What are the two factors in the operational duration of the MK 25 UBA?

• A. O2 supply or the canister duration
• B. depth and dive time
• C. battery life and pump speed
• D. crew size and workload

Answer: (A)

In the MK 25 UBA, how long you can stay down is set by two things: the amount of breathable oxygen in the system and the life of the CO2 scrubber canister. You’re constantly consuming oxygen as you breathe, so the O2 supply will run out at some point. At the same time, the scrubber canister that removes CO2 has a finite capacity; once the canister is exhausted, the gas becomes unsafe to breathe. The shorter of these two durations determines the practical operational time for the dive. Depth and workload affect how quickly you use oxygen and scrubber capacity, but they don’t set the duration by themselves. Battery life or pump speed aren’t central to the UBA’s duration, and crew size doesn’t define the unit’s breathing-gas longevity.