Workbook Slides By:
Kevin Gurr & Phil Short

• Protective case
•
Back-mounted counterlung
• Primary Display
•
Backup PO2 Display
•
Forward and Rear HUD
• Oxygen and Diluent gas blocks with isolators
• E x pedition version with
CO2 monitor

•2.2 KG Canister.
•4.5 Liter counter lung volume.
•O
2 solenoid valve with isolator.
•O
2 manual bypass.
•Diluent ADV with isolator.
•Diluent manual bypass.
•Water removal system.

•Integral protected counter lung.
•Backup oxygen display.
•Manual gas addition.
•Off-board gas plug-in option.
•Visual and tactile alarms.
•No ‘lock outs’.
•Data-logging.

• CDM (Canister duration monitor).
• CDM comprises TPM (Temperature Profile Meter) and O
2 injection counter.
• Auto-breathe breathing detection will turn unit on or;
– Auto turn on at 1.3 absolute pressure
– Manual turn on
• CO
2 sensor option on Expedition Sentinel

•Primary display, HUD and Rear HUD.
•Independent ‘Backup’ 3 sensor PO
2 display.
•On-board decompression.
•Variable and Auto PO
2 control while submerged.
•Dynamic HP alarms.
•Data logging system

• Critical components - redundancy
• Galvanic fuel cells
• Lead anode - gold plated cathode
- potassium hydroxide solution
• Lead is oxidized producing small voltage between anode & cathode
• Individually calibrated
• Affected by humidity and temperature

•Oxygen sensor with moisture tolerant membrane
•Removable with no special tools
•Moisture tolerant
•Robust connection system

•3 sensor polling.
•Ability to isolate ‘rogue’ sensors.
•Ability to force manual Set-point tracking.
•Variable valve control for fast ascents.
•Extremely accurate Set-point tracking.
•Automatic/manual air calibration.

2
• The PO
2
’s from the 3 Oxygen Cells are the most important data you have to monitor
• Compare the PO
2 displays to each other and to the
Set-point and the Backup Display
• Note the speed at which the PO
2 changes
– a slow reacting cell probably indicates moisture on that cell’s sensing face
• If in doubt confirm with Diluent flushes

• Minimum Set-point
– System will maintain a minimum of 0.4 at all times with the unit turned on even on an open circuit bailout
– Auto breathe ensures automatic turn on at less than 0.17
PO
2
• Changing Set-point
– Set-point can be changed Automatically or manually underwater
– Auto Set-point modes can be set for bottom and deco PO
2
’s
• Set-point range
– 0.4 to 1.6 is allowable

LED Mode PO
2
Mode
No flash-No Deco
Slow Flash – Deco ceiling above
Fast Flash – Violated ceiling/fast ascent
Solid Green
All good
Flashing Red/Buzzer
Dangerous Alarm Condition
Prepare to Bailout!
Monitor Displays
Flashing Green/Blue
Monitor Displays
Light
Status
Solid
Green
Meaning
At Setpoint
Slow Flash
Green
Below Setpoint
Fast Flash
Green
Above Setpoint

• Diluent primarily used only during descents
• Oxygen is more likely to limit dive duration
• Larger cylinders can be added or off-board cylinders attached

• Necessary for free breathing
– Empty bottle vs. paper bag
• Constant Buoyancy
– Exhale: lung volume decreased & bag volume increases
– Inhale: lung volume increases & bag volume decreases
– Compare to Open-Circuit Scuba
• Position to minimize pressure differential between lungs and counter lung

• Chest mounted bag - diver horizontal
– inhale less effort
– exhale more effort

• Back mounted bag - diver horizontal
– inhale more effort
– exhale less effort

• Shoulder mounted bags.
• Most positions: Inhale & exhale have a more balanced effort.

• Gas flow within a unit
• Size of hoses and orifices generate a resistance to breathing
• Includes design of mouthpiece, mushroom valves, hoses, counter lungs etc
• Gas density and depth dependent: deeper dives net denser gas, net higher resistive WOB
• Workload also affects resistive WOB-more gas flow equals more obstructions and turbulence
• CE Test data important to review

Absorbent canister for CO
2 removal
– Exhaled gas passes through this and is filtered for CO
2
– Efficiency and work of breathing is related to size / types of granules
– Duration affected by temperature and gas density
– Design also affects the efficiency

• Gas exposed to sufficient surface area of absorbent to remove CO
2
• Gas flow rate across absorbent allows sufficient time (dwell time) for chemical removal of CO
2
• Simple & correct packing to prevent ‘channeling’ of absorbent
• Prevents excess moisture from reaching absorbent

Radial Flow System - gas enters center of
‘doughnut’ cross section & radiates outwards through the absorbent (or from the outside inwards).

Barium Hydroxide - the earliest form of absorbent used
Lithium Hydroxide - long lasting and efficient, but must be carefully handled and is expensive
Soda Lime - a commonly used absorbent available under trade names such as Sofnolime™ and Dräger Divesorb®
All Absorbents will produce a caustic effect if mixed with water.

• Typical diving grade soda lime absorbent
– 94% Calcium Hydroxide [Ca(OH)2]
– 4% Sodium Hydroxide [NaOH]
– 1% Potassium Hydroxide [KOH]
– <1% Silica (binding agent)
• Some types change color with use
– Do not rely on this as an indicator of use
• Should be slightly hydrated to ensure production of Carbonic Acid

• CO
2 reacts with water (vapor) to form weak
Carbonic Acid
• Carbonic Acid reacts with base to produce salt
(chalk), water, & heat
• Resultant chemical reaction produces a strong alkaline material

2
• Chemical composition
• Canister volume
• Temperature
• Exertion level (CO
2 generation)
• Moisture level
• Gas density/depth
• Rebreather design

2
• The Sentinel was tested using:
– 1 - 2.5 mm (797 Grade) Sofnolime granules
– Water temp 4ºC
– Depth of 15m and 40m on air and 100m on Heliox
– CO
2 production rate of 1.6l/m
– 40l/m breathing rate

2
• At CE test rates on air at 40m, the canister will last 180 minutes
• At 100m on Heliox it will last 160 minutes
Durations with other absorbents have not been tested and cannot be guaranteed and may vary considerably

PCO
2
– 0.02 ATA/Bar - doubles breathing rate (dyspnea)
– 0.06 ATA/Bar - distress, confusion, lack of coordination
– 0.10 ATA/Bar - severe mental impairment
– 0. 12 ATA/Bar - loss of consciousness, death
CE CO
2 limits and alarms on the Sentinel
E x pedition are at 5 milibar and 10 milibar

2
• Empty used absorbent
• Remove absorbent stuck to walls
• Dispose of absorbent (use makers guidelines)
• Inspect cartridge and canister for damage
• Periodically flush canister with warm soapy water to clean residue. Ensure base screen slides up and down
•
Repack canister exactly following instructions on the attached label

• Rebreathers have limited gas supply
• Well fitting mask to prevent leaks
• Repeated mask clearing depletes gas supply
• Full face mask allows U/W communications
– full face must have a bite mouthpiece to prevent
CO
2 build-up

• More natural breathing than Open Circuit
• Breathing resistance depends on location of counter lung and diver’s body position
• Water in loop increases breathing resistance
• Humid gas reduces dehydration of diver
• Warm gas reduces heat loss from diver
– Both effects should reduce the risk of DCS

Turn on the unit by doing a short push of both buttons on the Primary display.
Aborted Pre-dive checks will be recorded in the Logbook.
An entry into the water without a complete Predive will record and abort in the logbook.

• Pre-breathe 5 minutes
– open mouthpiece and breathe normally WITH NOSE BLOCKED .
– Continue breathing for at least 1 minute if the graph is still red after
5 minutes, suspect flooding if yellow/green graph is not eventually displayed

• Initial in-water verification
• Descent - manual diluent addition
• Buoyancy control
• Monitoring PO
2
• Minimum loop volume
• Monitoring gas supplies
• Ascents

• Check for leaks
• Verify oxygen injection is working
• Verify ADV is operating
• Adjust buoyancy

• Counter lung collapses as ambient pressure increases
• Compensation by Automatic Diluent Valve (ADV) gas addition or manual bypass
• Rapid descents cause PO
2
• Select low PO
2 spikes
Set-point for descent or AUTO mode
• Switch to high PO
2
Set-point at target depth or check
AUTO switch has occurred.

• No buoyancy changes during breathing cycle
• Buoyancy adjustments using lung volume therefore not feasible
• Counter lung collapses during descent & expands during ascent
• Buoyancy change from fully collapsed to fully inflated is considerable. Use correct counter lung counter-weighting (approx. 4kg) to ensure unit is slightly negatively buoyant.

2
• Hypoxia & Hyperoxia are real dangers in all rebreathers
• Frequent cross checking of Primary and Backup displays
2

• Loop volume just enough for one normal breath
• Extra volume is wasted gas and added buoyancy
• PO
2 stays closer to Set-point
• Test loop volume with ADV disabled.

• Gas supplies used at much slower rate than OC, but monitoring is still necessary
• Small gas supply quickly used if there are leaks in the loop, frequent mask clearing or frequent ascents / descents
• O
2 supply not diluent supply typically limits the dive duration

• Buoyancy changes due to expansion of the counter lung, BCD, and dry suit
• PO
2 should not be allowed to drop
• The Sentinel will maintain close to the Setpoint during a normal ascent due to its dynamic control algorithm
• Oxygen can be manually added if necessary

Emergency Scenarios
– Hypoxia
– Hyperoxia
– Hypercapnia
– Solenoid/injection system failures
– Complete electronics failure
– Open circuit bailouts
In an emergency - it is the poorly learned survival skills which are lost first

See the training video and skills list for skill detail
• Complete Pre-dive check sequence, including the 5 minute Pre-breathe (with CDM monitoring).
• Complete automatic and manual calibration of cells.
• In water leak and function checks.
• Open circuit bailout (including BOV use) and open circuit bailout ascents.
• Manual control of PO2.
• CCR removal and replacement at surface.
• Set-point switching and automatic Set-point control.

See the training video and skills list for skill detail
• Delayed surface marker buoy use on CCR.
• Diluent flush.
• Oxygen volume drill.
• Simulated Hypoxia drill.
• Simulated Hyperoxia drill.
• Metabolic rate drill.
• Maintenance of PO
2 between deco stops.
• Partial flood recovery drill.
• Cell disabling and manual PO
2 control.

See the training video and skills list for skill detail
• HUD (Head Up Display) use.
• Semi Closed (gas extender drill).
• Electronics monitoring.
• Gas sharing.
• Various multi-part training scenarios.

• Disinfecting & cleaning
– CO
2 seal
– O-rings
– Canister
– Hoses
– Counter lungs
– BCD

– If the unit fails the negative test and the fault is not easily recognisable.
• Turn on all gases.
• Make sure the solenoid and ADV sliders are open
• Close the OPV
• Close the mouthpiece (open circuit mode).
– Fully immerse the unit (hoses, mouthpiece etc.) with the cover removed and look for leaks.
– If no leaks are visible but the OPV slowly vents gas, then suspect either the ADV or the solenoid.
• To test the ADV for leaks, close the gas block shutoff and see if the
OPV stops leaking. Service as required.
• To test the solenoid for leaks, close the gas block shutoff and see if the OPV stops leaking. Service as required.

• Rebreather - warm, damp environment is ideal for bacterial growth
• Breathing loop regularly disinfected & dried thoroughly
• Safe disinfectants only – Virkon is recommended
• Incorrect cleaning agents may affect Orings/counterlungs/mushroom valves
• O
2 compatible lubricants only on HP parts silicone grease on all else

• Full disinfect once a week
• Use only recommended disinfectant for all parts
• Stand part in solution for maximum of 10 minutes
• Fresh water flush
• Allow to dry

• Flush hoses and mouthpiece with fresh water
• Re-pack absorbent, fill cylinders as necessary
• If using absorbent again, keep sealed in the loop.
• If excessive moisture around the sensors, remove and dry.

• Rinse exterior of unit
• Remove/dispose absorbent
• Clean absorbent canister
• Rinse/disinfect breathing bags & hoses
• For storage, leave cylinders partially filled
• Allow unit to dry, lubricate all O-rings
• Remove oxygen sensors

• Do not disturb O-rings unnecessarily
• Carefully inspect prior to reassemble
• Replace damaged O-rings
• Excessive lubrication not required
• Check O-ring grooves for damage
• O
2 compatible lubricants only on HP parts
• Factory sealed compartments - don’t tamper

• Check for visible damage after every dive
• Store in a carry case
• Do not carry unit by hoses
• Do not place heavy equipment on hoses

• Keep dry (vented) when not in use.
• Beware of bugs crawling into counterlungs
• Check loop interface ports for damage to threads, etc.
• Use loop end caps

• Vital for buoyancy control & safety
• Visual inspections regularly
• Fully inflate and check for leaks, pre-dive

• Advantages of CCR greatly outweigh the disadvantages
• Correct training is obligatory
Always do all pre-dive checks
Always Pre-breathe the unit
Always know your PO
2
Practice your skills
Be Sensible, Be Safe