46 CFR §169.627
Verified against eCFR.gov as of June 20, 2026View official text on eCFR.gov ↗
Unless they are adequately ventilated, enclosed compartments or spaces containing diesel fuel tanks and no machinery must be provided with a gooseneck vent of not less than 2 1/2 inches in diameter. The vent opening must not be located adjacent to possible sources of vapor ignition.