SF2 Mixed Gas

As a TDI CCR Air Diluent Decompression or Helitrox Diluent Decompression Diver, the TDI Mixed Gas CCR Diver course is your next step into closed circuit rebreather diving, it is your opportunity to explore a little deeper. Using the latest in technology CCR’s maximize your gas supply and provide the optimum breathing gas for any depth by maintaining a constant partial pressure of oxygen (PPO2). During the dives your TDI Instructor will teach you all the necessary skills to conduct CCR dives utilizing helium as a diluent gas and oxygen levels as low as 16 percent to a maximum depth of 60 metres/200 feet.

The certified TDI Air Diluent Decompression or Helitrox Diluent Decompression Diver (or equivalent) looking to extend their depth limitations.

• Minimum age 18
• Provide a verified log of a minimum of 50 rebreather hours distributed over a minimum of 50 dives on the specific rebreather. If the diver has 50 hours on another CCR unit recognized by TDI, only 25 hours are required to be on the specific unit
• Have completed and qualified the TDI Air Diluent Decompression Procedures Rebreather/TDI CCR Helitrox Diluent Decompression Procedures Diver course or equivalent from agencies recognized by TDI

The TDI Diving Rebreathers Student Manual is required for use as a review/recap document. The instructor may use any additional text or materials they feel will represent the topic in an educational manner. The following topics must be covered during the course:

• Gas physiology
  • Oxygen (O2) toxicity
  • Hypoxia
  • Nitrogen absorption
  • Helium absorption
  • HPNS
  • Carbon dioxide (CO2) toxicity
  • Gas consumption
  • Gas mixing
• Formula Work
  • Oxygen (O2) metabolizing calculations
  • Manually controlled closed circuit rebreathers
  • Equivalent narcosis depth theory
  • Central nervous system (CNS) tracking
  • Oxygen tracking units (OTU)
  • Gas management
• Dive tables
  • Creation of custom dive tables appropriate to dive depths
  • Creation of lower percentage of oxygen (PO2) diluent to support loop flushing and bailout at depth
• Dive computers
  • Mix adjustable
  • Constant partial pressure of oxygen (PPO2)
  • Oxygen (O2) integrated
• Dive planning
  • Operational planning
• Equipment maintenance
  • Fuel cell management
  • Loop configurations
  • Additional fitted equipment and modifications

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

• No dives deeper than 60 metres/200 feet
• No dives shallower than 40 meters/130 feet, other than the 1 air diluent configuration dive are credited toward the dive requirements. Subsequent training dives in shallow water are permitted if necessary during the course
• Equivalent narcosis depth not to exceed 30 metres/100 feet
• Calculate all off-board gas at 45.30 litres/1.06 cubic feet per minute usage to cover stress situations
• PO2 not to exceed manufacturer recommendation or a working limit of 1.3 bar during the bottom phase of the dive and 1.4 bar during the decompression phase of the dive
• Diluent PO2 should not exceed 1.2 at maximum depth
• All dives to be completed within appropriate fixed PO2 decompression tables or decompression planning software
• All dives to be completed within CNS percentage limits with a recommend maximum of 80 percent of the total PO2 CNS limit
• The student is only certified for CCR mixed gas diving on the rebreather being used

Land drills:

• Build unit based on manufacturer’s specifications using manufacturer’s manual/build checklist
• Demonstrate familiarity with basic and intermediate hand signals
• Select and prepare equipment suitable for soft overhead environment with long decompression obligations
• Conduct team oriented drills for lift bag deployment and bailout procedures
• Drills for buddy rescue
• Properly analyze all gas mixtures to be used
• Demonstrate adequate pre-dive planning
• Limits based on system performance
• Limits based on bailout gas requirements
• Limits based on oxygen exposures at chosen PPO2 levels
• Limits based on manually controlled closed circuit rebreathers
• Limits based on nitrogen absorption at planned depth and PPO2 (set-point) level
• Limits based on helium absorption
• Correct narcotic depth planning and diluent selection to allow cell flushing at target depth (diluent should not exceed a PO2 of 1.2 at maximum planned depth)

Pre-dive drills:

• Conduct pre-dive checks using TDI Pre-flight checklist
• Use START* before every dive
• Stress analysis and mitigation

Open water skills:

• Show good awareness of buddy and other team members through communications, proximity and team oriented dive practices
• Demonstrate buoyancy control; ability to hover at fixed position in water column without moving hands or feet
• Properly execute a recovery from a system failure and conclude the dive and decompression on open circuit gases carried
• Properly execute a recovery from system failure and conclude the dive and decompression with the unit in manual mode
• Gas shutdowns and loss of gas, correct choice and switching to off board gases
• Broken hoses, catastrophic failure scenarios
• Flooded absorbent canister
• Cell errors
• SCR drill (minimum of 10 minutes)
• Oxygen rebreather mode in depths less than 6 metres/20 feet
• Stop at 3 to 6 metres/10 to 20 feet on descent for leak bubble check
• Demonstrate competence managing 2 bailout cylinders, including drop and recovery while maintaining position in the water column
• Deployment of a lift bag/delayed surface marker buoy (DSMB) at depth and mid water
• Simulate failed lift bag/DSMB deployment
• On 2 of the dives, demonstrate an ascent with ascent reel and lift bag and perform staged decompression
• Electronics systems monitoring for PPO2 levels
• Proper execution of the dive within all pre-determined dive limits
• Demonstration of decompression stops at pre-determined depths
• Demonstrate controlled ascent with toxed diver including surface tow at least 30 metres/100 feet with equipment removal on surface, in water too deep to stand in

Upon successful completion of this course, graduates may engage in technical diving activities utilizing the unit specific CCR to a maximum of 60 metres / 200 feet, utilizing a mixed gas diluent containing 16 percent or greater oxygen provided:

• The diving activities approximate those of training
• The areas of activities approximate those of training
• Environmental conditions approximate those of training
• Ability to enroll in TDI Advanced Mixed Gas CCR Diver course

• Complete to the instructors 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