Trimix II Diver

This course is to provide the diver with the experience and knowledge needed to minimize the risk of diving beyond 73m (240 ft.) while utilizing helium-based trimix breathing mixtures, hypoxic trimix breathing mixtures, helium based and EANx-based travel gases as well as EANx and oxygen during decompression.
Upon successful completion of this course, graduates are considered competent to plan and execute a team-based technical dive that requires travel gasses, staged decompression, helium based trimix breathing mixtures, and EANx and/or oxygen for decompression without direct supervision for dives that exceed 73m (240 ft.) provided the diving activities and the areas dived approximate those of training.

Get Started

Minimum age is 18 years of age and graduate from a NAUI Trimix I course or equivalent is required for all continuing NAUI Technical Diving courses. Additional training and experience requirements vary for each course. A qualified NAUI Instructor can evaluate your resume and answer questions about your readiness to pursue specific training.

What’s Next?

Continue your training by enrolling in a NAUI Technical course.


Academic: E-learning/Classroom

Practical Application:

Open Water Dives: 6 dives


      • Applied Sciences
        • Review decompression theory
        • Decompression tables
        • Maladies associated with diving and increased risks of decompression diving
        • Nitrogen narcosis
        • Thermal aspects of technical diving
        • Breathing gas calculations
        • Psychological aspects of technical diving
      • Technical Diving Equipment
        • Selecting and configuring diving equipment for staged decompression
        • NTEC
        • Equipment configurations being used and alternative configurations they may encounter
      • Decompression Procedures
        • Conducting a decompression dive
        • Oxygen breaks
        • Decompression systems
        • Methods (Drift, Line etc.)
        • Equipment
        • Safety
        • Introduction to support team operations
      • Dive Planning
        • Utilize the ODIGTML Dive Planning format or address each of the elements in the ODIGTML format
          •  Oxygen
          • Decompression
          • Inert Gas Narcosis
          • Gas Management
          • Thermal
          • Mission
          • Logistics
      • Breathing gas analysis
      • Predive equipment inspection
      • Dive planning
      • Safely execute each dive
      • When actual planned decompression stops are conducted, divers will conduct actual stops with the use of an upline or surface marker and reel when water conditions are conducive.
      • On at least one of the required dives, students are to ascend with ascent reel and surface marker and perform necessary staged decompression.
      • Contingency dive planning and problem solving situations are to include
        • Omitted decompression
        • Altered bottom time profile with increased or decreased decompression requirement and recalculation
        • Loss of ascent equipment (i.e. surface marker and reel, ascent line)
        • Loss of decompression breathing gas and gas supply loss with emergency ascent
        • Decompression gas supplied by dive partner.


  • Age. Minimum is 18 years by the water phase of the course.
  • Certification/Experience/Knowledge.
    • NAUI Trimix I Diver or equivalent.
    • Proof of at least 100 logged dives, of which at least 20 are decompression, 6 dives outside of Trimix I or equivalent.
    • The instructor is to ensure adequate student knowledge and capability before any open water training and shall use skill or other evaluations to do so. One open water dive (which does not count toward the minimum number of dives required for the course) may be used as a screening and evaluation dive. This is not required when the student’s diving proficiencies are well known to the instructor.