The TDI Trimix course provides the training required to competently and safely utilize breathing gases containing helium for dives that require staged decompression, utilizing nitrox and / or oxygen mixtures during decompression to a maximum depth of 60 metres / 200 feet. The objective of this course is to train divers in the benefits, hazards and proper procedures of utilizing custom oxygen / helium / nitrogen mixtures as breathing gases. Gas mixes are not to have any less than 18 percent oxygen.

Qualifications of Graduates

Upon successful completion of the TDI Trimix course, graduates may engage in technical diving activities utilizing custom trimix mixtures without direct supervision provided:

  • The diving activities approximate those of training
  • The areas of activities approximate those of training
  • Environmental conditions approximate those of training
  • Oxygen (O2) percentages are 18 percent or higher

Open Water Execution:

  • Four decompression dives are required with a minimum accumulated bottom time of 100 minutes
  • Two of the dives should be deeper than 40 metres / 130 feet

Course Structure:

  • TDI allows instructors to structure courses according to the number of students participating and their skill level


  • The minimum number of classroom and briefing hours is 8.

Course prerequisites:

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