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
- 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.
Strategy for Extinguishment