1. Sentinel CCR Diver Course Kevin Gurr & Phil Short Workbook Slides By:
Copyright IANTD/IAND, Inc. 2000

2. Sentinel Rebreather Layout
Copyright IANTD/IAND, Inc. 2000

3. Sentinel CCR Protective case Back-mounted counterlung Primary Display
Backup PO2 Display
Forward and Rear HUD
Oxygen and Diluent gas blocks with isolators
Expedition version with CO2 monitor
Copyright IANTD/IAND, Inc. 2000

4. Sentinel Key Features 2.2 KG Canister. 4.5 Liter counter lung volume.
O2 solenoid valve with isolator.
O2 manual bypass.
Diluent ADV with isolator.
Diluent manual bypass.
Water removal system.
Copyright IANTD/IAND, Inc. 2000

5. System Layout
Copyright IANTD/IAND, Inc. 2000

6. Sentinel Safety Features
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.
Copyright IANTD/IAND, Inc. 2000

7. Sentinel Safety Features
CDM (Canister duration monitor).
CDM comprises TPM (Temperature Profile Meter) and O2 injection counter.
Auto-breathe breathing detection will turn unit on or;
Auto turn on at 1.3 absolute pressure
Manual turn on
CO2 sensor option on Expedition Sentinel
Copyright IANTD/IAND, Inc. 2000

8. Sentinel Technical Data
Primary display, HUD and Rear HUD.
Independent ‘Backup’ 3 sensor PO2 display.
On-board decompression.
Variable and Auto PO2 control while submerged.
Dynamic HP alarms.
Data logging system
Copyright IANTD/IAND, Inc. 2000

9. Electrical Oxygen Sensors
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
Copyright IANTD/IAND, Inc. 2000

10. Sentinel Oxygen Cells Oxygen sensor with moisture tolerant membrane
Removable with no special tools
Moisture tolerant
Robust connection system
Copyright IANTD/IAND, Inc. 2000

11. Sentinel Oxygen Controller
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.
Copyright IANTD/IAND, Inc. 2000

12. Sentinel Power On Screen
Copyright IANTD/IAND, Inc. 2000

13. Sentinel Interpreting the PO2 Display
The PO2’s from the 3 Oxygen Cells are the most important data you have to monitor
Do It Regularly!
Compare the PO2 displays to each other and to the Set-point and the Backup Display
Note the speed at which the PO2 changes
a slow reacting cell probably indicates moisture on that cell’s sensing face
If in doubt confirm with Diluent flushes
Copyright IANTD/IAND, Inc. 2000

14. Sentinel Controlling Set-point
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 PO2
Changing Set-point
Set-point can be changed Automatically or manually underwater
Auto Set-point modes can be set for bottom and deco PO2’s
Set-point range
0.4 to 1.6 is allowable
Copyright IANTD/IAND, Inc. 2000

15. Sentinel Primary Dive Screens
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16. Sentinel Rebreather HUD
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
LED Mode
PO2 Mode
Light Status
Meaning
Solid Green
At Set-point
Slow Flash Green
Below Set-point
Fast Flash Green
Above Set-point
Copyright IANTD/IAND, Inc. 2000

17. CCR Design and Functionality

18. Cylinder Considerations
Diluent primarily used only during descents
Oxygen is more likely to limit dive duration
Larger cylinders can be added or off-board cylinders attached
Copyright IANTD/IAND, Inc. 2000

19. The Counter lungs Necessary for free breathing Constant Buoyancy
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
Copyright IANTD/IAND, Inc. 2000

20. Hydrostatic Effect Chest mounted bag - diver horizontal
inhale less effort
exhale more effort
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21. Hydrostatic Effect Back mounted bag - diver horizontal
inhale more effort
exhale less effort
Copyright IANTD/IAND, Inc. 2000

22. Hydrostatic Effect Shoulder mounted bags.
Most positions: Inhale & exhale have a more balanced effort.

23. Resistive Work of Breathing.
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

24. Breathing Loop Absorbent canister for CO2 removal
Exhaled gas passes through this and is filtered for CO2
Efficiency and work of breathing is related to size / types of granules
Duration affected by temperature and gas density
Design also affects the efficiency
Copyright IANTD/IAND, Inc. 2000

25. Absorbent Canister Design
Gas exposed to sufficient surface area of absorbent to remove CO2
Gas flow rate across absorbent allows sufficient time (dwell time) for chemical removal of CO2
Simple & correct packing to prevent ‘channeling’ of absorbent
Prevents excess moisture from reaching absorbent
Copyright IANTD/IAND, Inc. 2000

26. Absorbent Canister Types
Axial
Cross Flow
Radial
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27. Gas flows through a block of absorbent in linear direction
Axial Canister
Gas flows through a block of absorbent in linear direction
Copyright IANTD/IAND, Inc. 2000

28. Gas flows through a block of absorbent with a direction change
Cross Flow Canister
Gas flows through a block of absorbent with a direction change
Cross Flow
Copyright IANTD/IAND, Inc. 2000

29. Absorbent Canister
Radial Flow System - gas enters center of ‘doughnut’ cross section & radiates outwards through the absorbent (or from the outside inwards).
Copyright IANTD/IAND, Inc. 2000

30. All Absorbents will produce a caustic effect if mixed with water.
Absorbent Types
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.
Copyright IANTD/IAND, Inc. 2000

31. Carbon Dioxide Absorption
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
Copyright IANTD/IAND, Inc. 2000

32. Carbon Dioxide Absorption
CO2 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
Copyright IANTD/IAND, Inc. 2000

33. CO2 Absorbent Duration Variables
Chemical composition
Canister volume
Temperature
Exertion level (CO2 generation)
Moisture level
Gas density/depth
Rebreather design
Copyright IANTD/IAND, Inc. 2000

34. CO2 Absorbent Testing The Sentinel was tested using:
mm (797 Grade) Sofnolime granules
Water temp 4ºC
Depth of 15m and 40m on air and 100m on Heliox
CO2 production rate of 1.6l/m
40l/m breathing rate
Copyright IANTD/IAND, Inc. 2000

35. Sentinel CO2 Absorbent Duration
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
Copyright IANTD/IAND, Inc. 2000

36. Hypercapnia
PCO2
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 CO2 limits and alarms on the Sentinel Expedition are at 5 milibar and 10 milibar

37. Sentinel Dive Procedures

38. Packing Sentinel CO2 Absorbent Canister
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
Copyright IANTD/IAND, Inc. 2000

39. Face Masks 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 CO2 build-up
Copyright IANTD/IAND, Inc. 2000

40. Breathing Characteristics
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
Copyright IANTD/IAND, Inc. 2000

41. Sentinel Pre-Dive Checks
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 Pre-dive will record and abort in the logbook.
Copyright IANTD/IAND, Inc. 2000

42. Sentinel Pre-Breathe Sequence
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
Copyright IANTD/IAND, Inc. 2000

43. Basic Dive Procedures Initial in-water verification
Descent - manual diluent addition
Buoyancy control
Monitoring PO2
Minimum loop volume
Monitoring gas supplies
Ascents
Copyright IANTD/IAND, Inc. 2000

44. Initial in-water verification at 6 m
Check for leaks
Verify oxygen injection is working
Verify ADV is operating
Adjust buoyancy
Copyright IANTD/IAND, Inc. 2000

45. Descents Counter lung collapses as ambient pressure increases
Compensation by Automatic Diluent Valve (ADV) gas addition or manual bypass
Rapid descents cause PO2 spikes
Select low PO2 Set-point for descent or AUTO mode
Switch to high PO2 Set-point at target depth or check AUTO switch has occurred.
Copyright IANTD/IAND, Inc. 2000

46. Buoyancy Control 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.
Copyright IANTD/IAND, Inc. 2000

47. Sentinel PO2 Monitoring
Hypoxia & Hyperoxia are real dangers in all rebreathers
Frequent cross checking of Primary and Backup displays
Constant PO2 Monitoring is Vital
Copyright IANTD/IAND, Inc. 2000

48. Minimum Loop Volume Loop volume just enough for one normal breath
Extra volume is wasted gas and added buoyancy
PO2 stays closer to Set-point
Test loop volume with ADV disabled.
Copyright IANTD/IAND, Inc. 2000

49. Monitoring Gas Supplies
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
O2 supply not diluent supply typically limits the dive duration
Copyright IANTD/IAND, Inc. 2000

50. Sentinel Ascents
Buoyancy changes due to expansion of the counter lung, BCD, and dry suit
PO2 should not be allowed to drop
The Sentinel will maintain close to the Set-point during a normal ascent due to its dynamic control algorithm
Oxygen can be manually added if necessary
Copyright IANTD/IAND, Inc. 2000

51. Failure Modes 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
Copyright IANTD/IAND, Inc. 2000

52. See the training video and skills list for skill detail
Sentinel CCR Skills
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.
Copyright IANTD/IAND, Inc. 2000

53. Sentinel CCR Skills 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 PO2 between deco stops.
Partial flood recovery drill.
Cell disabling and manual PO2 control.
Copyright IANTD/IAND, Inc. 2000

54. Sentinel CCR Skills 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.
Copyright IANTD/IAND, Inc. 2000

55. Rebreather Maintenance
Disinfecting & cleaning
CO2 seal
O-rings
Canister
Hoses
Counter lungs
BCD
Copyright IANTD/IAND, Inc. 2000

56. Testing
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.
Copyright IANTD/IAND, Inc. 2000

57. Disinfecting & Cleaning
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 O-rings/counterlungs/mushroom valves
O2 compatible lubricants only on HP parts silicone grease on all else
Copyright IANTD/IAND, Inc. 2000

58. Disinfecting & Cleaning
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
Copyright IANTD/IAND, Inc. 2000

59. After Every Days Diving
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.
Copyright IANTD/IAND, Inc. 2000

60. Post Dive & Storage 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
Copyright IANTD/IAND, Inc. 2000

61. O-Rings 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
O2 compatible lubricants only on HP parts
Factory sealed compartments - don’t tamper
Copyright IANTD/IAND, Inc. 2000

62. Hoses 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
Copyright IANTD/IAND, Inc. 2000

63. Counter lungs 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
Copyright IANTD/IAND, Inc. 2000

64. BCD Vital for buoyancy control & safety Visual inspections regularly
Fully inflate and check for leaks, pre-dive
Copyright IANTD/IAND, Inc. 2000

65. Always do all pre-dive checks Always Pre-breathe the unit
Summary
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 PO2
Practice your skills
Be Sensible, Be Safe
Copyright IANTD/IAND, Inc. 2000