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Gas Management

Gas Management. Introduction. Recap – Advanced Nitrox Manual calculation prone to error Planning software Gas required = time x breathing rate x ambient pressure. Personal Gas Consumption. Surface gas consumption RMV Review personal RMV Work-rate & stress Example

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Gas Management

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  1. Gas Management

  2. Introduction • Recap – Advanced Nitrox • Manual calculation prone to error • Planning software • Gas required = time x breathing rate x ambient pressure

  3. Personal Gas Consumption • Surface gas consumption • RMV • Review personal RMV • Work-rate & stress • Example • Dive to 30m, RMV 16 litres/min • 4 Bar x 16 l/min = 64 l/min

  4. Rules • On dives: • Deeper than 40m • Involving decompression • Overhead environment • Rule of Thirds • Gas Reserves • Amount x 1.5 – decompression gas • Differing RMVs and Gas Supplies

  5. Gas Management - Example Dive 47m, 30 min RMV 16 l/min (Highest RMV of buddy group) Deco Gas: EAN 39 & EAN 80 • Bottom gas • 1.4 Bar/5.7 Bar = 0.2456 EAN 24 • EAD = 5.7 Bar x 0.76% N2 = 4.33 Bar ppN2 4.33 Bar ppN2/0.79% N2 = 5.48 Bar = 44.8m (45m)

  6. Gas Management - Example • Using 50/50 Tables, EAD 45m, 30 min • Mandatory Deco Stops

  7. Deep Stops • 1st Deep stop • (47m + 15m) / 2 = 31m • 2nd Deep stop • (31m + 15m) / 2 = 23m • 3rd Deep stop • 23m to 15m < 10m • 2 deep stops, 2 min each • Leave bottom at 26 min

  8. Deco Gas • EAN 39 from a depth of 31m (ppO2 1.6 bar) • EAN 80 from a depth of 9m (ppO2 1.52 bar) • Safety Margin • Decompression Software

  9. Example – Bottom Mix Descent & Bottom Phase: Gas Required = RMV at depth x Time 47m = 5.7 Bar RMV at depth = 16 x 5.7 = 91.2 l/min Gas required = 91.2 x 26 = 2371.2 litres

  10. Example – Bottom Mix Ascent on Bottom Mix: RMV at depth = RMV x Pressure Average pressure = (5.7 + 4.1)/2 = 4.9 Bar RMV at depth = 16 l/min x 4.9 Bar = 78.4 l/min Time for this ascent = 1.6 min. Gas Required = 78.4 l/min x 1.6 min = 125.44 litres

  11. Example – Bottom Mix Total Bottom Mix (EAN 24): 2,371 + 125 = 2,496 litres Rule-of-thirds Add 50% 2,496 x 1.5 = 3,744 litres If twin 10-litre cylinders, total 20 litres 3744/20 = 187 Each cylinder filled to at least 187 Bar

  12. Example – Deco Mix Ascent & Stops on EAN 39: Ascent • 4.1 Bar (31m) to 1.9 Bar (9m) • Average pressure = (4.1 + 1.9)/2 = 3 Bar • RMV at depth = 16 l/min x 3 Bar = 48 l/min • Time = 2.2 min. • Gas Required = 48 l/min x 2.2 min. = 105.6 litres

  13. Example – Deco Mix Deep Stops on EAN 39: • 31m RMV at depth = RMV x Pressure = 16 l/min x 4.1 Bar = 65.6 l/min Time at stop = 2 minutes 65.6 x 2 = 131.2 litres  • 23m RMV at depth = 16 l/min x 3.3 Bar = 52.8 l/min 52.8 x 2 min = 105.6 litres

  14. Example – Deco Mix Deco Stops on EAN 39: • 15m, 1 min RMV at depth = 16 l/min x 2.5 Bar = 40 l/min 40 x 1 min = 40 litres  • 12m, 4 min RMV at depth = 16 l/min x 2.2 Bar = 35.2 l/min 35.2 x 4 min = 140.8 litres

  15. Example – Deco Mix EAN 39 Required: 105.6 + 131.2 + 105.6 + 40 + 140.8 = 523.2 litres Rule-of-thirds: 523.2 x 1.5 = 784.8 litres (785 litres) 5-litre cylinder 785/3 = 157 Bar (Fill to capacity)

  16. Example – Deco Mix Ascent & Stops on EAN 80: Ascent • 1.9 Bar (9m) to 1 Bar (Surface) Average pressure = (1.9 + 1)/2 = 1.45 Bar RMV at depth = 16 l/min x 1.45 Bar = 23.2 l/min • Time = 0.9 min. • Gas Required = 23.2 l/min x 0.9 min. = 20.88 litres

  17. Example – Deco Mix Deco Stops on EAN 80: • 9m, 7 min RMV at depth = 16 l/min x 1.9 Bar = 30.4 l/min 30.4 x 7 min = 212.8 litres  -------------------------------------------------------------------------- • 6m, 3 min RMV at depth = 16 l/min x 1.6 Bar = 25.6 l/min 25.6 x 3 min = 76.8 litres -------------------------------------------------------------------------- • 4.5m, 21 min RMV at depth = 16 x 1.45 Bar = 23.2 l/min 23.2 x 21 min = 487.2 litres

  18. Example – Deco Mix EAN 80 Required: 20.88 + 212.8 + 76.8 + 487.2 = 797.68 litres Rule-of-thirds: 797.68 x 1.5 = 1,196.52 litres (1,197 litres) 7-litre cylinder 1197/7 = 171 Bar (Fill to capacity)

  19. Total Gas Requirements Bottom Mix: EAN 24: 3,744 litres 2 x 10-litre cylinders @ 187 bar Deco Mix: EAN 39: 785 litres 5-litre cylinder @ 157 bar EAN 80: 1,197 litres 7-litre cylinder @ 171 bar

  20. Manual Calculations • Laborious, Prone to Error • Disastrous Consequences • Desktop Software • V-Planner – VPM (www.v-planner.com) • Ross Hemingway, Eric Baker

  21. V-Planner Configure button Set surface interval Select the dive profile and mix Select your deco gases Use this button to enter a new deco gas Use this button to enter a new depth, bottom time and bottom mix

  22. Configure Parameters

  23. Enter Dive Details Calculate the dive profile

  24. Deco Profile & Gas Needs You must add 50% to these gas amounts to allow for Rule-of-Thirds.

  25. Rule-of-Thirds Bottom Mix: EAN 24: 2,733 x 1.5 = 4,099.5 (4,100 litres) 2 x 10-litre cylinders @ 205 bar For 210 bar fill: Turn Pressure = 210 x 0.66 = 150 bar Deco Mix: EAN 39: 500 x 1.5 = 750 litres 5-litre cylinder @ 150 bar EAN 80: 500 x 1.5 = 750 litres 5-litre cylinder @ 150 bar

  26. Summary • Individual gas consumption – RMV • Bottom mix • Deco mixes • Rule-of-thirds • Use of software

  27. Questions?

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