Mine Gases: Gas Detection Methods

Correl PPT

Catalytic-oxidation detectors

are used to measure the concentration of combustible gases, most notably methane and carbon monoxide, by measuring either the heat generated during the oxidation process or the change in resistance in an electrical circuit

Wheatstone bridge principle

In the _________, one leg of the bridge is 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

_______ 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.

Nondispersive infrared detector (Optical detectors)

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 (Optical detectors)

is based on the difference in the index of refraction between two gases. Basically, a beam 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 mixture. The difference in the velocity of the two beams is proportional to the concentration of the gas of interest (usually methane).

Electrical conductivity

uses special types of elements (semiconductors) that change resistance in the presence of certain gases.

Stain tubes

uses the reactive properties of gases and chemicals to cause color changes in the chemical

Handheld Detectors

The most commonly used type of instrument in the mining industry, handheld detectors, are small and lightweight.

❑Use to spot check the air quality at various locations underground

Safety Lamps

❑ 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.

❑ Today this is seldom used except for assessing oxygen deficiency

16%

A flame safety lamp will not burn in methane-free air having an oxygen content of less than approximately ____.

lower; 13%

In environments containing methane, a flame safety lamp will continue to burn at _____ oxygen concentrations; however, at oxygen contents of less than _____, the lamp will be extinguished regardless of the methane content of the air.

Oxygen Detectors

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.

oxygen

The actual ____ concentration can be measured using liquid absorption devices, stain tubes, paramagnetic analyzers, and electrochemical or fuel-cell detectors

Flame safety lamp

Which of the following is a detection method for methane?

A. Radiation detectors
B. Flame safety lamp
C. Paramagnetic analyzers
D. Hopcolyte optical IR

Thermal conductivity

Methane can be detected by which method that measures heat transfer?
A. Thermal conductivity
B. Radiation detectors
C. Electrochemical sensors
D. Liquid absorption

Optical (IR and interferometer)

Which optical methods can be used to detect methane?
A. Hopcolyte optical IR
B. Optical (IR and interferometer)
C. Radiation detectors
D. Paramagnetic analyzers

O₂

Which gas is commonly measured using paramagnetic analyzers?
A. CO
B. O₂
C. NOₓ
D. CH₄

Radiation detectors

Which of the following is NOT a detection method for oxygen?
A. Liquid absorption
B. Stain tubes
C. Paramagnetic analyzers
D. Radiation detectors

Oxygen

Which gas can be detected by both electrochemical sensors and paramagnetic analyzers?
A. Hydrogen
B. Oxygen
C. Methane
D. Sulfur dioxide

Liquid absorption

Which method is commonly used to detect carbon dioxide?
A. Radiation detectors
B. Liquid absorption
C. Flame safety lamp
D. Paramagnetic analyzers

All of the above

Carbon dioxide can be detected by:
A. Optical interferometer
B. Stain tubes
C. Liquid absorption
D. All of the above

CO

Which gas can be detected by hopcolyte optical IR?
A. CO₂
B. H₂S
C. CO
D. NOₓ

Radiation detectors

Which of the following is NOT a detection method for carbon monoxide?
A. Electrochemical sensors
B. Catalytic oxidation
C. Metal oxide semiconductors
D. Radiation detectors

Electrochemical sensors

Which detection method is used for oxides of nitrogen?
A. Electrochemical sensors
B. Flame safety lamp
C. Radiation detectors
D. Thermal conductivity

Stain tubes and electrochemical sensors

Oxides of nitrogen (NOₓ) can be detected by:
A. Catalytic oxidation and stain tubes
B. Stain tubes and electrochemical sensors
C. Optical interferometer and radiation detectors
D. Liquid absorption and flame safety lamp

Paramagnetic analyzers

Which of the following is NOT a method for detecting hydrogen sulfide?
A. Metal oxide semiconductors
B. Electrochemical sensors
C. Stain tubes
D. Paramagnetic analyzers

H₂S

Which gas can be detected using all of the following: electrochemical sensors, metal oxide semiconductors, and stain tubes?
A. SO₂
B. H₂S
C. CO₂
D. H₂

SO₂

Which gas can be detected by both stain tubes and electrochemical sensors?
A. O₂
B. CO₂
C. SO₂
D. CH₄

Stain tubes and electrochemical sensors

Sulfur dioxide can be detected by:
A. Optical interferometer
B. Stain tubes and electrochemical sensors
C. Radiation detectors only
D. Flame safety lamp

H₂

Which gas in the table is detected only by stain tubes?
A. H₂
B. CH₄
C. SO₂
D. NOₓ

Stain tubes

Which of the following is a method for detecting hydrogen gas?
A. Electrochemical sensors
B. Stain tubes
C. Radiation detectors
D. Paramagnetic analyzers

Radiation detectors

Radon is detected using which method?
A. Radiation detectors
B. Flame safety lamp
C. Metal oxide semiconductors
D. Catalytic oxidation

Radon

Which gas requires radiation detectors for monitoring?
A. Methane
B. Radon
C. Oxygen
D. Carbon dioxide