Oxygen Toxicity — What It Is and Why It Matters
Oxygen toxicity is a potentially life-threatening condition caused by breathing oxygen at partial pressures above safe limits. Central nervous system (CNS) oxygen toxicity can cause seizures, which underwater are almost always fatal due to drowning. Pulmonary oxygen toxicity affects the lungs over extended exposure periods and is primarily a concern for technical divers on long decompression hangs.
Recreational divers encounter oxygen toxicity risk mainly when using enriched air nitrox. A ppO2 of 1.4 bar is the widely accepted recreational maximum, and 1.6 bar is the absolute ceiling. Dive computers that support nitrox monitor your ppO2 in real time and alert you when approaching these limits.
Frequently Asked Questions
What is the maximum safe ppO2 for recreational diving?
The widely accepted recreational limit is 1.4 bar during the working phase of a dive. A ppO2 of 1.6 bar is considered the absolute maximum and is typically only used during decompression stops. These limits apply to all breathing gases, including air and nitrox.
Can I get oxygen toxicity on regular air?
Yes. Air is 21% oxygen, which reaches a ppO2 of 1.4 bar at approximately 56 meters (184 feet) — well beyond recreational limits. This is one reason recreational diving is limited to 40 meters. On enriched air nitrox (32% or 36%), the maximum operating depth is shallower.
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