UNDERSTANDING AND CONTROLLING LANDFILL FIRES

Characterizing a Fire

Signs of Fire:

Many landfill fires are not detected until flames break-out at surface or large sink holes develop on the landfill surface.  In many instances, early warning signs of an impending fire may be present weeks before the fire breaks out, but go unnoticed to the untrained eye.  Foremost, fires generate combustion gases and smoke.  The combustion gases generally make their way to the landfill surface to escape out of discrete vents or fissures we refer to as fumaroles.  Photo 4 illustrates a typical fumarole emitting smoke.  Note the carbon residue around the edges of the fumarole that is characteristic of an underground fire.

As a result of normal anaerobic decomposition processes, many landfills, particularly DLC sites, generate large quantities of landfill gas that also vents from fissures.  On cold days, moisture in the gas condenses to form steam, which often looks very similar to smoke.  We have found four indicator methods for assessing whether observed emissions from a fissure are steam or smoke.  Foremost, discolouration of the venting gases (e.g. grey or black colour) is a sure sign of fire activity.  Temperatures at surface above 65ºC are a second indicator of likely fire activity at depth.  Elevated carbon monoxide levels in the vented gases above 100 ppm are also felt to be an indicator of landfill fire.  Finally, the smell of burning material is distinctly different than that of landfill gas produced by normally decomposing waste.  However, using your sense of smell should only be considered when the gas is strongly diluted and the gas composition has been tested for toxic substances, especially carbon monoxide and hydrogen sulphide.  Never sniff gases coming directly from a fumarole or monitoring well, they could kill you.

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