California Code of Regulations
Title 8 - Industrial Relations
Division 1 - Department of Industrial Relations
Chapter 4 - Division of Industrial Safety
Subchapter 7 - General Industry Safety Orders
Group 20 - Flammable Liquids, Gases and Vapors
Article 145 - Tank Storage
Section 5594 - Vent Piping for Aboveground Tanks

(a) Vent piping shall be constructed in accordance with Article 146.

(b) Where vent pipe outlets for tanks storing Category 1 or 2 flammable liquids, or Category 3 flammable liquids with a flashpoint below 100 °F (37.8 °C), are adjacent to buildings or public ways, they shall be located so that the vapors are released at a safe point outside of buildings and not less than 12 feet above the adjacent ground level. In order to aid their dispersion, vapors shall be discharged upward or horizontally away from closely adjacent walls. Vent outlets shall be located so that flammable vapors will not be trapped by eaves or other obstructions and shall be at least five feet from building openings.

(c) The manifolding of tank vent piping shall be avoided except where required for special purposes such as vapor recovery, vapor conservation or air pollution control. When tank vent piping is manifolded, pipe sizes shall be such as to discharge, within the pressure limitations of the system, the vapors they may be required to handle when manifolded tanks are subject to the same fire exposure.

(d) Vent piping for tanks storing Category 1 or 2 flammable liquids or Category 3 flammable liquids with a flashpoint below 100 °F (37.8 °C) shall not be manifolded with vent piping for tanks storing Category 3 flammable liquids with a flashpoint at or above 100 °F (37.8 °C) or Category 4 flammable liquids or liquids with a flashpoint greater than 199.4 °F (93 °C) (formerly designated Class IIIB Combustible liquids), unless positive means are provided to prevent the vapors from Category 1 or 2 flammable liquids or Category 3 flammable liquids with a flashpoint below 100 °F (37.8 °C) from entering tanks storing Category 3 flammable liquids with a flashpoint at or above 100 °F (37.8 °C) or Category 4 flammable liquids or liquids with a flashpoint greater than 199.4 °F (93 °C) (formerly designated Class IIIB Combustible liquids), to prevent contamination and possible change in classification of the less volatile liquid.