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Are Scuba Tanks Filled With Pure Oxygen?

Are Scuba Tanks Filled With Pure Oxygen?

Among the most commonly misunderstood questions for non-divers is whether they breathe pure oxygen underwater. When learning to dive, students are taught about correcting their vocabulary by changing “flippers” to fins, “goggles” to masks, and “oxygen tank” to just a tank. 

Scuba tanks aren’t just filled with pure oxygen. Instead, they are filled with regular air, which has only 21% oxygen. A scuba tank’s air is overwhelmingly nitrogen, which comprises 78% of its volume. The remaining air is a mixture of carbon dioxide, helium, neon, and argon. However, pure oxygen is used by recreational and technical divers to prolong their bottom time and to quicken decompression.

What’s Inside A Scuba Diving Tank?

Diving with 100% pure oxygen in a scuba diving tank can potentially kill the diver, even at shallow points. Therefore, scuba diving tanks are filled with regular air that we breathe in.

Scuba tanks are filled with compact and refined normal air for holiday-diving purposes. The tank’s oxygen volume is 20.9% since several risks are associated with using 100% pure oxygen while scuba diving.

What is Oxygen Toxicity?

Many of us are not familiar with the fact that our bodies can only handle a specific percentage of oxygen gas. Because of this, we cannot dive on 100% oxygen because the body will absorb more oxygen than it can handle. Therefore, it results in Oxygen Toxicity that occurs in the central nervous system (CNS).

This condition causes the diver to go into convulsions if not ascended to a depth shallower than 20 ft immediately. The diver with oxygen toxicity in the CNS would not be able to retain a regulator in their mouth and would eventually drown. 

What Type Of Air Is Used In A Scuba Diving Tank?

The air in scuba diving tanks is a mix of various compressed air. Since oxygen is essential for our bodies, it is always a part of the air composition in scuba diving tanks.

The most commonly used air blend in scuba tanks is an air mixture called “Nitrox.” It is a mixture of regular nitrogen and oxygen, but the oxygen gas volume is 36% to 38%, which is higher than the typical air composition. The best advantage of using Nitrox is that it reduces the chances of decompression sickness in the diver.

Can We Breathe 100% Pure Oxygen?

The radicals of oxygen can harm the DNA, fats, and proteins in our bodies. In turn, this affects the eyes, resulting in blurred vision and causing lung damage that leads to improper breathing. Therefore, breathing 100% oxygen is not possible for the human body. And for scuba divers, it is not recommended.

Only those divers can use higher volumes of oxygen, with a composition of more than 40%, who are trained for recreational and technical purposes. Still, it requires special equipment and special procedures to do so. 


It is essential to learn what scuba tanks comprise if you want to learn scuba diving. It is required for safety purposes and helps you know what to look for. We hope you have understood that scuba diving tanks do not contain only pure oxygen but also other gases.