Copyright 2012 CFT GAS/1 Gas Management. Copyright 2012 CFT GAS/2 Introduction Recap – Advanced Nitrox Manual calculation prone to error Planning software.
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Copyright 2012 CFT GAS/1
Gas Management
Copyright 2012 CFT GAS/2
Introduction Recap – Advanced Nitrox Manual calculation prone to error Planning software Gas required = time x breathing rate x ambient
pressure
Copyright 2012 CFT GAS/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
Copyright 2012 CFT GAS/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
Copyright 2012 CFT GAS/5
Gas Management - Example
Dive 47m, 30 minRMV 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)
Copyright 2012 CFT GAS/6
Gas Management - Example Using 50/50 Tables, EAD 45m, 30 min Mandatory Deco Stops
Depth(m) Stop Time (min) Gas
15 1 EAN 24
12 4 EAN 24
9 7 EAN 24
6 3 EAN 50
4.5 21 EAN 50
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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
Copyright 2012 CFT GAS/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
Copyright 2012 CFT GAS/9
Example – Bottom Mix
Descent & Bottom Phase:Gas Required = RMV at depth x Time47m = 5.7 BarRMV at depth = 16 x 5.7
= 91.2 l/min
Gas required = 91.2 x 26 = 2371.2 litres
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Example – Bottom Mix
Ascent on Bottom Mix:RMV at depth = RMV x PressureAverage pressure = (5.7 + 4.1)/2 = 4.9 BarRMV at depth = 16 l/min x 4.9 Bar
= 78.4 l/minTime for this ascent = 1.6 min.Gas Required = 78.4 l/min x 1.6 min
= 125.44 litres
Copyright 2012 CFT GAS/11
Example – Bottom Mix
Total Bottom Mix (EAN 24):2,371 + 125 = 2,496 litres
Rule-of-thirdsAdd 50%2,496 x 1.5 = 3,744 litres
If twin 10-litre cylinders, total 20 litres3744/20 = 187Each cylinder filled to at least 187 Bar
Copyright 2012 CFT GAS/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
Copyright 2012 CFT GAS/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/minTime at stop = 2 minutes65.6 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
Copyright 2012 CFT GAS/14
Example – Deco Mix
Deco Stops on EAN 39: 15m, 1 min RMV at depth = 16 l/min x 2.5 Bar
= 40 l/min40 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
Copyright 2012 CFT GAS/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 cylinder785/3 = 157 Bar (Fill to capacity)
Copyright 2012 CFT GAS/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 BarRMV 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
Copyright 2012 CFT GAS/17
Example – Deco MixDeco 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/min25.6 x 3 min = 76.8 litres
-------------------------------------------------------------------------- 4.5m, 21 min RMV at depth = 16 x 1.45 Bar
= 23.2 l/min23.2 x 21 min = 487.2 litres
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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 cylinder1197/7 = 171 Bar (Fill to capacity)
Copyright 2012 CFT GAS/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 litres7-litre cylinder @ 171 bar
Copyright 2012 CFT GAS/20
Manual Calculations Laborious, Prone to Error
Disastrous Consequences
Desktop Software
V-Planner – VPM (www.v-planner.com)
Ross Hemingway, Eric Baker
Copyright 2012 CFT GAS/21
V-PlannerSet surface interval
Configure button
Select the dive profile and mix
Select your deco gases
Use this button to enter a new depth, bottom time and bottom mix
Use this button to enter a new deco gas
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Configure Parameters
Copyright 2012 CFT GAS/23
Enter Dive Details
Calculate the dive profile
Copyright 2012 CFT GAS/24
Deco Profile & Gas Needs
You must add 50% to these gas amounts to allow for Rule-of-Thirds.
Copyright 2012 CFT GAS/25
Rule-of-ThirdsBottom 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 litres5-litre cylinder @ 150 bar
Copyright 2012 CFT GAS/26
Summary Individual gas consumption – RMV Bottom mix Deco mixes Rule-of-thirds Use of software
Copyright 2012 CFT GAS/27
Questions?
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