Oxygen Toxicity in Diving and Hyperbaric Medicine

By Rubicon Foundation editorial team

5 min read · 1 November 2026

Oxygen toxicity is injury caused by breathing oxygen at a partial pressure or for a duration that overwhelms the body’s defences. In diving and hyperbaric medicine, pressure raises oxygen partial pressure, making exposure a practical concern for divers and patients receiving oxygen under pressure.

Why can oxygen become toxic underwater?

Oxygen is essential to metabolism, but its reactive chemical forms can damage cells when their production exceeds the body’s capacity to control them. The risk depends on both oxygen partial pressure and exposure time; depth, breathing-gas composition and the dive profile therefore matter.

As a diver descends, ambient pressure increases. The oxygen fraction in a breathing gas is multiplied by that pressure to determine oxygen partial pressure. A gas that is suitable at one depth may create excessive oxygen exposure at another.

What forms of oxygen toxicity matter to divers?

The two clinically important patterns are central nervous system toxicity and pulmonary toxicity. They differ in how they arise and present, but both relate to oxygen exposure rather than to oxygen being inherently harmful at ordinary conditions.

Central nervous system toxicity: associated with high oxygen partial pressure, it can cause visual or auditory changes, nausea, twitching and, in severe cases, a seizure.
Pulmonary toxicity: associated especially with prolonged exposure, it can irritate and injure the airways and lungs, with symptoms such as chest discomfort, cough or difficulty breathing.
Exposure management: oxygen partial pressure, time at pressure, breathing gas and the sequence of exposures are considered together.

A seizure underwater is especially dangerous because loss of control can compromise the breathing system and lead to drowning. Symptoms can vary, and a diver may not receive a reliable warning before a serious central nervous system event.

How do breathing gas and dive planning affect risk?

Oxygen-enriched gases can reduce inert-gas exposure, but their usable depth is limited by oxygen partial pressure. Technical and scientific divers therefore plan a maximum operating depth for each gas and track exposure across the dive, including decompression phases when oxygen-rich mixtures may be used.

Planning also has to account for the actual profile, not merely the deepest point. Time spent at elevated oxygen partial pressure accumulates, and repeated exposures can matter. Gas analysis, correct labelling and switching only to a gas appropriate for the current depth are basic safeguards.

These limits are part of a wider effort to balance decompression benefit against oxygen risk. A safe plan depends on the gas, pressure, duration and operational conditions; a single oxygen value cannot describe every exposure.

How is oxygen toxicity relevant to hyperbaric treatment?

Hyperbaric oxygen therapy deliberately exposes a patient to oxygen at increased pressure for medical purposes. Clinicians must weigh the treatment’s intended effect against possible central nervous system and pulmonary toxicity, while controlling pressure and exposure time.

The same physiology links clinical treatment with diving practice, but the settings are not interchangeable. A hyperbaric chamber allows staff to monitor a patient and manage the treatment environment; underwater, a seizure or breathing problem carries additional hazards. Treatment schedules and dive limits belong to their respective clinical or operational protocols.

What should divers and clinicians keep in view?

Oxygen toxicity is one part of dive risk management, alongside decompression illness, gas supply, cold and workload. Its prevention relies on knowing the breathing gas, calculating exposure at pressure and following a plan suited to the dive or treatment.

Possible symptoms during or after an exposure warrant prompt attention, particularly if there is breathing difficulty, chest discomfort, neurological change or a seizure. Divers with questions about fitness to dive or a suspected oxygen-related problem should consult a diving-medicine physician; hyperbaric treatment decisions require the treating clinical team.

Frequently asked questions

Can oxygen toxicity happen while using ordinary air?

Yes. Air contains oxygen, and its partial pressure rises as ambient pressure increases. Risk depends on the pressure and duration of exposure, so gas choice and depth both matter.

Are a seizure and lung irritation the same type of oxygen toxicity?

No. A seizure is a possible manifestation of central nervous system oxygen toxicity, while lung irritation is associated with pulmonary toxicity, particularly during prolonged exposure. They have different patterns and implications.

Is oxygen toxicity relevant in a hyperbaric chamber?

Yes. Hyperbaric treatment uses oxygen under increased pressure, so clinicians manage exposure while delivering the intended therapy. If you have concerns about a treatment or symptoms, discuss them with the treating team.

An original research-library explainer written by the Rubicon editors. It is not a summary of a specific publication.