Methane occurs naturally in the atmosphere but in small concentrations. Methane underground, in mining, tunnelling and coal mining, is extremely hazardous as it can occur in much higher levels reiterating the necessity of gas monitoring.
What Is Methane?
Chemical Compound: CH4
Methane, or methyl hydride, is a colourless, odourless gas which is lighter than air. In the atmosphere, Methane is eventually transformed into water and carbon dioxide; it is also one of the most potent greenhouse gases.
Methane is naturally emitted from the decomposition of organic matter and the digestive process of ruminant animals; other sources include fossil fuel extraction, landfill, industrial process, food production and mining. It is commonly referred to as marsh gas, as it occurs abundantly in wetlands.¹
What are the Hazards of Methane in Mining?
Methane occurs naturally in the atmosphere, however, at these concentration levels, it has not been shown to have adverse effects on human life.
If Methane levels rise, the risk also increases; initially individuals experience fatigue, dizziness and headaches, progressing to more severe symptoms of nausea, agitation and displaced speech. In high concentrations, Methane deposes oxygen causing asphyxiation.¹
Currently, there are no specified occupational expose limits for Methane gas. The National Institute for Occupational Safety and Health’s (NIOSH) in the United States recommends a maximum of 1000 ppm (0.1%) during an eight hour work period.²
Table 1 Methane exposure levels and effects
Exposure level (ppm) Effect or symptom
1000 NIOSH 8-hours TLV*
50,000 to 150,000 Potentially explosive
* TLV = Threshold Limit Value
Methane is a highly flammable and explosive gas, easily ignited when exposed to heat, sparks or flames. When sufficient quantities of CH4 accumulate, 5 – 15% by volume, within a mixture of air it forms a highly explosive gas. Above 15% (150,000 ppm) insufficient amounts of oxygen is present in the air, and the gas burns without explosive elements.¹
The hazard and associated risks of the effect of ignition and explosion of Methane is one of the most severe natural hazards. The explosive nature is one of the reasons Methane poses such a high risk in the mining industry.
Methane in Mining
Methane is recovered from mines due to two main reasons, safety and energy production. Coal reserves are available in almost every country worldwide; the most significant reserves are found in the USA, Russia, China and India.
Coal Mine Methane (CMM) is a blend of air and Methane released from rock strata as a direct result of mining activities. Methane trapped within a coal seam emerges in a mine after layers of a coal face are removed. Additionally, Methane can seep out of vents from abandoned mines, or appear after a rock collapse from a post-mining area.³
Due to its volatile nature, Methane poses an extreme working hazard and is required to be effectively removed from the ventilation system. In some cases, further subtraction occurs through a series of wells, boreholes and pipelines forming a degasification system (drainage system). Ventilation systems move the Methane contaminated air away from areas where personnel are working and into the shafts directed towards the surface. This air is captured and utilised in gas engines rather than pumped into the atmosphere due to its high greenhouses gas effect.4
Monitoring Methane Levels in Mines
NIOSH states, Methane monitors are required by law to be mounted on machinery and throughout the mine to alert personnel of any increase in the gases levels while extracting coal.
Monitors are required to provide alerts when levels exceed 1%. As levels can rise and fall rapidly, and the reaction times of personnel are critical, there is a warning at 1% rather than the dangerous level of 5% to ensure an adequate and timely response.5
Fixed gas monitors can provide constant readings from a set location. Routine monitoring of Methane is required at the working face of mine, due to the higher propensity for ignition. It is also recommended to distribute fixed gas monitors throughout a mine site or building. These site-wide warning systems relay data from a particular area to the control room and across the safety network. If abnormalities in gas levels are detected, automatic alerts and safety measures are activated. Fixed systems can have the ability to remotely shut down an area, isolating the hazard and ensuring the safety of all personnel in the event of an emergency.
The concentration of Methane can occur away from the working face, which is often monitored less frequently. To ensure workers are continually protected, portable gas monitors need to be carried reducing the risk to personnel moving across the site.
In Western Australia, the Mines Safety and Inspection Regulation 1995 outlines the legislative requirements for the occupational health and safety standard of gases such as Methane.
9.29. Monitoring of toxic, asphyxiant and explosive gases
(1) Each responsible person at a mine must ensure that adequate precautions are taken to monitor and control the risk from, the formation or emission of toxic, asphyxiant and explosive gases in the mine.6
Aura-FX Sensor Technology
In a refuge chamber, the Aura-FX Methane Monitor measures CH4 levels; ensuring it remains within a safe range. The sensor emits an initial warning signal at 1.1%, with an alarm sounding when levels reach 2.2%.
The monitor utilises a nondispersive infrared (NDIR) sensor, with a range of 0 – 5%. Calibration and sensor replacement are both required just once every 12 months.
Future developments in MineARC gas monitoring capabilities include external gas monitors for refuge chambers, nodes and portable devices.
1.National Centre for Biotechnology Information. PubChem Compound Database; CID=297, pubchem.ncbi.nlm.nih.gov/compound/297 (accessed Mar. 29, 2018). 2. Methane Safety www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/agdex9038 August 2014 7. https://www.cdc.gov/niosh/ipcsneng/neng0291.html (accessed Mar. 29, 2018). 3.Coal Mine Methane Sources United States Environmental Protection Agency JANUARY 31, 2018 www.epa.gov/cmop/coal-mine-methane-sources 29.03.2018 4.Methane Risk Assessment in Underground Mines by Means of a Survey by the Panel of Experts (Sope), Journal of Sustainable Mining, Volume 13, Issue 2, 2014, www.sciencedirect.com/science/article/pii/S2300396015300033 (accessed 29 March, 2018). 5. Mining Topic: Methane Detection and Monitoring www.cdc.gov/niosh/mining/topics/MethaneDetectionandMonitoring.html (accessed 5 April, 2018). 6. Mines Safety and Inspection Regulation 1995 slp.wa.gov.au/statutes/regs.nsf/(DownloadFiles)/Mines+Safety+and+Inspection+Regulations+1995.pdf/$file/Mines+Safety+and+Inspection+Regulations+1995.pdf