1. Sport Diver Supplementary Training
Nitrox Workshop

2. Aim To further the learning of qualified divers
To enable BSAC Sport Divers (or similar) to plan and execute nitrox dives for gas mixes up to 36% using computers/tables controlled by the MOD of the selected gas

3. Sports Diver
Dive within maximum operating depth (MOD) of the gas carried
Plan decompression dives on nitrox tables or nitrox computers
Dive within the depth limit of the diver’s experience or qualification

4. Oxygen Partial Pressures
Fraction of oxygen (FO2) in mix
FO2 = %O2 divided by 100
e.g. FO2 of nitrox 36 = 0.36
Oxygen partial pressure (PO2)
PO2 = FO2 x absolute pressure
Example - nitrox 32 at 30 m
PO2 = 0.32 x 4.0 bar = 1.28 bar
Safety limit
Maximum recommended PO2 is 1.4 bar

5. Maximum Operating Depth (MOD)
The depth at which the PO2 of the mix reaches 1.4 bar
Example
(PO2)max ÷ Fraction of Oxygen = MOD
1.40 bar ÷ 0.32 bar = 4.38 bar (33.8 m)
Do not exceed your MOD
Select a mix with an MOD greater than your “just deeper” planned depth
Limits of 36%=30m and 32%=35m still OK for No-Stop dives only

6. Partial Pressure table
What is the maximum MOD for nitrox 32%?
Answer: 33 metres
For no-stop dives only:
Max depth is 35 metres

7. Partial Pressure table
What is the PO2 of nitrox 32% at 30 metres?
Answer: 1.28 bar
Partial Pressure Table reduces calculation errors.

8. Oxygen Partial Pressure Scale (bar)
Oxygen Exposure
Oxygen Partial Pressure Scale (bar)
At high concentrations oxygen is toxic
Know and observe your MOD to control the PO2!
Keep within accepted oxygen exposure limits
Hyperoxic
1.0
0.5
0.21
1.6
1.4
Short term toxicity risk
Long term toxicity risk
AIR

9. Hyperoxia What is it? There are two different effects of hyperoxia:
Too much oxygen
Oxygen becomes toxic at elevated partial pressures
There are two different effects of hyperoxia:
Whole Body Oxygen Toxicity when PO2 > 0.5 bar for long periods (recompression)
Central Nervous System (CNS) toxicity when PO2 > 1.4 bar for even short periods (on a dive)

10. Hyperoxia Causes: Inaccurate dive planning Failure to analyse gas
Incorrect marking or fitting of cylinders
Failure to observe MOD!

11. Hyperoxia Aggravating factors
Actual PO2
Duration of exposure
Level of exertion
Cumulative O2 exposure
Long term (whole body) toxicity risk not an issue at this level
Short term (CNS) toxicity risk needs to be understood

12. CNS Toxicity Also known as acute oxygen toxicity
Reaction to PO2 generally > 1.4 bar
Signs & Symptoms:
CON - Convulsions
V - Vision
E - Ears, hearing disturbances
N - Nausea
T - Twitching
I - Irritability
D - Dizziness
Until convulsions begin, minor symptoms:
Can occur in ANY order or combination
Increase in severity 61 61 60 63 60

13. CNS Toxicity – Convulsions
Tonic phase – do not lift
Casualty becomes rigid and holds breath
Clonic phase – do not lift
Casualty jerks violently (convulsion)
Relaxation phase - assist
Casualty relaxes and is unconscious
Potential loss of mouthpiece
Signs can still occur after PO2 is reduced 61 61 60 63 60

14. CNS Toxicity - Incident Management
If a diver suffers from CNS toxicity:
CBL to surface even if deco stops omitted
If casualty is rigid, holding breath or convulsing …
Do NOT attempt to lift
Risk of embolism
Wait until the casualty has relaxed
Remove casualty from water
Do administer oxygen therapy if suspect DCI or barotrauma

15. Hyperoxia Avoidance: Plan the dive; dive the plan Max PO2 of 1.4 bar
Do not exceed MOD
High PCO2 predisposes to oxygen toxicity
Breathe normally throughout the dive
Reduce PO2 for high exercise dives
Accurately track your oxygen exposure

16. Monitoring Oxygen Exposure
CNS toxicity needs to be monitored
BSAC Oxygen Toxicity Table
Dive planning software / nitrox computers
CNS% should not exceed 80%
While at the surface
CNS% is reduced by half every two hours
Add outstanding CNS% to next dive

17. Oxygen Toxicity Table Using the Oxygen Toxicity Table
Find PO2 in left hand column (round-up)
e.g., PO2Actual = 1.28 bar; PO2 Table = 1.30 bar
Find time spent at PO2 along the top row, e.g. 5 minutes
Where lines intersect (yellow column) indicates CNS% uptake

18. Dive Computers
Some dive computers capable of being programmed for nitrox mixes:
Left set for air – reduced risk of DCI
Set for actual nitrox % - longer dive duration at same risk of DCI as for air
Set to intermediate nitrox % - a bit of both benefits
All other procedures as for air diving
Nitrox capable dive computers also track oxygen exposure (CNS %)
Some nitrox computers capable of being programmed to change nitrox mix during dive

19. Practice - Oxygen Toxicity Table
What is the accumulated CNS% for a total dive time of 27 minutes at a PO2 of 1.38 bar?
Method one
CNS% = 1.34 (2 mins) (5 mins) (20 mins)
= %
Method two
CNS% = 27 mins × 0.67 (1 min) = %
2 hours later the divers plan a second dive, what is the residual CNS% at the start of the dive?
CNS% halves every 2 hours,
CNS% = ÷ 2 = %
Note: dive computers may use a different method for calculating residual CNS%

20. Nitrox Tables - planning a dive using Nitrox 32
Dive to 20 metres for 30 minutes
Depth and/or time is ‘in between’ values
Use next greater depth
Use next longer time
Surface Code is D

21. Planning - dive one Nitrox 32
First Dive
Nitrox 32
26 metres
33 min
Surface code = F

22. Surface Interval Table
Surface interval 3 hours
Second dive CTC = C

23. Planning - dive two Nitrox 36
Second Dive
Nitrox 36% Table C
20 metres
25 min
Stops = 1 6m
Surface Code = G

24. Practice - planning two dives using different nitrox mixes
Good practice to increase oxygen % for second dive
Dive one
25 m for 30 min on nitrox 32 (Use Table A 32%)
Surfacing code = E
Surface interval of 5 hours
Dive two
18 m for 40 min on nitrox 36
CTC = B (apply to Table B 36%)
Surfacing code = D (no-stop dive)

25. Dive Management Divers using different mixes Dive plan limited by: and
MOD of highest % oxygen mix
and
Decompression requirements for the lowest % oxygen mix
Dive Manager should additionally ensure recording of percentage mix and MOD of each diver.

26. Summary Sport Diver Partial Pressure Table Oxygen Exposure
Max PO2 of 1.4 bar
Partial Pressure Table
Oxygen Exposure
Hyperoxia
CNS Toxicity
Convulsions
Incident Management
Oxygen Toxicity Table
BSAC Nitrox Tables
Dive planning
Dive Management
% Mix
MOD