46 CFR § 153.408 - Tank overflow control.
(1) A second high level (cargo overflow) alarm.
(2) A system that automatically stops cargo flow to the tank (automatic shutdown system).
(b) The high level alarm and the cargo overflow alarm or automatic shutdown system must:
(1) Be independent of one-another; and
(2) Operate on loss of power.
(c) The cargo overflow alarm or the automatic shutdown system must operate early enough to:
(1) Stop the loading operation before the cargo tank overflows; and
(d) A tank overflow must be identified with the legend “TANK OVERFLOW ALARM” in lettering as specified for the warning sign in § 153.955.
(e) A tank overflow alarm must be audible and visible in that part of the deck where the containment systems are located and at the point where cargo loading is controlled on the tankship.
(f) The automatic shutdown system or tank overflow alarm must be able to be checked at the tank for proper operation (for example, by electrically simulating an overfill at the tank gauge connection).
(g) In this section, “independent” as applied to two systems means that one system will operate with a failure of any part of the other system except high level power sources and electrical feeder panels. Conduit need not be independent; the control wiring for several independent systems may be carried in a single conduit.