TDI Inner Space Sytsems
Megalodon
Closed Circuit Rebreather Course
TDI Megalodon
Closed Circuit Rebreather Diver Course
Overview of Course Structure
• 1 - Introduction and Welcome
• 2 - The History and Development of Rebreathers
• 3 - Mechanics of the Megalodon
• 4 - Electronics
• 5 - Physiology - A Reflection for the CCR Diver
TDI Megalodon
Closed Circuit Rebreather Diver Course
Overview of Course Structure continued
•
•
•
•
•
6 - Let’s Go Diving the Rebreather - Preparation
7 - Let’s Go Diving the Rebreather - In the Water
8 - Avoiding Rebreather Incidents - Safe Diving
9 - Mod 2 Extension (Optional extra course)
10 - Mod 3 Extension (Optional extra course)
TDI ISC Megalodon
Rebreathers Diver Course
Section 1:
Introduction and Welcome
Introduction and
Welcome
• Welcome to a new way of thinking about diving
• Understand that you are ALL novices again
• You will develop new skills for CCR diving
including:
– Attitudes
– Disciplines
– Awareness
Introduction and Welcome
Who the course is for and what you can expect to get out of it.
• COURSE PREREQUISITES
–
–
–
18 years of age
Logged 100+ dives
Nitrox and Advanced Nitrox training
• COURSE CREDENTIALS
–
To become qualified to dive the Inner Space Systems
Megalodon on Air Diluent up to 40m/132ft with safety stops
and 5 minutes max deco at 6m/ 20ft
Introduction and Welcome
• Why CCR Diving
– Longer dive durations possible with very
little equipment
– Almost silent and bubble free unless
ascending
– Extremely efficient use of breathing gas
– Optional Nitrox mix for all depths according
to user-selectable PPO2 setpoint
– Warm and moist comfortable breathing gas
reducing risk of hypothermic tendencies
Introduction and Welcome
•
What else can you expect to experience on this course?
– Many new terms for CCR not used in OC or SCR diving
– Change from a constant percentage Nitrox mix in OC to
a variable percentage Nitrox mix with constant partial
pressure in CCR mode
– Computer controlled gas injection system on ascent
causes accelerating bouyancy characteristics
• We need to think differently
– Jump a billion years of evolutionary development
• An opportunity to almost evolve into a sea-going mammal
with hours of sub-surface capability, and be back on land
again for another fun filled experience
TDI ISC Megalodon Rebreather
Divers Course
Section 2:
The History and
Development of Rebreathers
The History and Development
of Rebreathers
• Rebreathers in basic form have been around for
over a century underwater, and longer for mine
rescue work
• The earliest makes were pure oxygen devices
• The Englishman Henry Fleuss achieves a major
milestone covering over 300 meters (1000 feet)
underwater in the construction of the Severn
railway tunnel a century ago
• Military rebreathers developed and used-Stealth
The History and Development
of Rebreathers
•
The advent of readily available Nitrox to the recreational
market fuelled the development of recreational nitrox SCR
rebreathers
•
Progress and need in the military theater saw the
development of a number of electronic controlled CCR
machines over the last two decades
•
Some cave divers opted for passive mechanical SCR with
no electronics
•
Makes include the Electrolung; Cis Lunar; Drager Atlantis,
Dolphin and Ray and Inspiration/Evolution.
•
We see the advent of recreational CCR’s with the Inspiration
in 1997, followed by Prism, Megalodon,Ouroboros, Optima
and Kiss, and in 2005 the Evolution
The History and Development
of Rebreathers
CONCEPTUAL REBREATHER DESIGN
• All need a scrubber for CO2 removal
• Pure Oxygen rebreather – no need for electronics in basic
form just keep manually adding gas when loop volume falls
• Semi Closed SCR uses a known nitrox for loop addition
• Mechanical rebreathers use a fractional volume technique to
refresh gas
• Either Passive by sucking in fresh gas when oxygen in the
loop volume is depleted and a diaphragm regulator re-injects
to bring loop volume back up, or
• Active – Constant flow rate of Nitrox to loop-vent excess
The History and Development
of Rebreathers
Megalodon Rebreather
• Closed Circuit rebreathers (CCR)
• State of the art electronic controls
• Onboard sources of air and oxygen, scrubber,
computer controlled variable Nitrox mixing
• Everything the recreational and technical diver
needs
TDI ISC Megalodon
Rebreather Diver Course
Section 3:
Mechanics and basic functioning
of the Megalodon rebreather
Mechanics and basic functioning
of the ISC Megalodon
•
•
•
•
•
•
•
•
Diver’s Lungs
DSV and Hoses
Exhalation
Counterlung
Manual Inject Buttons
Over Pressure
Release Valve
The Scrubber
The Scrubber
Cartridge
The Head and
handsets
• Three Independent
Oxygen Sensors
• The Handsets and Gas
Control
• Battery Compartments
• Cell Connectors
• The Oxygen Supply
• Inhalation Counterlung
• Diluent Gas Supply
• Heads Up Display
Mechanics and basic functioning
of the ISC Megalodon
• Including Optional System Components
– Auto-Diluent Additional Valve (ADV) and inline
LP Flow Stop control device
– Tiger Gear Mounting System
– Mixed Gas Bypass
– Radial scrubber
– Neoprene Counter Lungs
– Choice of Different Back plates and wing
Sytems
Mechanics and basic functioning
of the ISC Megalodon
DIVERS LUNGS
• The motor that powers the gas around the
rebreather gas loop
• The point of exchange for O2 rich gas to the body
and CO2 rich gas from the body
• When we inhale, “clean” O2 rich gas comes in from
the Right.
• The flow is from the divers lungs through the
mouthpiece to the Left
Mechanics and basic functioning
of the ISC Megalodon
MOUTHPIECE and HOSES
• Mouthpiece and one-way mushroom valves control
direction of gas flow
• Timing of gas flow is in sympathy with diver’s
breathing pattern.
• Hoses are large bore. This reduces the work of
breathing (WOB)
• (Always close the mouthpiece to prevent fluding)
Mechanics and basic functioning
of the ISC Megalodon
EXHALATION COUNTERLUNG
• Counterlungs come from the factory as standard
5.5 ltr lungs made from highly durable cordura.
(Neoprene Counter lungs can be order from ISC)
• Flexible breathing bag to contain gas from body
• Contains both the ADV, Mixed Gas By-pass
(Additional Extra) and the Gas Loop Over
Pressure Release Valve
Mechanics and basic functioning
of the ISC Megalodon
THE CO2 SCRUBBER (or Stack)
• Gas path is from the exhalation counterlung,
through the T-piece down to the bottom of the CO2
scrubber
• It fans out to a large bore axial flow through the
scrubber to reduce gas velocity and increase
“Dwell Time” for CO2 removal
• The scrubber can is clear allowing the diver to see
the Internal Dive Sorb.
Mechanics and basic functioning
of the ISC Megalodon
THE SCRUBBER CARTRIDGE
• Designed to remove CO2 from the gas loop.
• Situated on a spacer fitted with moisture pads to
maintain air gap at bottom and soak up an
moisture from the canister
Mechanics and basic functioning
of the ISC Megalodon
The Scrubber Cartridge – continued
• Different scrubber makes can give different
duration times due to different granule sizes
• Only designed to remove CO2, not any other toxic
compounds or contaminants in the breathing gas
Mechanics and basic functioning
of the ISC Megalodon
SCRUBBER MATERIALS
• Have a defined shelf life time and in use up to 3 hours
• Effectiveness altered by time, temperature and moisture
• Sofnolime 797 grade recommended ( Other makes include
Dragersorb and Sodasorb)
• Sofnolime is primarily a Sodium Hydroxide compound
• Needs proper packing to prevent CO2 channeling
• Efficiency is reduced by high gas flow rates (fast or skip
breathing) or focused “channeling” characteristics
• In a properly assembled and properly functioning CCR
system the CO2 scrubber is the “Achilles Heel”
Mechanics and basic functioning
of the ISC Megalodon
SCRUBBER MANAGEMENT
• No partial filling of the scrubber. New full canister
every time
• Do not empty scrubber into a bag and re-pack the
scrubber later- new and used granules are then
mixed
• Do not store partly used scrubber for more than a
few days. The material absorbs CO2 and grows
mold
Mechanics and basic functioning
of the ISC Megalodon
CONTROLLERS
GENERAL
• Power On
– Primary and Secondary Electronics
– Switch on manually
– Self testing electronics.
– (hear solenoid firing, HUD Flashing)
– 2 control buttons.
– Sleep mode to conserve power
ELECTRONIC WORKSHOP
Mechanics and basic functioning
of the ISC Megalodon
HANDSET CONTROLLER GENERALITIES
• Handset controllers are electronic – handle carefully
• There are two independent handset “controllers” on the ISC
Megalodon and a HUD
• The main function of the primary controller is to control
oxygen injections and display real time information to the
diver
• The main function of the secondary controller is to provide
the diver with a totally independant PO2 reading.
• Can be switched on and off separately
Mechanics and basic functioning
of the ISC Megalodon
CONTROLLER FEATURES
• User Selectable Setpoints
• Built in System Monitor (Mv, Battery output,
Temperature)
• Back light feature
• User Selectable Oxygen Injection Time
• Metric - Imperial / Fresh - Salt water
• User selectable O2 % for Calibration.
Mechanics and basic functioning
of the ISC Megalodon
THE PRIMARY HANDSET
• Redundant controller PPO2 readings displayed to the diver
• Responsible for driving the Solinoid
• Requires independant Calibration.
• Primary Handset has a SSI (System Status Indicator +&- )
• Must be switched on to have a chance to drive the oxygen solenoid
• Will give indications of battery health (load / no load), Cell health,
Loop Temp, Outside Temp.
• Redundancy so that 1 controller can fail while the other allows you
to safely exit the water
• Need to constantly be checking PPO2 on the handset No Audio
Alarm.
Mechanics and basic functioning
of the ISC Megalodon
THE SECONDARY HANDSET
• Redundant controller PPO2 readings displayed to the diver
• Passive Heads UP Display (All HUD functions are controlled by the
secondary Handset)
• Requires independant Calibration.
• Will give indications of Battery health, Cell health, Loop Temp,
Outside Temp.
• Need to constantly be checking PPO2 on the handset No Audio
Alarm.
Mechanics and basic functioning
of the ISC Megalodon
HEADS UP DISPLAY (HUD)
• Three Colour Indicator powered by the secondary handset
• Can be disabled by the diver
• Adjustable Brightness control
• The HUD works by benchmarking setpoint 1.0 in ORANGE
• Cell Readings Higher than 1.0 are indicated by blinking
GREEN
• Cell Readings Lower than 1.0 are indicated by blinking RED
• Each Cell will blink seperately with a short pause between
each announcement.
Mechanics and basic functioning
of the ISC Megalodon
THE CANNISTER “ LID”
• The electronic “brains” of the device
• Consisting of two indipendant Battery packs, wiring for the
handsets and HUD, Oxygen Sensor Pod & Solinoid
• Great care should be taken when handling them
• For transport fully assemble rebreather or carry lid and
handsets separately in a padded bag
• Treat it with the same care as a laptop
Mechanics and basic functioning
of the ISC Megalodon
3 INDEPENDENT OXYGEN SENSORS
• 3 galvanic fuel cells each with a milli-volt output
proportional to the oxygen exposure across their outer
faces (breathing gas)
• The computers oxygen control averages all three Cells
togethor to provide the PPO2
• This information is displayed to the diver both
handsets
• Delicate pin connections
• Should never smell of “toxic” or other vapors
Mechanics and basic functioning
of the ISC Megalodon
• CONSTANT PPO2 GAS CONTROL
• Remember Dalton’s Law from Advanced Nitrox
Pressure gas = FO2 x Pressure
• At different depths (gas pressures) for a constant
PPO2 controller setting we will have a Nitrox mix
that changes proportionally to pressure
• At any given depth we can calculate the Nitrox
mix for any given PPO2 setting
Mechanics and basic functioning
of the ISC Megalodon
Mechanics and basic functioning
of the ISC Megalodon
BATTERY COMPARTMENT
• Two independant battery compartments
• Sealed to atmospheric pressure
• Battery packs consist of either 2 x 3.6v Lithium cells
or 5 Alkaline batterys supplied by ISC
WARNING! YOUR ELECTRONICS REQUIRE BATTERY POWER FOR
OPERATION, ENSURE YOU HAVE ENOUGH POWER PRIOR TO EACH
DIVE. CELLS READING 5.0V OR LESS SHOULD BE REPLACED
Mechanics and basic functioning
of the ISC Megalodon
CELL CONNECTORS
• These are delicate and covered with red or blue
moisture caps with holes for pressure equalization
• Take great care not to damage wires or connectors
if changing cells
• Check Mv output from cells before each dive
• Repalce your cells when Mv output falls below 9mv
Your Instructor will run through the correct procedure for calibrating the
handsets and conducting the required linearity checks
Mechanics and basic functioning
of the ISC Megalodon
THE OXYGEN SUPPLY
• Dive tank switched on
• HP to SPG on front of Inhilation lung gives O2 pressure
• LP hose feeds O2 to the LID for the solenoid from the first
stage regulator
• First stage regulator I/P is usually 10 bar with a range of
between 9.0 - 10.4 bar being acceptable
• You can choose dive tank size to suit your requirements
• Remember:- Rich mix Right, Lean mix Left
Mechanics and basic functioning
of the ISC Megalodon
DILUENT GAS SUPPLY
• Need to use diluent below 6msw (20fsw)
• Manually add diluent on descent depressing the ADV “to
equalize” the loop volume with pressure changes
• LP feeds to both the wing BCD and ADV
• Tank pressure is displayed on the SPG via HP hose over left
shoulder
• Do not use for Drysuit inflation – use off board gas
• IP normally set to 10 Bar
WARNING The Megalodon CCR does not have on-board bailout, surficient
bail out gas must be carried at all times.
TDI ISC Megalodn Rebreather
Divers Course
Section 6: Physiology –
A Reflection for the CCR Diver
Physiology – A Reflection for the
CCR Diver
BASIC PREMISE
• We need to breathe clean (CO2 and toxic gas free),
appropriately oxygenated gas at all depths at all times
to sustain life and to minimise DCS risk
• Appropriate nitrox mixes are delivered to the diver
under software control according to the PPO2 selected
by the diver
Physiology – A Reflection for the
CCR Diver
ADDITIONAL CONCEPTS
• Ascent must be controlled at less than 9m per minute
as per normal diving practice. DSC and DCI risks still
apply
• Dangers of hypoxia, hyperoxia, asphyxia and the
insidious CCR carbon dioxide poisoning (hypercapnia)
need examination
• Lets review sources of contamination of breathing loop
• NOAA toxicity guidelines apply for Whole Body and
Pulmonary Toxicity
Physiology – A Reflection for the
CCR Diver
CO2 and HYPERCAPNIA
• Humans consume O2 at a cellular level and
generate CO2 as a waste product
• Blood transports O2 to the cells and removes CO2
• Blood exchanges CO2 for O2 at the lung Alveoli
• The urge to breathe is driven by the level of CO2
retained in the body (blood and cells)
• With hypercapnia and elevated CO2 levels, the
breathing rate is increased (panting – dypsnea) to
try to vent the lungs and alveoli
Physiology – A Reflection for the
CCR Diver
HYPERCANPNIA SYMPTOMS
• Mild Symptoms
– Headache
– Anxiety and dizziness
– Shortness of breath
• Severe Symptoms
– Strong anxiety bordering on panic
– Muscular difficulty and loss of dexterity in closing
mouthpiece to bail out to OC
– Diluent flush doesn’t seem to have any effect at first so
divers often stop flushing when in fact they should
continue flushing non-stop
Physiology – A Reflection for the
CCR Diver
RE-INHALATION OF CO2
• CO2 normally removed by Sofnolime scrubber
• Conditions when this doesn’t occur properly
–
–
–
–
–
–
Scrubber expired or ignoring 3 hour duration rule
Strenuous activity on rebreather
Incorrect assembly of rebreather
Wet or flooded scrubber
Damaged mushroom valves – gas goes backwards
Skip breathing or breath holding – creates pockets of
very high CO2 content in the breathing loop
– Incorrect scrubber packing
Physiology – A Reflection for the
CCR Diver
DEPTH VERSUS CO2
• As depth increases, work of breathing increases to
push more gas molecules around the breathing loop.
More CO2 is generated as a result.
• As gas density of molecules increases the efficacy of
the scrubber granules to absorb CO2 across its surface
decreases
Physiology – A Reflection for the
CCR Diver
HYPEROXIA
• Too much oxygen results in O2 toxicity risk
• Track O2 toxicity per NOAA tables (see manual)
• At a default setpoint of 1.3, NOAA limit = 180 minutes - But
80% of that is 144 minutes
• Do not exceed 80% of CNS and OTU tables
• Need to monitor CNS% and OTU’s carefully on multi-dive
days or multiple repeat dive days
Physiology – A Reflection for the
CCR Diver
SYMPTOMS OF HYPEROXIA
• CONVENTID
– CON Convulsions
– V
Visual disturbances/Tunnel vision
– E
Ears ringing (Tinnitus)
– N
Nausea
– T
Tingling or twitching (facial)
– I
Irritability
– D
Dizziness or vertigo
Physiology – A Reflection for the
CCR Diver
PULMONARY TOXICITY
• O2 causes the alveoli surfaces in the lung to dry
out thus slowly reducing lung efficiency
• OTUs – 1 minute of 100% oxygen breathing at
the surface
• Happens above a PPO2 of 0.5 thus very real
danger for CCR Divers
Physiology – A Reflection for the
CCR Diver
HYPOXIA
• Occurs if the PPO2 drops below 0.16 at any time
• Real danger on ascent if solenoid fails
• Real danger if Oxygen tank is off or empty
• Symptoms can typically be breathlessness and
panting, and lack of co-ordination
• Unconsciousness resulting in drowning can be
sudden and without warning
Physiology – A Reflection for the
CCR Diver
CNS TOXICITY AND OTU’s
• Real danger of convulsing and drowning if your
CNS is not monitored properly
• Always know the PPO2 in the loop and do a
diluent flush to check any odd readings
• Track your CNS % and OTU’s on the NOAA
tables in your manuals
Physiology – A Reflection for the
CCR Diver
ASPHYXIA
• Like strangulation it is caused by a shortage of
oxygen and buildup of CO2
• Restrictions in the breathing loop like a kinked
mouthpiece hose can cause it
• Easily noticed early in a dive
• Ineffective or exhausted scrubber also can cause
asphyxia
• Eventually results in unconsciousness
TDI ISC Megalodon Rebreather
Divers Course
Section 7:
Let’s Go Dive the Rebreather Preparation
Let’s Go Diving the Rebreather Preparation
EQUIPMENT ASSEMBLY and INSPECTION
• Preparation
– Assemble the rebreather according to a checklist (refer to
manual), initially under Instructor guidance
– Be meticulous and do not get distracted
Let’s Go Diving the Rebreather Preparation
Pay particular attention to the following during assembly and inspection;
•
Positive & negative pressure tests
•
HUD LEDs functioning (if HUD used)
•
Cylinder contents analysis
•
•
•
Cylinder pressure on SPGs
Wing and Auto-Air checks
Listen for solenoid firing when handsets
switched on
•
Switches on handsets working normally
•
Scrubber packing
•
Mushroom valve checks on the
mouthpiece assembly
•
Hose O-ring lubrication
•
Battery power levels
Let’s Go Diving the Rebreather Preparation
WEIGHTING AND TRIM
• Ensure the unit is well weighted at the top.
• Add to the sides on the waistband to trim
• More weight needed if diving in a drysuit
Let’s Go Diving the Rebreather Preparation
MACHINE CALIBRATION
• Absolutely critical part of the preparation process
• Always put in % of oxygen in the lid at 98% - all
the air cannot be displaced from the lid
• Is the Mbar reading on the Megalodn handset are
Automatically sensed
• Mbar readings are critical for altitude diving
• Watch the cell readings rise during calibration and
check for any “slow” or “limited” cells
Your Instructor will demonstrate correct calibration procedures
Let’s Go Diving the Rebreather Preparation
GETTING THE FEEL OF THE MACHINE ON LAND
• Putting on the machine for a “dry dive”
– Adjust straps to fit body correctly and tuck away
loose ends
– Power up and sequence handset control through
to dive mode under guidance of Instructor
– Select your Setpoint
– Put on mask to prevent breathing through nose
– Breathe on the machine while watching PPO2
readings on handsets listen for solenoid firing
Let’s Go Diving the Rebreather Preparation
• Dry dive simulations (approx 30 minutes)
• These provide useful simulations in a safe
environment for learning and troubleshooting
Let’s Go Diving the Rebreather Preparation
OVERFILLED BREATHING LOOP
• Allow loop volume to increase by injecting a
little diluent.
• Get the feel of “over pressurized loop”
inhibiting the exhale cycle
• Release excess gas – repeat again
Let’s Go Diving the Rebreather Preparation
UNDERFILLED BREATHING LOOP
• Exhale fully through the nose, twice
• Feel the effect of too little pressure in the loop,
difficulty inhaling properly
• Add gas using the ADV, for volume adjustment
Let’s Go Diving the Rebreather Preparation
NORMAL LOOP VOLUME
• Continue normal breathing mode while seated or
stationary
• Observe PPO2 readings and how closely they
follow the setpoint
• Listen to solenoid firing and ensure you are
feeling fine on machine
Let’s Go Diving the Rebreather Preparation
GENTLE EXERCISE
• Walk about with the rebreather on
• Simulate moderate exercise
• Notice breathing, rate increases, and solenoid
firing more often than when at rest.
Let’s Go Diving the Rebreather Preparation
INCREASED WORK LEVEL
• Jog in place for a couple of minutes, or do a few
squats with the machine on to raise heart and
respiratory rates
• Observe PPO2 tracking, hear solenoid firing and
notice little or no change in loop volume
• The student should still feel fine and have no
CO2 problems
Let’s Go Diving the Rebreather Preparation
SETPOINT CHANGES
• Switch Setpoint when the PPO2 rises observe
PPO2 on handset to ensure fuctionality
• Test how long it takes to breathe the loop back
down to a PPO2 of 0.4 at rest
REMEMBER! There or no audio alarms for High or Low Oxygen on the
Megalodon the diver should be monitoring the handsets at all times.
Let’s Go Diving the Rebreather Preparation
OPEN CIRCUIT BAIL-OUT
• Close mouthpiece and come off the loop
• Switch to OC bailout – take 3 breaths, return to
the loop and open mouthpiece
• Observe loop volume increase as O2 is injected
to bring PPO2 back up to setpoint because of the
air you introduce to the loop
•
Let’s Go Diving the Rebreather Preparation
DILUENT FLUSH
• Inject diluent using the ADV
• Vent gas through by exhaling
• Repeat three times and observe reduction in
PPO2. Listen to solenoid firing.
Let’s Go Diving the Rebreather Preparation
MANUAL GAS ADDITION
• Give a small squirt of O2 with the manual addition
button and observe the PPO2 reading
• Repeat the exercise with diluent
• Repeat to get a “feel” for the addition buttons
TDI ISC Megalodon Rebreather
Divers Course
Section 8:
Let’s Go Dive the Rebreather
– In the Water
Let’s Go Diving the Rebreather –
In the Water
Rule No 1
• If in doubt – bail out!
Rule no 2
• If something feels wrong – it is!
Let’s Go Diving the Rebreather –
In the Water
DIVE PLANNING
• Select depth and time for a safe no-deco time
• Scrubber monitoring and planning (2.5 – 3 hour rule)
• Gas volume planning – enough for a bail-out
• Oxygen planning – CNS% and OTUs
• Is this a repetitive dive?
• Thermal protection appropriate for conditions and duration
of dive
• Brief team, do ABCs and enter the water under
guidance of your Instructor
Let’s Go Diving the Rebreather –
In the Water
FIRST IMPRESSIONS IN THE WATER
• Silence
• Bubble-free
• Listen for the solenoid firing
• Check PPO2 on the handsets every minute
• Dynamic bouyancy change caused by computercontrolled oxygen
• Unit is bouyant at shoulder level due to air volume in
counterlungs and hoses
• Add weight at the top for trim
• Remember – no matter how experienced you are on OC,
you are now a beginner again
Let’s Go Diving the Rebreather –
In the Water
EARLY TECHNIQUE POINTERS
• Do not expect to get it right first time
• Try to keep the loop volume at a minimum for comfort
• Keep a steady depth level
• Try to maintain a horizontal, neutral bouyancy, attitude
while swimming
• Use vertical attitude only when testing skills under
instructor guidance
• Be generous with weighting (1 or 2kg over)
Let’s Go Diving the Rebreather –
In the Water
BASIC WATER SKILLS DEVELOPMENT
• Mouthpiece opening and closing techniques
• Open Circuit bail-out
• Diluent flushes and checking PPO2 drop
• Check diluent flush predictions
• Bouyancy normalisation while swimming
• Constant checking of PPO2 on handsets
• Understanding and reacting to alarm conditions
(mostly simulated while on course)
• Loop volume control
Let’s Go Diving the Rebreather –
In the Water
BAD – DAS DRILLS
• In the event of in-water problems, rely on
BAD-DAS drills
– B Bail-out to open circuit
– A Anxiety breaths (3)
– D Decide what to do
• If returning to the loop, then:
– D Diluent flush – breathe fresh gas
– A Always know your PPO2 – check handsets
– S Skills. Apply appropriate skills gained
during training to overcome the problem
Let’s Go Diving the Rebreather –
In the Water
LOW O2 DRILLS
• Manual flight
– 1
Using O2 inflator
– 2
Adding oxygen using O2 tank valve
– 3
Using machine in semi-closed circuit
mode
• Low oxygen danger
– 1
Solenoid stuck closed
– 2
O2 tank empty or switched off
• Handset failure or switched off
– If both are blank, go open circuit or if gas
volumes dictate, switch to semi-closed
circuit mode
Let’s Go Diving the Rebreather –
In the Water
HIGH OXYGEN DRILLS
• Open circuit bailout
• Use of diluent flush to drop PPO2
• Closing oxygen tank if solenoid fails open
Let’s Go Diving the Rebreather –
In the Water
MENU MODE DRILLS
• Sequencing through menu commands in water to
become familiar with functionality
• Changing Setpoints
• Observe System Monitor
• Observe SSI indicator
Let’s Go Diving the Rebreather –
In the Water
HYPERCAPNIA DRILLS
• Open Circuit Bailout
• Diluent flushes
• Practice/Practice/Practice
Let’s Go Diving the Rebreather –
In the Water
ELECTRONICS MALFUNCTIONS
• Handset and controller problems
• Cell errors or missing cells
• Poor PPO2 tracking to setpoint
• Possible Loop Floods
TDI ISC Megalodon Rebreather
Divers Course
Section 9:
Avoiding Rebreather Incidents
– Safe Diving
Avoiding Rebreather incidents –
Safe Diving
All the training in the world is useless if you
do not adopt the following as your personal
mantra for CCR Diving:
– Safe Attitude
– Safe and enhanced Awareness
– Safe and structured Discipline
Avoiding Rebreather incidents –
Safe Diving
OPERATIONAL MAINTENANCE
• Check battery connections are clean and dry
• Ensure handsets are cleaned in fresh water,
• Keep O-rings well cleaned and lubricated to
prevent abrasion and other damage
Avoiding Rebreather incidents –
Safe Diving
REMEMBER DURING PRE-DIVE PREPARATION
• Properly assemble and check according to a
check list
• Do not get distracted during calibration
• Do all the pre-dive checks and then “go live”
for a short “dry-dive” to pre-breathe prior to
entering water in order to ensure dynamic
functionality of the machine
Avoiding Rebreather incidents –
Safe Diving
DIVE PLANNING
• Break dive into logical “waypoints” to do
checks and flushes for safety
• Usual waypoints
_ 6msw (20fsw) bubble leak check
– On descent - switch to high setpoints
– On reaching bottom - diluent flush and
check guages and handsets
– After pre-set time or leaving bottom diluent flush
– On ascent (10msw or less) - gas venting to
control bouyancy
Avoiding Rebreather incidents –
Safe Diving
REMEMBER ON THE DESCENT
• Do a shallow (6msw/20fsw) bubble check
• Descend slowly to control breathing loop volume
• Watch the PPO2
• Switch to high setpoint according to plan
Avoiding Rebreather incidents –
Safe Diving
REMEMBER ON THE ASCENT
• PPO2 will drop, solenoid should fire, and oxygen
should come into the loop quickly – rapid
bouyancy increase
• Check PPO2 closely on ascent to reduce Hypoxic
risk if there is insufficient O2 in the loop
• Carefully control ascent rate
• 3 potential bouyancy devices – drysuit, wing and
loop counterlungs
Avoiding Rebreather incidents –
Safe Diving
REMEMBER AT THE SURFACE
• NEVER switch off the handsets or tanks at the surface
above deep water
• Only shut down after equipment has been taken off
• You still need to watch your PPO2 if you breathe on
the loop at the surface
• It’s the best snorkel you ever bought!!!
Avoiding Rebreather incidents –
Safe Diving
REMEMBER AFTER THE DIVE
• Gas up again for the following dive
• Check and replace batteries/scrubber
as necessary
• Disinfect and clean as necessary
• Conduct all other system checks to ensure
correct functionality of cells and handsets
• Log your dives
Avoiding Rebreather incidents –
Safe Diving
TDI Training and Manufacturers Manuals
– Errors and troubleshooting are well documented
for reference
– Maintain your own service log for
batteries/scrubber and other service needs
– Document your rebreather experiences