METHANE DETECTION

Methane

Methane is a chemical compound with the chemical formula CH4. It is the simplest alkane, and the principal component of natural gas. Burning methane in the presence of oxygen produces carbon dioxide and water.
 
The relative abundance of methane and its clean burning process makes it an attractive fuel. However, because it is a gas at normal temperature and pressure, methane is difficult to transport from its source. In its natural gas form, it is generally transported in bulk by pipeline or LNG carriers; few countries transport it by truck.
 
At room temperature and standard pressure, methane is a colorless and odorless gas; the smell characteristic of natural gas as used in homes is an artificial safety measure caused by the addition of an odorant, often methanethiol or ethanethiol.
 
Methane is mostly detected in %LEL or %VOL. There are two sorts of detectors on the market: Infrared or Catalytic. Infrared is less sensitive to sensor poisoning but more sensitive to moisture. Infrared is ideal for detection of the %VOL range.
 
A Catalytic sensor can be subject to sensor poisoning but is cheaper in purchase and can resist higher humidity.  
 
For more information about methane monitoring, contact your local Air-Met office today.
 
Methane Characteristics
Synonyms Methylhydride, Firedamp, Marsh gas, Natural gas, (1)
CAS No. 74-82-8
Chemical formula CH4
Vapour density 0.55 (air = 1)
Safe Work Australia ES TWA Simple asphyxiant
STEL ---
Flammable limits LEL 4.4 % by volume
UEL 17.0 % by volume
Equipment group Industrial:  IIA  
Coal mines:  I
Temperature classification T1
Chemical/physical properties Methane at room temperature is a colourless, odourless and very flammable gas. It burns readily in air forming CO2 and water vapour; CO can also be formed depending on the amount of oxygen present. 
Any odour associated with methane is due to other gases, either added deliberately (e.g. odourants in natural gas) or present in naturally occurring mixtures (e.g. with H2S in landfill and sewage).
It is a strong absorber of infra-red radiation and is therefore a potent greenhouse gas.
Hazardous properties Toxicologically, methane is practically inert but with slight anaesthetic properties; at very high concentrations it is a simple asphyxiant.
Methane’s main hazards arise from its flammability. Being lighter than air it will readily form easily ignitable explosive mixtures.
Uses and occurrence Methane is formed during anaerobic (without oxygen) decay of organic matter and occurs in coal mines (firedamp), landfill sites, sewage, stagnant water (marsh gas) and, of course, natural gas production wells.
Methane is the main constituent (typically 80 %) of natural gas, a popular domestic fuel due to its high heat of combustion and clean burning properties.
Methane is used as a raw material for the production of substances such as ammonia, acetylene and methanol.
Detectors available Catalytic bead (0 – 100 % LEL)
Infra-red (NDIR) (0 – 100 % LEL and 0 – 100 % by volume)
Thermal conductivity (0 – 100 % by volume)
Flame Ionisation (FID) (0.5 – 50,000 ppm)
Suggested alarm levels Lo: 5 % LEL (2,200 ppm)
Hi: 10 % LEL (4,400 ppm)
Notes (1) Naturally occurring methane (e.g. natural gas, firedamp, marsh gas, biogas) is always in a mixture with other gases, mainly low molecular weight hydrocarbons such as ethane, propane and butane.

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