Are Scuba Diving Tanks Filled With Regular Air? (Yes, But..)

A widespread misconception among those unfamiliar with SCUBA is that the diver’s tanks are full of oxygen.

Are Scuba Diving Tanks Filled With Regular Air? Yes, scuba diving tanks are filled with regular air, partly comprises oxygen 21%. The highest percentage of the air in the tank is usually nitrogen, at about 78%, and the remainder is a mixture of helium, neon, carbon dioxide, and argon. But the trained recreational and technical divers use pure oxygen tanks or those with a higher composition of oxygen such as trimix and nitrox, to speed decompression and increase the amount of time spent underwater.

Generally, that is the air makeup of the contents in a scuba tank. Another thing is that regular air is compressed, allowing divers to breathe underwater only for a prescribed time. This article will explain why scuba tanks not always are filled with regular air. If you are still confused. Read on.

What Is In a Scuba Diving Tank?

Scuba diving tanks are filled with regular air. That is because diving with 100% oxygen could potentially kill a diver even at shallow depths.

Scuba tanks for recreational purposes are generally filled with purified and compressed regular air. The oxygen proportion in this air is merely 20.9%- numerous risks are associated with using pure oxygen during diving.

Are Scuba Diving Tanks Filled With Regular Air? (Yes, But..)

Many do not know that our bodies are created to handle only a specified amount of oxygen. Therefore, when you go diving with only pure oxygen in your tank for over 20 feet, your body will absorb more oxygen than it can handle in the system.

That results in oxygen toxicity in your CNS (central nervous system). CNS oxygen toxicity is a condition that could cause the diver to convulse, among other complications. At this point, to stop the convulsions, the diver will be required to ascend to a shallower depth.

Unfortunately, if the diver is convulsing, they will not control their depth or even retain the regulator in their mouth. In most cases, such divers end up drowning.

You may also like: Troubleshooting a Smoking Boat Motor: 8 Causes And Fixes

What Type Of Air Are Used In Scuba Tanks?

Scuba tanks are filled with a mixes of compressed regular air. Since we all need oxygen for our body’s essential metabolic functions, oxygen is always part of the scuba tank’s regular air composition.

However, as earlier mentioned, oxygen in more considerable quantities could have toxic effects on our bodies, especially when subjected to the higher-pressure levels associated with scuba diving. It poses a risk to the visual function, pulmonary function, and the central nervous system.

On the other side of the coin, nitrogen also has its ill-effects as it can result in a popular ailment called decompression sickness. When underwater, the nitrogen that is absorbed into the body is subjected to a more significant deal of pressure than when at surface level.

Therefore, when you ascend to the surface, if the nitrogen did not have sufficient time to dissolve from your bloodstream, then it could form nitrogen bubbles on your tissues and joints. That causes extreme pain, and you will need extended time to decompress.

There are several other mixes that divers employ for various purposes to compensate for the additional pressure, especially if they are going for longer hours than the typical recreational user. The commonly used mixture is nitrox


Nitrox is a specific mixture comprising oxygen and nitrogen. The only difference is that the oxygen levels are higher, between 32 and 36%, than the typical regular air percentage. This ratio is put in place to allow more oxygen absorption than nitrogen into the bloodstream.

That, in turn, reduces the likelihood or severity of decompression sickness. However, even with the nitrox mixture, it does not mean that the divers can disregard the dive tables.

The universal system tells divers the amount of time they can be underwater, the specific depths, and the ascending rate to avoid decompression sickness. Such a mistake could lead to oxygen toxicity, a condition we are trying to avoid.

Moreover, every diver’s responsibility is to ensure that their tank features the exact mixture appropriate for the dive. It is important to note that not many dive shops are keen on the nitrox composition yet, which comes with an element of risk when selecting nitrox as your air source of choice.

There are usually markings on the tank that indicate the tank’s oxygen percentage and the maximum depth you are allowed to dive to help you know if you have the right nitrox tank when done correctly.

As a diver, an essential aspect in diving is to ensure that you understand and practice the safe techniques, the air you are using notwithstanding. Ensure that you carry out comprehensive and thorough research before deciding to try out new methods- it is a matter of life and death.

Does Higher Oxygen Percentages Require Special Training And Gear?

If you need to use pure oxygen or the mixtures that comprise oxygen with a proportion of over 40%, it will require some special equipment.

Oxygen is a significant catalyst, and it has the potential to cause the ordinary materials and lubricants employed in recreational scuba diving to burst into flames or explode.

Therefore, before coming into contact with the pure oxygen tanks, divers are cautioned to familiarize themselves with special procedures like opening the tank valves with pure oxygen very slowly, and so on. There is a lot of information and training required if you want to use the oxygen safely.

You may also like: What Kind Of Boat Trailer Do I Need? (Ultimate Buyer’s Guide)

Can You Breathe 100% Oxygen?

Oxygen radicals are known to harm the fats, DNA, and protein in the human body. That, in turn, affects your eyes, so you end up not seeing correctly and damages your lungs, and therefore you cannot breathe normally. Therefore, breathing pure oxygen is quite dangerous. And for divers, it is not advisable.

Is Pure Oxygen Is Used In Technical Diving?

With the knowledge that pure oxygen can be dangerous, if not fatal, it is easy for one to assume that it is unlikely to find pure oxygen on a dive boat. But that is not the case.

The trained recreational and technical divers use pure oxygen tanks or those with a higher composition of oxygen such as trimix and nitrox to speed decompression and increase the amount of time spent underwater.

However, when on the surface, pure oxygen is a recommended remedy and first aid for most diving injuries. Therefore, it should not come as a surprise if a recreational diver encounters a pure oxygen cylinder at any point in his diving career.

However, even for technical divers, they must keep in mind the risks pure oxygen poses to their body; central nervous system oxygen toxicity, fires, and explosions.

You may also like: 12 Myths About Drinking Water (Things People Get Wrong)

What Type Of Air Is Used For Scuba And Surface Supplied Diving?

Are Scuba Diving Tanks Filled With Regular Air? (Yes, But..)

Did you know there is an option of diving tankless but with enough air to get as deep as you can? Scuba-surface-supplied diving allows the divers to get regular air directly from a scuba-diving support vessel or the shore. It’s provided through a diver’s umbilical or diving bell. Here are the two types of air supplied.


Air is the most accessible and cheapest gas used in scuba/surface-supplied diving. It’s easily compressed using simple machines.

Another advantage of using regular air is that it’s known to produce a less fatal mixture than regular gas mixing. However, it does also come with its disadvantages.

At high partial pressures experienced when diving deep underwater, the nitrogen negatively affects the cell membrane function, resulting in nitrogen narcosis.

The diver is also likely to experience mild impairment of their intellectual function at 30m depth. Upon further descent, there is the tolerant impairment of the function, and at depths around 100m, the diver could lose consciousness.

Furthermore, the nitrogen absorbed in the bloodstream at specific depths will need to be released upon decompression or ascent.

With nitrogen being highly soluble at high gas volumes and decompression rate (ascent) becomes too fast, lots of bubbles liberate from the body’s supersaturated tissues.

For most regular air divers, the recommended ascent rate should not be faster than 10-15m/min. For the long and deep dives, the diver must perform decompression stops to allow the gas release without the formation of excessive bubbles in vulnerable tissues.

Bubbles in small amounts are common in innocuous dives, but if they are too many or are in the wrong place, they could cause decompression sickness.

Even for the breath-hold divers that tend to dive repeatedly to 20-30m for a few minutes, with more minor surface breaks, the nitrogen accumulation can be enough to cause the illness.

Generally, nitrogen is comparatively a denser gas; therefore, breathing at a depth of 30m can be twice as great as when at surface level.

Any breathing system requires the exhaust- low oxygen and high nitrogen and carbon dioxide, to be liberated in bubbles.


There have been several approaches when it comes to dealing with nitrogen problems. The initial one involved breathing pure oxygen with the use of a rebreathing system and carbon dioxide absorber.

The divers who breathe pure oxygen will need a lesser gas amount, with no bubbles production. However, some problems could arise.

If the diver is breathing from the oxygen rebreather, enjoy zero inspired nitrogen. The body contains liters of dissolved nitrogen. The pressure gradient causes the nitrogen to find its way back to the diver’s lungs into the counterlung.

In this case, oxygen is being consumed, and carbon dioxide gets expelled. The nitrogen gets accumulated with the gradual reduction of oxygen percentage in counterlung. That could result in unconsciousness. You can overcome this problem by periodically flushing the system using pure oxygen.

You may also like: Is It Required To Have A Whistle On A Boat? (Solved!)


If you want to try out scuba diving or already, it is essential to understand what the tanks are filled with. It is not only a safety precaution but also helps you to know what to look for. Hopefully, you now understand in depth, Are Scuba Diving Tanks Filled With Regular Air? (Yes, But..).


Hi, I’m John who owns multiple different boats and i love all kinds of water activities. From boating to fishing, from scuba diving to windsurfing, from water tubing to snow tubing.

Recent Posts