46 CFR §153.970

1. (a)Cargo is transferred to or from a cargo tank only through the tankship's cargo piping system;
2. (b)Vapor not returned to shore through the tankship's vapor return system is discharged at the height required for the cargo's vent riser in Table 1, and
3. (c)All cargo vapor is returned to shore through the valved connection on the venting system if:
   1. (1)The cargo requires closed gauging, is referenced to § 153.372 or is referenced to § 153.525;
   2. (2)The transfer terminal has vapor return equipment; and
   3. (3)In his estimation the vapor return equipment is adequate to handle the vapor expected from the tank.