1310.12 Prohibited Devices. No device shall be placed

inside the gas piping or fittings that reduces the cross-sectional area or otherwise obstructs the free flow of gas, except where proper allowance in the piping system design has been made for such a device and where approved by the Authority Having Jurisdiction. [NFPA 54:7.10]

Section 1312.3.1 shall be permitted.

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FUEL GAS PIPING

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FUEL GAS PIPING

sion vents in accordance with sound engineering principles. Such rooms or below-grade installations shall have adequate positive ventilation. (2) Where gas-mixing machines are installed in well ventilated areas, the type of electrical equipment

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side the Flammable Range.1310.13 Systems Containing Gas-Air Mixtures Out- Where gas-air mixing machines are employed to produce mixtures above or below the flammable range, they shall be provided with stops to prevent adjustment of the mixture to within or approaching the flammable range. [NFPA 54:7.11] Mixtures. 1310.14 Systems Containing Flammable Gas-Air Systems containing flammable gas-air mixtures shall be in accordance with Section 1310.14.1 through Section 1310.14.6.

The blower shall be equipped with a gas-control valve at its air entrance arranged so that gas is admitted to the airstream, entering the blower in proper proportions for correct combustion by the type of burners employed, the said gas-control valve being of either the zero governor or mechanical ratio valve type that controls the gas and air adjustment simultaneously. No valves or other obstructions shall be installed between the blower discharge and the burner or burners. [NFPA 54:7.12.4] Installation of gas-mixing machines shall comply with 1310.14.5 Installation of Gas-Mixing Machines. the following: (1) The gas-mixing machine shall be located in a well ventilated area or in a detached building or cutoff

1310.14.1 Required Components. A central premix system with a flammable mixture in the blower or compressor shall consist of the following components: (1) Gas-mixing machine in the form of an automatic

gas-air proportioning device combined with a down

(1) Gas-mixing machine in the form of an automatic

gas-air proportioning device combined with a downstream blower or compressor. (2) Flammable mixture piping, minimum Schedule 40. (3) Automatic firecheck(s). (4) Safety blowout(s) or backfire preventers for systems

utilizing flammable mixture lines above 2 ¹ ⁄2 inches

(2) Where gas-mixing machines are installed in well ventilated areas, the type of electrical equipment shall be in accordance with the California Electri- cal Code, for general service conditions unless other hazards in the area prevail. Where gas-mixing machines are installed in small detached buildings or cutoff rooms, the electrical equipment and wiring shall be installed in accordance with the California Electrical Code for hazardous locations (Articles 500 and 501, Class I, Division 2). (3) Air intakes for gas-mixing machines using com pressors or blowers shall be taken from outdoors

(3) Air intakes for gas-mixing machines using com pressors or blowers shall be taken from outdoors whenever practical. (4) Controls for gas-mixing machines shall include

interlocks and a safety shutoff valve of the manual

(4) Safety blowout(s) or backfire preventers for systems

utilizing flammable mixture lines above 2 ¹ ⁄2 inches (64 mm) nominal pipe size or the equivalent. [NFPA 54:7.12.1] 1310.14.2 Optional Components. The following components shall also be permitted to be utilized in any type of central premix system: (1) Flowmeter(s) (2) Flame arrester(s) [NFPA 54:7.12.2] 1310.14.3 Additional Requirements. Gas-mixing machines shall have nonsparking blowers and shall be constructed so that a flashback does not rupture machine casings. [NFPA 54:7.12.3] 1310.14.4 Special Requirements for MixingBlowers. A mixing blower system shall be limited to applications with minimum practical lengths of mixture piping, limited to a maximum mixture pressure of 10 inches water column (2.5 kPa) and limited to gases containing no more than 10 percent hydrogen.

(4) Controls for gas-mixing machines shall include

interlocks and a safety shutoff valve of the manual reset type in the gas supply connection to each machine arranged to automatically shut off the gas supply in the event of high or low gas pressure. Except for open-burner installations only, the controls shall be interlocked so that the blower or compressor stops operating following a gas supply failure. Where a system employs pressurized air, means shall be provided to shut off the gas supply in the event of air failure. (5) Centrifugal gas-mixing machines in parallel shall be

reviewed by the user and equipment manufacturer

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(5) Centrifugal gas-mixing machines in parallel shall be

reviewed by the user and equipment manufacturer before installation, and means or plans for minimizing the effects of downstream pulsation and equipment overload shall be prepared and utilized as needed. [NFPA 54:7.12.5.1 – 7.12.5.5] Blowouts, or Backfire Preventers.1310.14.6 Use of Automatic Firechecks, Safety Automatic firechecks and safety blowouts or backfire preventers shall be provided in piping systems distributing flammable air-gas mixtures from gas-mixing machines to protect the piping and the machines in the event of flashback, in accordance with the following: (1) Approved automatic firechecks shall be installed

upstream as close as practical to the burner inlets fol

(1) Approved automatic firechecks shall be installed

upstream as close as practical to the burner inlets following the firecheck manufacturer’s instructions. (2) A separate manually operated gas valve shall be pro vided at each automatic firecheck for shutting off the

The gas-mixing machine shall be located in a well ventilated area or in a detached building or cutoff room provided with room construction and explo

(2) A separate manually operated gas valve shall be pro vided at each automatic firecheck for shutting off the flow of the gas-air mixture through the firecheck after a flashback has occurred. The valve shall be located upstream as close as practical to the inlet of the automatic firecheck. Caution: These valves shall not be reopened after a flashback has occurred until the firecheck has cooled sufficiently to prevent re-ignition of the flammable mixture and has been reset properly. (3) A safety blowout or backfiring preventer shall be

provided in the mixture line near the outlet of each

A safety blowout or backfiring preventer shall be

provided in the mixture line near the outlet of each gas-mixing machine where the size of the piping is

2019 CALIFORNIA MECHANICAL CODE 263

FUEL GAS PIPING any other purpose or distributed to any other persons or parti es.

FUEL GAS PIPING any other purpose