Session 15: Gas Measurement

Question 1

Tell me the use and principle of a Explosimeter

Answer 1

Use: Explosimeters are used to detect and measure the concentration of flammable gases and vapors in the air to ensure that levels do not reach an explosive threshold.

Principle: They typically work on the principle of catalytic combustion or thermal conductivity. A catalytic bead sensor becomes hot when a combustible gas oxidizes on its surface, changing the electrical resistance of the bead and producing a reading.

Question 2

What are the limitations and testing methods for explosimeter?

Answer 2

Limitations:

• They can become poisoned or inhibited by certain substances, which can make the sensors less reliable or cause them to fail.
• They are specific to combustible gases and will not detect toxic gases or oxygen deficiency.

Testing:

• Regular bump tests with a known concentration of combustible gas are necessary to ensure the instrument is working correctly.
• Calibration checks with certified calibration gases should be performed according to the manufacturer’s recommendations.

Question 3

What is the use and principle of a tank scope?

Answer 3

Use: Tank scopes are typically used to measure the concentration of hydrocarbons within the air space of a fuel storage tank.

Principle: Many such devices use a piston-type pump to draw an air sample from the tank and pass it over detector tubes filled with a chemical agent that changes color in the presence of the target gas. The length of the color change along the tube corresponds to the concentration of gas.

Question 4

What are the limitations and testing of tank scope?

Answer 4

Limitations:

• They require specific detector tubes for different gases.
• Human error in reading the color change can lead to inaccurate readings.
• They cannot give continuous monitoring and need manual operation for each test.

Testing:

• A functional check should be done to ensure the pump and system are working properly.
• Zero-air checks and span-gas tests are conducted to ensure the detector tubes are providing accurate readings.

Question 5

What is the use and principle of a oxygen analyzer?

Answer 5

Use: Oxygen analyzers are used to measure the percentage of oxygen in an environment. They are essential in spaces where there is a risk of oxygen deficiency or enrichment, such as in confined spaces.

Principle: There are various types of oxygen analyzers; some use electrochemical cells, others use paramagnetic or zirconia sensors. Electrochemical sensors produce a current that is proportional to the concentration of oxygen in the air.

Question 6

What are the limitations and testing of a oxygen analyzer?

Answer 6

Limitations:

• Sensors have a limited lifespan and can be affected by temperature, pressure, and other gases.
• Inaccurate readings can occur if the sensor is not regularly calibrated.
• Some sensors require a minimum oxygen level to operate correctly.

Testing:

• A bump test with a known concentration of oxygen should be carried out to confirm sensor functionality.
• Regular calibration with calibration gases is essential to maintain accuracy.

Question 7

What is the principle and use of a multi gas detector?

Answer 7

4. Multi-Gas Detector

Use: Multi-gas detectors are used to simultaneously detect multiple gases, which typically include a combination of flammable, oxygen, carbon monoxide, hydrogen sulfide, and other toxic gases.

Principle: They usually combine different types of sensors (catalytic, electrochemical, photoionization, infrared, etc.) in one device, each designed to detect specific gases.

Question 8

What are the limitations and testing of a multi gas detector?

Answer 8

Limitations:

• Complexity of the device can lead to higher maintenance requirements and costs.
• Sensor cross-sensitivity can sometimes cause inaccurate readings for certain gas combinations.
• The response time and range can vary for different sensors within the device.

Testing:

• Bump tests with appropriate gas mixtures should be performed to ensure all sensors are responding accurately.
• Full calibration is necessary if any of the sensors fails a bump test or according to the manufacturer’s suggested schedule.