Welcome to the Recreational Trimix Diver Course

Always Evolving

Evolution. This word is a constant in today’s world. Thanks to technological advances, we are surprised daily by new products and services that come to make our lives easier.

The diving world it is no different. What appears to be a never-ending cycle of dive equipment change, is just a means by which the diver is ensured to be always diving with equipment that possesses the latest features. What appears to be a near constant change in technology requires us to keep an open mind and to constantly update our knowledge to take advantage of the latest in technology and recognize the advantages that these changes provide us. Keeping an open mind and continually learning is directly related to the quality and safety of scuba diving.

Let’s look at an example. When diving with EANx first entered the sport diving industry, there was a lot of resistance and mis-information due to the lack of knowledge about the technology. Some thought it was only for deep diving; Some thought it was going to kill you under water; and it was even banned in some areas.

Today its benefits are obvious, and the practice of diving with EANx is widely recommended and there isn’t a diver that isn’t aware of the benefits of EANx (nitrox) diving provides.

Today, the same thing is about to happen with Trimix. Trimix’s advantages were also recognized initially only for deep diving. Now the recreational diver has begun to evolve into a safer dive - within limits - using Recreational Trimix.

Like technical divers, advanced recreational divers also perform deep dives to the depth limit of 40m/ 132 ft. The difference is that technical divers learned long about the advantages of using Trimix as a bottom mix.

So, if the dive word is to evolve, the diver need to learn about the benefits of Trimix and that is the purpose of this course. During your course, you will have the opportunity to discuss and observe in practice the differences and advantages of using Trimix, acquiring new knowledge that will be extremely useful in broadening the possibilities of your dives.


A Little History of Trimix

Although the use of Helium as a breathing gas dates back almost 100 years and today has wide spread use was with deep military and commercial dives, the use of helium mixtures for recreational dives has a much younger history. This history includes a number of people who took these procedures and applied them to the deep recreational diver and now are using trimix breathing gases in more typical recreational depth limits.

  • 1970, Tom Mount introduced a Heliox program at the University of Miami and between 1970 and 1976, hundreds of research dives were conducted safely.
  • 1975, the Trimix 15/45 was used to explore the Blue Springs, MO USA.
  • 1981, Peter Gimbel opens a large hole in the Andrea Doria in 190 ft.
  • 1987, The first massive use of Trimix / Heliox is used by the WKPP Team for exploratory dives in caves. That year, Exley was the first instructor to teach recreational divers Trimix.
  • 1989, A team of divers lead by Ken Clayton, dive the US battleship Washington off the coast of Virginia in 290 ft/ 88 m
  • 1990, Ken Clayton’s team of divers completes dives on the German Battleship Ostfriesland off the coast of Virginia in 410 ft/ 125 m using various gases including trimix and argon
  • 1991, Tom Mount developed the first Trimix Training Standard for IANTD.
  • 1992, Gary Gentile completes a number of trimix dives to the USS Monitor in 235 ft/71 m
  • 1994, a team of UK / USA divers successfully completed the Lusitania Project in 320 ft/100 m and in Brazil, Gilberto Menezes de Oliveira held a deep cave exploration below 198 msw.
  • 1996, Kevin Denlay lead dives to the USS Atlanta in the Solomon Islands 400 ft/126 m and an expedition was held to Britannic, led by Kevin Gurr, 395 ft/120 m
  • 1998, IANTD introduced the first Recreational Trimix Training Standards

Today, trimix dives at all depths are common.

What is Trimix?

We call Trimix any mixture containing, Oxygen; Nitrogen; and Helium. Trimix mixtures can be mixtures that contain fractions of oxygen less than 18% (hypoxic) and those that contain more than 21% oxygen (hyperoxic) and those that contain 18 – 21 % oxygen (Normoxic).

What is Recreational Trimix?

The Recreational Trimix is a breathing gas that has in its composition Oxygen, Nitrogen and Helium. The only difference is that the Recreational Trimix mixtures are not necessarily hypoxic. IANTD Recreational Trimix Mixes contain a fraction of oxygen of at least 21% and a percentage of helium that provides an equivalent narcosis depth of 80 fsw or shallower.

Why use Recreational Trimix?

In general, the advantages of Recreational Trimix are that we can enjoy using the advantages of deep Trimix to increase the safety of recreational deep dives. Recreational Trimix is best described as any mixture of breathing gas that contains:

Oxygen based on the maximum partial pressure of oxygen (PO2) at the depth of the dive and a partial pressure of Helium (PHe) that provides a low narcosis condition in which the diver continues to reason with clarity at the maximum depth of the dive.

During your nitrox(EANx) course, we learned that because of higher partial pressures of oxygen, there is less absorption of inert gases that can cause decompression sickness. This allows us to extend the bottom time. Now with the presence of helium, the partial pressure of narcotic gas (nitrogen) is also decreased. Thanks to this reduction, it is possible to minimize the effects of narcosis and, consequently, increase the quality of diving in a more superior way than just using Air and/or EANx.

Furthermore, due to lower density of helium, by adding helium to the mix a divers’ breathing is much easier at depth because the diver will inhale a mixture containing a less dense gas. Due to the ease of breathing, the respiratory effort is smaller as well as retention of CO2.


As the Recreational Trimix is composed of three gases, we have the need to manage the usage of each one. As helium is a gas whose speed of absorption and elimination is 2.65 times faster than Nitrogen, therefore decompression times are smaller in relation to dives with air and EANx. For this, the use of non-decompression tables or different software or computers for dive planning will be necessary.

Another factor to which we should pay attention is the ascent rate. Because the helium have a 2.65 times faster than the absorption of nitrogen, its release will happen faster. Thus, a slower ascent will be key. If we do not take proper care of the ascent speed, bubbles can form more easily in our body, increasing the possibility of Decompression illness.

Furthermore, there are few sources of helium in the world and none in some countries. This causes the gas to have a higher cost. However, in this training level, the amount of helium present in the mixture is not high, and the price of the mixture becomes almost equal to the EANx.

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