Several years ago, while in a code upgrade class, the question came up regarding multiwire branch circuits based on Article 210-4. It became evident what the code requirement was that when the two phases supplied two or more devices on a single yoke and only in a dwelling did it need to have the breakers connected. An example is a duplex receptacle that is split so that the top is fed by one phase and the bottom is fed by another, must be fed by breakers that are interconnected but only in a dwelling. If you had a 2 gang box with two receptacles and one duplex is fed by one phase and the other duplex from another phase then the breakers are not required to be connected. Your situation appears to be outside of the requirement as it is not a dwelling. The untrained, unsuspecting and unauthorized may have a problem with a multiwire branch circuit due to the hadzard of lifting a neutral they think is from a circuit that is dead. The code is a minimum and it's not a bad idea to have a common trip breaker for a multiwire branch circuit.
Dave
