Sport Diver Supplementary Training Nitrox Workshop Nx Wksp

Sport Diver Supplementary Training Nitrox Workshop Nx. Wksp.

Sport Diver Nitrox Training Aim To further the learning of qualified divers To enable BSAC Sport Divers (or similar) to plan and execute nitrox dives for gas mixes up to 36% using computers/tables controlled by the MOD of the selected gas 2

Sport Diver Nitrox Training Sports Diver Dive within maximum operating depth (MOD) of the gas carried Plan decompression dives on nitrox tables or nitrox computers Dive within the depth limit of the diver’s experience or qualification 3

Sport Diver Nitrox Training Oxygen Partial Pressures Fraction of oxygen (FO 2) in mix ! FO 2 = %O 2 divided by 100 ! e. g. FO 2 of nitrox 36 = 0. 36 Oxygen partial pressure (PO 2) ! PO 2 = FO 2 x absolute pressure Example - nitrox 32 at 30 m ! PO 2 = 0. 32 x 4. 0 bar = 1. 28 bar Safety limit ! Maximum recommended PO 2 is 1. 4 bar 4

Sport Diver Nitrox Training Maximum Operating Depth (MOD) The depth at which the PO 2 of the mix reaches 1. 4 bar Example ! (PO 2)max ÷ Fraction of Oxygen = MOD ! 1. 40 bar ÷ 0. 32 bar = 4. 38 bar (33. 8 m) Do not exceed your MOD Select a mix with an MOD greater than your “just deeper” planned depth Limits of 36%=30 m and 32%=35 m still OK for No-Stop dives only 5

Sport Diver Nitrox Training Partial Pressure table What is the maximum MOD for nitrox 32%? Answer: 33 metres For no-stop dives only: Max depth is 35 metres 6

Sport Diver Nitrox Training Partial Pressure table What is the PO 2 of nitrox 32% at 30 metres? Answer: 1. 28 bar Partial Pressure Table reduces calculation errors. 7

Sport Diver Nitrox Training Oxygen Exposure Oxygen Partial Pressure Scale (bar) Long term toxicity risk 0. 21 AIR 0. 5 1. 0 Hyperoxic 1. 4 1. 6 Short term toxicity risk At high concentrations oxygen is toxic Know and observe your MOD to control the PO 2! Keep within accepted oxygen exposure limits 8

Sport Diver Nitrox Training Hyperoxia What is it? ! Too much oxygen ! Oxygen becomes toxic at elevated partial pressures There are two different effects of hyperoxia: ! Whole Body Oxygen Toxicity when PO 2 > 0. 5 bar for long periods (recompression) ! Central Nervous System (CNS) toxicity when PO 2 > 1. 4 bar for even short periods (on a dive) 9

Sport Diver Nitrox Training Hyperoxia Causes: ! Inaccurate dive planning ! Failure to analyse gas ! Incorrect marking or fitting of cylinders ! Failure to observe MOD! 10

Sport Diver Nitrox Training Hyperoxia Aggravating factors ! Actual PO 2 ! Duration of exposure ! Level of exertion ! Cumulative O 2 exposure Long term (whole body) toxicity risk not an issue at this level Short term (CNS) toxicity risk needs to be understood 11

Sport Diver Nitrox Training CNS Toxicity Also known as acute oxygen toxicity Reaction to PO 2 generally > 1. 4 bar Signs & Symptoms: CON V E N T I D - Convulsions - Vision - Ears, hearing disturbances - Nausea - Twitching - Irritability - Dizziness Until convulsions begin, minor symptoms: ! Can occur in ANY order or combination ! Increase in severity 12

Sport Diver Nitrox Training CNS Toxicity – Convulsions ! Tonic phase – do not lift # Casualty becomes rigid and holds breath ! Clonic phase – do not lift # Casualty jerks violently (convulsion) ! Relaxation phase - assist # Casualty relaxes and is unconscious # Potential loss of mouthpiece Signs can still occur after PO 2 is reduced 13

Sport Diver Nitrox Training CNS Toxicity Incident Management If a diver suffers from CNS toxicity: ! CBL to surface even if deco stops omitted If casualty is rigid, holding breath or convulsing … ! Do NOT attempt to lift ! Risk of embolism ! Wait until the casualty has relaxed Remove casualty from water Do administer oxygen therapy if suspect DCI or barotrauma 14

Sport Diver Nitrox Training Hyperoxia Avoidance: ! Plan the dive; dive the plan ! Max PO 2 of 1. 4 bar ! Do not exceed MOD ! High PCO 2 predisposes to oxygen toxicity # Breathe normally throughout the dive # Reduce PO 2 for high exercise dives ! Accurately track your oxygen exposure 15

Sport Diver Nitrox Training Monitoring Oxygen Exposure CNS toxicity needs to be monitored ! BSAC Oxygen Toxicity Table ! Dive planning software / nitrox computers CNS% should not exceed 80% While at the surface ! CNS% is reduced by half every two hours ! Add outstanding CNS% to next dive 16

Sport Diver Nitrox Training Oxygen Toxicity Table Using the Oxygen Toxicity Table ! Find PO 2 in left hand column (round-up) # e. g. , PO 2 Actual = 1. 28 bar; PO 2 Table = 1. 30 bar ! Find time spent at PO 2 along the top row, e. g. 5 minutes ! Where lines intersect (yellow column) indicates CNS% uptake 17

Sport Diver Nitrox Training Dive Computers Some dive computers capable of being programmed for nitrox mixes: ! Left set for air – reduced risk of DCI ! Set for actual nitrox % - longer dive duration at same risk of DCI as for air ! Set to intermediate nitrox % - a bit of both benefits ! All other procedures as for air diving Nitrox capable dive computers also track oxygen exposure (CNS %) Some nitrox computers capable of being programmed to change nitrox mix during dive 18

Sport Diver Nitrox Training Practice - Oxygen Toxicity Table What is the accumulated CNS% for a total dive time of 27 minutes at a PO 2 of 1. 38 bar? Method one ! CNS% = 1. 34 (2 mins) + 3. 35 (5 mins) + 13. 40 (20 mins) = 18. 09 % Method two ! CNS% = 27 mins × 0. 67 (1 min) = 18. 09 % 2 hours later the divers plan a second dive, what is the residual CNS% at the start of the dive? CNS% halves every 2 hours, ! CNS% = 18. 09 ÷ 2 = 9. 045 % Note: dive computers may use a different method for calculating residual CNS% 19

Sport Diver Nitrox Training Nitrox Tables - planning a dive using Nitrox 32 Dive to 20 metres for 30 minutes Depth and/or time is ‘in between’ values ! Use next greater depth ! Use next longer time Surface Code is D 20

Sport Diver Nitrox Training Planning - dive one Nitrox 32 First Dive ! Nitrox 32 ! 26 metres ! 33 min Surface code = F 21

Sport Diver Nitrox Training Surface Interval Table Surface interval 3 hours Second dive CTC = C 22

Sport Diver Nitrox Training Planning - dive two Nitrox 36 Second Dive ! Nitrox 36% Table C ! 20 metres ! 25 min ! Stops = 1 min @ 6 m ! Surface Code = G 23

Sport Diver Nitrox Training Practice - planning two dives using different nitrox mixes Good practice to increase oxygen % for second dive Dive one 25 m for 30 min on nitrox 32 (Use Table A 32%) Surfacing code = E Surface interval of 5 hours Dive two 18 m for 40 min on nitrox 36 CTC = B (apply to Table B 36%) Surfacing code = D (no-stop dive) 24

Sport Diver Nitrox Training Dive Management Divers using different mixes Dive plan limited by: ! MOD of highest % oxygen mix and ! Decompression requirements for the lowest % oxygen mix Dive Manager should additionally ensure recording of percentage mix and MOD of each diver. 25

Sport Diver Nitrox Training Summary Sport Diver ! Max PO 2 of 1. 4 bar Partial Pressure Table Oxygen Exposure ! Hyperoxia CNS Toxicity ! Convulsions ! Incident Management Oxygen Toxicity Table BSAC Nitrox Tables ! Dive planning Dive Management ! % Mix ! MOD 26

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