Detection Methods: There are five types of detection methods which are as:  Catalytic oxidation detectors  Electrochemical detectors  Optical detectors  Electrical conductivity (semiconductors) detectors  Chemical adsorbents detectors.

1. SUBMITTED BY: Ghulam Mehdi
(Balochistan University of Information Technology,
Engineering & Management Sciences, Quetta)
……………………Buitems,Quetta…………………………..
Mine Gas Detections & Monitoring:
Detection Methods:
There are five types of detection methods which are as:
 Catalytic oxidation detectors
 Electrochemical detectors
 Optical detectors
 Electrical conductivity (semiconductors) detectors
 Chemical adsorbents detectors.
Catalytic-Oxidation Detectors:
Catalytic-Oxidation detectors are used to measure the concentration of
combustible gases, most notably methane (CH4) and carbon monoxide (CO), by
measuring either the heat generated during the oxidation process or the change in
resistance in an electrical circuit (Wheatstone bridge).
In the Wheatstone bridge principle, one leg of the bridge is used to burn the gas,
thus heating that leg and causing an imbalance in the bridge resistance, which is
proportional to the concentration of the combustible gases present.
Electrochemical Sensors:
Electrochemical sensors have found application in determining the concentration of
oxygen, carbon monoxide, hydrogen sulfide, and oxides of nitrogen. In these
sensors, the gas being measured reacts with a special electrode in an electrolyte.
This reaction generates an electrical current that is proportional to the concentration
of the gas present.
Optical Detectors:
Optical detectors are basically of two types.
 Non-dispersive Infrared Detector
 Interferometer
Non-dispersive Infrared Detectors:
The non-dispersive infrared detector is based on the principle that different gases
absorb light at specific and distinct wavelengths. By passing light through a gas
mixture and measuring the amount of absorption, the concentration of the gas is
determined.
Interferometer detectors:
Interferometer is based on the difference in the index of refraction between two
gases. Basically, a beamof light is split, with one part passing through a chamber
filled with air and the other passing through a chamber filled with an unknown gas

2. mixture. The difference in the velocity of the two beams is proportional to the
concentration of the gas of interest (usually methane).
Electrical Conductivity Detectors:
The newest method of gas detection, electrical conductivity, uses special
types of elements (semiconductors) that change resistance in the presence
of certain gases.
Chemical Absorbents Detectors/Stain Tubes:
The last method of gas detection, stain tubes, uses the reactive properties
of gases and chemicals to cause color changes in the chemical. These color
changes are proportional to the gas concentration, measured as either the
length or the intensity of stain.
The types of instrumentation available to the mining industry for measuring gas
concentrations fall into four basic classes:
 Handheld detectors
 Machine-mounted monitors
 Area monitors
 Personal dosimeters
Handheld Detectors:
The most commonly used type of instrument in the mining industry,
handheld detectors, are small and lightweight. They are used to spot check
the air quality at various locations underground.
In general, the permissibility label signifies only that the instrument is safe
for use in a methane-air mixture. Further, detectors that are tested in a
methane-air mixture should not be used to make checks for gases that are
more explosive than methane. For example, a methane detector should not
be used to check for hydrogen in a battery-charging station.
Safety Lamps:
The flame safety lamp is the oldest type of gas detector.
For many years it was the only means available to check for methane. It is
also useful for checking for oxygen deficiency. A flame safety lamp will not
burn in methane-free air having an oxygen content of less than
approximately 16%. In environments containing methane, a flame safety
lamp will continue to burn at lower oxygen concentrations; however, at
oxygen contents of less than 13%, the lamp will be extinguished regardless of
the methane content of the air. It should be recalled that at an oxygen
content of approximately 13%, there may be a loss of consciousness if the
exposure is prolonged.
Flame safety lamps should be clean, in good condition, and properly
assembled, because numerous accidents and explosions have reportedly
been caused by defective lamps. Flame safety lamps should never be opened
underground and should be relit only in intake air. One common type of
flame safety lamp is shown in figure.

3. (Safety Lamp)
Today the flame safety lamp is seldom used except for assessing oxygen
deficiency.
Methane Detectors:
Handheld methane detectors or methanometers use two basic methods of
detection.
 Catalytic oxidation
 Optical interferometry
Catalytic Oxidation:
Catalytic-oxidation detectors operate on the Wheatstone bridge principle. In
addition to detecting methane, this type of detector is sensitive to higher
hydrocarbons such as ethane and propane, hydrogen, and other flammable
gases. If these gases are present, they cause erroneous high readings. In
addition to being affected by other flammable gases, the catalytic-oxidation
detector is also sensitive to oxygen deficiency. Tests have
shown that this type of detector should not be used when the oxygen
content of the air falls below approximately 10%.
Handheld Optical Detectors:
Handheld optical detectors used for detecting methane are of the
interferometer type. These detectors compare the velocity of light through
pure air with the speed through the air being tested. The two beams of light
are combined, producing interference fringes. The position of these fringes is
indicative of the methane concentration. As with the catalytic-oxidation
methane detector, the interferometer also is sensitive to gases other than
methane.
Methane Detectors:
Methane detectors are the only instruments used for making gas
determinations that are approved for both electrical safety and performance.
Oxygen Detectors:
As noted previously, the most commonly used oxygen detector is the flame
safety lamp. In addition to the flame safety lamp, which indicates only an
oxygen-deficient environment, the actual oxygen concentration can be
measured using liquid absorption devices, stain tubes, paramagnetic
analyzers, and electrochemical or fuel-cell detectors. Instruments are now

4. available that combine methane detectors and oxygen detectors in
one package.
Detectors for Carbon Monoxide and Other Toxic Gases:
All toxic gases found underground are detectable using colorimetric indicator
tubes (stain tubes). These devices usually consist of a mechanical pump, a
limiting orifice that regulates the airflow rate, and a glass tube that contains a
chemical reagent that is sensitive to the gas of interest. Two basic types of
stain tubes are used in the mining industry. The first utilizes the length of the
stain generated by the reaction of the gas of interest with the chemical
reagent in the tube as a measure of the gas concentration. The other type
compares the intensity of the color created by the reaction with a standard
color chart for the tube. One difficulty with stain tubes is the cross-sensitivity
of some of the tubes. That is, some tubes are sensitive to more than one gas.
For this reason, the person making the measurement should know
characteristics of the tube being used.
(Gas Detection Methods)
Monitoring:
The term gas monitoring implies continuous or cyclic measurement of a
gaseous contaminant as opposed to gas detection, which implies intermittent
checks for contaminants. Two types of monitoring systems are used in
underground mining.
 Machine-mounted monitors

5.  Area monitors.
Monitors may be used for protection from a safety hazard such as fires or
explosions or for protection from a health hazard such as a toxic gas.
Machine-mounted methane monitors are required in coal mines on all
electric face-cutting equipment, continuous miners, longwall face equipment,
and loading machines. The function of these monitors is to detect methane
liberated during the mining process and to protect the miner by giving warn-