Cummins has managed to combine the use of nitrogen with its popular foam generating system – Compressed Air Foam System – to create the Compressed Nitrogen Foam System (CNFS), designed to extinguish more difficult sub-surface or deep mine fires.
The Pinnacle fire, 2000ft deep, was believed to have been started from a lightning strike to the methane gas recovery system that was being used to collect the gas for commercial markets.
After several attempts to control the fire with regular fire fighting methods the company tried the latest inertization technologies from Poland and Australia. After another mine explosion three months after the original, inertization by jet engine was halted and it was decided to try one last new technology that had been developed 15 years earlier from experiments with the now retired Bureau of Mines.
The earlier experiments were conducted with the help of a geologist, Stanley Michalski, who had experience with mine fire projects in eastern Pennsylvania. He was involved with the fire plan at the Troy-Bryant mine fire in Kentucky and provided his expertise in evaluating the state of the fire and the effectiveness of the fire control measures. Michalski is now a senior geologist for GAI Consultants in Pittsburgh, Pennsylvania.
Since the Pinnacle experience, NIOSH (the National Institute for Occupational Safety and Health) has produced a White Paper on the nitrogen foam injection, which presents detailed graphs from instrumentation that actually captured, in real time, the first documented coal mine explosion. That information gave Cummins’ engineers the exact position of the ignition source and Halliburton Drilling Company were hired to bore a 6in cased hole right on top of the spot where the fire originated.
“We were then able to form an injection plan to pump a wet, soaking formulation of the nitrogen foam that would fill the cavities in the entries and the gob area to penetrate into the ash and reach the hidden ignition source,” Cummins representative Mark Cummins said.
“Then we changed the formula into dense, long lasting and high heat resistant foam that filled all of the voids to displace the unwanted gases that were created by the fire and the jet engine exhaust application which was causing problems for the instrumentation that was being used for monitoring and detection.
“We drilled several other bore holes for monitoring and additional foam injection to complete the displacement of the fire gases and to assure [us] there could be no new ignition sources. MSHA then approved the re-entry plan after four days of continuous foam pumping.”
The cost of the Cummins foam injection part of the fire control expenses was less than $150,000. Cummins said the cost of the nitrogen used was not known because PinnOak decided to continue the nitrogen gas injection as a security measure while the mine was being re-entered. “Foam injection is the lowest cost application available because it requires the least amount of time and effort to complete the operation,” Cummins said.
“Nitrogen is the best inert gas for inertization but it is expensive and it requires great quantities and extensive applications to be effective without the foam as a carrier,” he said.
Cummins is currently working on a plan to provide emergency foam response to future coal mine fires. The service will include equipment and personnel to work with the mine rescue teams and mine company managers to place the first bore hole near the mining machinery and start the injection of a dense high heat resistant foam directly onto the machinery to cover it with a blanket of durable long lasting foam to protect it.
Then Cummins will drill additional boreholes to continue the fire control plan. “This should save time, prevent major damage to the machinery and reduce the recovery expenses for the mining companies,” Cummins said.
He said the clean-up after a foam injection was not a problem as the environmentally friendly and non-toxic foam simply deflates and the water that was in it evaporates away or soaks into the ground.