Understanding The Different Types of Gas Mixtures for Your Scuba Tank

22 Mar 2017

Understanding The Different Types of Gas Mixtures for Your Scuba Tank

The air we breathe is a mixture of different gases.

It is composed of mostly nitrogen and oxygen, with small proportions of other gases such as carbon dioxide.

Did you know that a scuba tank also contains a mixture of different gases?

Many divers incorrectly call the gas in their scuba tank oxygen. Some even call the gas cylinder ‘oxygen tank’.

While that statement is not entirely correct, it does have some truth in it.

Yes, oxygen is one of the gases you will find in a scuba tank. However, there are other gas mixtures available that make the sport of scuba diving safer.

These other gas mixtures enable scuba divers to stay longer underwater compared to when scuba divers use conventional atmospheric air.

Common scuba tank gas mixtures that divers use

Here is a quick review of the mostly used gas mixtures you’re likely to find in a scuba tank.

1. Atmospheric air

Most recreational scuba diving tanks contain compressed air (filtered and dehumidified)

Just as in the atmosphere, it is composed of 79% nitrogen, 21% oxygen, and small proportions of trace gases.

Air is the gas of choice for many dive resort in the world. Why? It is cheaper and contains enough oxygen to sustain divers underwater.

However, it has limitations too as the deeper you go, the more narcotic nitrogen becomes.

For this reason, 40m is considered the safest depth you can go on atmospheric air tanks.

2. Nitrox

Also known as oxygen-enriched gas, nitrox was designed to mitigate the problems with nitrogen for long duration divers.

Nitrox is basically a mixture of nitrogen and oxygen. It contains 22-40% oxygen. Most mixes that you’ll find generally contain 32-36% oxygen.

The reduced nitrogen levels in Nitrox minimizes the effects of residual nitrogen in the body when deep sea diving.

The limitation of nitrox is oxygen toxicity. At higher pressures, oxygen causes acute toxicity which leads to convulsions. This can be very unhealthy to divers since our bodies absorb more oxygen under pressure.

For this reason, Nitrox is only safe for use within the recreational diving limit of up to 130ft.

3. Trimix

To mitigate the dual hazards of oxygen and nitrogen on depths beyond 130 feet, divers use a gas mixture called Trimix.

Trimix is composed of nitrogen, oxygen, and helium. Why helium?

Since helium is an inert gas, it doesn’t react with our bodies at conventional depths.

This means that if we replace some of the nitrogen with helium, we can be able to dive beyond the conventional depths with no health problems or complications.

For this reason, trimix can be used for dives beyond 130 ft.

4. Heliox

Heliox is another breathing gas that contains helium, but unlike trimix, heliox does not contain nitrogen.

Instead, it contains 79% helium and 21% oxygen.

Removing nitrogen from the mix dramatically increases the diving depth and time limits. And since it has a lower percentage of oxygen than nitrox, the risk of toxicity is also reduced.

On the downside, the thermal conductivity of helium is six terms higher than that of nitrogen. This means that a diver using Heliox will lose heat faster than the one breathing Nitrox or air.

You will only encounter heliox in the worlds of technical and commercial diving.

5. Hydreliox

Hydreliox combines oxygen, hydrogen, and helium in the scuba tank.

With this mix in their tanks, divers can go as deep as 400m and still have a clear head.

Other gas mixtures you’ll encounter in deep sea diving include hydrox, which is a special blend of oxygen and nitrogen used for deep dives beyond 500m, and Neox, another deep diving gas mixture mostly used in military applications.


Scuba divers are greatly concerned about the gas mixture in the scuba tank.

Professional divers never go for dives without checking what is inside their diving tank.

For safety purposes, you should make this your priority too.

And if you are a newbie in the world of scuba diving, contact us for all your training needs. We’re good at what we do, so expect to complete training with excellent scuba diving skills!