Rebreather Fundamentals

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BSAC Rebreather Diving
Rebreather Fundamentals
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Try-dive outline

• Theory
• Rebreather Fundamentals
• Managing Rebreather Divers (optional)
• Dry Session
• Unit configuration operation
• 2 students per instructor
• Own mask fins
• Tee-shirt / pool suit recommended
• Be ready on pool side
• Try-dive
• Unit start-up functional checks
• Try-dive (20 minutes)
• Shut down procedures

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Aims

• Why Dive a Rebreather?
• Rebreathers in Practice
• Simple Rebreather
• Semi-Closed Rebreather
• Closed Circuit Rebreather
• Buddying a Rebreather Diver
• What If?

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Why Dive a Rebreather?

• Gas extender
• Breathing rate independent
• Decreased gas usage
• Easier Logistics in remote locations
• Nitrox benefits
• Longer bottom times, i.e., increased no stop
  times
• Reduce decompression obligation
• Warm, moist breathing media
• Reduced chilling
• No dry throat
• Less dehydrated
• Reduced breathing effort
• Reduced effect on the environment
• Reduced bubbles
• Reduced noise
• Get closer to marine life

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Longer Gas Duration

• Metabolic Consumption 1 litre of oxygen / minute
• CCR 20 bar oxygen per hour (3 litre cylinder)
• SCR lt 10 l/min supply gas independent of depth
• OC depth workload dependent

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PO2 Advantage
CCR Maximises PO2 SCR as per Nitrox
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Decompression limits
Longer decompression no stop limits
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Rebreathers in Practice

• Meticulous attention required to
• Unit maintenance preparation
• Personal dive skills
• Additional procedures
• Initially daunting
• Become normal diving practice
• Non-rebreather buddies
• Need to know what to expect
• Need to understand implications

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Simple Rebreather
Counterlung
Breathing Loop
Dump Valve
Oxygen
Scrubber
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Simple Rebreather
Simple Rebreather
Difference is in the way that the addition of
oxygen is effected
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Semi-Closed Rebreather
Metering flow orifice (jet)
Bypass
Vent Valve
Off-board Bailout
On-board Bail-out?
Nitrox
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Closed Circuit Rebreather
On-board bail-out
Handsets
Buzzer
OptionalAuto Demand Valve
Oxygen inject valve
Oxygen
Oxygen sensors (3)
Diluent
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Static Lung Loading

• Definition
• Pressure imbalance between the counterlungs and
  divers lungs in different body positions
• Counterlung position higher

• Easier to exhale
• Harder to inhale, e.g., Dräger Dolphin

• Compromise is over the shoulder!
• Example, APD Inspiration

Counterlung position lower

• Easier to inhale
• Harder to exhale

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Buddying a Rebreather Diver

• Redundant gas supply
• DSMB / surface detection aids
• Both divers conduct most conservative dive
  profile
• Must be familiar with rebreather mouthpiece
  implications

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SCR Rebreather Diving
Gas GaugeGag
Unit shut down
Post entry bubble checks
Monitor Gas Supply FO2
Vent loop
Buoyancy
Buoyancy
Swim around not over
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CCR Rebreather Diving
Start-up function checks
Unit shut down
Post entry bubble checks
Set point change
Monitor handsets
Set point change
Add diluent
Vent loop
Buoyancy
Buoyancy
Swim around not over
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What if
Something goes wrong with the unit

• If in doubt
• Close mouthpiece then Bail-out!

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Summary

• Why Dive a Rebreather?
• Simple rebreather
• Semi-Closed Rebreather
• Closed Circuit Rebreather
• Buddying
• What If

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Questions?
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