A scuba tank is essential for underwater breathing, but what exactly is inside it? Many people assume it contains pure oxygen, but that’s not the case. Divers carefully select the gas mixture in a scuba tank based on dive depth, duration, and safety considerations.

In this guide, we will look at the gases used in scuba tanks. We will discuss why people choose different mixtures. We will also cover the safety factors that divers need to know.

What Gases Are in a Scuba Tank?

A scuba tank typically contains compressed air, but divers use specialized gas mixtures for technical and deep diving. The goal is to provide safe, breathable gas while avoiding risks like nitrogen narcosis and decompression sickness.

Types of Gases Used in Scuba Tanks

Compressed Air (21% Oxygen, 79% Nitrogen)

Compressed air is the most common gas mixture for recreational scuba diving. They filter and dry it to remove moisture and dirt. It keeps the same oxygen-to-nitrogen ratio as the air we breathe on land.

Used for dives up to 130 feet (40 meters).

Widely available at dive shops and easy to refill.

Requires proper ascent rates to avoid decompression sickness (the bends) due to nitrogen absorption.

Nitrox (Enriched Air, 22-40% Oxygen)

Nitrox has a higher oxygen percentage (usually 32% or 36%) than regular compressed air.

Reduces nitrogen intake, lowering the risk of decompression sickness.

Extends dive time at shallower depths.

Not suitable for deep dives, as high oxygen levels can lead to oxygen toxicity below 100 feet (30 meters).

Related Reading:How Far Down Can You Scuba Dive Without Scuba Gear

Trimix (Oxygen, Nitrogen, Helium)

Trimix is used for technical and deep diving beyond 130 feet (40 meters). Technicians replace some nitrogen with helium to reduce the risk of nitrogen narcosis.

Prevents narcosis, which can impair thinking and coordination at depth.

Allows for deeper dives by reducing nitrogen and oxygen exposure.

Requires specialized training and equipment.

Heliox (Helium & Oxygen, No Nitrogen)

Heliox contains only helium and oxygen—no nitrogen. People mainly use it in commercial and military deep-sea diving.

Eliminates nitrogen narcosis, making it ideal for extreme depths.

Special equipment is necessary, and divers do not use it in recreational diving.

Pure Oxygen (100% Oxygen)

Despite common belief, scuba tanks rarely use pure oxygen. It is only used in specific cases, such as:

Emergency decompression at shallow depths (20 feet or less).

Rebreather systems that recycle exhaled air.

Medical treatments for decompression sickness.

⚠ Warning: Breathing pure oxygen below 20 feet (6 meters) can cause oxygen toxicity, leading to seizures underwater.

Why Are Different Gas Mixtures Used?

Diving involves managing gas exposure to prevent decompression sickness, narcosis, and oxygen toxicity. Each gas blend serves a specific purpose for different dive conditions.

How Nitrogen Affects Diving

At greater depths, nitrogen dissolves into the bloodstream.

Too much nitrogen can cause decompression sickness if a diver ascends too quickly.

Nitrogen narcosis can impair thinking below 100 feet (30 meters).

Why Helium Is Used in Deep Dives

Helium is lighter than nitrogen, reducing the effects of narcosis.

It allows safer deep dives by preventing mental impairment.

Oxygen Toxicity Risks

Oxygen becomes toxic under high pressure.

Breathing oxygen-rich gas (above 21%) below 100 feet (30 meters) can cause seizures.

Nitrox divers must monitor their depth to avoid exceeding safe oxygen exposure limits.

How Scuba Tanks Are Filled and Pressurized

Scuba tanks go through a strict filling process to ensure safety and purity.

Air Filtration and Compression

Filtered to remove moisture, carbon monoxide, and contaminants.

Compressed to 3,000 PSI (200 bar) or more.

Some tanks for deep diving hold 3,500 PSI (240 bar).

Related Reading:How Much Pressure to Fill Scuba Tanks

Why Gas Mixtures Must Be Carefully Measured

Too much nitrogen increases the risk of decompression sickness.

Too much oxygen at depth can cause oxygen toxicity.

Gas fills require specialized equipment and trained technicians.

Scuba Tank Safety Considerations

Using the Right Gas for the Right Dive

Compressed air is standard for recreational diving.

Nitrox allows longer dives but has depth limits.

Divers use Trimix and Heliox for deep dives, and they require training.

Related Reading:Is Scuba Diving Dangerous

Dangers of Using the Wrong Gas

Pure oxygen at depth can cause seizures.

Using Nitrox without training can lead to oxygen toxicity.

Skipping decompression stops can result in serious injury.

How Divers Prevent Gas-Related Issues

Pre-dive checks ensure the correct gas mix is in the tank.

Dive computers and gas analyzers help monitor oxygen and nitrogen exposure.

Proper ascent rates allow nitrogen to safely leave the bloodstream.

Common Misconceptions About Scuba Tanks

Myth: Scuba Tanks Contain Pure Oxygen

❌ Reality: Most tanks use compressed air (21% oxygen, 79% nitrogen).

Myth: Any Gas Can Be Used for Any Dive

❌ Reality: Gas mixtures are carefully chosen based on depth and safety requirements.

Myth: Tanks Are Just Filled with Normal Air

❌ Reality: Air must be filtered and pressurized before use in diving.

Final Thoughts

Scuba tanks contain carefully selected gas mixtures to ensure safe and efficient underwater breathing. Choosing the right gas is important for safety and performance. This applies to both recreational diving with compressed air and deep technical dives with Trimix.

Knowing what is in a scuba tank is important. People use different gases for specific reasons. Learning how to dive safely will help you avoid risks. This knowledge will let you dive with confidence.