Which of the following is a prevention measure for CNS Oxygen Toxicity?

• A. Ignore CO2 absorbent status.
• B. Observe depth-time limits.
• C. Increase exertion during ascent.
• D. Dive deeper to reduce exposure.

Answer: (B)

Preventing CNS oxygen toxicity comes from keeping the oxygen your body is exposed to at depth within safe limits. The key factor is the partial pressure of oxygen (PIO2); as this value rises with depth and longer exposure, the risk of CNS symptoms or seizures increases. By following established depth-time limits for your gas mix (whether using air or a nitrox mix), you ensure that PIO2 stays below a safe threshold. Dive tables or a dive computer enforce these limits, guiding you to stay within safe bottom time at a given depth and to avoid excessive exposure to high oxygen levels.

Ignore CO2 absorbent status isn’t about CNS oxygen toxicity; it can lead to other dangerous issues, especially on rebreathers. Increasing exertion during ascent or diving deeper both raise risk rather than reduce it, because they either don’t limit or actually increase your exposure to high oxygen levels.