What is Trimix? Trimix Diving Guide

Last Updated: February 3, 2023

Trimix diving is means diving with a mixture of oxygen, helium, and nitrogen often at depths of 100 feet (30 m) or greater. The addition of helium adds necessary advantages to deep sea dives such as the reduction of oxygen poisoning and nitrogen narcosis.

In this article, you will learn what trimix is, the different types of trimix that exist, why divers use trimix, the advantages, the difference between trimix and heliox, how deep you can dive with trimix, and the equipment needed for a trimix dive.

What is Trimix?

Trimix is the mixture of three different gases – nitrogen, oxygen, and helium – used by scuba divers to dive to deeper depths while reducing the risk of nitrogen narcosis. Trimix tanks can use a varying combination of the three gases and the best indicator of the proportions of the mixture is the notation on the tank.

Tanks with trimix will be marked Tx for trimix, followed by a number representing the percentage of oxygen, a backslash, and a second number representing the percentage of helium. The percentage of nitrogen in the mixture is the difference of the sum of the two numbers from one hundred.

Types of Trimix

There are two types of trimix used for diving – hypoxic and normoxic. Normoxic mixes contain the normal amount of oxygen you would find in a regular scuba tank mixture, usually between 18% and 21%, with the remainder of the tank being a combination of nitrogen and helium.

Hypoxic mixes are used for dives of depths 200 feet (60 m) or more. The oxygen percentage in this mixture is far less, at about 10% to 15%, because beyond 213 feet (65 m) oxygen starts to become toxic to breathe.

Why Do Divers Use Trimix?

scuba tank with trimix gases

Trimix is used by divers that achieve deep dives below depths of 100 feet (30 meters). Adding helium to the normal mixture of oxygen and nitrogen gases in a scuba tank aids in reducing the risk of nitrogen narcosis, which can be extremely dangerous. The helium allows for less nitrogen to be used and thus introduced into the body.

Not only can nitrogen cause damage, but beyond 213 feet (65 m) oxygen can be poisonous as well. With Trimix, an increase of helium allows for a decrease in oxygen so that deep dives are possible.

What is the Advantage of Diving with Trimix?

The advantage of diving with trimix is the chance to experience depths that would be unreachable by mankind without it. Beyond 100 feet (30 m), the nitrogen in scuba tanks can have a detrimental effect by causing deep sea drunkenness, known formally as nitrogen narcosis.

Beyond 213 feet (65 m), the oxygen in scuba tanks can also be toxic to breathe. Trimix reduces the risks of these harmful health conditions by substituting with helium which our bodies are able to process and use.

At deeper depths, breathing in denser gases like nitrogen and oxygen can be taxing on our lungs. The addition of helium, a gas with less density, allows for a more comfortable diving experience and easier breathing.

What is the Difference Between Trimix and Heliox?

While trimix contains oxygen, helium, and nitrogen, heliox is only a mixture of the first two. Heliox is also used for deep sea dives greater than 200 feet (60 m) and has the advantage of no nitrogen to negate the possibility of nitrogen narcosis.

The decompression time is the same, if not more, with heliox than with any mixture containing nitrogen. Although it can save you from suffering deep sea drunkenness, heliox is much more expensive and harder to come by due to the price and availability of helium.

Heliox is most often used for saturation dives rather than recreational because of the higher concentration of helium than trimix has. Heliox typically contains close to 80% helium while trimix has a lower percentage because of the addition of nitrogen.

How Deep Can You Dive with Trimix?

deep dive with trimix gas mix

Technically you can dive as deep as the pressure on your body will allow you to with trimix, although most instructive courses do not go deeper than 300 feet (90 m). Trimix is generally recommended for use with dives below 100 feet (30 m) because that is when the risk of nitrogen narcosis begins to increase.

The world’s deepest scuba dive was accomplished using trimix by Ahmed Gabr when he reached 1090 feet (332 m) depth in the Red Sea off the coast of Egypt. The deeper he dove, the lower the percentage of oxygen and nitrogen and the higher the percentage of helium he used. It goes to show there are virtually no limits to trimix!

Equipment Needed for Trimix Diving

The list of gear needed for trimix diving is extensive and expensive. Scuba diving is very rewarding but for the faint of heart or the light of wallet. You will need at three different cylinders with regulators for each as different mixtures of trimix will be staged along the descent line for appropriate decompression to avoid nitrogen narcosis and the bends.

A bailout cylinder and regulator are also highly recommended, so you don’t get caught in a situation hundreds of feet below the surface with nothing to breathe. As with other scuba activities you will need a quality BCD, preferably a wing-type, with a back plate and a backup bladder.

Two masks, one for use and one for backup, and reliable fins are essential for diving. An air integrated dive computer or possibly two of them are necessary for swapping out the different blends of gases during the progression of descent and ascent. An ascent reel and brass pressure gauge are needed as well.

For safety gear, two lights, a knife, and a buoy to mark the surface are a good start. When diving to depths greater than 100 feet (30 m), the environment will be very cold, so a drysuit dive is usually the norm. In addition to your suit, you will need an inflation cylinder typically filled with a gas such as argon to help retain body heat and prevent hypothermia.


Trimix introduces a whole new level of diving by opening up the world of unimagined depths. With the combination of helium, oxygen, and nitrogen, depths greater than 100 feet (30 m) can be explored without the unnecessary risks of falling victim to nitrogen narcosis or oxygen toxicity.

Breathing at depths hundreds of feet below the surface is more comfortable with trimix. It allows for a slightly less expensive option of deep sea diving than heliox due to the lower percentage of helium which is pricey because of its difficulty to obtain.

Although trimix is cheaper than heliox, it is still not a cheap hobby. There is a plethora of different pieces of equipment, not the least of which is four different scuba cylinder tanks and potentially a dry suit to optimize comfort and minimize hypothermia.

Overall, trimix diving can be absolutely exhilarating and such an astounding experience that is most definitely worth all the training and expense. The ability to witness waters inhabited by the most bizarre creatures, which very few humans dare to venture in is an opportunity that is hard to pass up.

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