Managing Fire Risks at Compost Facilities: Case Study

When training compost facility operators about fire risks and safety for composting facilities, I begin by saying that “fires are more common at compost facilities than most realize, particularly outdoor waste yardwaste composting sites during a warm, dry summer.”  I realized that this statement may lead one to a false sense of security that compost fires don’t happen during the winter months.

As I am currently updating the “Compost Facility Operator Manual”, I have to reflect on what is recommended. Its always helpful to have reality shape recommendations. I realize that the list of “key conditions for spontaneous combustion in compost” doesn’t include season or time of year. They do include the following:

“1. biological activity

2. relatively dry materials

3. dry pockets

4. large well insulated piles

5. limited air flow

6. time for temperature to build up

7. Non-uniform mix of materials and poor moisture distribution

8. Lapse or oversight in monitoring” (Compost Facility Operator Manual)

There are the times when the “perfect storm” can occur at times other than expected – “during warm dry summers.”

This post is a case study of such an occurrence, where a fire developed just before Christmas at a compost facility on agricultural land. As I look back on the above checklist, the key conditions for spontaneous combustion were there, but  perhaps there remains a sense of wonder of how this could occur.

We can see a heterogeneous blend of materials being piled up at this site in October. Steam is already present.

A heterogeneous blend of materials being piled up at this site in October. Steam is already present.

In this case, the wood waste materials may have included wood chips from trees that had already been dead from beetle kill for a number of years. It also appears to have included wetter wood residue from perhaps log or chip sort yards. There may also be ground residential yard waste included.

In November, the heterogeneous pile of material gets larger and becomes more insulated as equipment drives on top of it.

In November, the heterogeneous pile of material gets larger and becomes more insulated as equipment drives on top of it.

We can see from the photographs that the criteria on the checklist for spontaneous combustion is slowly being checked off, as we have dry material, a contiually growing  pile, biologically active materials, inconsistent mixing of dry and wet material…

in early December the cold northeast winds blew upon the pile.

in early December the cold northeast winds blew upon the pile.

The cold north wind came for a number of weeks in early December.  While one would perhaps expect that this may work to cool the pile and reduce the risk of fire, wind can also act like a type of bellows – to push oxygen in to the pile. The dry air and the lack of steam provided the illusion that all was well with this pile.

As the north wind stopped, it appeared that significantly more than steam was escaping the wood waste pile.

As the north wind stopped, it appeared that significantly more than steam was escaping the wood waste pile.

The north wind stopped, the air warmed up and the rains began to fall, as is very common during the winter in southcoastal British Columbia. We observed what the Compost Operator Manual predicted: “in large unmonitored piles with limited oxygen supply, a smoldering fire starts when materials reach their ignition temperature. This type of fire is inefficient, producing gases, smoke and heat, but no flame.”

“Warning: a large pile containing a smoldering fire could change to a flaming fire if the material is opened up, and oxygen is allowed to fuel the fire!”

It is important to use caution when using large equipment to fight a fire in a compost pile because a smoldering fire can begin to flame when exposed to oxygen.

It is important to use caution when using large equipment to fight a fire in a compost pile because a smoldering fire can begin to flame when exposed to oxygen.

 

When fighting a large smoldering fire, one has to be careful where to locate equipment that is being used to fight the fire. “consider equipment such as tractors and skid steers as they may be used to fight a fire. Ensure operators understand how to use this equipment safely during a fire.”

Although it can be argued that damage was minimal in this fire, other than the loss of valuable wood waste material, it does provide lessons for compost facility operators and  fire fighters. In this case as well, it is helpful to: “involve the local fire department in the planning of the facility, and meet with your local fire department and discuss compost fires and guidelines to manage fires. Explain the composting process, the organic matter that may be stored, and the risks of spontaneous combustion,” 

I suppose that in this case it was good to know that there was an active stream running beside the compost facility that could provide water.

In hindsight, there were no surprises with this situation, and the Compost Facility Operator Manual appeared to be consistent with the real world, except that the fire did not occur in the warm and dry summer months. The chapter on safety and fire prevention will be amended to state: “fires are more common at compost facilities than most realize, particularly outdoor waste yardwaste composting sites. Although they are more common during a warm, dry summer, they can occur at any time of the year.”

References:

all italized sections of this post are direct excerpts from the Compost Facility Operator Manual, published in 2009 by John Paul and Dieter Geesing. This manual is available from John Paul, or from JG Press (editors of Biocycle Magazine).

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