Trimix I Diver

This course is to provide the diver with the skills and knowledge needed to minimize the risks of utilizing helium based trimix breathing gas mixes for dives to a maximum depth of 73m (240 ft.) requiring staged decompression and utilizing EANx mixtures and/or oxygen during decompression. Upon successful completion of the Trimix I Diver course, graduates are considered competent to plan and execute technical dives that require staged decompression and utilize helium based trimix breathing gas mixtures and EANx and/or oxygen for staged decompression without direct supervision to depths not to 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 Technical Decompression Diver 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 Trimix II Diver course.


Academic: E-learning/Classroom

Practical Application:

Open Water Dives: 8 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
      • Each diver is to demonstrate switching and isolating a malfunctioning regulator at a depth between 33 and 66 feet (10 to 20 m) and underwater navigation appropriate to the dive plan.
      • Students shall participate in a diver rescue simulation to include management of a diver experiencing oxygen toxicity underwater.


  • Age. Minimum is 18 years by the water phase of the course.
  • Certification/Experience/Knowledge.
    • NAUI Technical Decompression Diver or equivalent.
    • Proof of at least 100 logged dives, of which at least 20 are decompression dives.
    • 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.