1. BSAC Ocean Diver Training
Planning to go Diving

2. 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

3. Diving & Effects of Nitrogen
Atmosphere
79% Nitrogen, 21% Oxygen N2 O2
Nitrox
A breathing gas usually having more than 21%O2
Gases
Dissolve in the blood - a liquid
Oxygen utilised, carbon dioxide produced
Oxygen, carbon dioxide come out of blood as gases in alveoli
Diving - ambient pressure increases
Higher concentration of gas delivered to diver
Higher concentration of gases dissolved in the blood including nitrogen

4. Nitrogen Absorption On the surface On a dive
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

5. Nitrogen Release On ascent If a diver ascends too quickly
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

6. BSAC Decompression Tables
Nitrogen Management
BSAC Decompression Tables
Dive Computers
Understanding the principles of tables will help to understand computers

7. BSAC Tables - Definitions 1
Depth
Deepest depth reached during the dive 6m
Descent rate
Maximum is 30m/minute
Deepest Depth
Ascent rate
Maximum is 15m/minute up to 6m
1 minute from 6m to the surface
Dive time 6m
Ascent/Dive time check depth
6m pause to check dive time
Dive time
From leaving surface, to arriving at 6m

8. 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

9. Using BSAC Tables Ocean Divers Ocean Divers dive within this area
Maximum depth 20 metres
“No-Stop” dives for minimum risk - the white zone
Ocean Divers dive within this area
Table ‘A’
For divers with a CTC of ‘A’

10. BSAC Tables - Planning a No-Stop Dive
Dive to 9m for 17 min.
Surface Code is B
If depth or time between values
Use next longer time
Use next greater depth
Dive to 20m for 30 min.
Surface Code is E

11. Planning a Second Dive 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
Plan second dive shallower than first
CTC SC
CTC
Surface Interval

12. BSAC Tables - Using the Surface Interval Table
To find your CTC for a second dive
Enter at your SC
Move across to Surface Interval
Read new CTC from table
Example
SC = ‘E’
Surface interval + 5 hours
New CTC = ‘B’

13. Table Levels Table ‘Level’ depends on atmospheric pressure
Pressure range marked on each Table
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

14. Flying & Diving Flying before diving Flying after 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’

15. Diving using BSAC Tables
To Dive the Plan using Tables you need
A depth gauge to monitor depth
A dive watch to monitor time
A dive slate as a reminder of the plan
PLAN THE DIVE AND DIVE THE PLAN

16. 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

17. Difference between Tables and Computers
Dive Profile
Profile of depth and time
Dive Table Profile
‘Square’ profile
‘Calculated for maximum depth
Dive Computer Profile
Continuous tracking depth and time
Continuous tracking of nitrogen load
No-stop times vary from square profile of tables

18. Whether using Tables or Computers
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

19. 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

20. 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)

21. Introducing BSAC NITROX Tables
Ocean Divers
“No-Stop” dives using 32% Nitrox, planned on 21% air table
Maximum depth 20 metres
Ocean Divers dive within this area
Table ‘A’
For divers with a CTC of ‘A’

22. 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

23. Nitrox – Using an analyser
1. Switch on the gas analyser
2. Calibration - essential before use
3. Slowly open the valve - gas gently hissing out
4. Present the analyser to the cylinder valve

24. Nitrox – Analysing a mix
Take a reading
Record the analysis

25. 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

26. Dive Planning – Breathing Gas
The rule for planning and monitoring breathing gas on a dive
Rule of Thirds
1/3
One third gas supply for descent, to half way or turn around point
One third gas supply for second half of dive or return journey including ascent
1/3
1/3
One third gas supply as a reserve

27. Breathing Gas Planning
The Rule of Thirds
10 Litre cylinder filled to 210 bar
Divide 210 bar by 3 = 70 bar for each 1/3 of dive
First third
= 140 bar - at turn around/half way point
Second third
= 70 bar - at surface
Third third
70 leaves approximately 70 bar as reserve
Always aim to surface with 1/3 cylinder as reserve

28. 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

29. Summary Plan the Dive and Dive the Plan Management of Nitrogen
Tables or computer
Plan with common sense
Management of Breathing Gas
Rule of Thirds and constant monitoring