46 CFR §154.345

1. (a)An air lock may be used for access from a gas-dangerous zone on the weather deck to a gas-safe space.
2. (b)Each air lock must:
   1. (1)Consist of two steel doors, at least 1.5 m (4.9 ft.) but not more than 2.5 m (8.2 ft.) apart, each gasketed and tight when tested with a fire hose at not less 207 kPa gauge (30 psig);
   2. (2)Have self-closing doors with no latches or other devices for holding them open;
   3. (3)Have an audible and visual alarm on both sides which are actuated when both door securing devices are in other than the fully closed position at the same time;
   4. (4)Have mechanical ventilation in the space between the doors from a gas-safe area;
   5. (5)Have a pressure greater than that of the gas-dangerous area on the weather deck;
   6. (6)Have the rate of air change in the space between the doors of at least 8 changes per hour; and
   7. (7)Have the space between the doors monitored for cargo vapor leaks under § 154.1350.
3. (c)In addition to the requirements of paragraphs (a) and (b) of this section, no gas-safe space on a liquefied flammable gas carrier may have an air lock unless the space:
   1. (1)Is mechanically ventilated to make the pressure in the space greater than that in the air lock; and
   2. (2)Has a means of automatically de-energizing all electrical equipment that is not explosion-proof in the space when the pressure in the space falls to or below the pressure in the air lock.