Journeyman Plumbers Exam Gas Piping Systems 4 — Questions and Answers
Question 1: What substance is added to natural gas to give it its distinctive odor?
- Propane
- Methane
- Mercaptan (ethyl mercaptan) (Correct answer)
- Carbon monoxide
Correct answer: Mercaptan (ethyl mercaptan)
Mercaptan (ethyl mercaptan) is the odorant added to natural gas by the utility to make odorless gas detectable by smell at very low concentrations.
Question 2: Which of the following is the correct pipe thread sealant to use on gas piping threaded joints?
- Teflon tape only
- Pipe dope approved for gas service (Correct answer)
- Standard plumber's putty
- Silicone caulk
Correct answer: Pipe dope approved for gas service
Only pipe thread compound (pipe dope) specifically listed and approved for gas service should be used on gas pipe threaded joints; standard Teflon tape alone is not sufficient.
Question 3: When a gas appliance is installed in a bedroom or bathroom, which special requirement applies?
- The appliance must be direct-vent or have a sealed combustion chamber (Correct answer)
- The gas meter must be indoors
- No gas appliances are permitted in bedrooms or bathrooms
- A CO detector must be installed within 1 foot of the appliance
Correct answer: The appliance must be direct-vent or have a sealed combustion chamber
Gas appliances in sleeping rooms and bathrooms must use direct-vent or sealed combustion systems to prevent combustion air from being drawn from the occupied space.
Question 4: What is the primary purpose of a pressure regulator on a gas system?
- To increase gas pressure to appliances
- To reduce and stabilize supply pressure to a safe, usable level (Correct answer)
- To shut off gas flow during a leak
- To measure gas consumption for billing
Correct answer: To reduce and stabilize supply pressure to a safe, usable level
A pressure regulator reduces the higher distribution pressure to the lower, stable pressure required by appliances and maintains that pressure under varying flow conditions.
Question 5: CSST (corrugated stainless steel tubing) installations require bonding because:
- It corrodes faster than black steel pipe
- Lightning or electrical surges can arc through it and cause failures (Correct answer)
- It cannot withstand operating pressure without grounding
- Building codes require all metal piping to be bonded
Correct answer: Lightning or electrical surges can arc through it and cause failures
CSST must be bonded because lightning-induced electrical surges can arc through the thin corrugated walls, potentially causing pinhole leaks and gas fires.
Question 6: What is the minimum clearance required between unprotected gas piping and an electrical panel?
- 6 inches (Correct answer)
- 12 inches
- 18 inches
- No clearance requirement exists
Correct answer: 6 inches
Gas piping must maintain a minimum clearance of 6 inches from electrical panels and service equipment to reduce the risk of arcing igniting a gas leak.
Question 7: Which document primarily governs gas piping installation standards for most US jurisdictions?
- NFPA 54 / International Fuel Gas Code (IFGC) (Correct answer)
- IPC (International Plumbing Code)
- NEC (National Electrical Code)
- ASME B31.1 Power Piping
Correct answer: NFPA 54 / International Fuel Gas Code (IFGC)
NFPA 54 (National Fuel Gas Code) and its companion IFGC are the primary standards adopted by most US jurisdictions for fuel gas piping installation.
