UNDERSTANDING AND CONTROLLING LANDFILL FIRES

Extinguishment Methods

Water Application (Con't):

Although water is effective on near surface fires, ensuring that water can reach a deep-seated fire can be problematic.  Water tends to flow along paths of least resistance such as pockets of poorly compacted or highly pervious DLC refuse.  The process of channelizing can result in significant short-circuiting, and inability of the water to reach the active burn zone at depth.  Water does not readily penetrate cover layers composed of low permeability soils such as clay, silt, glacial till or fly ash, especially if the cover has been compacted by vehicle traffic.

In situations where a soil cover is present at surface or at depth, surface application of water is ineffective.  Stripping of the soil cover should never be considered because it will facilitate air entry which will accelerate the burn.  To deliver water beneath cover soils, the preferred approach is to inject water into wells or injection stingers.  Wells can be quickly drilled with a 150 to 300 mm diameter auger rig.  Well screens can be dropped into the boreholes to keep them open.  Due to the high permeability of DLC waste, injection wells must be spaced close together to be effective (e.g. about 5 m spacing).  Water can then be deployed into the injection wells from tank trucks or pumped directly if a fire hydrant or water body is located nearby.  Application of water into augered wells has been effective in cooling combustion temperatures at the Burnsville DLC site in Minnesota.  Photo 7 shows a typical injection port in the foreground and one of three off-road water trucks used to haul and pump water from the nearest hydrant located over 400 m away.

Capillary forces can prevent water from penetrating into the hot zone of burning materials.  Addition of surfactant chemicals such as Class-A foams can dramatically improve water penetration by breaking the surface tension.  On the recent Delta Shake and Shingle Fire, the Class-A foam product Silv-Ex was utilized for this purpose, mixed at 0.5% on a volume basis with water.

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