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TDI CCR Helitrox Decompression Procedures

This is the second level certification course for divers wishing to utilize a Closed Circuit Rebreather (CCR) for mixed gas diving using a Helitrox Diluent. The objective of the course is to train divers in the benefits, hazards and proper procedures for diving a CCR and to develop basic CCR diving skills, to a maximum of 45 metres/150 feet, using an air/nitrox/helium diluent for formal decompression diving. Students are permitted to utilize a diluent and bailout mix with no greater than a 35% helium content and no less than a 21% oxygen content, and are permitted to use up to 100% oxygen for decompression.

Who this course is for:

  • The certified TDI Air Diluent Diver (or equivalent) who is looking to extend their depth limitations, learn CCR decompression procedures, and reduce narcosis
  • The open circuit TDI Advanced Nitrox and Decompression Procedures or Helitrox Diver looking to utilize CCR technology to extend their depth limits and bottom times

Course prerequisites:

  • Minimum age 18
  • Proof of 50 logged dives
  • Minimum certification level of TDI Advanced Nitrox Diver, Deco Procedures Diver or Helitrox diver or equivalent from agencies recognized by TDI
  • If the rebreather is a TDI approved sidemount rebreather, the student must hold the TDI Sidemount Diver Certification or equivalent and provide proof of 10 logged sidemount dives


  • Minimum age 18
  • TDI Air Diluent CCR Diver certified or equivalent
  • 30 hours on the CCR unit
  • Six months CCR diving experience

What you can expect to learn:

The TDI Diving Rebreathers Student Manual and the manufacturer’s manual are mandatory for use during this course but instructors may use any additional text or materials that they feel help present these topics. The following topics must be covered during the course:

  • History and evolution of rebreathers
  • Comparison of open circuit, closed circuit and semi closed circuit rebreather systems and the benefits/problems with each
  • Practical mechanics of the system
    • Assembly and disassembly of the unit
    • Layout and design of the unit
    • Absorbent canister design and maintenance
    • Proper packing of canister, in accordance with manufactures recommendations
    • Breathing loop de-contamination procedures
    • Manufacturer supported additional items (automatic diluent valve, etc.)
  • Gas physiology
    • Oxygen toxicity
    • Nitrogen absorption
    • CO2 toxicity
    • Gas consumption
  • Electronic and manual systems design and maintenance
    • O2 metabolizing calculations
    • Fuel cells
      • Maintenance
      • Replacement
      • Manufacturing date
    • System electronics functionality and calibration procedures
  • Dive tables
    • Constant partial pressure of oxygen (PPO2) theory
    • Central nervous system (CNS) and awareness of oxygen tracking units (OTU)
  • Dive computers
    • Mix ajustable
    • Constant PO2
    • O2 integrated
  • Dive planning
    • Operational planning
    • Gas requirements including bailout scenarios
    • Oxygen limitations
    • Nitrogen limitations
  • Emergency procedures
    • Use of B.A.D.D.A.S.S.
    • Three H’s problems
    • Flooded loop
    • Cell warnings
    • Battery warnings
    • Bailout gas requirements
  • Helium considerations
    • Helium absorption and elimination
    • Advantages of hyperoxic mixes for decompression
    • Advantages of helium for bottom gas
    • Hypoxia
    • HPNS
    • Effects on respiration
    • Effects as an insulator
    • Helium limitations

Required skill performance and graduation requirements

All standards set by both TDI and the rebreather manufacturer must be met, while maximum limits of neither may be exceeded.

The following open water skills must be completed by the student during open-water dives with the following course limits:

  • All open water dives must be between 9 metres/30 feet to 45 metres/150 feet
  • Two dives must be deeper than 20 metres/66 feet and two dives must be deeper than 35 metres/115 feet
  • PO2 not to exceed manufacturer recommendation or a working limit of 1.3 bar
  • All dives to be completed within CNS% limits with a recommend maximum of 80% of the total PO2 CNS limit
  • Safety stops to be conducted with a minimum 3 minutes at 6 metres/20 feet
  • Where the user opts for an automatic diluent valve (ADV) fitted by the manufacturer additional skills such as regular diluent gauge monitoring and addition control must be emphasized
  • Calculate all off board gas at 45.3 litres/1.06 cubic feet per minute usage to cover stress situations
  • All dives to be completed within appropriate constant PO2 decompression tables
  • Student is only certified for Helitrox decompression diving on the specific CCR unit
  • Students must do one bailout from depth on o/c to include simulated decompression

Open Water Skills:

  • Pre dive checks
    • Unit build-up
    • Scrubber packing
    • Positive and negative checks
  • Verify diluent and O2 cylinder contents using O2 analyzer where appropriate
  • Demonstrate correct pre dive planning procedures including
    • Limits based on system performance
    • Limits based on oxygen exposures at chosen PPO2 levels
    • Limits based on nitrogen absorption at planned depth and PO2 set-point
    • Thermal constraints
  • Emergency procedures
    • Mouthpiece familiarity drills
    • Gas shutdowns and loss of gas
    • Broken hoses
    • Flooded absorbent canister
    • CO2 breakthrough
    • Semi-closed mode
    • Low oxygen drills
    • High oxygen drills
    • Flooding loop
    • Electronics and battery failure
    • Properly execute the ascent procedures for an incapacitated CCR diver
  • Use of BCD/suit and effective management of loop breathing volume for buoyancy control
  • Stop at 3-6 metres/10 – 20 feet on descent for leak bubble check
  • Electronics systems monitoring for PO2 levels (SETPOINT) and switching set-points
  • Manual control of set-point if electronically controlled CCR is not used
  • Use of lift-bag/delayed surface marker buoy and reel
  • Proper execution of the dive within all pre-determined dive limits
    • Constant-loop volume management
  • Post dive clean of unit to avoid contamination and spread of disease

If this is the first CCR course taken the following must be included:

  • Post dive clean of unit
    • Mouth piece and hoses
    • Clean and disinfect unit
    • Inspect components of unit
  • Dive maintenance of unit
    • Cell remove and replace
    • Mouth piece strip and rebuild
    • Replacing batteries

Decompression related in water skills:

  • Demonstrate comfort swimming on surface and at depth carrying 1 bailout/decompression cylinder
  • Demonstrate ability to drop and retrieve one bailout/decompression cylinder while maintaining position in the water column
  • Demonstrate ability to deploy SMB or lift-bag solo and as a member of a team
  • Demonstrate appropriate reaction to gas hemorrhage from manifold or first stage, SPG and primary regulator
  • Demonstrate appropriate reaction to simulated free-flowing deco regulator
  • Buddy breathing deco gas for at least 1 minute
  • Oxygen rebreather mode at less than 6 metres/20 foot stop
  • Complete 1 bailout scenario at depth to include decompression obligation on open circuit

What’s in it for you?

Upon successful completion of this course, graduates may engage in decompression diving activities utilizing a CCR 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

Upon successful completion of this course, graduates are qualified to enroll in:

  • TDI Mixed Gas CCR unit specific course
  • TDI Advanced Wreck Course

TDI Helitrox Diluent CCR Decompression Diver minimum requirements:

  • Satisfactorily complete the written examination with a pass mark of 80% and 100% remediation
  • Complete to the instructor’s satisfaction all confined and open water skill development sessions
  • Demonstrate mature, sound judgment concerning dive planning and execution
  • Course must be completed within 6 weeks from the starting date
  • Complete a refresher course following a period of inactivity greater than 6 months following the course

How to take this course!

pdf Course Standards & Procedures

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