EXTINGUISHING THE DELTA SHAKE AND SHINGLE LANDFILL FIRE 

Cause of Ignition.
Potential causes of landfill fires include:

• embers in a hot load;
• careless smoking;
• methane flash from equipment spark;
• arson; and
• spontaneous combustion.

Although we will never be sure what caused the Delta Shake and Shingle Landfill fire, there was strong evidence to suggest that spontaneous combustion was the cause. A second fire broke out on the backside of the landfill mid way through the firefight. 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 2 m deep berm in an inactive are that was not accessible from surface, the first four triggering mechanisms were quickly eliminated leaving spontaneous combustion as the most likely ignition mechanism.

The mechanics of spontaneous combustion in refuse are not well understood. Wood starts to burn with open flame once temperatures rise above 315 degrees C. Pyrolysis, the process of chemical oxidation of wood, can start at temperatures of 95 degrees C.. The reaction reaches an exothermic (heat producing) and self-sustaining state at temperatures as low as 149 degrees C. Temperatures approaching the 149 degrees ignition point are seldom reached in properly operated landfills where refuse decomposition is occurring under anaerobic conditions. Anaerobic bacteria thrive at temperatures that seldom exceed 60 degrees C. Aerobic bacteria generally thrive at temperatures below 75 degrees C. and typically die was the temperatures climb above 80 degrees C.

Heat released during rapid oxidation of pyrophoric substances in the landfill is believed to be triggering mechanism that elevates internal temperatures above the 159 degrees C. threshold required to initiate the spontaneous combustion process in wood. Common pyrophoric substances include rags soaked in vegetable oils (e.g. linseed oil), low grade coal, grass, straw and certain metal compounds such as irin sulphite.    

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