What is the primary reason to monitor O2 exposure during a dive?

• A. To prevent CNS O2 toxicity
• B. To improve buoyancy control
• C. To minimize gas cost
• D. To maximise dive duration

Answer: (A)

O2 exposure monitoring is about managing the oxygen partial pressure in your breathing gas as depth increases, because high PO2 can trigger central nervous system toxicity. When the ambient pressure rises, the partial pressure of oxygen you inhale also rises, and if it gets too high it can cause seizures or other neurologic effects underwater. Keeping your PO2 below safe limits (a common practical ceiling around 1.4 atm for continuous exposure, with 1.6 atm used in some plans) helps prevent these dangerous events and allows you to plan depth, time, and gas mix safely. While gas cost or dive duration can be influenced by choosing different mixes, the primary reason to monitor O2 exposure is to prevent CNS O2 toxicity and maintain dive safety.