Mulch fire creates burning questions about composting and green waste management


August 14, 2019 07:06:10

We are all doing the right thing by putting food scraps and garden waste in our green bins, right?

Key points:

  • A mulch fire at Lismore’s council-run tip has been smouldering for days
  • It appears the mulch self-combusted due to the heat generated by the composting process, combined with low humidity and strong winds
  • The fire prompted public health warnings to be issued due to the smoke

Well, yes — but that is only the start of a story that has ended with an intense blaze at a council tip in northern New South Wales.

Up to 20,000 tonnes of mulch at the Lismore Recovery and Recycling Centre continue to smoulder, days after they self-combusted due to a combination of heat generated by the composting process, low humidity and strong winds.

The fire spread to a huge recyclables storage shed, sending plumes of acrid smoke across parts of Lismore and forcing the local Public Health Unit to issue an air pollution health alert.

Lismore City Council is still waiting to safely extinguish the mulch using water and heavy machinery to pull the piles apart.

Playing with fire

Waste management and recycling expert, Shane McIntosh, said the essential ingredient for converting green waste and food scraps into compost was heat.

Temperatures above 55 degrees Celsius need to be maintained for at least 15 consecutive days to eliminate pathogens.

Dr McIntosh said it was unusual for compost to self-combust, but not unheard of, given the chemical processes at work and the size of the piles held at many council and commercial facilities.

“It’s a biological process and sometimes nature decides it is going to work in overdrive and you do get these conditions where you get excessive heat build-up very quickly,” he said.

The Council’s executive director of infrastructure services, Gary Murphy, said compost was not normally a difficult substance to manage, even with the strict safety regime imposed by the NSW Environment Protection Authority (EPA) that requires regular wetting and aerating of the piles.

The EPA also limits how much waste a facility can receive each year and how much can be stored at any one time.

Mr Murphy said in this instance, the fire was unavoidable.

“Compost can ignite and normally the controls are adequate, but with those extreme conditions, it just led to a combustion event,” he said.

Don’t try this at home

Rob Jansen, from Fire and Rescue NSW, said anyone working with green waste and compost should be aware of its capacity to self-combust.

“You can have a pile that is slowly smouldering and that can be very difficult to tell, until it becomes a big hollow area within that pile and it all falls in on itself, and then that fire becomes external,” Mr Jansen said.

He said the best way to avoid fire in green waste was to follow the same safety practices as followed by the large commercial operators.

“These types of incidents can happen,” Mr Jansen said.

“If it’s a 40-degree day in summer, that heat is adding to the heat within the pile.

“It’s just a matter of all little circumstances lining up and when all those combinations of things all add up together, then there is a possibility of spontaneous combustion.”

The EPA will be investigating the fire at Lismore once it is fully extinguished.








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