Underground » Detection and Prevention of Fires and Explosions
Surface and underground trials of the GAG-3A jet inertisation device were held at the Collinsville No 2 underground coal mine from 7th to 18th April 1997. The selection criteria for the trial developed by the Moura related Task Group 5 Committee were met with the exception that output flow rates were slightly below the levels predicted (19 m3/s against an expected 20-25 m3/s). This diminution in flow rates was attributed to higher ambient air and water temperatures.
The unit operated safely during all aspects of the trial and no mechanical problems were encountered.
Over 100 industry stakeholders visited the demonstration and feedback questionnaires were generally positive. The demonstration supported the view that the device was suitable for coal mine use. No external flame was visible on the device.
The unit produced noise levels in excess of 124 dB(A) (when measured 1 m from the jet) in both surface and underground operations.
Environmental noise levels measured 2.3 km from the GAG-3A were not impacted by the operation of the unit.
The limited stratification experiment conducted indicated that the gas produced by the GAG-3A tended to move closer to the roof than the floor.
The trial demonstrated that the GAG-3A device has applications in underground coal mines and that it outperformed all other available technologies with respect to volume of inert gas produced.
It is clear that the GAG-3A produces lower oxygen levels over a wider range of excess air conditions and therefore has a much wider range of applicability.
Introduction
Coal mine fires and explosions are an ever-present and dangerous problem facing underground coal miners. Both of these events require the presence of oxygen (generally in excess of 10%) to pose a significant problem and thus one approach to reduce or eliminate the potential for fire or explosion is to reduce the oxygen concentration. This trial involved the use of a device which produces large volumes of low oxygen inert gas (approx. 20 m3/s of <3% oxygen) which can be used to replace a potentially explosive atmosphere in an underground coal mine.
The GAG-3A inert gas generating device was developed in Poland in the early 1970's and has been used extensively in Poland, Czech Republic, CIS, China, and more recently, to combat frequent and extensive gold mine fires in South Africa. A variation of this device was used, mounted on a remotely controlled tank, to extinguish the oil well fires in Kuwait following the Gulf War. The GAG-3A has been used for tens of thousands of operational hours with no serious accidents reported to date. The device was brought to Australia by the Polish Mines Rescue Service with SIMTARS providing operational support for this ACARP and industry-funded project.
Moura No 2 Inquiry
Following the explosion at the Moura No 2 coal mine in 1994, the subsequent inquiry recommended that various forms of inertisation be investigated with regard to their suitability for use in Queensland coal mines.
Task Group 5 under the auspices of the Moura Implementation Committee was formed with two main foci, inertisation and the suitability of the current sealing strategies in use in underground coal mines.
This project focussed on the demonstration of one particular inertisation strategy
Conclusions
The GAG-3A jet inertion device was trialed under a variety of circumstances at the Collinsville No 2 Mine. The device produced large volumes of inert gas and complied with the criteria set down by Task Group 5 with the exception that due to site-specific conditions at Collinsville No 2 Coal Mine, relating to water and ambient temperatures the flow rate of inert gas was 19 m3/s rather than 20 m3/s nominated in the Task Group 5 selection criteria. The diagrams presented in the body of the report indicate the flow of inert gas through the mine on a rapid time scale.
This compares very favourably to the only other significant trial of inertisation in Queensland, at Moura No 4 in 1986, where 700 tonnes of liquid nitrogen were injected into a mine area over a period of 5 days to produce an oxygen level of less than 10%.
The GAG-3A achieved similar results in 6 hours at a fraction of the cost ($600,000 liquid nitrogen versus $4,500 Jet A fuel).
In the mine the device operated faultlessly although there was one minor stoppage due to dirty fuel filter problems. The jet was re-started in less than 10 minutes.
The operation of the device should be supervised by a competent ventilation engineer.
It is clear that the GAG-3A produces lowered oxygen levels over a wide range of excess air conditions and therefore has a wide range of applicability.
Recommendations
- On the basis of the trials conducted at Collinsville No 2 Coal Mine, SIMTARS is of the opinion that the GAG-3A device is applicable with respect to conducting inertisation in underground coal mines.
- Each usage of the device would be dependent upon site-specific factors and the GAG-3A may not be suitable for every mine situation.
- With respect to other currently available high flow inertisation devices, the GAG-3A is markedly superior in every aspect of operation.
- Suitable operational practices should be established to ensure operators of the GAG-3A are not exposed to safety risks.