NOTE Natural gas and LP gas are conveyed by physically distinct systems whose engineering differs in ways that touch nearly every clause of this standard. Natural gas is lighter than air (specific gravity approximately 0.60) and disperses upward on release; LP gas is denser than air (specific gravity approximately 1.52) and pools in low points, pits, and floor channels on release. This density difference changes pipe sizing tables, leak migration behavior, ventilation and detection strategy, and material compatibility, which is why LP and natural gas distribution are governed by separate code chapters and are kept distinct in this standard. (1.3.1)

NOTE Where the jurisdiction adopts the IFGC in lieu of or alongside NFPA 54, both documents cover the same core requirements and the locally adopted code governs; conflicts are resolved in favor of the more stringent provision. (1.4.1)

NOTE Site natural gas service piping from the street main to the building meter is furnished under the serving utility's scope and is specified in Natural Gas Piping, not here. (1.5.1)

NOTE Fuel oil storage tanks, day tanks, and fuel oil distribution piping are excluded and are covered by Fuel Oil Systems. (1.5.2)

NOTE Gas-fired boilers, burners, combustion controls, and appliance venting are excluded; this standard stops at the appliance shutoff and connector. See Boilers and Furnaces. (1.5.3)

NOTE LP bulk storage tank design, siting setbacks, and fill connections are governed by NFPA 58 Chapter 6 as a building and site design matter and are outside this interior-piping standard. (1.5.4)

NOTE Compressed air distribution piping is excluded and is covered by Compressed Air Systems. (1.5.5)

NOTE Control and instrumentation associated with gas equipment - flame-safeguard, modulating gas valves, and combustion sensors - are excluded and are covered by Hvac Controls Instrumentation. (1.5.6)

NOTE Industrial process piping operating above 125 psi is governed by ASME B31.3 and is outside the facility building-distribution scope of this standard. (1.5.7)

NOTE Component listings are not interchangeable between gas services: a regulator listed for natural gas is not acceptable on an LP system. (4.3.1)

NOTE Gas type and operating-pressure tier are the two decisions that cascade through the entire design: they set the pipe material, schedule, valve pressure rating, regulator strategy, and which sizing table applies. (5.1.1)

NOTE LP gas carries roughly 2.5 times the heating value per cubic foot of natural gas but a much higher specific gravity, so LP and natural gas use different sizing tables; applying natural gas tables to an LP system oversizes the pipe and understates velocity, which can mask regulator instability. (5.1.2)

NOTE NFPA 54 limits concealed interior piping to 5 psi precisely to keep a higher-pressure leak from accumulating inside a wall or chase; medium-pressure distribution above 5 psi inside an occupied building is a frequent and serious code violation. (5.2.1)

NOTE Threaded malleable-iron fittings are acceptable for steel piping sized 1/2 in. through 4 in. NPS at low and medium pressure. (6.1.1)

NOTE LP gas can react with copper and copper alloys, so NFPA 54 and most jurisdictions prohibit copper for undiluted LP. (6.3.1)

NOTE CSST is dominant in light-commercial and retrofit work because it routes around structure without threaded joints, but it is a listed system, not a generic material - the tubing, fittings, and bonding are qualified together and cannot be mixed across manufacturers. (6.6.1)

NOTE Standard white PTFE tape is a frequent source of field RFIs when the wrong product is specified. (6.11.3)

NOTE Two-stage regulation is required because reducing tank pressure - which varies from roughly 100 to 200 psi with temperature - directly to appliance pressure in a single step produces unstable delivery pressure and is not code-compliant for building installations. (7.1.1)

NOTE The first stage typically reduces tank pressure to an intermediate value of about 10 psig, and the second stage reduces that to the appliance delivery pressure of 11 in. WC for standard LP appliances. (7.1.2)

NOTE On LP systems, liquid-side relief is typically set at about 250 psi and vapor-distribution relief at roughly 5 to 15 psi, matched to the protected component's rating. (8.2.1)

NOTE Because LP vapor is heavier than air, relief discharge points and any low-point accumulation areas must be evaluated for pooling; terminating discharge low or near a pit defeats the protection. (8.3.1)

NOTE The main shutoff at the building entry is the first device emergency responders and operators reach for; NFPA 54 requires it to be accessible and identified, and a lockable handle is recommended for security in commercial occupancies. (9.3.1)

NOTE California, Oregon, and Nevada require automatic seismic shutoff valves in defined seismic design categories; projects in these jurisdictions that omit them will fail inspection. (9.6.1)

NOTE Seismic shutoff valves typically trip at 0.15g to 0.25g horizontal ground acceleration per the locally adopted code. (9.6.2)

NOTE Corrugated stainless-steel appliance connectors are not reusable after disconnection; reusing one risks a fatigue failure at the corrugations, so reconnected equipment always gets a new connector. (10.3.1)

NOTE Low-pressure systems shall be sized to a maximum pressure drop of 0.5 in. WC by default per the NFPA 54 sizing tables; medium-pressure systems may be sized to a 1 psi maximum drop. (11.1.1)

NOTE Natural gas piping shall be sized using the NFPA 54 Schedule 40 steel table at specific gravity 0.60; LP gas piping shall be sized using the LP table at specific gravity 1.52; CSST shall be sized using the listed manufacturer's charts. (11.1.2)

NOTE Omitting future-load provisions is a common and costly mistake: adding capacity after the fact often means replacing entire mains, so the sizing basis should state which future loads are included. (11.2.1)

NOTE Connecting CSST only to a grounded appliance does not satisfy the bonding requirement; standard-jacket CSST needs a dedicated bonding conductor back to the grounding electrode to dissipate energy from a nearby lightning strike. (12.2.1)

NOTE Arc-resistant CSST (a listed conductive or jacketed system) carries relaxed bonding rules under ANSI LC-1; that relaxation applies only when the specific listed product and the manufacturer's instructions are explicitly invoked and the authority having jurisdiction accepts them. (12.3.1)

NOTE The test medium, pressure, and duration must be stated explicitly because using combustible gas to test is prohibited and an under-specified test is a common cause of rejected inspections. (13.3.1)

NOTE PE pipe cannot penetrate a fire-rated assembly; it must transition to steel before reaching the rated wall or floor, and the steel penetration is then firestopped. (14.4.1)

NOTE Liquid LP must vaporize before it can be burned; in cold climates a high-demand load can outrun the tank's natural vaporization rate, so an electric immersion or atmospheric vaporizer is added - a coordination item with Boilers and the LP supplier. (14.6.1)