Journeyman Plumbers Exam Gas Piping Systems 5 — Questions and Answers
Question 1: A gas pipe run exposed in a garage must be protected from vehicle damage by:
- Painting it yellow for visibility
- Routing it at least 6 feet above the floor or installing mechanical protection (Correct answer)
- Enclosing it in a conduit
- Installing a pressure relief valve
Correct answer: Routing it at least 6 feet above the floor or installing mechanical protection
Gas piping in garages must either be installed at least 6 feet above the floor or protected by physical barriers to prevent damage from vehicles.
Question 2: What is the flammability range (lower explosive limit to upper explosive limit) of natural gas in air?
- 1% to 5%
- 5% to 15% (Correct answer)
- 15% to 25%
- 20% to 50%
Correct answer: 5% to 15%
Natural gas is flammable when its concentration in air is between approximately 5% (LEL) and 15% (UEL); outside this range it will not ignite.
Question 3: When installing a propane (LP) system, the tank must be located a minimum of how far from any building opening?
- 3 feet
- 5 feet
- 10 feet (Correct answer)
- 25 feet
Correct answer: 10 feet
NFPA 58 requires LP-gas containers to be located at least 10 feet from any building opening such as windows, doors, or dryer vents.
Question 4: When using the pressure drop method to size gas piping, what two factors are primarily used in the calculation?
- Pipe length and material only
- Appliance BTU demand and pipe diameter
- Gas pressure at meter and altitude
- Flow rate (CFH) and pipe length (Correct answer)
Correct answer: Flow rate (CFH) and pipe length
The pressure drop sizing method uses the calculated flow rate in cubic feet per hour (CFH) and the actual pipe run length to select the appropriate pipe diameter from sizing tables.
Question 5: A gas line passing through a concrete slab must be:
- Sleeved in a conduit that extends beyond the slab on both sides (Correct answer)
- Wrapped in fiberglass insulation
- Made of copper tubing only
- Painted with coal tar epoxy
Correct answer: Sleeved in a conduit that extends beyond the slab on both sides
Gas piping penetrating a concrete slab must be installed in a protective sleeve that extends beyond the slab on both sides to prevent corrosion and allow for movement.
Question 6: Which of the following appliances requires a 100% safety shutoff (automatic gas valve) as part of its control system?
- Gas range cooktop
- Outdoor grill
- Residential gas boiler with standing pilot (Correct answer)
- Decorative fireplace log lighter
Correct answer: Residential gas boiler with standing pilot
Residential gas boilers must have a 100% safety shutoff control that automatically closes the gas valve if the pilot or ignition fails, preventing unburned gas accumulation.
Question 7: What is the correct procedure when a gas leak is suspected in a building?
- Open windows and use an electric fan to ventilate the area
- Locate the leak with a flame before evacuating
- Shut off the gas at the meter, evacuate, and call the gas company from outside (Correct answer)
- Tighten all fittings while the gas is still on
Correct answer: Shut off the gas at the meter, evacuate, and call the gas company from outside
When a gas leak is suspected, the correct response is to shut off gas at the meter, evacuate all occupants, avoid any ignition sources, and call the utility from outside the building.
