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

• A. 50 fsw for 10 minutes
• B. 25 fsw for 240 minutes
• C. 20 fsw for 500 minutes
• D. 30 fsw for 180 minutes

Answer: (B)

The test is about recognizing the published normal working limit for a UBA system, which is the maximum depth and time you can operate in routine, non-decompression diving under standard conditions. For the MK 25 Mod 2 UBA, the published limit is a shallow depth paired with a long duration, allowing you to work for several hours without needing decompression or special procedures.

Why this is the best choice: staying within that shallow depth and long duration keeps the breathing gas conditions and physiological load within safe, tested limits for routine operations with this apparatus. It avoids the risks that come with deeper depths or longer bottom times, which would push you into decompression requirements or other constraints. The other options propose deeper depths or shorter/longer times than the standard envelope, which would exceed the UBA’s recommended operating limits.

So the option that reflects the published shallow depth with the long, four-hour window is the correct one.