46 CFR § 129.570 - Overfill protection.
(a) This section applies to OSVs of at least 6,000 GT ITC (500 GRT if GT ITC is not assigned).
(b) Each cargo oil tank with a capacity of 1,000 or more cubic meters (approximately 6,290 barrels) must have one overfill device that is permanently installed on each oil tank, with an intrinsically safe high-level alarm that meets the requirements of this section.
(c) The high-level alarm and tank overfill alarm required by paragraph (b) of this section must—
(1) Be independent of each other;
(2) Alarm in the event of loss of power to the alarm system or failure of electrical circuitry to the tank level sensor; and
(3) Be able to be checked at the tank for proper operation prior to each transfer or contain an electronic self-testing feature that monitors the condition of the alarm circuitry and sensor.
(d) The high-level alarm required by paragraph (b) of this section must—
(1) Alarm before the tank overfill alarm, but before the tank capacity goes below 95 percent;
(2) Be appropriately marked at the indicator panel; and
(3) Have audible and visible alarm indications that can be seen and heard on the vessel where oil transfer is controlled.
(e) The tank overfill alarm required by paragraph (b) of this section must—
(1) Be independent of the oil gauging system;
(2) Alarm early enough to allow the person in charge of transfer operations to stop the transfer operation before the oil tank overflows;
(3) Be appropriately marked at the indicator panel; and
(4) Have audible and visible alarm indications that can be seen and heard on the vessel where oil transfer is controlled and in the cargo deck area.