METHANE GAS DETECTIONRepor ts show the Deepwater Horizon blast was triggered by methane bubble. Investigation re-veals that the accident on Gulf of Mexico rig was caused when meth-ane gas escaped from oil well be-fore exploding.In the correct concentration, meth-ane can be very dangerous and can cause huge explosions if ignited. It has been the cause of many disas-ters in the mining, water, oil and gas industries.

In 1984, 8 people were killed in the Abbeystead disaster and more re-cently a methane gas bubble was found to be the cause of an explo-sion on the BP platform Deepwater Horizon in the Gulf of Mexico which killed 11 people and caused incom-prehensible damage to the environ-ment from the resultant oil spill.

METHANE GASMethane is a colourless, tasteless, odourless gas and has the chemi-cal formula CH4. It is the main com-ponent of natural gas. To clarify, it is

made up of one atom of carbon and four atoms of hydrogen.Methane is produced naturally by the process of methanogenesis and is found under the ground and sea-bed. It is commonly used in chemi-cal industries and also for electricity generation. It is non toxic but highly explosive (more on that later.)

WHERE IS METHANE GAS USED?Methane gas is commonly used in chemical industries and is used to refine petrochemicals. It is also used

GAS DETECTIONBy Mr. Chris Dodds

Mr. Chris Dodds is UK Sales & Marketing Manager at Thorne & Derrick UK. Mr. Dodds has grown the company’s presence through multiple channels including SEO, Social Media, and Blog Writing. As well as managing T&D’s own campaigns, Mr. Dodds works with suppliers to develop content marketing strategies and supporting with joint

initiatives.

METHANE

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as a fuel and is burned in gas tur-bines or steam generators to pro-duce electricity. It is widely used do-mestically for heating and cooking in homes.Methane is the main component of Liquefied Natural Gas (LNG) and Compressed Natural Gas (CNG). Methane is generated by the de-composition of biodegradable sol-id waste as well as animal and hu-man waste. It is therefore commonly present in landfill sites and sewage treatment works.

THE DANGER OF METHANE GASMethane is not generally considered a toxic gas, however it is extreme-ly flammable even in low concentra-tions when mixed with other chemi-cals. It is also an asphyxiant as it will displace oxygen. This is particularly dangerous in confined spaces.In order to create a fire/explosion, you need three things, Oxygen, an ignition source and a fuel. Take away the oxygen and you remove the risk of explosion, in contrast high levels of oxygen will cause fuels to burn faster and more vigorously. For an explosive atmosphere to exist, a cer-tain ratio of oxygen and fuel must ex-ist. The ratio differs depending on the fuel. In the gas detection indus-try, such ratios are known as lower explosion limits (LEL) and upper ex-plosion limits. (UEL)LEL is defined as “the minimum con-centration of a particular combus-tible gas necessary to support its combustion in air.” Concentrations below this level will not burn. The UEL is defined as “Highest concen-tration (percentage) of a gas or a va-por in air capable of producing a flash of fire in presence of an ignition source. The range between LEL and UEL is referred to as the flammable range and as the name suggests is when fire/explosions will occur.As can be seen from the table, the LEL for methane is 5% and UEL is 15%. Concentrations of 9% are thought to be the most volatile. It may sound strange but concentra-tions above 15% will not be explo-sive as the air is too saturated with Methane. However this is when as-phyxiation can be just as hazardous.

Asphyxiation becomes a risk when there are high concentrations of methane. This is because the meth-ane displaces the oxygen. We need approximately 18% oxygen to breath, levels below 16% can be dangerous and levels below 10% can cause im-mediate loss of consciousness and inevitably death. Working in confined spaces can be extremely danger-ous if exposure to methane (or any other gas for that matter) is consid-ered a risk.

COAL MINING & METHANECoalbed methane occurs natural-ly in coal seams. Methane recov-ered from underground coal mines is generally grouped under the term Coal Mine Methane (CMM). 2 key factors influence CMM recovery: mine safety and the opportunity to mitigate significant volumes of meth-ane emissions arising from coal min-ing activities.The UK coal mining industry has been producing large volumes of methane gas as an unwanted haz-ard since the 1800’s.Methane Emissions in Mines Arise at Two Key Stages:1. Methane is released as a direct

result of the physical process of coal extraction. In many modern underground mines, the coal is extracted through longwall min-ing. Longwall mining, as with other sub-surface techniques, releases methane previously trapped within the coal seam into the air supply of the mine as lay-ers of the coal face are removed, thus creating a potential safety hazard.

2. Methane emissions arise from the collapse of the surrounding rock strata after a section of the coal seam has been mined and the ar-tificial roof and wall supports are removed as mining progresses to another section. The debris re-sulting from the collapse is known as gob and also releases meth-ane or "gob gas" into the mine.

ADVICE & CONSIDERATIONS FOR METHANE GAS DETECTIONThere are no specific guidelines for detection of methane but the HSE does provide information for the se-lection and use of flammable gas detectors.Fixed and portable methane gas de-tectors should be used to help mini-mise risk and provide early warnings should gas levels become danger-ous. They can be a life saving piec-es of equipment and it is important that the correct gas detection mea-sures are implemented to ensure your plant is protected but more im-portantly that people return home from work.Part of this measure should also in-clude adequate training for the users. As some people pointed out follow-ing a recent blog article about porta-ble gas detectors, “the gas detector will not prevent accidents if the user doesn’t know how to use it”.This may sound obvious but there are many stories about people incor-rectly using gas detectors, ignoring warning alarms, failing to bump test and calibrate sensors. Gas detectors usually measure in either % volume or PPM (parts per million).

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programme including regular cali-bration should be considered when using this type of technology. This can and will add to the lifetime cost of the product. A further disadvan-tage is that they will fail to work properly if oxygen isn’t present and therefore they are not always suit-able for gas detection in confined

spaces. In contrast Infrared sensors do not require the presence of oxy-gen and should therefore be used when oxygen depletion is a possi-bility. IR sensors also have a failsafe function whereby if the detector be-comes obscured or fails, no radia-tion will register and an alarm will be raised. ■

Flammable gases are usually mea-sured by % volume and toxic gas-es by PPM. As mentioned earlier the LEL for Methane is 5%. Typically warning levels on gas detectors can be set between 0-100% of the LEL. The HSE recommend that first alarm level should be set no high-er than 10% of the LEL and the sec-ond alarm level should be no more than 25% of the LEL. There are two main types of detector technology used for measuring flammable gas-es: Infrared and Pellistor.

INFRARED GAS DETECTORSGases such as methane which con-tain more than one type of atom can be detected by IR gas sensors. This is because the gas will absorb infra-red radiation. An infrared gas detec-tor is made up of an infrared source (transmitter) and an infrared detec-tor (receiver).If methane passes between the transmitter and receiver, it absorbs the radiation and the intensity of the signal at the receiver is weak-ened. Specific gases are detect-ed by measuring the amount of ab-sorbed infrared radiation at specific wavelengths, the difference being related to the concentration of gas present.

PELLISTOR DETECTORSPellistor sensors are commonly used in both fixed and portable gas de-tectors. Pellistors can be used to detect combustible gases such as Methane. The principal of operation is based around changes in resis-tance caused by target gases on the small pellets of catalyst loaded ce-ramic. As the gas comes into con-tact with the sensor, it is burned which generates heat and alters the resistance of the detecting element of the sensor which is proportional to the target gas.Pellistor sensors are accurate are remain unaffected by changes to ambient temperatures, humidity or pressure. The main drawback to pellistor technology is the possibil-ity of contamination or poisoning. They are susceptible to sulphides, silicones, hydrocarbons and lead. Therefore a routine maintenance

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