UNDERSTANDING AND CONTROLLING LANDFILL FIRES

Characterizing a Fire

Spontaneous Combustion (Con't):

For spontaneous combustion to occur, conditions must be ideal. The following conditions may lead to spontaneous combustion:

• a pile of sufficient size to retain heat (the Ontario Fire Marshal’s office recommends that woodchip piles be stored in piles less than 4 metres high, 8 metres wide and overall volume of 1,000 cubic metres to avoid spontaneous combustion (Government of Ontario, 1998)
• moisture content around 25% on a wet basis (House, 1998) (dryer conditions prevent biological activity, wetter conditions reduce porosity and prevent temperatures increasing beyond biological levels)
• supply of oxygen (many spontaneous combustion fires occur near the windward edge of a pile of material during windy conditions, others are initiated by overdrawing on landfill gas extraction wells resulting in oxygen intrusion).
• sufficient insulating capabilities to retain heat in the pile (Swedish researchers found that uncovered loosely packed piles of demolition material piled up to 5 metres high did not spontaneously combust whereas compacted piles regularly spontaneously ignited (Hogland et. al., 1996))
• prolonged storage of organic materials (the Ontario Fire Marshal’s office recommends storage of wood chips for less than 3 months (Government of Ontario, 1998).

For example, at the Delta Shake and Shingle Landfill fire that broke out in November, 1999 there was strong evidence to suggest that spontaneous combustion was the cause.  A second fire broke out on the back side of the landfill mid way through the fire fight.  The second fire started in an old inactive area of the landfill in mixed roofing material and wood waste.  Because the fire started beneath a 6’ deep berm in an inactive area that was not accessible from surface, the first four triggering mechanisms were quickly eliminated, leaving spontaneous combustion as the most likely ignition mechanism.

In the case of the Vancouver Landfill fire, the fire occurred behind an approximately three metre high bank of demolition material adjacent to an internal site access road in an inactive area of the landfill.  The road was located on top of the first layer of demolition material, and the bank represented the edge of the second layer of demolition material.  The bank had been partially covered with soil, but sufficient void space was present to allow wind to blow into the bank.  Photo 2 illustrates the condition of the exposed bank at the onset of the fire while Photo 3 shows the same bank properly covered to control oxygen entry while the fire was being extinguished.  The bank was located on the windward side of the demolition lift.  Material in the area of the fire had been in place approximately six months.

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