Division .6 A main transverse bulkhead may be stepped provided that it meets one of the following conditions:F1

the combined length of the two compartments, separated by the bulkhead in question, does not exceed either 90 % of the floodable length or twice the permissible length, except that, in ships having a subdivision factor equal to 1, the combined length of the two compartments in question shall not exceed the permissible length;

additional subdivision is provided in way of the step to maintain the same level of safety as that secured by a plane bulkhead;

the compartment over which the step extends does not exceed the permissible length corresponding to a margin line taken 76 mm below the step.