GPT Safety & Leak Detection 2 — Questions and Answers
Question 1: When using electronic combustible gas detectors, the sensor tip should be held how far from the surface being tested?
- Flush against the surface
- 1/4 to 1/2 inch from the surface (Correct answer)
- 2 to 3 inches from the surface
- 6 inches from the surface
Correct answer: 1/4 to 1/2 inch from the surface
Holding the sensor tip 1/4 to 1/2 inch from the surface allows the instrument to sample gas concentrations escaping from joints or fittings without contaminating the sensor.
Question 2: Which condition makes a soap bubble test unreliable for detecting small gas leaks?
- High ambient temperature above 90°F
- Wind or air currents near the test area (Correct answer)
- Testing on horizontal pipe runs
- Using liquid dish soap instead of commercial leak detector
Correct answer: Wind or air currents near the test area
Wind or air currents disperse escaping gas before bubbles can form, making soap bubble tests unreliable outdoors or in drafty areas.
Question 3: A technician detects a gas odor inside a building but cannot locate the source. What is the FIRST action?
- Shut off the gas meter immediately
- Ventilate the building by opening windows and doors
- Evacuate all occupants and call 911 from outside (Correct answer)
- Use a lighter to trace the leak source
Correct answer: Evacuate all occupants and call 911 from outside
Life safety takes priority — evacuate all occupants and call emergency services from outside before taking any other action.
Question 4: What does LEL stand for in the context of gas hazard measurement?
- Lowest Explosive Level
- Lower Explosive Limit (Correct answer)
- Leak Exposure Limit
- Liquid Equivalent Level
Correct answer: Lower Explosive Limit
LEL (Lower Explosive Limit) is the minimum concentration of gas in air at which ignition can occur, typically around 5% for natural gas.
Question 5: During a pressure test, a technician notices a slow but steady pressure drop over 30 minutes with no soap bubble visible. What should the technician do?
- Accept the test as passing since no bubbles were seen
- Increase the test pressure and retest
- Use an electronic detector to locate the concealed leak (Correct answer)
- Record the drop and notify the utility
Correct answer: Use an electronic detector to locate the concealed leak
A steady pressure drop indicates a real leak that must be located; an electronic detector is appropriate when visual methods fail to find the source.
Question 6: Which gas has a lower vapor density than air, causing it to rise and accumulate at ceiling level in an enclosed space?
- Propane (LP gas)
- Butane
- Natural gas (methane) (Correct answer)
- Ethane
Correct answer: Natural gas (methane)
Natural gas (methane) has a vapor density of about 0.55 relative to air, so it rises and concentrates at ceiling level rather than pooling on the floor.
Question 7: A gas appliance produces a yellow or orange flame instead of blue. This indicates what condition?
- The appliance is operating at peak efficiency
- Incomplete combustion due to insufficient air supply (Correct answer)
- Excess air causing a lean mixture
- The gas pressure is too high
Correct answer: Incomplete combustion due to insufficient air supply
A yellow or orange flame indicates incomplete combustion, usually caused by insufficient air (primary or secondary), which can produce dangerous carbon monoxide.
GPT Safety & Leak Detection 2
When using electronic combustible gas detectors, the sensor tip should be held how far from the surface being tested?