a flame with oxygen, but in order to get that flame, you have to heat whatever it is to ignition point. That's going to be way above the temperature at which plastic melts. An ordinary clothes iron will melt a lot of plastic but contact doesn't set anything on fire.

[Baccy Man]

Actually it is only usually compost heaps which are not properly aerated which spontaneously combust.
A so called slow heap will eventually attain enough mass for the thermophillic reaction to start in the middle of the heap. As slow heaps are rarely turned this results in an anaerobisis in the middle of the heap which traps the carbon dioxide, methane & nitrous oxide gases produced by the thermophillic reaction breaking down the material. If the heap is turned these gases are released into the atmosphere if not then they will continue to build up & can in very rare instances where the heap has a moisture content between 25%-45% can cause the heap to spontaneously combust.
It is far more common in commercial windrows where tempereatures in the heap regularly exceed 93°C. Typically you would require a heap at least 4 meters high to acheive those temperatures so it is extremely unlikely do be the cause in a domestic compost heap.

[Lauren S]

I did a google to find out about compost heaps self combusting. This is what I found.  ::)

http://news.bbc.co.uk/2/hi/europe/isle_of_man/5232382.stm

Lauren  :o

[telboy]

Lauren,
Well it would self ignite on the Isle of Man after midnight wouldn't it?