Closed Circuit Diving Fundamentals Practice Exam 2026 – Complete Test Prep

PPO2 management on a closed-circuit rebreather is about keeping the oxygen partial pressure within a safe window that avoids both hypoxia and oxygen toxicity while allowing for depth and workload.

For combat dives, the setpoint is commonly targeted around 0.8 to 1.2 atm because this range provides sufficient oxygen delivery during active work and at typical operating depths, without pushing into high toxicity risk. A hard ceiling near 1.4 atm is used to limit CNS oxygen toxicity risk, giving a safety buffer if readings drift or if depth increases.

The other ranges aren’t appropriate for combat dives: too low would risk hypoxia during exertion or deep dives; too high would exceed safe CNS O2 limits; and a very tight 0.95–1.05 atm range offers little margin for operational changes.