Although naturally occurring in the atmosphere, methane is hazardous in high concentrations. Widely used in industrial processes, heating and electricity generation, methane can become a severe hazard if accidental release, leaks, or transportation incidents occur. Knowing what methane is, as well as its health and safety risks, is critical.
What is Methane?
Methane, or methyl hydride, is a colourless, odourless gas which is lighter than air. In the atmosphere, the gas is 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 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.
CAS Number: 74-82-8
Chemical Compound: CH4
Other names: fire damp, marsh gas, biogas, methyl hydride, carbane
Molecular weight: 16.043 g/mol
Boiling point: -161°C
Melting point: -183°C
Relative vapour density (air = 1): 0.6
Auto-ignition temperature: 537°C
Safety Hazards of Methane
Methane hazards can occur during manufacture, use, and transportation. Although we inhale methane as we breathe, exposure to high concentrations of methane is dangerous.
Hazardous events occur due to accidents during transport, accidental releases at manufacturing facilities, and farming accidents. An in-depth emergency response plan and ongoing training are necessary to mitigate the risk of a crisis.
Methane occurs naturally in the atmosphere; however, it has not been shown to have adverse effects on human life at these concentration levels.
If 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.
Currently, there are no specified occupational exposure 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.
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 in the USA, Russia, China and India.
Coal Mine Methane (CMM) is a blend of air and methane released from rock strata due to mining activities. Methane trapped within a coal seam emerges in a mine after removing layers of a coal face. Additionally, the gas can seep out of vents from abandoned mines or appear after a rock collapse from a post-mining area.
Due to its volatile nature, methane poses an extreme working hazard, requiring effective removal 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.
How to Monitor Methane Levels
Methane gas monitors feature a non-dispersive infrared (NDIR) sensor. Measurement is based on the physical property that CH4 molecules absorb infrared light or particular wavelengths. By shining light through the target gas and using suitable optical filters, the light detector gives an output that is converted into a CH4 concentration value.
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%.
Methane Safety Regulation
NIOSH states, methane monitors are required by law to be mounted on machinery and throughout a mine to alert personnel of any increase in the gases levels while extracting coal.
Routine monitoring of methane is required at the working face of mine due to the higher propensity for ignition. Monitors are needed to provide alerts when levels exceed 1%. As levels can rise and fall rapidly, and personnel’s reaction times vary, there is a warning at 1% rather than the dangerous level of 5% to ensure an adequate and timely response.
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. The DMIRS specifically outlines maximum atmospheric levels of methane in the code of practice:
Numerous gases associated with mining, tunnelling and underground construction are generalised into combustible, toxic and asphyxiate types. Because of the hazardous nature of these gases and the unique and restrictive structure of underground environments, these gases must be continuously monitored to mitigate risk.
Check out our other articles on hazardous gases including, carbon dioxide, carbon monoxide, and hydrogen sulfide.