46 CFR §154.340

1. (a)Each cargo tank must have a manhole from the weather deck, the clear opening of which is at least 600 mm by 600 mm (23.6 in. by 23.6 in.).
2. (b)Each access into and through a void space or other gas-dangerous space in the cargo area, except spaces described in paragraph (e) of the definition for “gas-dangerous space” in § 154.7, must—
   1. (1)Have a clear opening of at least 600 mm by 600 mm (23.6 in. by 23.6 in.) through horizontal openings, hatches, or manholes;
   2. (2)Have a clear opening of at least 600 mm by 800 mm (23.6 in. by 31.5 in.) through bulkheads, frames or other vertical structural members; and
   3. (3)Have a fixed ladder if the lower edge of a vertical opening is more than 600 mm (23.6 in.) above the deck or bottom plating.
3. (c)Each access trunk in the cargo area must be at least 760 mm (30 in.) in diameter.
4. (d)The lower edge of each access from the weather deck to gas-safe spaces in the cargo area must be at least 2.4 m (7.9 ft.) above the weather deck or the access must be through an air lock that meets § 154.345.
5. (e)The inner hull in the cargo area must be accessible for inspection from at least one side without the removal of any fixed structure or fitting.
6. (f)The hold space insulation in the cargo area must be accessible for inspection from at least one side from within the hold space or there must be a means, that is specially approved by the Commandant, of determining from outside the hold space whether or not the hold space insulation meets this part.