46 CFR §151.50-76

1. (a)
   1. (1)Gravity type cargo tanks must be designed and tested to meet the rules of the American Bureau of Shipping for a head of water at least 8 feet above the tank top or the highest level the lading may rise, whichever is greater. The plate thickness of any part of the tank may not be less than three-eighths inch. A shell plating of a barge may not be on the boundary of any part of the cargo tank.
   2. (2)Gravity tank vents must:
      1. (i)Terminate above the weatherdeck, clear of all obstructions and away from any from any source of ignition; and
      2. (ii)Be fitted with a single flame screen or two fitted flame screens as described in § 151.03-25. Neither a shut-off valve nor a frangible disk may be fitted in the vent lines.
2. (b)Openings in the tanks are prohibited below deck, except for access openings used for inspection and maintenance of tanks, or unless otherwise specifically approved by the Commandant (CG-ENG). Openings must be fitted with bolted cover plates and acid-resistant gaskets.
3. (c)Where special arrangements are approved by the Commandant (CG-ENG) to permit a pump suction to be led from the bottom of the tank, the filling and discharge lines must be fitted with shutoff valves located above the weatherdeck or operable from it.
4. (d)The outage may not be less than 1 percent.
5. (e)An enclosed compartment containing, or a compartment adjacent to, a cargo tank:
   1. (1)May have no electrical equipment that does not meet or exceed class I-B electrical requirements; and
   2. (2)Must have at least one gooseneck vent of 2.5 inch diameter or greater. The structural arrangement of the compartment must provide for the free passage of air and gases to the vent or vents.
6. (f)No lights may be used during the cargo transfer operations, except installed electric or portable battery lights. Smoking is prohibited and the person in charge of cargo transfer shall ensure that “No Smoking” signs are displayed during cargo transfer operations.
7. (g)Tanks approved for the transportation of acid cargoes subject to this section may not be used for the transportation of any other commodity, except upon authorization by the Commandant (CG-ENG).
8. (h)Each cargo tank must be examined internally at least once in every 4 years. If the lining of the cargo tank has deteriorated in service or is not in place, the Marine Inspector may require the tank to be tested by such nondestructive means as he may consider necessary to determine its condition.