CCR Diver CourseCCR Diver CourseSentinelSentinel

Workbook Slides By:

Kevin Gurr & Phil Short

Sentinel Rebreather Layout

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

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.

System Layout

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.

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

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

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

Sentinel Oxygen Cells

•Oxygen sensor with moisture tolerant membrane

•Removable with no special tools

•Moisture tolerant

•Robust connection system

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.

SentinelPower On Screen

SentinelInterpreting 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

SentinelControlling 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

Sentinel Primary Dive Screens

Sentinel Rebreather HUD

Light Status

Meaning

Solid Green

At Set-point

Slow Flash Green

Below Set-point

Fast Flash Green

Above Set-point

PO2 Mode

No flash-No DecoSlow Flash – Deco ceiling above

Fast Flash – Violated ceiling/fast ascentSolid Green

All good

Flashing Red/BuzzerDangerous Alarm Condition

Prepare to Bailout!Monitor Displays

Flashing Green/BlueMonitor Displays

LED Mode

CCR Design and Functionality

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

The Counter lungs

• 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

Hydrostatic Effect

• Chest mounted bag - diver horizontal– inhale less effort

– exhale more effort

Hydrostatic Effect

• Back mounted bag - diver horizontal– inhale more effort

– exhale less effort

Hydrostatic Effect

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

balanced effort.

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

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

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

Absorbent Canister Types

AxialCross Flow

Radial

Axial Canister

Gas flows through a block of absorbent in linear direction

Cross Flow Canister

Cross Flow

Gas flows through a block of absorbent with a direction change

Absorbent Canister

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

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®

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

• 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

Carbon Dioxide Absorption

CO2 Absorbent Duration Variables

• Chemical composition

• Canister volume

• Temperature

• Exertion level (CO2 generation)

• Moisture level

• Gas density/depth

• Rebreather design

CO2 Absorbent Testing

• 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

– CO2 production rate of 1.6l/m

– 40l/m breathing rate

SentinelCO2 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

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

Sentinel Dive Procedures

Packing SentinelCO2 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

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

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

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.

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

Basic Dive Procedures

• Initial in-water verification• Descent - manual diluent addition• Buoyancy control

• Monitoring PO2

• Minimum loop volume• Monitoring gas supplies• Ascents

Initial in-water verification at 6 m

• Check for leaks

• Verify oxygen injection is working

• Verify ADV is operating

• Adjust buoyancy

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.

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.

Constant PO2 Monitoring

is Vital

SentinelPO2 Monitoring

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

displays

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.

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

SentinelAscents

• 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

In an emergency - it is the poorly learned survival skills which are lost first

Failure ModesEmergency Scenarios

– Hypoxia

– Hyperoxia

– Hypercapnia

– Solenoid/injection system failures

– Complete electronics failure

– Open circuit bailouts

Sentinel CCR Skills

• 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 detailSee the training video and skills list for skill detail

Sentinel CCR SkillsSee the training video and skills list for skill detailSee 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.

Sentinel CCR SkillsSee the training video and skills list for skill detailSee 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.

Rebreather Maintenance

• Disinfecting & cleaning– CO2 seal– O-rings– Canister– Hoses– Counter lungs– BCD

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.

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

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

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.

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

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

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

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

BCD

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

dive

Always do all pre-dive checksAlways Pre-breathe the unit

Always know your PO2

Practice your skillsBe Sensible, Be Safe

Summary

• Advantages of CCR greatly outweigh the disadvantages

• Correct training is obligatory