Gas Piping Systems Design Flashcards

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?

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

Interlocking the exhaust fan with the gas valve ensures the appliance cannot fire unless ventilation is confirmed, preventing carbon monoxide buildup from incomplete combustion in an unventilated space.

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

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

Seismic gas shutoff valves use an internal ground motion sensor — typically a ball that displaces from its seat when shaking exceeds a set acceleration threshold — to automatically close the gas supply.

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:

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

NFPA 54 defines a confined space for combustion air purposes as a room with less than 50 cubic feet per 1,000 BTU/hr of total installed appliance input, requiring additional outdoor air provisions.

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

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

A vent limiter restricts the flow of gas through the regulator vent to a rate low enough to prevent dangerous accumulation indoors if the diaphragm ruptures, as an alternative to piping the vent to the outdoors.

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:

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

NFPA 54 requires readily accessible manual shutoff valves at each floor in high-rise buildings to enable emergency isolation of gas service to individual floors without affecting the rest of the building.

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

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

Anodeless risers or approved PE-to-steel transition fittings are required where underground plastic gas piping transitions to above-grade steel piping; they provide a gas-tight connection rated for the service conditions.

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

Answer: Black steel pipe — interior and exterior including buried with coating

Black steel pipe is acceptable for interior gas piping and for underground exterior use when properly coated and wrapped for corrosion protection; PE is limited to underground only, and CSST is generally prohibited underground.