Copyright 2012 CFT GAS/1 Gas Management. Copyright 2012 CFT GAS/2 Introduction Recap – Advanced...

Copyright 2012 CFT GAS/1

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

Dive to 30m, RMV 16 litres/min 4 Bar x 16 l/min = 64 l/min


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


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)


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


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


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


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



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



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


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



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



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



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)



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


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



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)


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


Manual Calculations Laborious, Prone to Error

Disastrous Consequences

Desktop Software

V-Planner – VPM (www.v-planner.com)

Ross Hemingway, Eric Baker


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


Configure Parameters


Enter Dive Details

Calculate the dive profile


Deco Profile & Gas Needs

You must add 50% to these gas amounts to allow for Rule-of-Thirds.


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


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


Questions?

Copyright 2012 CFT GAS/1 Gas Management. Copyright 2012 CFT GAS/2 Introduction Recap – Advanced...

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