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

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§543. Storage, Transfer and/or Vaporization of Natural Gas Within Buildings For the Purpose of Filling Motor Fuel Tanks or For Operating Stationary Internal Combustion Engines.

(a) CNG may be stored and LNG may be stored or vaporized within a building or an enclosure providing that the structure is of non-combustible construction, that it is used for industrial purposes only and that the floor area does not exceed 500 square feet.

(b) The space shall be used exclusively for the vaporization of the CNG or LNG or for the storage of not more than a total of 41,500 standard cubic feet of CNG or 500 gallons of LNG. If vapors heavier than air can be present, the structure shall not be below ground level and the space below the floor shall either be of solid fill or else properly ventilated to the open air.

(c) In all cases ventilation must be provided at both floor and ceiling levels and shall be considered adequate when no mixture of flammable gases is permitted in concentrations exceeding 20 percent of the lower flammability limit for the mixture. The requirements of this paragraph may be met by either:

(1) A continuously operating mechanical ventilation system.

(2) A gravity ventilation system composed of a combination of wall vents at the floor level and roof ventilators, or

(3) A combination of the two.

(d) Pumps and compressors should be located outdoors in a freely ventilated area. If installed within a building, such building shall be open on at least one side or be of louvered construction on at least two sides unless other acceptable ventilation is provided and it shall also be equipped with adequate roof ventilators.

(e) All electrical wiring and electrical equipment shall be suitable for use in Class 1, Division 1 location if natural gas is transferred within a building or enclosure. All other electrical wiring and electrical equipment located within a building where there is no transfer shall be suitable for use in a Class 1, Division 2, hazardous location.

(f) All gas piping to the building shall be provided with shutoff valves located outside the building. (Title 24, T8-543)


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

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