OT4.1 08/02 BSAC Ocean Diver Training Planning to go Diving.

OT4.108/02

BSAC Ocean Diver Training

Planning to go DivingPlanning to go DivingPlanning to go DivingPlanning to go Diving

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Planning to go Diving

Planning to go Diving Planning to go Diving

Aims

Every dive requires a plan for safety and enjoyment

Two of the most important considerations Nitrogen management Ensuring sufficient breathing gas

for the dive

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Planning to go Diving Diving & Effects of Nitrogen

Gases Dissolve in the blood - a liquid

N2

O2

Atmosphere 79% Nitrogen, 21% Oxygen

Diving - ambient pressure increases Higher concentration of gas delivered to diver Higher concentration of gases dissolved in the blood including nitrogen

Oxygen utilised, carbon dioxide produced Oxygen, carbon dioxide come out of blood as gases in

alveoli

Nitrox A breathing gas usually having more than 21%O2

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Planning to go Diving Nitrogen Absorption

On the surface Nitrogen in body in equilibrium with air

On a dive Increase in ambient pressure results in more nitrogen absorbed into body tissues - “on-gassing”

Going deeper or longer increases body’s uptake of nitrogen

Different tissues absorb nitrogen at different rates ‘Fast tissues - good blood supply ‘Slow’ tissues - poorer blood supply, fatty tissues

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Planning to go Diving Nitrogen Release

On ascent Nitrogen released from tissues - “off-gassing”

Tissues release nitrogen at different rates Body can tolerate a certain excess of nitrogen Nitrogen still being released when back on the

surface

If a diver ascends too quickly Nitrogen will be released as bubbles in the

tissues or bloodstream Can cause Decompression Illness (DCI)

Nitrogen release needs to be managed

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Planning to go Diving Nitrogen Management

BSAC Decompression Tables

Dive Computers

Understanding the principles of tables will help to understand computers

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Planning to go Diving BSAC Tables - Definitions 1

Depth Deepest depth reached during the dive

Deepest Depth

6m

Descent rate Maximum is 30m/minute

Ascent rate Maximum is 15m/minute up to 6m

Dive time From leaving surface, to arriving at 6m

Ascent/Dive time check depth 6m pause to check dive time

Dive time

6m 1 minute from 6m to the surface

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Planning to go Diving BSAC Tables - Definitions 2

Current Tissue Code (CTC) Represents body’s present level

of nitrogen saturation Starting point for dive planning

CTC SC

Surfacing Code (SC) Represents change to CTC at

end of dive

Tissue Codes : A B C D E F G

Nitrogen Load

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Planning to go Diving Using BSAC Tables

Ocean Divers Maximum depth 20 metres “No-Stop” dives for

minimum risk - the white zone

Table ‘A’ For divers with a CTC

of ‘A’

Ocean Divers dive within this area

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BSAC Tables - Planning a No-Stop Dive

Dive to 9m for 17 min.

If depth or time between values

Dive to 20m for 30 min.

Surface Code is B

Surface Code is E

Use next longer time Use next greater depth

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Planning to go Diving Planning a Second Dive

Plan second dive shallower than first

CTC SC CTC

Surface Interval

On the surface after a dive “Off-gassing” reduces tissue Nitrogen loading Surface Interval reduces Surfacing Code Gives new Current Tissue Code for the second dive

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BSAC Tables - Using the Surface Interval Table

Enter at your SC

Example SC = ‘E’

Surface interval + 5 hours

Move across to Surface Interval

Read new CTC from table

New CTC = ‘B’

To find your CTC for a second dive

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Planning to go Diving Table Levels

Pressure range marked on each Table

Table ‘Level’ depends on atmospheric pressure

Use Altitude/Atmospheric Chart with Transfer Table

When to use: Travelling - hills and mountains Living or diving at altitude Inland sites and bad weather Flying

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Planning to go Diving Flying & Diving

Flying before diving Tissues off-gas Stresses of flying Recover before diving - 10

hours minimum

Flying after Diving Increased level of off-gassing -

DCI Stresses of flying Ensure long Surface Interval

between last dive and flying Need CTC of ‘A’ or ‘B’

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Planning to go Diving Diving using BSAC Tables

To Dive the Plan using Tables you need

PLAN THE DIVE AND DIVE THE PLAN

A depth gauge to monitor depth

A dive watch to monitor time

A dive slate as a reminder of the plan

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Planning to go Diving Dive Computers

The basic functions: Theoretical body tissue

‘models’ to calculate nitrogen on and off-gassing

A timer & pressure sensor Planning information -

depth/time Audible or screen warnings Stored log of previous dives Integrated temperature

sensors

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Difference between Tables and Computers

Dive Profile

Dive Table Profile

Dive Computer Profile

‘Square’ profile

Profile of depth and time

Continuous tracking of nitrogen load No-stop times vary from square

profile of tables

Continuous tracking depth and time

‘Calculated for maximum depth

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Planning to go Diving Plan the Dive and Dive the Plan

Whether using Tables or Computers Two dives - plan the deepest first Never push the limits of tables or

computers Table and computer mix, dive the tables Plan a dive that avoids “saw-tooth”

profiles BSAC ’88 Tables allow for 3 dives in 24

hours Computers may have similar allowance Ensure a good surface interval after

diving and before flying

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Planning to go Diving Using Tables or Computers

Tables or Computers are not infallible They are planning tools to minimize the risk of DCI

DCI can happen . . . Be fit to dive Avoid getting cold Do not dive in a dehydrated state Avoid excessive exercise Do not dive with a hangover Abort a dive if anxious or worried

Remember

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Planning to go Diving Use of Nitrox to manage Nitrogen

Ocean Divers may use 32% and 36% Nitrox mixes using air tables or air computers

Advantages of Nitrox – less nitrogen means Safety factor Reduced risk of DCI

Disadvantages of Nitrox Nitrox divers can still get DCI Certain equipment must be dedicated

to the use of Nitrox Oxygen Toxicity (explained in OT6)

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IntroducingBSAC NITROX Tables

Ocean Divers “No-Stop” dives using 32%

Nitrox, planned on 21% air table Maximum depth 20 metres

Table ‘A’ For divers with a CTC of ‘A’

Ocean Divers dive within this area

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Nitrox – Procedures and Practices

Higher percentage of oxygen Oxygen supports combustion Materials and greases must be safe

with higher oxygen percentages Equipment must be cleaned periodically

removing combustible contaminants

Percentages must be checked with an O2 analyser before use Follow analyser manufacturer’s guidance Must not use gas more than 1% different

from desired mix All cylinders should be marked with mix %

and MOD

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Planning to go Diving Nitrox – Using an analyser

4. Present the analyser to the cylinder valve

1. Switch on the gas analyser

2. Calibration- essential before use

3. Slowly open the valve - gas gently hissing out

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Planning to go Diving Nitrox – Analysing a mix

5. Take a reading

6. Record the analysis

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Planning to go Diving Analysing essentials

Calibrate prior to use Keep flow rate even and low as possible Erratic readings point towards a analyser failure Avoid windy conditions Avoid moisture Your analysis must be within +/- 1% of your

target mix Store analyser away from elevated oxygen levels

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Planning to go Diving Dive Planning – Breathing Gas

The rule for planning and monitoring breathing gas on a dive

Rule of Thirds

One third gas supply for second half of dive or return journey including ascent

One third gas supply as a reserve

1/3

1/3 One third gas supply for descent, to half way or turn around point

1/3

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Planning to go Diving Breathing Gas Planning

The Rule of Thirds10 Litre cylinder filled to 210 bar

Divide 210 bar by 3 = 70 bar for each 1/3 of dive

First third

210 - 70 = 140 bar - at turn around/half way point

Second third

140 - 70 = 70 bar - at surface Third third

70 leaves approximately 70 bar as reserve

Always aim to surface with 1/3 cylinder as reserve

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Planning to go Diving Gas Monitoring

Always monitor contents gauge throughout a dive – it’s your lifeline!

Running low or out of gas should not arise under normal diving conditions

Gas consumption increases when: Physical effort increases Divers are cold or anxious

Shorten or terminate the dive

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Planning to go Diving Summary

Management of Breathing Gas Rule of Thirds and constant monitoring

Plan the Dive and Dive the Plan

Management of Nitrogen Tables or computer Plan with common sense

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OT4.1 08/02 BSAC Ocean Diver Training Planning to go Diving.

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Transcript of OT4.1 08/02 BSAC Ocean Diver Training Planning to go Diving.