What are the two categories of O2 exposure limits?

• A. Transit with Excursion Limits
• B. Single Depth Limits
• C. Transit with Excursion Limits and Single Depth Limits
• D. Temperature-based Limits

Answer: (C)

O2 exposure limits in closed-circuit diving are managed in two patterns: during depth transitions (transit) and at a fixed depth (single depth). In transit, you may briefly exceed the limit when moving between depths, as long as the time spent at the higher exposure is kept short so total exposure stays within safe bounds. At a single depth, you must remain within the limit for the entire time you stay at that depth. These two categories, Transit with Excursion Limits and Single Depth Limits, capture the different ways oxygen exposure accumulates during a dive.