Geology Reference
In-Depth Information
19.1. Modern-Foam-Injection
Technology
Lisa LaFosse'
Mark Cummins
Brown 79 493 L (21 000 gallon) frac
(fracturing tanks) installed at the Buchanan
No. 1 Mine; used for mixing water with
firefighting foam to extinguishing this
underground coal-mine fire.
Photo by Mark Cummins, 2007.
Introduction
I
n the past, there have been several traditional methods for extinguishing coal mine fires. Two of these methods
used, digging out the refuse and quenching with water until cooled, or drilling bore holes in the fire zone and
injecting a foamed grout, or mud slurry have not been very successful. The method of drilling bore holes to inject a
mud like slurry is not entirely successful because the slurry is heavy and peaks out, not fully reaching the
'
or all areas of the void where the combustion has burned. Then the slurry dries and cools, it shrinks and cracks
allowing new air to come into the combustion zone to reignite the fire. The method of digging out and soaking has
left many sub-surface fires out of the reach because for every cubic foot of burning material dug out, there is a hole
that is generated that needs to be filled with clean material and a pile that needs to be extinguished, which makes
digging out a fire that lay several hundred to several thousand feet below the surface, impractical.
'
ceiling
The federal Surface Mining Control and Reclamation Act (SMCRA) started regulating all coal mining August 3,
1977, and designated coal fires that were burning before 1977 were considered
'
historical
'
.
In the 1980s there were several experiments using a new foam-generating method that enabled a much safer and
more effective way to fight the subterranean fires by use of bore holes from the surface, drilled into the area of the
mine cavities and areas of combustion.
This new foam technique was different from earlier attempts to use highly aerated foam, which was called
“
high-
expansion foam.
The high-expansion foam was generated by a fan blowing air into a device with a foaming agent
mixed with water, similar to dish washing soap, sprayed onto a screen, which created massive amounts of bubbles
that were supposed to absorb the heat and block ventilation of fresh air coming into the mine.
”
This high-expansion foam (developed in the early 1900
s) had several faults. One of the faults of this type of foam
system was that it had to be brought into the burning mine and set up as close to the fire as possible. In most cases
this is impossible, due to the heat and toxic gases that fill the burning mine. High-expansion foam or blown foam,
as it is sometimes called, cannot be pushed though a hose, pipe or bore holes because of back pressures causing
the foam to back up into the fan. Another problem was that high-expansion foam contained a lot of air and oxygen
and the bubbles were very large and fragile. These fragile bubbles burst immediately when they came in contact
with smoke and heat, releasing the oxygen in the bubble into the combustion area. This generally fed the fire,
instead of extinguishing it.
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An interesting fact about water-based foam is that the water in the thin film of the bubbles is composed of hydrogen
and oxygen molecules (H
2
O). When the thin film of the large bubbles comes in contact with extreme heat, the
hydrogen and oxygen can be separated back into their elemental forms, where hydrogen is a fuel and oxygen in the
presence of heat completes the old fire triangle. This is a reason the compressed-foam method of generating very
small, and very durable bubbles (more like shaving cream), has proven to be far more effective than the high
expansion foam generators in extinguishing super heated fires.
