TDI Trimix Diver
Reduce narcosis, extend your depth, and operate with clarity in serious technical diving environments
Overview
The TDI Trimix Diver course trains divers to safely plan and conduct staged decompression dives using helium-based breathing gases.
By introducing helium into the breathing mix, this course significantly reduces narcosis and improves diver performance at depth. Divers learn to plan and execute dives using normoxic trimix blends (minimum 18% oxygen) while managing multiple gases and decompression obligations. 
This program represents the transition from deep air diving into true mixed gas operations. At N9BO℠, the focus is on precision, discipline, and controlled execution under increased depth, task loading, and environmental complexity.
Course Facts
- Course name: TDI Trimix Diver
- Level: Technical mixed gas decompression course
- Minimum prerequisites: Minimum age 18, TDI Advanced Nitrox Diver and TDI Decompression Procedures Diver (or equivalent), minimum 100 logged dives
- Ratio: Maximum of 4 students per instructor (small groups recommended for quality training)
- Configuration: Technical configuration (backmount doubles or sidemount) with multiple stage/decompression cylinders and trimix bottom gas
- Depth / environment: Maximum 60m / 200ft with mandatory staged decompression
- Format: Academic development + confined/open water skills + and staged decompression dives using multiple gases
- Duration: Typically completed in 4 days (Minimum 4 decompression dives)
What You’ll Learn
- Plan and execute decompression dives using trimix blends.
- Manage narcosis and gas density at depth through helium use.
- Use multiple gases including bottom, travel, and decompression gases.
- Execute precise gas switches and staged decompression profiles.
- Maintain control, awareness, and team coordination in deep technical dives.
Prerequisites
- Be at least 18 years old.
- Hold certifications in Advanced Nitrox and Decompression Procedures (or equivalent).
- Provide proof of at least 100 logged dives.
- Be medically fit for diving.
FAQ
This course is for technical divers who want to reduce narcosis and safely extend their depth beyond air limits using helium-based gas mixtures.
Trimix is a breathing gas composed of oxygen, helium, and nitrogen. In this course, normoxic trimix is used, meaning oxygen content remains at 18% or higher, allowing the gas to be breathed safely from the surface while reducing narcotic effects at depth.
You will complete multiple staged decompression dives with progressively increasing depth, managing multiple gases, executing gas switches, and maintaining strict control throughout the dive.
Trimix replaces part of the nitrogen with helium, reducing narcosis and improving clarity at depth, making deep dives safer and more controlled compared to air-based extended range diving.
You will be qualified to plan and conduct decompression dives using trimix to a maximum depth of 60 metres, within conditions similar to training and with appropriate equipment and team procedures.
Ready to Go Deeper with Control?
Send us your certifications and experience. We’ll help you transition into trimix diving with the structure and discipline required for deep technical operations.
Go Pro with TDI Trimix Instructor
Take your mixed gas diving to the professional level and start teaching trimix diving. Delivered by a TDI Instructor Trainer, this pathway builds the precision, discipline, and instructional ability required to train divers safely in deep technical environments.
