SSI recommends that a decompression diver should not exceed what CNS "clock" value?

The correct CNS "clock" value recommended by SSI for a decompression diver is 80-90%. This range is important for ensuring the safety and well-being of divers who are engaging in activities that involve extended exposure to elevated partial pressures of oxygen.

The central nervous system (CNS) toxicity risk increases as the partial pressure of oxygen increases, and staying within the 80-90% range helps to mitigate the potential for oxygen toxicity symptoms, which can include visual disturbances, seizures, and other serious neurological effects. By adhering to this guideline, divers can perform their dives more safely, allowing them to complete their dives without jeopardizing their health.

Maintaining the CNS clock within this threshold balances the advantages of breathing enriched oxygen blends for longer dive times and deeper dives, while still preserving high safety margins against the adverse effects of oxygen toxicity. This knowledge is crucial for divers, especially when planning for dives with multiple stages or when using different gas mixes.