What is the maximum working limit of the MK 25 Mod 2 UBA?

• A. 25 fsw for 240 minutes
• B. 50 fsw for 10 minutes
• C. 60 fsw for 6 minutes
• D. 40 fsw for 20 minutes

Answer: (B)

The maximum working limit tests how far you can operate the MK 25 Mod 2 UBA safely in a typical task without stepping into decompression or requiring a different gas plan. This limit is set by the balance between the unit’s CO2 scrubber life and the safe oxygen partial pressure inside the loop.

For the MK 25 Mod 2 UBA, the standard working limit is 50 feet of seawater for 10 minutes. That depth is about 15 meters, where the scrubber can still effectively remove CO2 and the oxygen levels in the breathing loop stay within safe margins for a short, routine task. Going deeper or staying longer would push the scrubber or the oxygen balance toward unsafe conditions, which is why longer durations at shallower depths or deeper depths for the same duration aren’t the approved working limits.