UNDERSTANDING AND CONTROLLING LANDFILL FIRES

Monitoring

Gas Composition Monitoring:

Monitoring of gas composition provides very useful insight of fire conditions at depth and the success of fire fighting measures.  Parameters that we measure routinely include methane, oxygen, carbon monoxide and hydrogen sulphide.  Of those four gases, we have found that carbon monoxide is the most useful indicator of subsurface fire. LANDFILLFIRE.com staff have developed the following empirical scale that we now use routinely to assess fire conditions in construction demolition landfills.

                                     Carbon Monoxide Concentration (ppm)

No Fire Indication                             0  -  25

Possible Fire in Area                       25  -  100

Potential Smouldering Nearby         100  -  500

Fire or Exothermic Reaction Likely   500  -  1000

Fire in Area                                      >1000 

The presence of oxygen at concentrations above 1% provides an indication that existing oxygen intrusion barriers (i.e. soil or membrane covers) are not effective in keeping oxygen out and that additional soil covering is required.  On the other hand, a build-up of methane to levels in excess of 40 % is a positive indicator that oxygen is being successfully excluded and the biologic regime is reverting to cooler anaerobic conditions.

Gas composition monitoring proved to be a big part of fire control efforts during the extinguishment of the DLC fire at Vancouver Landfill.  At the start of the monitoring program, sub-surface oxygen levels within the burn area were typically in the range of 15 to 21% oxygen.  As fire fighting and capping efforts progressed, oxygen levels dropped consistently.  By the time the monitoring program was completed on November 3^rd, oxygen levels in most wells dropped below 1%.

Similarly, subsurface methane concentrations were below 1% methane in many of the sampling ports at the onset of monitoring.  Low methane concentrations indicated that decomposition was occurring in an aerobic regime.  As mentioned previously, aerobic decomposition is associated with greater generation of heat, and can lead to spontaneous combustion.  By November 3^rd, methane concentrations had climbed above 40% in most of the wells.

On the Vancouver Landfill extinguishment carbon monoxide (CO) proved to be the most effective indicator of landfill fire.  Initially, CO concentrations up to 315 ppm were noted in the vicinity of the active burn zone.  These concentrations gradually declined as fire was brought under control.  Because elevated CO concentrations were not noted in steam vents and barhole punch sites outside the active burn zone and because there was a direct relationship between CO concentrations and fire activity, we believe that CO provides an excellent indication of subsurface fire activity.

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