More diving time. Faster deco. Fewer tanks.

The appeal of rebreather diving is clear: efficiency. Depth. Range.

But what many technical divers underestimate:

Oxygen is not just a lifesaver. It is also a risk.

This article takes a look at the research findings around oxygen toxicity in technical CCR divers.

When rebreather diving, we breathe gas-mixed atmospheres with increased partial pressure of oxygen (PO₂) over long periods of time.

The problem:

Too much oxygen for too long can damage the body.

A distinction is made between:

CNS toxicity (central nervous system toxicity):

Acute danger that can lead to seizures under water.

Pulmonary toxicity:

Long-term exposure of the lungs with gradual symptoms such as a chesty cough or breathing restrictions.

Visual effects:

Some CCR divers report temporary short-sightedness (hyperoxic myopia) after long expeditions.

In a study by Fock et al., CCR divers were accompanied on expeditions lasting several days.

Key findings:

Many divers have exceeded the recommended REPEX limits:

(REPEX = Recommended Exposure Limits for Oxygen Doses)

Lung function? 

No significant permanent damage measured but some reported irritating cough or retrosternal discomfort.

Visual disturbances? Yes:

Some divers experienced temporary short-sightedness during or after the expedition, but this returned to normal within weeks.

CNS toxicity?

No acute CNS symptoms during the dives but many reported unusually vivid dreams towards the end of the expedition.

Oxygen dose is cumulative!

Gerade auf Multi Day Expeditionen mit zwei oder mehr langen Tauchgängen pro Tag kann sich die Sauerstoffbelastung auf gefährliche Werte aufsummieren selbst wenn pro Tauchgang alles „im grünen Bereich“ aussieht.

✅ Plan your total oxygen exposure per day, not just per dive.

✅ Make regular off-days or low-PO₂ dives to minimize your risk.

✅ Listen to your body:

Persistent cough or vision problems after expeditions → See a doctor!

✅ Allow for an individual tolerance threshold:

The reaction to oxygen is extremely different what your Buddy can cope with can make you ill.

✅ Be careful with the "extra deco-PO₂ number", a short-term boost is okay, but it adds to the total dose!

CCR Tauchen gibt dir mehr Reichweite. Mehr Tiefe. More possibilities.

Aber Sauerstoff bleibt ein kontrolliertes Gift. Atem für Atem. Jeder Prozentpunkt mehr PO₂ ist ein Deal. And you should know what you are signing.

Quelle: Fock et al., 2013: „Oxygen exposure and toxicity in recreational technical divers“, Diving and Hyperbaric Medicine.