Are Scuba Tanks Filled with Pure Oxygen?

Are SCUBA tanks filled with oxygen

Marine exploration and recreational diving were made possible through innovations that help us breathe underwater. Since we need oxygen to stay alive, are scuba tanks filled with pure oxygen?

Yes, but very rarely because of the risk and danger associated with pure O2. For context, the air that we breathe is a mixture of several types of gasses. Approximately, only 21% of it is oxygen.

Therefore, the compressed air in a recreational scuba tank mimics that same composition. Although, there are specific situations that require tanks containing pure oxygen.

We’ll go in-depth on that in a while, so stick around.

When Are Scuba Tanks Filled with Pure Oxygen Used?

Some instances may call for the use of pure-oxygen scuba tanks, but divers need specialized training for that. Read about them below.

1. Decompression Diving

Only properly trained divers can use scuba tanks containing pure oxygen during decompression diving. What is a decompression dive, though?

As you descend into the water, the pressure increases. This causes the nitrogen in the air that we breathe to dissolve into the body’s tissues.

Later, as you ascend toward the surface after the dive, the nitrogen in the tissues dissolves into the lungs. Then it leaves the body as we exhale.

However, after an intense technical dive, you can’t just ascend straight to the surface. Instead, you’ll need to take a safety stop every once in a while to give the body time to decompress, or safely release the nitrogen along with other gasses.

Divers usually plan a decompression dive to conclude technical, scientific, commercial, or military dives. Therefore, these are always discussed before the activity, so divers already know what to do when it’s time to ascend.

To speed up decompression, trained divers use tanks with higher oxygen content or sometimes pure oxygen. For safety, pure oxygen is only used in depths no more than 13 feet.

A hundred-foot dive could take a diver an hour to ascend, and about twenty minutes for half that depth. However, the body could take up to 24 hours to decompress completely or return to normal gas levels after the dive.

2. First Aid for Diving Injuries

After scuba diving, nitrogen may form bubbles in different parts of your body such as skin, muscle, or joints. This results in decompression sickness, otherwise known as “the bends”.

Symptoms of decompression sickness may include the following:

  • Nausea
  • Vomiting
  • Weakness

The first aid for decompression sickness is giving the patient pure oxygen to breathe immediately after the dive. This usually soothes the symptoms, which is why divers may keep tanks of 100% oxygen on their scuba boat in case of an injury.

The patient will later be brought into a clinic or hospital for hyperbaric oxygen therapy.

Tips on Expediting Decompression Dive Safely With Pure Oxygen

There are times that you’re going to need to speed up the ascend by using pure oxygen during decompression. This allows the lungs to take in more oxygen to displace nitrogen.

Below are some tips to speed up a decompression dive and save time.

1. Planning

Before the dive, you’d already know the gas requirements, how deep you’re going, and an estimate of the dive’s duration. Consequently, you’d also have known whether you’re going on a recreational or technical dive.

When preparing for a technical dive, it’s recommended to discuss with your team how you’re going to execute the decompression dive. Using the information mentioned above, plan the distance and time intervals between decompression stops.

This is to ensure that you’re giving your body enough time to release the dissolved nitrogen in your body. Otherwise, you’re putting yourself at risk for decompression injuries.

2. Practice the Necessary Skills

A diver should know the skills needed during a decompression dive. For example, you’ll need to hover at a certain depth for a specific duration for effective off-gassing.

Not mastering certain skills could defeat the purpose of expediting the decompression dive. Even if you’re using pure oxygen, you could still waste time underwater when you’re not executing the moves properly.

3. Follow Diving Instructions

Presence of mind is an absolute must during decompression diving, or throughout the dive, for that matter. This is for your safety, as well as that of the entire team.

Therefore, be aware of the potential dangers around you, but remain calm at all times. This will also help you remember the decompression plans and instructions as discussed before the dive.

4. Exercise During Decompression Stops

For faster nitrogen release, shake up your body with light exercises during a decompression stop. Usually, simply swimming around the line does the trick.

This step helps the driver get in touch with his body’s orientation in the water for a smooth ascend. Remember to stick to light exercises only because shaking too much could make the nitrogen bubbles worse.

Why Not Use Pure Oxygen for Recreational Diving?

Scuba divers don’t use 100% pure oxygen to breathe underwater because it’s neither safe nor healthy. Here’s a more elaborate explanation.

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1. It Isn’t Normal

For recreational scuba diving, the tank contains everyday air:

In other words, no, we don’t normally breathe 100% oxygen. In fact, the air in our atmosphere isn’t even 100% gas.

We may not know it but we breathe in various matters as well, including aerosols, moisture, and other particles. Our bodies can handle these substances when kept at modest amounts.

2. The Risk of Oxygen Toxicity

Too much of anything could be lethal, even oxygen. The condition where there’s too much oxygen in the body is called oxygen toxicity, and here’s how it happens.

What is Oxygen Toxicity?

The hemoglobin in our blood is responsible for transporting oxygen from the lungs to other parts of the body. When there’s way too much oxygen, our body could get overwhelmed.

The excess oxygen could disrupt the central nervous system’s operation and lead to other complications. It could injure the retina and prompt temporary near-sightedness, as well as irreversible damage to the lungs.

If left untreated, it could even result in death.

What Are the Symptoms of Oxygen Toxicity?

Besides temporary near-sightedness, a patient suffering from oxygen toxicity may also experience coughing and difficulty breathing.

Other symptoms include:

    Mild to moderate throat irritation

Is Oxygen Toxicity Reversible?

Fortunately, a healthy adult can fully recover from oxygen toxicity without any kind of treatment. In severe cases, however, such as a collapsed lung, the patient may need to use a ventilator.

Furthermore, recovery from oxygen toxicity usually takes a few weeks.

3. Pure Oxygen is Expensive

Even if breathing pure oxygen was a safe option for a recreational dive, it wouldn’t be practical.

Regular atmospheric air is free, so all you need is a compressor to fill up the scuba tank. Luckily, this compressor is portable and easy to use, but make sure that you’re using the appropriate compressor type for safe, breathable air.

That said, tanks with pure oxygen may stand by until it’s absolutely needed.

Who Can Use 100% Oxygen Scuba Tanks?

Only licensed technical divers can use pure oxygen. That’s because recreational divers are only allowed no-stop dives wherein a decompression dive isn’t necessary.

Besides, scuba divers only use pure oxygen scuba tanks if they intend to speed up off-gassing. Otherwise, the decompression dive could still be successful even without using pure oxygen.


Are scuba tanks filled with pure oxygen? Yes, some scuba tanks are, but they’re not for recreational diving use.

Divers reserve 100% oxygen scuba tanks for administering first aid to a patient with decompression injuries. Other times, they use pure oxygen to speed up decompression after long, deep diving sessions.

Therefore, you won’t need pure oxygen for a leisurely scuba dive. You only need the same air composition as you would on land.

Gas Laws of Scuba Diving – The Science Behind Scuba Diving

Gas Laws

Gas laws for scuba diving

There is a whole science behind SCUBA (Self-Contained Underwater Breathing Apparatus), diving. These laws are what protect a SCUBA Diver from the pressure that the water exerts on the human body as well as safety standards for your air tank and other factors.

For every 33 feet of water, the pressure increases by 14.7 psi, so pressure builds up very fast. So for example at the surface (1 atm), the pressure is 14.7 psi and then at 33 feet (2 atm), the pressure is 29.4 psi, then at 66 feet the pressure is 44.1 psi (3 atm), and so on …

IMPORTANT: SCUBA diving is a sport filled with many dangers and requires specialized training and equipment. Do not attempt any diving activity without proper training and always have a buddy diver or someone topside with you.

Some Scuba Basics

The atmosphere that we breathe every day is composed of 78% Nitrogen, 21% Oxygen, and 1% of other gases.

SCUBA Divers use a scuba tank (air tank), of compressed air to breath with underwater and they are made out of steel or aluminum. The air is fed from a valve at the top of the tank, via a hose and a regulator that takes the high pressure (≈ 3000 psi) of the tank and drops it down to safe levels for the diver to breath off of.

Gas Laws

Gay-Lussac’s Law

P1 / T1 = P2 / T2

In SCUBA diving, Gay-Lussac’s law impacts the amount of breathable air you have in your tank. It has to do with the heating and cooling of the air in the tank during filling. An empty tank has a pressure of around 500 psi. You must always keep some pressure in the tank to help preserve and always make sure that you are filling it with dry air.

As you fill a tank the pressure and heat go up. A tank can reach temperatures around 150° F and when it cools the pressure will drop too. So for our example let’s assume the ambient temperature is 70° F. Now that we got these values we can apply Gay-Lussac’s formula by converting to the temperatures to the Rankine scale as follows:

T1 = 150 + 460 = 610 R

T2 = 70 + 460 = 530 R

P1 = 3000 psi

3000 psi / 610 R = P2 / 530 R

P2 = 2606 psi

So based on the above calculation we can see that after filling up from empty we are not quite full yet. So we could now that is has cooled down we can top up the tank.

Boyle’s Law

P1V1 = P2V2

Boyles Law

A fundamental rule of SCUBA diving is to never hold your breath. Boyle’s law explains why this rule exists. When a diver breathes in air from a tank, the air is at ambient pressure. This is the pressure that is surrounding the diver at the time they take a breath. So a regulator adjusts the pressure to the ambient pressure surrounding it.

When a diver breathes in the air at the surface, then their lungs would be at 1 atm. Now say that diver dives down to 99 feet, which is 4 atm. By knowing this and assuming that the diver’s lungs hold 1 L of air we can complete the left side of Boyle’s law.

P1 = 4 atm

V1 = 1 L

P2 = 1 atm

4 atm × 1 L = 1 atm × V2

V2 = 4 atm

This means that if the diver is at 99 feet and takes a breath of air then rises to the surface holding their breath, their lungs would expand to 4 times the limit thus rupturing the lungs and probably killing the diver. So NEVER hold your breath while SCUBA diving!!

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By Boyle’s law we can now also see that a diver at 99 feet would require 4 times as much air per breath than on the surface so keeping a close eye on your air supply is critical, don’t you think?

Because a Freediver takes a breath of air on the surface, 1 atm, and holds it, they do not have to worry about the effects of Boyle’s law on them. Their lungs actually get crushed in size, so a diver at 99 feet would have lungs a quarter of the normal size.

Charles’s Law

V1 / T1 = V2 / T2


Ok, I am going to explain this law using the example of what happens with a dry suit.

Dry suits are worn for extreme cold waters, like ice diving where you actually go and dive under the ice. You wear a pair of wool long- johns and some other warm clothing under the dry suit and the suit keeps a layer of air between you and the suit.

When a diver has been down for a long period of time the air in the suit can become colder, and thus less dense, than the air outside. So when they get out of the water the suit gets squeezed around them and they either have to put air into the suit to alleviate the squeeze or unzip their zippers.

And that shows the effect of Charles’s Law on a diver.

Dalton’s Law

PTotal = P1 + P2 + P3 . . .


Dalton’s Law states that the total pressure of a gas mixture is equal to the sum of the partial pressures of its component gases.

Oxygen poisoning can occur when the partial pressure being breathed is above 1.6 atm. It will cause seizures, dizziness, vertigo, and changes in vision. Any of these can be fatal to the diver. Imagine being at 99 feet and having a seizure or you start to vomit because of dizziness or vertigo. It would be a really bad situation don’t you think?

So to calculate at what depth this may occur we can use Dalton’s law. As mentioned earlier dry air is made up of mainly 78% Nitrogen and 21% Oxygen. Thus at 1 atm, the partial pressure of Oxygen would be 0.21 atm. So to get the partial pressure of Oxygen to 1.6 atm we would need a total air pressure of 7.6 atm (1.6/0.21 atm). So, therefore, you would need to be at around 216 feet to begin to be in the danger zone.

Remember the 78% Nitrogen in the air? Well, a diver can get Nitrogen Narcosis whose effects are very similar to being drunk. The deeper you go the more the effect intensifies. Nitrogen Narcosis can start occurring as shallow as 45 feet and deeper.

You will get head spins, nausea, and fumble around trying to use your equipment just as if you were drunk or start doing stupid stuff like feeding the fish your air.

Henry’s Law


Henry’s law states that the solubility of a liquid is directly proportional to the partial pressure of the gas above the liquid. To a diver, this means that as you go deeper the pressure will increase. Because of this, the air is forced into your bloodstream at a faster and faster rate the deeper you go.

So when ascending to the surface you need to “bleed” off all that air in the bloodstream. This is why there are decompression stops after long deep dives. This is to get all that air/gas back out of the bloodstream SLOWLY. If you ascend too fast then the air/gas comes out too fast in the form of tiny air bubbles (like Champagne), that stay in the bloodstream and get distributed throughout the body.

These tiny bubbles tend to collect in the joints and under the skin. This causes extreme pain, convulsions, blisters and even death. This is called DCS, Decompression Sickness or more commonly called “The Bends”.

decompression chamber

This is why using your Dive Tables is so important. If you would like to know how to read your Dive Tables then take a look at the article on how to use your Dive Tables .

You have to be treated in a Hyperbaric Chamber to be cured of DCS and they are very expensive and are few and far between (not readily available around the world).

Archimedes’s Law


Even though this is not a gas law it still applies to the SCUBA diver. Archimedes’s Law states that any body completely or partially submerged in a fluid (gas or liquid) at rest is acted upon by an upward, or buoyant, force the magnitude of which is equal to the weight of the fluid displaced by the body.

Well, that wraps up the science behind SCUBA Diving, I hope that you found it interesting and informative.

Combined Gas Law

Combined Gas Law

Ok, when we take Boyle’s law, Gay-Lussac’s law, and Charles’s law and combine them we get the Combined Gas Law which states:

Pressure is inversely proportional to volume, or higher volume equals lower pressure. Pressure is directly proportional to temperature, or higher temperature equals higher pressure.

Please if you have any comments or questions, please feel free to leave a comment below and I will gladly get back with you. Thanks for stopping by.

How Long Does An Oxygen Tank Last For Scuba Diving?

You might have been wondering how long does an oxygen tank last for scuba diving.

You might have been wondering how long does an oxygen tank last for scuba diving? Or maybe, you are wondering about the best time of day to go on a dive? With all the technology that snorkeling and Scuba diving has on this day and age, you might find yourself getting concerned about your diver’s life. Thankfully, we will get into more detail to help with these deep questions.

So, as you are planning a scuba diving trip and you need to know how long those tanks will go. You might have seen articles or infographics floating around the internet, but why don’t take a look at this post? Lets explain it in more depth.

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How Long Does An Oxygen Tank Last For Scuba Diving?

What is an Oxygen Tank?

An oxygen tank is a cylinder filled with compressed oxygen that divers use when they are underwater. Oxygen tanks can last anywhere from 45 minutes to six hours, depending on the type of diving and how heavily the diver uses the tank.

When the oxygen in an oxygen tank expires, it becomes useless and dangerous to dive with. Always check the expiration date on your oxygen tank before diving to make sure you have enough gas for your planned dive.

How Does it Work

A scuba diving oxygen tank is an important piece of equipment that divers use to breathe underwater. It contains compressed oxygen gas and is connected to the diver’s mouth and nose via a hose. When the diver needs to breathe, he or she pulls on the hose to send air into the tank. This causes the gas inside the tank to expand, which in turn provides enough oxygen for the diver to breathe.

How Long Does An Oxygen Tank Last

When scuba diving, you are literally counting on the oxygen tanks to keep you alive. Many people mistakenly think that a tank will last for multiple dives. There are gadgets available in market to tell you about the level of remaining oxygen like ScubaPro G2.This is not the case; in fact, scuba diving tanks rarely last more than two dives before they need to be replaced.

The lifespan of an oxygen tank depends on a number of factors, including the type of diving equipment used, the quality of the nitrox mixture being used and how often it is recharged. The average oxygen tank will typically last around 200 dives, but this number can vary depending on the individual user and the particular equipment being used.

Types of oxygen tanks

One of the most important considerations when choosing an oxygen tank for scuba diving is what type you will be using. Here are the different types:

Scuba oxygen tank types

Nitrox tanks are the most common type of scuba diving tank. They use a blend of oxygen and nitrogen to supply the diver with a constant amount of air, regardless of how much breathing gas they use. This means that nitrox tanks can last significantly longer than other types of tanks. However, they require special equipment and training to operate, so they are not ideal for everyone.

Compressed air tanks are another popular type of scuba diving tank. They use a small pump to force air into a metal container, which is then stored in the tank until you need to use it. Unlike nitrox tanks, compressed air tanks do not have a gauge that shows how much air is left; instead, you have to watch the pressure gauge to know when you need to switch to another tank. This can be inconvenient, especially if you are running low on gas.

Scuba diving regulators are one of the most important pieces of equipment for scuba diving. Most dive gear manufacturers supply dive computers with standard diving regulators that control your breathing rate and let you set your own air flow. To determine the air volume you will use for your diving, first note the ambient pressure at that depth. The SCBA manufacturer usually provides the breathing gas flow table so you can enter the air pressure at the surface into their computer and then review your settings to choose an appropriate regulator and dial positions.

Buying oxygen tanks for scuba diving

Buying oxygen tanks can be overwhelming, but it doesn’t have to be. There are a few things you can do to help narrow your choices down and make the process easier. Here are a few tips:

  • First and foremost, consider the amount oftime you will be diving for. A tank that lasts for 3 hours might not be necessary if you only plan on diving for an hour or two.
  • Secondly, consider what type of diving you will be doing. If you are mostly diving in recreational water, a tank that is rated for recreational diving will suffice. If you are diving in more challenging waters (like deep sea), a tank with a higher pressure rating may be necessary.
  • Finally, consider what type of device you will be using to breathe underwater. A SCUBA DIVING helmet uses air from the tanks to provide air to the diver when they breathe underwater. A self contained breathing apparatus (SCBA) like the regulators used by professional divers needs its own air supply and will typically require a bigger tank than a helmet does.

Dangers with old tanks

The Scuba Diving Industry is constantly evolving and with it comes new dangers that have to be taken into account. Recently, a study was released indicating that scuba divers should no longer use tanks over two years old because the air inside them is so poisonous that it can kill you.

There are a few simple things you can do to make sure your tank lasts as long as possible: choose a reputable retailer, always double check the expiration date and keep your tank in a clean and dry place.


If you are planning on scuba diving, it is important to know how long an oxygen tank will last for. Generally speaking, a twin oxygen tank system will provide around 45 minutes of breathing time underwater, while a quad system will give you roughly 90 minutes of diving time before you’ll need to switch tanks. Keep in mind that the longer your dive, the more air you will need and the more often you will have to switch tanks. Make sure to plan your dives accordingly!




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