GPT Safety & Leak Detection 3 — Questions and Answers
Question 1: Which type of leak detection fluid is approved for use on gas piping systems by most codes and manufacturer guidelines?
- Standard dish soap diluted 50/50 with water
- Any commercial soap solution that produces a foam
- Listed combustible gas leak detection solution (Correct answer)
- Motor oil mixed with water
Correct answer: Listed combustible gas leak detection solution
Codes require a listed (UL or equivalent) combustible gas leak detection solution because unlisted soaps may damage certain fittings or produce false readings.
Question 2: A technician is purging air from a new gas line. To prevent a flammable mixture from forming inside the pipe during purging, what method should be used?
- Purge slowly to allow air and gas to mix gradually
- Use nitrogen to displace air before introducing gas (Correct answer)
- Ignite gas at the purge point immediately to burn off the mixture
- Purge into the building interior with fans running
Correct answer: Use nitrogen to displace air before introducing gas
Introducing an inert gas like nitrogen first displaces oxygen so the pipe never passes through the flammable range when gas is introduced.
Question 3: At what natural gas concentration in air (approximate % by volume) does the mixture become ignitable?
- 1% to 3%
- 5% to 15% (Correct answer)
- 16% to 25%
- 30% to 50%
Correct answer: 5% to 15%
Natural gas is flammable between approximately 5% (LEL) and 15% (UEL) by volume in air; outside this range ignition cannot be sustained.
Question 4: What is the primary purpose of a gas regulator's vent pipe on a pressure regulator installed indoors?
- To relieve excess inlet pressure back to the supply main
- To allow relief of gas to a safe outdoor location if the diaphragm fails (Correct answer)
- To equalize pressure between inlet and outlet
- To provide a test port for pressure measurement
Correct answer: To allow relief of gas to a safe outdoor location if the diaphragm fails
The vent pipe routes gas released by the regulator's relief mechanism to a safe outdoor location, preventing accumulation of gas indoors in the event of a diaphragm failure.
Question 5: Which personal protective equipment (PPE) is MOST critical when a gas technician is working in a confined space suspected of containing gas?
- Chemical-resistant gloves
- Self-contained breathing apparatus (SCBA) (Correct answer)
- Hard hat with face shield
- Flame-resistant coveralls only
Correct answer: Self-contained breathing apparatus (SCBA)
An SCBA provides breathable air in oxygen-deficient or gas-contaminated atmospheres, which is the primary hazard in a confined space with potential gas accumulation.
Question 6: A two-pound LP gas system has a regulator that fails open. What is the immediate hazard?
- The appliances will receive full tank pressure (over 100 psig), risking fire or explosion (Correct answer)
- The system will shut down automatically due to excess flow
- Appliances will operate at reduced efficiency only
- Carbon monoxide levels will rise gradually without risk of ignition
Correct answer: The appliances will receive full tank pressure (over 100 psig), risking fire or explosion
A regulator that fails open allows full cylinder pressure to reach appliances and piping rated for only 2 psi, creating a serious risk of fitting failure, gas release, and ignition.
Question 7: According to NFPA 54, gas piping must be tested with air, CO2, or nitrogen at what minimum pressure to be considered a valid strength test before gas is introduced?
- 1.5 psi for 10 minutes
- 3 psi for 30 minutes
- 1.5 times the maximum allowable operating pressure (Correct answer)
- 10 psi for 60 minutes
Correct answer: 1.5 times the maximum allowable operating pressure
NFPA 54 requires a strength test at 1.5 times the maximum allowable operating pressure to verify the piping system can safely handle normal operating conditions.
GPT Safety & Leak Detection 3
Which type of leak detection fluid is approved for use on gas piping systems by most codes and manufacturer guidelines?