Transcript PPT
BSAC Ocean Diver Training
Planning to go Diving
OT4.1
08/02
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
Atmosphere
O2
79% Nitrogen, 21% Oxygen
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
OT4 3
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Higher concentration of gas delivered to diver
Higher concentration of gases dissolved in
the blood including nitrogen
N2
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
OT4 5
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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
OT4 6
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Planning to go
Diving
BSAC Tables - Definitions 1
Depth
Deepest depth reached during the
dive
6m
Descent rate
Maximum is 30m/minute
Ascent rate
Deepest Depth
Maximum is 15m/minute up to 6m
1 minute from 6m to the surface
6m
Ascent/Dive time check depth
6m pause to check dive time
Dive time
OT4 7
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From leaving surface, to arriving at 6m
Dive time
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
Surfacing Code (SC)
Represents change to CTC at
end of dive
Tissue Codes :
Nitrogen Load
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A B C D E F G
SC
Planning to go
Diving
Using BSAC Tables
Ocean Divers
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’
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Planning to go
Diving
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
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Planning to go
Diving
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
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Planning to go
Diving
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’
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Planning to go
Diving
Table Levels
Table ‘Level’ depends on atmospheric pressure
Pressure range marked on each
Table
Use Altitude/Atmospheric Chart
with Transfer Table
When to use:
OT4 13
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Travelling - hills and mountains
Living or diving at altitude
Inland sites and bad weather
Flying
Planning to go
Diving
Flying & Diving
Flying before diving
Tissues off-gas
Stresses of flying
Recover before diving - 10
hours minimum
Flying after Diving
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Increased level of off-gassing DCI
Stresses of flying
Ensure long Surface Interval
between last dive and flying
Need CTC of ‘A’ or ‘B’
Planning to go
Diving
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
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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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Planning to go
Diving
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
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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
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Remember
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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Planning to go
Diving
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’
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Planning to go
Diving
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
1. Switch on the
gas analyser
3. Slowly open
the valve
- gas gently
hissing out
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2. Calibration
- essential
before use
4. Present the
analyser to
the cylinder
valve
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
1/
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
One third gas supply
as a reserve
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08/02
1/
3
1/
3
3
Planning to go
Diving
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
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
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
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Planning to go
Diving
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