46 C.F.R. § 64.55
Relief device location
A pressure relief device must be located on an MPT in a place that—
(a) Is the highest practical point of the tank; and
(b) Allows direct communication with the vapor space.
A pressure relief device must be located on an MPT in a place that—
(a) Is the highest practical point of the tank; and
(b) Allows direct communication with the vapor space.