Trimix 60–75m

The Narcosis Reversal

Divers who train at 50m on air and then switch to trimix for the first time at 60m describe a consistent experience: arriving at depth and finding, unexpectedly, that they can think clearly. The mental fog that was manageable at 50m is gone. Decisions that took deliberate effort at depth feel straightforward. The workload they were managing carefully becomes easier.

This isn't a small difference. It's a fundamental change in the dive — and it's why helium isn't really about going deeper. It's about diving with the cognitive resources the depth actually demands.

The 60–75m range is where this matters operationally. The deep walls across the Indian Ocean, the significant wrecks of Southeast Asia, the blue-water dive sites of the Maldives — the diving worth doing in this depth range requires a diver who is genuinely functional at depth. Trimix provides that. Air at these depths doesn't.

What This Depth Range Opens Up

The deep wall dives that matter across the region — where visibility stretches further than anywhere else, where the big pelagics patrol below 60m — sit in exactly this range. The same depth band holds the accessible section of most historically significant wrecks and the productive zone on most Indian Ocean reefs.

This is the training for the diving that's actually worth doing out here.

What You'll Learn

Trimix Gas Planning — The Full Logic

Not the simplified version. The actual reasoning behind every number.

• Normoxic trimix for 60–65m: helium fraction selection based on END target, not convention
• Hypoxic trimix for 70–75m: oxygen below 18%, the handling implications, why it's necessary at this depth
• END calculation: choosing the helium fraction that gives you the narcosis level you can manage
• Gas density with helium: how it changes breathing mechanics, CO₂ clearance, and work of breathing
• PPO₂ management from hypoxic bottom gas through the full decompression sequence
• Rock-bottom gas calculation for multi-stage trimix — realistic numbers, not conservative estimates that leave you confused
• CNS oxygen budget across a full dive day on trimix profiles

Isobaric Counterdiffusion

Mixing gases during ascent creates counterdiffusion risk when the switch is made incorrectly. You'll learn the actual mechanism, the conditions that make it a genuine hazard, and the protocols that prevent it — not the simplified rule, the physiology.

Decompression Strategy for Helium-Containing Mixes

Helium off-gasses differently from nitrogen. This changes how decompression is planned and executed:

• Fast-tissue helium off-gassing vs. slow-tissue nitrogen behaviour across a long profile
• Gradient factor adjustments for high-helium bottom mixes
• Deep stop evidence in the trimix context — what the data actually shows
• Ascent curve shaping for cold, high workload, and high-helium conditions
• Managing slow-tissue loading across multiple decompression gases

Multi-Stage Logistics

• Gas stacking: bottom mix, EAN50, 100% oxygen — planning, labelling, rigging, pre-dive checks
• Gas switch discipline at 21m and 6m in current and low visibility
• Managing three cylinders simultaneously without confusion under stress
• Planning for the loss of any single gas at any point in the dive

Failure Scenarios — Trained Until Automatic

• Lost deco gas before the planned switch point
• Hypoxic mix confusion on the bottom
• Narcosis breakthrough despite helium when workload increases unexpectedly
• Regulator freeflow at 70m
• Team separation with asymmetric decompression obligations
• Long-hose deployment in current at depth
• CO₂ buildup recognition and managed ascent response

All dives are filmed and reviewed before progression to greater depth. If a scenario isn't handled cleanly in practice, we don't progress.

Helium Logistics — Handled

Helium is the constraint most Asia-based technical divers eventually hit. Supply is concentrated, lead times are real, and incorrect mix delivery isn't theoretical.

I've worked with verified gas suppliers across the training locations for years. Gas logistics — sourcing, mix verification, cylinder coordination — are handled as part of course organisation. You won't arrive to find helium unavailable, delayed, or incorrectly blended.

Prerequisites

• Tec 50 / TDI Extended Range, or equivalent open-circuit technical certification with documented decompression dives
• 100+ logged dives
• Solid buoyancy and trim under full stage load
• Demonstrated gas switching and decompression execution competence

If you're unsure whether your Tec 50 skills are at the required standard, an honest assessment is part of the pre-training process. No one benefits from starting trimix with gaps in the preceding foundation.

Course Duration

4–5 days, mastery-based. Training starts at 60m and extends to 75m only when 60m performance is genuinely solid under task loading.

Gear

• Twinset or sidemount balanced for trimix
• Two to three stage cylinders (EAN50 + O₂ mandatory; trimix bottom mix as required)
• Long-hose primary configuration
• Two cutting tools
• Primary and two backup lights
• Wrist slates and wetnotes
• Two DSMBs with reels
• Two computers with trimix/decompression capability

Training Locations

Training runs across India, Sri Lanka, and the Maldives. The deeper stages — 70m and above — work best in locations with blue water and reliable deep wall access. Location is confirmed when scheduling based on your goals and the season.

What Comes Next

• Advanced Trimix / Road to 100m — hypoxic planning at full depth
• Sidewinder CCR MOD1 — remove the gas volume constraint at depth
• Cavern — if overhead environment training is the parallel goal

Frequently Asked Questions

What's the difference between normoxic and hypoxic trimix?

Normoxic trimix contains at least 18% oxygen — it can be breathed at the surface safely. Hypoxic trimix has less than 18% oxygen and is only safe to breathe at depth. For 60–65m, normoxic mixes are standard. For 70m and below, the additional helium required to meaningfully reduce narcosis pushes the oxygen fraction below 18%, requiring hypoxic mix handling. This course covers both.

TDI Trimix or PADI Tec 65 Trimix?

Both cover normoxic trimix to the 60–75m range. TDI Trimix is the pathway toward TDI Advanced Trimix and the 100m progression. PADI Tec 65 leads into PADI Tec 100. Your long-term agency pathway determines which is appropriate — discuss this when you enquire.

What does helium actually cost for this course?

Gas is billed at cost from verified local suppliers — no markup. Estimates are provided when scheduling.

Is there a difference between 60m and 75m trimix?

Yes. At 60–65m, normoxic trimix with modest helium fractions (10–20%) addresses narcosis meaningfully while keeping gas handling simple. At 70–75m, effective narcosis management requires higher helium fractions that push the bottom mix into hypoxic territory. Planning, handling, and failure responses differ. The course builds both levels sequentially.

Enquire About Training

Enquire here — Donarun responds personally to every enquiry.