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VANCOUVER LANDFILL DEMOLITION FIRE
Why The Fire Started
Spontaneous combustion is the outbreak of fire without application
of heat from an external source. Spontaneous combustion may occur
through the storage of organic materials such as woodwaste, coal,
tire chips, compost or hay.
In organic materials, spontaneous combustion
occurs when heat initially produced through biological degradation
is not allowed to dissipate thus raising the temperature of the
material. Biological degradation will generally cause temperatures
to increase to approximately 70 °C.
At temperatures much higher than 70 °C
microorganisms die. Temperatures beyond 70 °C
are associated with chemical oxidation of organic materials in
the presence of oxygen. For wood, exothermic oxidation of wood
commences around 200 °C
and combustion with open flame commences aroud 300 °C
(National Fire Protection Association, 1976). Following
is a practical reference summary for evaluating landfill fire
temperatures based on our experience on six major landfill fire
projects.
<60°
C Anaerobic
Decomposition
<75°
C Aerobic
Decomposition
80 °C
Microbes Die-off
93 °C
Pyrolysis Starts
149 °C
Exothermic Oxidation of Wood Starts
315°
C
Wood Ignites Spontaneously (Combustion)
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)
- 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).
1
. Partially Capped Bank
on Edge of Demolition Cell
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