The daily mail today reported a devastating fire that wrecked a family’s home. The source of the fire was a compost bin.
Anything that can be done to avoid something similar would seem advisable. We have no reason to doubt the source of the fire as a dry compost heap, however the term ‘spontaneous combustion’, is always a mysterious word that conjures up things outside our control.
Was it spontaneous? Perhaps we’ll never really know and it is doubtful those affected will really care – a fire is a fire. If we have an expert in our facebook community, or we know someone from the fire brigade they might like to help with a little more detail. Here’s what we researched about ‘compost heaps catching fire’ as one of the myths & legends for our compost FAQ.
We looked up a number of papers on the topic and they all used the same science and technical facts on combustion to establish is it possible (yes it is) and is it probable/likely (no it is not).
Spontaneous combustion is well documented in large haystacks and occasionally large compost heaps – both can create the same dry conditions, poor airflow, and poor heat transfer to result in the heat from decomposition being ‘trapped’ and resulting in further oxidation reactions that eventually lead to organic material self-igniting at around 150C – ie spontaneous combustion. There is a good (if rather detailed) summary at: http://www.jgpress.com/BCArticles/2000/01004.html.
I have to stress no-one at HOTBIN is a combustion expert, but our reading of the literature makes us think that it is near impossible to ignite a small compost heap – you had to have a very large dry heap, a 2m*2m heap was signalled as risky. Most domestic heaps are half or a quarter of this size. The reports normally comment that fires in dry waste and/or compost sites are most often linked to the inadvertent addition of hot ashes, cigarettes and other materials that were already alight.
So what doHOTBIN users need know? Well the HOTBIN is designed to work HOT (up to 75C), but it the inside compost rarely over dries. Water vapour and carbon dioxide are constantly flowing to the valve. The combination of damp waste, steam and carbon dioxide reduce the chance of combustion. The sun will not create overheating inside the HOTBIN – the insulation works both ways it keeps bacterial heat in but it also keeps the suns heat out. The compost bin pictured in the newspaper report is not ours so we are not best placed to comment directly on its design.
So yes avoid super dry compost bins – but pelase don’t go out and saturate your HOTBIN compost with water – if you do, for sure it won’t burn, but it also won’t compost – you’ll just get and anaerobic stinky mess.
In conclusion as with most things there are risks and we can’t say no never BUT the conditions in a HOTBIN make it most unlikely HOWEVER we cannot account for human error either.