Does Air in a Scuba Tank Go Bad?

Does air in a scuba tank go bad?

The answer is no, the air will stay breathable for us no matter how long it is sealed in the SCUBA tank. Moisture is the issue here and without any moisture reacting with the O2 inside the tank, it will stay the same as the day it was put into the tank under pressure.

Air – we breathe it, it surrounds us and we have evolved to be in equilibrium with it.

We can’t survive as an organism if we are deprived of oxygen for more than a few minutes, being essential for our very survival. There are times we leave our atmosphere on Earth and we have to take air with us, be that on the International Space Station or when we venture underwater.

The air we breathe is a mix of gasses, primarily Nitrogen (N2) and Oxygen (O2), but also smaller amounts of other gases like Helium (He) and Carbon Dioxide (CO2).

The air is constantly changing and different gasses are being refreshed as animals produce CO2 and other carbon-based gasses, while plants produce O2.

We generally notice the difference when we leave a city and head out into the countryside that the air often breathes better or even tastes better with less Carbon-based pollution.

So what about the air that’s in a SCUBA tank? It’s not being refreshed as it’s sealed inside, so can it go bad? Can it become unbreathable over time?

The answer is no, the air will stay breathable for us no matter how long it is sealed in the SCUBA tank. Moisture is the issue here and without any moisture reacting with the O2 inside the tank, it will stay the same as the day it was put into the tank under pressure.

Oxygen, while we breathe it and rely on it for our very existence, is a very corrosive gas as it wants to bind with many other elements causing oxidization.

Think of rust on a metal surface after it comes into contact with water and air.

Iron (Fe) is a great example as it changes fast, turning red or orange whenever it comes into contact with water and then it literally starts to dissolve and fall apart.

The tanks that are used for SCUBA diving are made out of Aluminum (Al), which is a much lighter metal than Iron and unlike Iron that rapidly oxidizes all the way through, Aluminum reacts to Oxygen slightly differently.

It actually has a great affinity for O2 and rapidly forms an oxide layer when exposed to air, but unlike other metals, this oxide layer actually protects the Aluminum from rusting all the way through.

As it’s a lighter metal, with its own protective layer, it is commonly used for all sorts of applications and due to its properties – the majority of the worlds SCUBA tanks are made from it.

The protective oxide layer stops any reactions going on within the SCUBA tank and the tank itself.

As when using air, the tanks are filled by a compressor that pushes the air into the tank under pressure and it stays at high pressure in the tank.

Because the air is already in an equilibrium state (any reaction between gases that could occur, already has), adding the amounts of pressure we need to keep it in the tank, won’t cause it to react in any way and staying breathable to us as a result.

Air will only be bad in a SCUBA tank if it was filled with contaminated air in the first place.

It’s something that shouldn’t happen, but it does sometimes and is almost always caused when CO2 or worse Carbon Monoxide (CO) that is produced from an engine exhaust accidentally gets into the air intake of the compressor.

These gasses, if we breathe them under pressure can cause us to pass out and potentially can be fatal if we are not restored to breathing normal air again. This is why filling SCUBA tanks is an important job to get right and dive centres around the world use experienced staff to do this.

It’s also why we sniff or try to taste the air in our tanks when setting up our equipment, if we sense exhaust or any strange smell, we then don’t use the tank. (Although Carbon Monoxide doesn’t have a smell).

This is extremely rare and hardly ever happens, however, it could.

Another issue is what happens to the air we breathe out of the tank as we increase the pressure on our bodies when we go deeper into the ocean. Both N2 and O2 can cause us issues when the depth increases and we use things like safety stops to mitigate its effects or actually change the mix of gases we breathe.

But when it comes from a normal SCUBA tank filled with air, you can be confident that you can breathe easily underwater without the issue of the air going bad.

How long can air be stored in a SCUBA tank?

The maximum amount of time a tank should sit at full capacity is 3 months or 90 days. Any longer and the integrity of the tank itself could become an issue.

Actually having the air stay breathable is one thing, but what about the effects on the tank itself? The tank needs to hold air under pressure and be stable for potentially a long time and the tank itself can start to have issues if it’s not treated properly.

Tanks have to be inspected regularly and all SCUBA tanks should have a sticker on them with the month and year they were last inspected. Every 12 months they should have visual inspection both inside and outside – looking for flaws on the interior or on the valve thread and determining if they will affect the tanks ability to store air.

Tanks also undergo a Hydrostatic test every 5 years, where they are filled to capacity with water and pressurizing it to 1.5 times its design limit. This is to ensure the integrity of the tank is retained and it can still be used for SCUBA and is done may a quailed technician.

Don’t Forget Your Dive Insurance!

Before you go out on any dive trip or holiday, it is essential to make sure you have insurance that covers you if something goes wrong. Check out our dive insurance article for more information.

Or go straight to these dive insurance company websites:


Diver Alert Network (DAN)

If you liked this article, please follow us on Instagram, Twitter and like our Facebook page

What happens when the tank runs out of air?

Firstly, this is something that you do not want to happen to you under the water as an emergency ascent or assistance from your dive buddy will be required (make sure you know your scuba hand signals).

But what happens to the tank? Once the tank is out of breathable air, it’s important we stop using it to prevent any moisture from getting inside it. If this does occur, the tanks will need to be properly dried out and inspections will be conducted to ensure it is safe to use again.

Please share this article using the social media buttons!

Paul Fulbrook

Paul Fulbrook is a writer, scuba diver, ex-science teacher and marine biologist. He has a passion for coral reef biology, diving on coral reefs and writing about diving. He also loves cats and his children (sometimes).

Recent Posts

Seraphinite AcceleratorBannerText_Seraphinite Accelerator
Turns on site high speed to be attractive for people and search engines.