46 CFR §108.469

1. (a)Except as provided in paragraph (b) of this section, each foam extinguishing system with outlets—
   1. (1)In a tank must have enough foam producing material to discharge foam for at least 5 minutes at each outlet; and
   2. (2)In a space must have enough foam producing material to discharge foam for at least 3 minutes at each outlet.
2. (b)If a foam system has outlets in more than one tank or space, the system need have only enough foam producing material to cover the largest space that the system covers or, if the liquid surface of a tank covered by the system is larger, the tank with the largest liquid surface.