Is the Compost Bin Likely to Self Combust (Spontaneously Combust)?
It is highly unlikely that a compost heap will self-combust under any normal composting conditions due to the moisture left in the decomposing waste. In fact most organic chemicals will only self-ignite around the 120°C mark and the maximum temperature most domestic compost heaps will achieve is 75°C.
The Science Behind The Theory
Scientific experts report that combustion is possible but only in extremely rare circumstances and it is near impossible to ignite a small domestic heap.
It can happen with very large dry heaps or haystacks and as such sizes over 2x2 meters are considered as a risk. The damp inner core decays creating heat and this heat does not escape fast enough (materials are self-insulating) and airflow becomes restricted. If this heat persists for long enough it can lead to ‘self-oxidation heating’ and push the temperature up to 120°C and hence self-ignite. Most reported compost fires have started with a poorly managed pile of wood or dry plant matter and 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.
Worried That Your HOTBIN May be Too Hot?
The internally generated heat in the HOTBIN will dry the contents to a certain extent, however once the temperature reaches 70-75°C these bacteria cannot survive and heat production is slowly reduced. You will often see a sharp spike in temperature when adding easy to digest items such as chicken pellets and grass.
The HOTBIN is designed to hot compost between 40-60°C (rarely over 70°C but not unheard of). Air is drawn in through the bottom of the bin and rises through the waste to be released as water vapour and carbon dioxide (both flame-retardants) through the valve. The combination of damp waste, steam and carbon dioxide reduce the chance of combustion significantly. The sun will also not create overheating inside the HOTBIN – the insulation properties of the material works both ways it keeps bacterial heat in but it also keeps the sun's heat out.
Although we stress that we are not combustion experts the science speaks for itself, so in summary it is extremely unlikely to happen - especially in a HOTBIN.
What if my HOTBIN’s Temperature is Consistently Above 70°C?
If your HOTBIN is sustaining temperatures of 70°C+ over a period of days you can take steps to cool it down. We advise opening the valve on the HOTBIN lid so it’s in a vertical position for a couple of hours (keeping a close eye on it) and once the internal temperature has fallen back to within hot composting temperatures of 40°-60°C to return the valve to its original position.
Please note: We do not recommend leaving the valve open for more than a couple of hours.
If you are concerned or have any questions you can contact the HOTBIN team freephone on 0808 168 8499 or email us at firstname.lastname@example.org.