Whose concurrence is necessary when not using an octopus second stage on regulators?

The necessity for the Commanding Officer's discretion when not using an octopus second stage on regulators is rooted in the principle of command authority in diving operations. A Commanding Officer typically oversees the overall safety and operational efficacy of diving missions, making them ultimately responsible for any deviations from standard practices, such as not employing a backup system like an octopus.

Diving safety protocols emphasize redundancy, especially in equipment, as it serves as a crucial safety measure to manage potential emergencies underwater. By requiring the Commanding Officer's discretion, the procedure ensures that any decision to omit this safety feature is made with full understanding of the associated risks and is backed by the authority responsible for the safety of the entire diving team.

While input from a Diving Officer or a Safety Officer is valuable, and medical considerations must also be respected in safe diving practices, the final say for allowing such deviations rests with the Commanding Officer. This hierarchy ensures there's a clear line of accountability and responsible oversight for any changes in established safety protocols.