On a vapor control system, what must each vessel's vapor connection flange have?

Correct Answer: Option A — stud at least 1" long projecting from the flange face

Under 46 CFR 39.2001, each vapor connection flange must have a cylindrical stud at least 1 inch long projecting from its face. This physical indexing pin prevents the accidental connection of a liquid cargo line to the vapor recovery system.