BSAC Rebreather Diving Rebreather Fundamentals Rebreather Fundamentals Try-dive outline Theory Rebreather Fundamentals Marshalling 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 Rebreather Fundamentals Aims Why Dive a Rebreather? Rebreathers in Practice Simple Rebreather Semi-Closed Rebreather Closed Circuit Rebreather Buddying a Rebreather Diver What If? Rebreather Fundamentals 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 potential for DCI 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 Rebreather Fundamentals Longer Gas Duration Metabolic Consumption 1 litre of oxygen / minute CCR 20 bar oxygen per hour (3 litre cylinder) SCR <= 10 l/min supply gas independent of depth OC depth & workload dependent 160 Consum ption 140 rate (l/m ) 120 100 80 CC 60 SCR 40 OC (25) 20 0 0 3 6 9 12 15 18 21 24 27 30 33 36 39 42 45 48 51 Depth (m ) Rebreather Fundamentals PO2 Advantage Inspiration Maximises PO2 SCR as per Nitrox PO2 1.60 1.40 1.20 1.00 0.80 OC 0.60 SCR 0.40 CC 0.20 0.00 0 3 6 9 12 15 18 21 24 27 30 33 36 39 42 45 Depth (m) Rebreather Fundamentals Decompression limits Longer decompression no stop limits No stop time 200 (mins) 150 100 Air Nitrox 50 PO2 0 12 15 18 21 24 27 30 33 36 39 42 45 Depth (m) Rebreather Fundamentals 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 Rebreather Fundamentals Simple Rebreather Counterlung Breathing Loop Dump Valve Scrubber Oxygen Rebreather Fundamentals Simple Rebreather Simple Rebreather Semi-closed Closed Circuit Circuit Rebreather Rebreather Difference is in the way that the addition of oxygen is effected Rebreather Fundamentals Semi-Closed Rebreather Metering flow orifice (jet) Bypass Vent Valve On-board Off-board Nitrox Bail–out Bail-out? Rebreather Fundamentals Closed Circuit Rebreather On- board bail-out Handsets Buzzer Optional Auto Oxygen Demand inject Valve valve Oxygen sensors Diluent (3) Oxygen Rebreather Fundamentals Static Lung Loading Definition: Pressure imbalance between the counterlungs and diver’s 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 Rebreather Fundamentals Buddying a Rebreather Diver Redundant gas supply DSMB / surface detection aids Both divers conduct most conservative dive profile Must be familiar with how to rescue a rebreather diver: CBL of rebreather diver Rebreather mouthpiece implications Rebreather Fundamentals SCR Rebreather Diving Gas Gauge Unit shut Gag down Post entry & bubble checks Monitor Gas Supply & Vent loop FO2 Buoyancy Buoyancy Swim around not over Rebreather Fundamentals CCR Rebreather Diving Start-up & function Unit shut checks down Post entry & bubble checks Set point change Monitor Set point handsets change Add Vent loop diluent Buoyancy Buoyancy Swim around not over What if……… Rebreather Fundamentals Something goes wrong with the unit…… If in doubt… Close mouthpiece then Bail-out! Rebreather Fundamentals Summary Why Dive a Rebreather? Simple rebreather Semi-Closed Rebreather Closed Circuit Rebreather Buddying What If… Rebreather Fundamentals Questions?