CPD Gas Piping Systems Design 3

Question 1

For a commercial kitchen exhaust system using a gas-fired appliance, what is the purpose of specifying an interlock between the exhaust fan and the gas valve?

Accepted Answer

To prevent gas flow to the appliance if the exhaust fan is not operating, reducing CO accumulation risk

Answer

To increase gas pressure when the fan is running

Answer

To allow higher BTU input when ventilation is confirmed adequate

Answer

To comply with energy codes requiring fan-assisted combustion

Question 2

An automatic gas shutoff valve (seismic shutoff valve) is typically required in areas of high seismic activity and operates by:

Accepted Answer

A ground motion sensor (ball-type or trigger mechanism) that closes the valve when seismic acceleration exceeds a threshold

Answer

A pressure sensor detecting a drop in line pressure after a pipe break

Answer

A manual pull-station activated by building occupants

Answer

A temperature sensor detecting heat from a post-earthquake fire

Question 3

When designing combustion air for a gas-fired boiler installed in a mechanical room, NFPA 54 defines a 'confined space' as one with less than:

Accepted Answer

50 cubic feet per 1,000 BTU/hr of installed appliance input

Answer

1,000 cubic feet total volume regardless of appliance load

Answer

1 cubic foot per 1,000 BTU/hr of installed appliance input

Answer

500 cubic feet per appliance regardless of BTU rating

Question 4

What is the primary purpose of a pressure regulator vent limiter (or vent-limiting orifice) on a gas pressure regulator installed indoors?

Accepted Answer

To limit the release of gas to a safe rate if the regulator diaphragm fails, preventing rapid accumulation of gas indoors

Answer

To increase the regulated outlet pressure to appliance requirements

Answer

To allow the regulator to function without a vent line to the exterior

Answer

To reduce noise from pressure regulation

Question 5

A plumbing designer specifying gas piping in a high-rise building above the fourth floor should be aware that NFPA 54 requires the gas distribution system to include:

Accepted Answer

Manual shutoff valves at each floor level in addition to the main service shutoff

Answer

Only a single main service shutoff at the meter

Answer

Automatic pressure relief valves on every riser segment

Answer

Threaded joints exclusively — no welded connections above grade

Question 6

When transitioning a gas supply line from underground (PE plastic) to above-grade (steel) piping at a building, the designer must specify which fitting?

Accepted Answer

A PE-to-steel transition (anodeless riser or steel casing) approved for gas service

Answer

A dielectric union to prevent galvanic corrosion

Answer

An electrofusion coupling to join the two pipe materials

Answer

A compression fitting rated for the operating pressure

Question 7

Per NFPA 54, which of the following gas pipe materials is acceptable for both interior and underground exterior natural gas service?

Accepted Answer

Black steel pipe — interior and exterior including buried with coating

Answer

Polyethylene (PE) — interior and exterior

Answer

CSST — interior and exterior including buried

Answer

Copper tubing — interior and exterior including buried in all soil types