46 CFR 154.459: General.

(a) Each cargo tank must have a secondary barrier that meets Table 3 and except as allowed in Table 3, the hull must not be the secondary barrier.

(b) If the Commandant (CG-ENG) specially approves an integral tank for a design temperature at atmospheric pressure lower than −10 °C (14 °F), the integral tank must have a complete secondary barrier that meets § 154.460.

(c) If the Commandant (CG-ENG) specially approves a semi-membrane tank under the requirements of an independent tank type B, the semi-membrane tank may have a partial secondary barrier specially approved by the Commandant (CG-ENG).

(d) If Table 3 allows the hull to be a secondary barrier, the vessel's hull must:

(1) Meet §§ 154.605 through 154.630; and

(2) Be designed for the stresses resulting from the design temperature.

Table 3—Secondary Barriers for Tanks

Tank type Cargo temperature (T) at atmospheric pressure

T≥−10 °C (14 °F) T<-10 °C (14 °F)≥55 °C (−67 °F) T<−55 °C (−67 °F)

Integral No secondary barrier required Tank type not usually allowed 1 Tank type not allowed.

Membrane ......do Complete secondary barrier 1 Complete secondary barrier.

Semi-membrane ......do ......do Do.

Independent:

Type A ......do ......do Do.

Type B ......do Partial secondary barrier 1 Partial secondary barrier.

Type C ......do No secondary barrier required No secondary barrier required.

1 The hull may be a secondary barrier.