1305.7.1 Size.
MC § 1305.7.1
Normal vent sizes shall comply with the sizes listed in Tables 1305.7(1) and 1305.7(2); provided, however, for tanks other than those complying with the alternate tank design and construction standards contained in Section 1305.14, the normal vent shall not be smaller in size than the fill pipe. Table 1305.7(1)Vent Piping for Underground Tanks Tank Size Minimum Vent Diameter 660 gallons (2498 L) or less1 1/4 inch (31.8 mm) 661 gallons (2505 L) to 3,000 gallons (11 355 L)1 1/2 inch (31.8 mm) 3,001 gallons (11 360 L) to 10,000 gallons (37 850 L)2 inch (50.8 mm) 10,001 gallons (37 855 L) to 20,000 gallons (75 700 L)2 1/2 inch (63.5 mm) Larger than 20,000 gallons (75 700 L)3 inch (76.2 mm) Table 1305.7(2)Normal Vent Piping for Tanks Installed Inside Buildings Tank Size Minimum Vent Diameter 660 gallons (2498 L) or less1 1/4 inch (31.8 mm) aLarger than 660 gallons (2498.4 L)Sized to prevent abnormal pressure in the tank during filling but not smaller than the pipe size specified in Table 1305.7(1) a. For tanks constructed to UL 80 specifications, the minimum vent diameter shall be 2 inches (50.8 mm). For tanks constructed to UL 142 specifications, the minimum vent diameter shall not be less than as required by Section 1305.8.4.
