49 CFR 193.2181
Impoundment capacity: LNG storage tanks.
Each impounding system serving an LNG storage tank must have a minimum volumetric liquid impoundment capacity of:#
(a)110 percent of the LNG tank's maximum liquid capacity for an impoundment serving a single tank;#
(b)100 percent of all tanks or 110 percent of the largest tank's maximum liquid capacity, whichever is greater, for the impoundment serving more than one tank; or#
(c)If the dike is designed to account for a surge in the event of catastrophic failure, then the impoundment capacity may be reduced to 100 percent in lieu of 110 percent.#