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Subchapter 1. Unfired Pressure Vessel Safety Orders
Article 7. Compressed and Liquefied Natural Gas System

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§544. Installation of Fuel Tanks or Cylinders For Motor Vehicles and Industrial Trucks.

NOTE: This Section does not apply to those vehicles under the control of the Department of Highway Patrol, except subsections (p), (q), and (r).

(a) Motor fuel tanks or cylinders shall be located in a place and in a manner to minimize the possibility of physical damage.

(b) Motor fuel tanks or cylinders for passenger type vehicles may be located in the trunk compartment provided the trunk compartment is properly ventilated and the safety relief valve discharge is piped outside. When a motor fuel tank or cylinder is installed inside a trunk or other compartment, positive means shall be provided to prevent leakage of natural gas into the passenger or driver's compartment. Vehicle tanks or cylinders that have their connections or appurtenances in the end shall have as much space as possible for connecting the required flexible metal hose or tubing and for operating the manually operated shutoff valve.

(c) If radio transmitting or receiving equipment is located in the same compartment as the fuel tank or cylinder, such transmitting or receiving equipment shall be enclosed in a vapor-tight compartment or otherwise protected from escaping fuel, unless the radio equipment is approved for use in a Class 1, Division 1, Group D location.

(d) For passenger-carrying or other commercial vehicles, motor fuel tanks or cylinders and their valves and appurtenances may be installed in a recess which is vapor-tight to the inside of the vehicle and accessible from and vented to the outside.

(e) Valves, fittings and appurtenances containing natural gas shall not be located in the passenger or driver compartment unless all such valves, fittings and appurtenances are positively sealed off from and vented to a point outside the passenger or driver compartment.

(f) Each motor fuel tank shall be provided with a manually operated shutoff valve screwed directly into the tank connection. The manual shutoff valve shall be readily accessible or an electrically operated valve shall be installed in the line next to the manual valve. The manual shutoff valve shall be legibly labeled "Shutoff Valve". In installations of multiple cylinder manifolding, there shall also be a master shut-off valve either electrically or manually operated and located downstream from but as close as possible to the last cylinder in the series. In these cases there shall be a label indicating "Shut-off Valve" at the master valve and the individual tank valves need not be labeled.

(g) Motor fuel tanks or cylinders shall be installed in such a manner that the bottom of the vessel and/or any connection thereto shall not be lower than the lowest horizontal axle when the vehicle is fully loaded.

(h) Vents from control devices shall discharge outside the trunk compartment or other confined space.

(i) Motor fuel tanks or cylinders shall be secured in a manner to prevent jarring loose, slipping or rotating of the tanks. Such fastening shall be designed to withstand loadings in any direction equal to the filled weight of the tank with a factor of safety of at least 8. Motor fuel tanks or cylinders shall not be fastened directly to the gasoline fuel tank. Compensation shall be made for the added weight by proper design or redesign of the vehicle suspension system when the loaded weight of the vehicle exceeds the manufacturer's maximum specifications.

(j) Manifolded motor fuel tanks or cylinders shall be supported and held together as a unit by structurally adequate means. Manifolded branch lines shall be sufficiently flexible to prevent damage to the lines, valves and tanks due to vibration, expansion or contraction. Valves and appurtenances shall be protected from mechanical damage either by being located in recessed wells or by adequate guarding.

(k) All connecting parts of the fuel system shall be installed in such a manner as to prevent abrasion, vibration or fatigue and physical damage.

(l) Field welding, where necessary, shall be made only on saddle plates, brackets or other non-pressure parts that were provided and installed by the manufacturer of the tank or cylinder. There shall be no welding on the vessel shell or heads other than that by the manufacturer unless the welding is acceptable to the authorized inspector.

(m) The connection between the motor fuel tanks or cylinders and the reducing valves, vaporizer or other devices used to reduce the pressure to that needed for carburetion shall be of flexible metallic tubing, wire-braided hose or equivalent with a factor of safety of not less than 5 for the most severe pressure and temperature design conditions. There shall be as few connections and fittings as practicable.

(n) Automatic pressure reducing equipment shall be used for the purpose of reducing the pressure of natural gas to the carburetor, which shall not exceed 5 psi. Positive means shall be provided to prevent malfunction due to refrigeration effects. There shall be a device in the fuel supply system which will automatically stop the flow of fuel when the engine is not running.

(o) Each driver shall be trained in the safe use of this fuel system and be provided with a set of operating instructions. The driver's employer shall be responsible to see that this is done.

(p) While the natural gas motor fuel tank or cylinder is being filled, the vehicle parking or emergency brakes shall be set and the motor shut off. All transfer operations shall be supervised by an attendant familiar with the transfer operation. The attendant may be considered familiar with the transfer operation after he has been provided with a set of instructions and has performed the transfer operation at least through 3 full cycles under supervision. Where LNG motor fuel tanks or cylinders are being filled, the attendant shall remain at the controls necessary to stop the transfer operation.

(q) Fill connections for motor fuel tanks or cylinders shall have at least one back-flow check valve or device. Quick disconnect couplings may be used provided they are designed for the most severe pressure and temperature conditions with a factor of safety of at least 5 and provided they are leak-tight in the connected and disconnected shutoff conditions. These couplings shall not be used in lieu of any required manually operated shutoff valves.

(r) When motor vehicles are to be parked within buildings, adequate provisions shall be made such as roof ventilation to prevent gases lighter than air from being trapped at ceiling level. No source of ignition, electrical or otherwise, shall be permitted at those levels. (Title 24, T8-544(r)).


1. Amendment filed 4-1-77; effective thirtieth day thereafter (Register 77, No. 14).

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