Methane Gas Detection - Using Crowcon Gas Detector Products. The following article has been written for anyone working in industries where exposure to methane gas is a risk. The article begins by identifying common industries where methane gas is present or used and goes on to discuss the hazards it poses to plant and personnel. Finally the article looks at Crowcon gas detection technologies and solutions including infrared and Pellistor type gas sensors. The full length version of this shortened Editorial version is available via this link http://bit.ly/methanegasdetection T&D are an approved distributor and stockist of the Crowcon portable gas detector range which consists of single and multigas detectors and gas monitors suitable for a wide range of applications.

1. METHANE GAS DETECTION
Reports 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 GAS
Methane 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 re-
fine petrochemicals. It is also used as
GAS DETECTION
By 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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2. a fuel and is burned in gas turbines or
steam generators to produce elec-
tricity. It is widely used domestical-
ly 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
GAS
Methane 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 & METHANE
Coalbed 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 recov-
ery: mine safety and the opportu-
nity to mitigate significant volumes
of methane emissions arising from
coal mining 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 with-
in the coal seam into the air supply
of the mine as layers 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.
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3. 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 DETECTORS
Pellistor sensors are commonly
used in both fixed and portable gas
detectors. Pellistors can be used
to detect combustible gases such
as Methane. The principal of oper-
ation is based around changes in
resistance caused by target gases
on the small pellets of catalyst load-
ed ceramic. As the gas comes into
contact 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
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 ox-
ygen 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. ■
ADVICE &
CONSIDERATIONS FOR
METHANE GAS DETECTION
There 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
detectors should be used to help
minimise risk and provide early
warnings should gas levels become
dangerous. They can be a life sav-
ing pieces of equipment and it is im-
portant that the correct gas detec-
tion measures are implemented to
ensure your plant is protected but
more importantly 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).
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
DETECTORS
Gases 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
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