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With the 50 largest mining companies in the world worth a total of 1 trillion dollars, mining has become a big business.1 Globally, the mining industry is responsible for the direct employment of 3.7 million people, and small-scale mining operations indirectly supports more than 150 million people.2 Many other sectors, like high-tech industry, are also completely dependent on mined supplies of materials.
While creating and operating within subterranean tunnels, there is an inherent danger which leads to a high mining death rate. In China alone, over five deaths per day have been recorded due to mining accidents.3 This is a global issue, as high-profile incidents are taking place in the last decade in Russia, New Zealand, and the US among others.4,5,6
Explosion of methane gas is the most common source of mining accidents, mainly in coals mines. Methane, an odorless, colorless gas, is trapped in mines as part of the coal formation process. When coal is formed from compressed plant matter, methane is produced as a by-product. When rocks are excavated, this methane is released into the local atmosphere with potentially harmful consequences.
Methane Explosions in Mines
The concentration of a methane leak in a closed environment causes methane explosions in mines. When methane reaches a critical concentration in the air, which is between 5 to 15 %, it reacts with the oxygen to form water, carbon dioxide, and heat. A source of ignition is required to start this reaction. The source need not have to be an open flame, just a high localized temperature (over 600 °C) on hot equipment, or sparks from mining processes, can be sufficient to cause an explosion.7
When compared to the initial explosion, the pressure wave created by a methane explosion is often more dangerous, displacing large amounts of coal dust and spreading highly flammable particles throughout the air. The dust can ignite as part of a chain reaction, which spreads flames along the mining shaft, consumes any available oxygen to further fuel the fire, and generates large amounts of toxic gases.
Safety Measures to Avoid Methane Explosions
It is impossible to avoid methane release in coal mines as it is always present. The issue with methane explosions is not limited to active mining sites alone. Many abandoned mining sites also leak methane gas, potentially into residential areas where it can still reach high enough concentrations to be at risk of explosion.
Considering the risk of methane gas accumulation in mines, gas sensing is an important part of any mining safety network. Ventilation equipment is used in mines to keep methane concentrations below the explosion limit, so that the risk of methane accumulation is reduced.8
In mines, sensors can be placed at ventilation exits to measure the outgassing of methane and thus ultimately determine that the concentration of methane in the mine itself is not close to critical methods. External sensors are also essential in monitoring the release of methane to the environment surrounding the mine.
For gas sensing to be an effective safety measure, the gas sensors used should be able to detect low concentrations of methane gas with high reliability.
The Guardian NG for Methane Detection
The Guardian NG series from Edinburgh Sensors is one sensor range that is appropriate for the critical safety issue of detecting methane outgassed from mines. The infra-red based sensors can detect methane concentrations between 0 and 1%, and are also sensitive enough to detect even the smallest of leaks.9
Designed as an easy-to-use, standalone gas sensor, the Guardian NG series can constantly monitor and log methane concentrations in situations where the gas is present between 0 and 100% volume, with the most sensitive sensor capable of detecting leaks between 0 and 1%. The sensor has an extraordinarily rapid warm-up time of 1.5 minutes and can operate in a range of conditions varying between 0 and 95% relative humidity and 0 – 45 °C.
The easy integration into existing ventilation equipment makes the Guardian NG series particularly well-suited to mining applications. Since the sensor itself is electronic and could produce sparks, it should be located on the surface of the mine measuring gas concentrations outgassed from the mine vents. This ensures that ventilation systems are working and can also be employed in monitoring the off-gassing of old mining sites.
Infra-red sensors provide some advantages over the conventional heat of combustion sensors that are generally used for mining applications. As methane absorbs infra-red light very strongly at characteristic wavelengths, infra-red sensors are usually used in other areas where methane detection is required. They also provide faster response times and potentially have longer service lives when compared to heat and combustion sensor alternatives.
The fail-safe nature of the IR sensors’ technology is one huge advantage in safety applications. If the IR lamp and therefore the sensor fail, then the detector does not receive any signal, which is an equivalent effect to the sensor detecting a high methane concentration. Consequently, a full alarm would sound, alerting staff that the sensor has failed and there is a potentially dangerous situation.
With its accuracy and sensitivity for methane detection and short response time of less than 30 seconds from sample injection, the Guardian NG series is the only solution to the critical safety issue of explosion prevention in mining.
Download the Guardian NG Brochure for More Information
References and Further Reading
- Value of Mining Companies (accessed January 2018)
- W. Ming-Xiao et al., Public Health Rep., 2011, 126(2), 270-275
- Pike River Royal Commission Report, http://pikeriver.royalcommission.govt.nz/Final-Report, (accessed January 2018)
- Russian Mine Accident, http://www.bbc.com/news/world-europe-35681242, (accessed January 2018)
- Historical Data on Mining Accidents, (accessed January 2018)
- C. Robinson, D. B. Smith, Journal of Hazardous Materials., 1984, 8, 199-203
- Methods for Controlling Explosion Risk, https://www.cdc.gov/niosh/mining/UserFiles/works/pdfs/mfcer.pdf, (accessed January 2018)
- The Guardian NG, https://edinburghsensors.com/products/gas-monitors/guardian-ng/, (accessed January 2018)
This information has been sourced, reviewed and adapted from materials provided by Edinburgh Sensors.
For more information on this source, please visit Edinburgh Sensors.