By Dora Farkas – TDI Instructor Trainer

Trimix Definitions

First of all, what is Normoxic Trimix? According to some definitions, normoxic gas contains a “normal amount” of oxygen, which would be 21%. This would give a maximum depth of 57 m/187 feet. (If you can’t remember, look up Dalton’s triangle quickly). So even for 60m, we need to reduce the oxygen level. Divers, who use standard gasses, take 18/45 for this depth. 18% of oxygen has a maximum depth of 68m.

Some have different definitions of “normoxic” trimix

16% is a widely accepted limit shared between the dive community and medical professionals. With this oxygen level, you can dive up to 77m without the need for travel gas. In this case, you can use the same procedures you are learning on the TDI Trimix course – needing only two stages.

What is TDI Trimix?

Where did the idea come from? Last year I took a course with Jani Santala, and during some conversation, I mentioned my issues with the TDI Trimix course limits. He suggested the great idea to apply for a unique speciality, by explaining the situation in Malta concerning diving our stunning wrecks.

Most of them are just below 60m up to the depth of 73m. Then after a gap, more are around 90-120m which are clearly hypoxic trimix levels. We really needed a certification which can cover the shallower sites. Not everybody is interested in going 100m deep, but going to 65-67m, while the certification allowed only 60. This caused lots of trouble for divers and dive organisers as well. I am pretty sure Malta is not the only place with such characteristics.

As soon as I had some time, I contacted TDI HQ about whether adding this option would be possible, and they all found the proposition interesting.

Now I “only” had to write the standards and procedures for the course… The best thing was, about ten minutes after I sent the email to HQ, I got the first student asking about whether this option exists in TDI. I replied, “Well, no, not yet, but very soon.”

After some emails there and back we finalised all the necessary details. Thank you Wes Kilgore for your support!

What does the Trimix-75 course include?

You can take this course instead of the TDI Trimix course. It has one additional, more advanced, dive compared to the TDI Trimix course (remember, you must prove that you are ready for the depth and your skills are top-notch).

This course does not give you credit for the Advanced Trimix course since there are no new skills introduced compared to the Trimix level.

How can you become a TDI Trimix 75m instructor?

For now, if you are a TDI Advanced Trimix instructor, you can simply apply for the rating. Maybe later TDI will introduce upgrade opportunities for Trimix instructors too, so stay tuned.

This course has high potential. As open circuit trimix diving is slowly being replaced by CCRs, there is still quite an intake on Normoxic Trimix diving. Up to this depth limit, there is still a good combination of reasonable bottom time/deco ratio on open circuit. Also, gas costs are bearable (depending on where are you in the world).

If you are interested in becoming a Trimix 75m instructor, please contact your Regional Office.


If you wish to become a Trimix 75m diver, you are more than welcome to visit Malta, or check with the Regional Office to see if you have a Trimix75 instructor in your area. You can find the contact details here:

Take this great opportunity, extend your limits! Either as a diver or as instructor, I would be the happiest if many other fellow trimix users will enjoy the benefits of this rating.

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