G3 Leak Detection and Testing Procedures 2 — Questions and Answers
Question 1: Electronic combustible gas detectors measure gas concentration as a percentage of which value?
- Maximum allowable operating pressure (MAOP)
- Lower explosive limit (LEL) (Correct answer)
- Upper explosive limit (UEL)
- Stoichiometric combustion ratio
Correct answer: Lower explosive limit (LEL)
Electronic gas detectors display readings as a percentage of the Lower Explosive Limit (LEL), alerting technicians before concentrations reach dangerous levels.
Question 2: What type of electronic leak detector is best suited for detecting very small leaks in high-pressure gas distribution mains?
- Catalytic bead sensor
- Flame ionization detector (FID) (Correct answer)
- Thermal conductivity sensor
- Photoionization detector (PID)
Correct answer: Flame ionization detector (FID)
Flame ionization detectors (FID) have extremely high sensitivity and are ideal for detecting very small hydrocarbon gas leaks in distribution mains.
Question 3: Under CSA B149.1 Natural Gas and Propane Installation Code, which test medium is NOT acceptable for leak testing gas piping?
- Natural gas
- Nitrogen
- Air
- Oxygen (Correct answer)
Correct answer: Oxygen
Oxygen must never be used as a test medium because it creates an explosive mixture with any combustible gas residue in the piping.
Question 4: When using an electronic leak detector in a confined space, the technician should check gas concentration at which level first?
- At floor level, since all fuel gases are heavier than air
- At ceiling level, since methane (natural gas) is lighter than air
- At mid-height where mixing occurs
- It depends on the specific fuel gas being tested (Correct answer)
Correct answer: It depends on the specific fuel gas being tested
The testing level depends on the fuel gas: natural gas (methane) is lighter than air and rises to the ceiling, while propane is heavier and sinks to the floor.
Question 5: A G3 technician is called to a suspected gas leak. What is the FIRST action upon arriving at the scene?
- Begin leak testing with electronic detector immediately
- Eliminate all ignition sources and ventilate the area (Correct answer)
- Call the gas utility to shut off supply
- Apply soap solution to all visible pipe joints
Correct answer: Eliminate all ignition sources and ventilate the area
Eliminating ignition sources and ventilating the area are the first priority to prevent ignition of any accumulated gas before testing begins.
Question 6: Which instrument is used to measure gas pressure with the highest accuracy for low-pressure systems operating at or below 14 in. W.C.?
- Bourdon tube pressure gauge
- Manometer (water column gauge)
- Digital compound gauge
- Slant-tube manometer (Correct answer)
Correct answer: Slant-tube manometer
A slant-tube manometer provides the highest accuracy for low-pressure measurements because the inclined tube magnifies small pressure differences for easier reading.
Question 7: When testing a gas system that has been out of service for an extended period, why must the system be purged before returning to service?
- To remove moisture and debris from the piping
- To displace air or inert test gas that could create a flammable mixture at the burner (Correct answer)
- To increase the system pressure to operating levels
- To reset all pressure regulators to factory settings
Correct answer: To displace air or inert test gas that could create a flammable mixture at the burner
Purging removes air or inert test gas that could form a flammable air-gas mixture at burners during ignition, creating a safety hazard.
G3 Leak Detection and Testing Procedures 2
Electronic combustible gas detectors measure gas concentration as a percentage of which value?