VANCOUVER LANDFILL DEMOLITION FIRE 

Monitoring Program

On October 20^th the City of Vancouver retained Sperling Hansen Associates Inc. to monitor the progress of the fire fight and to provide recommendations on future actions. Through a simple monitoring program focusing on the installation of subsurface probes in the demolition area, Sperling Hansen was able to show conclusively that the fire had been completely extinguished and that the conditions that had created the potential for a fire had been resolved.

The monitoring program involved collecting temperature and gas composition data throughout the demolition cell. Readings were taken at all observed steamer vents as well as over a grid of regularly spaced “barhole punch” probes installed through the intermediate cover into the shallow sub-surface. 

Barhole punch monitoring points were created by driving a solid steel bar approximately 1.5 m below grade with an excavator, then pushing a hollow steel 2.5 cm diameter sampling pipe into the cavity.  An oversize bolt was used to prevent the pipe annulus from clogging during insertion.  On achieving full depth, the sampling pipe was pulled back approximately 15 cm, dislodging the bolt and allowing sub-surface samples of gas composition to be collected. 

Maximum temperatures noted at surface using a hand held infra-red sensor were 54.1 °C.  On this project, as well as on several other landfill fire projects investigated by Sperling Hansen, temperature readings taken at surface did not prove to be particularly useful in indicating the extent of the fire zone.  Subsurface temperature readings from thermister strings installed in boreholes within the waste typically provide a much more effective indication of fire conditions in the subsurface. On this project, thermisters were not installed because of the relatively shallow fill and also on the basis that the gas composition data from the barhole punch monitoring program indicated that the extent of the fire was limited. Gas samples were analyzed using portable sensors for oxygen, methane, carbon monoxide and hydrogen sulphide. 

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 this project 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.  Contours showing the gradual reductions in CO concentrations are shown in Figure 2. 

Based on observations on this project as well as on experience at landfill fires at Campbell Mountain Landfill, the Delta Shake and Shingle Landfill and the recent landfill fire in Minnesota, Sperling Hansen Associates 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 Smoldering Nearby              100                 -      500
Fire or Exothermic Reaction Likely       500                 -    1000
Fire in Area                                                       >1000

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