46 CFR § 153.409 - High level alarms.
When Table 1 refers to this section or requires a cargo to have a closed gauging system, the cargo's containment system must have a high level alarm:
(a) That gives an audible and visual alarm before the tank fills to 97 percent of its capacity;
(b) That can be seen and heard where cargo transfer is controlled and on the open deck;
(c) Whose operation can be checked prior to each loading; and
(d) That must be marked as described in § 153.408(c)(6) with the legend “HIGH LEVEL ALARM.”