Understanding Oxygen Toxicity

Written by DAN Staff

It’s rare to be on a dive boat without seeing someone diving enriched air nitrox, and considering the popularity of the PADI Enriched Air Diver course, this is not too surprising. Enriched air offers longer bottom times and shorter surface intervals, but it also comes with additional considerations and potential hazards, such as oxygen toxicity.

Oxygen toxicity can easily be  avoided by recreational divers, but should it occur underwater, it can be deadly. Every enriched air diver needs to understands the basics of oxygen toxicity and know how to avoid it. Here are a few reminders and suggestions for reducing risk.

What is Oxygen Toxicity?

Breathing oxygen at increased partial pressure for prolonged periods can have harmful effects on the body. There are two types of oxygen toxicity that divers should know about.

The first is pulmonary oxygen toxicity. It’s of less concern to divers because it results from prolonged breathing of high concentrations of oxygen, such as  while undergoing hyperbaric chamber therapy or breathing 100 percent oxygen during an extended evacuation. Pulmonary oxygen toxicity involves time periods that exceed the length of a dive, so it will typically be encountered on land following hours or days of oxygen administration.

It often begins with airway inflammation, which then spreads to the lungs. There, alveolar damage and/or collapse and decline in lung function may occur. Damage caused by this type of oxygen toxicity is entirely reversible.

The type of oxygen toxicity that is of serious concern to divers is central nervous system (CNS) oxygen toxicity. CNS oxygen toxicity can occur with very short exposures to significantly elevated partial pressures of oxygen and can affect any diver who exceeds or improperly calculates the maximum depth of their gas mix. This type of toxicity affects the tissues of the brain and spinal cord, and it can arise suddenly, causing vital tissue damage or seizures. Less serious symptoms of oxygen toxicity (lip or eye twitching, confusion and anxiety, among others) are unreliable indicators; in many instances convulsions present with no precursors.

If a diver begins convulsing underwater, drowning is possible if the diver loses the ability to keep a regulator in the mouth. Getting the diver to the surface is the best course of action if a seizure occurs.

Reduce the Risk

While even divers breathing air are at risk for oxygen toxicity if they exceed recreational limits, it’s mostly a concern for divers breathing enriched air or using rebreathers. Divers need to be certified as enriched air or rebreather divers if they want to breathe a gas mixture with more than 21 percent oxygen. Even with proper training and certification, it doesn’t hurt to monitor the gas analysis and oxygen exposure calculations of the divers you’re supervising. Being ready to refresh procedures or answer questions about gas mix testing and dive planning is in everyone’s best interest.

As the gas blender and cylinder provider, you want to be sure that your fill station is properly maintained, staff who fill cylinders have proper credentials, and that you follow all fill station documentation and logging procedures. Doing this is your responsibility as a dive professional or business owner, but it will also shows your customers that you care about their well-being and enjoyment.

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