News
Rebreather Pre-Dive Checks
The following is a discussion and review of the subject of Pre Dive checks when diving rebreathers – a much discussed, varied and often controversial matter!
When we first learn to dive, the concept of a buddy check, pre dive check or safety drill is installed in us as a means to make the dive safer by spotting potential problems before they can manifest and potentially evolve into accidents.
This is not a procedure limited to diving, it is extremely common in the Aviation, Aerospace and military communities, but to bring it closer to home it is present when we drive a car. When we drive a simple, mainly mechanical, car we are aware of the pre drive steps of checking the coolant level, the tyre pressures and the oil level and then adjusting the seat, wing and rear view mirrors to the individual driver. In a more modern, computer controlled car, many of these checks may be completed by the control system and communicated to the driver via dash board instrumentation and at the high end, even the seat and mirror settings can be altered to individual drivers with the push of a button. What is most common is a combination of automated computer generated checks and manual human checks; either way we are assured of the functionality of the vehicle before heading out on the road.
With rebreather technology the source of the pre dive check sequence and method could come from a variety of places. The manufacturer of the specific rebreather, a training agency that teach a specific rebreather, a generic training agency rebreather check list to suit all rebreathers and a learnt acronym to prompt the required checks.
Of course it would be best if available to use the specific rebreather check list or system supplied by the manufacturer.
Within the above there are different ways to complete checks:
- A written check list
- A check list acronym – e.g a common rebreather check list reminder is the acronym of F.L.A.G.S.
- Flow
- Loop
- Analyse
- Gauges
- Stack/Sensors
- Electronic check lists within the rebreathers display
- Electronic check lists that analyse data from the actual components of the rebreather.
What should be checked?
Pre-Assembly
Mushroom (One Way) Valves. The one way check valves within the Mouthpiece assembly that ensure the gas flows around the rebreather in a single correct direction should be tested to ensure they open with and close against FLOW.
The Oxygen, Diluent, Single supply gas and all bailout cylinders for the planned dive should be ANALYSED.
The absorbent canister (STACK) should be either re-packed or replaced. Or the used time of a previously used canister should be noted and the remaining time available compared to the dive plan.
Pre-Dive
There are as many pre dive check sequences as there are rebreathers, in fact many more! So for initial discussion of the steps of pre dive checks we will here use the acronym FLAGS as a starting point. Although not exhaustive if the printed check sheets or on screen check prompts of most of the currently available rebreathers are reviewed all steps within them can be classified under one of the following prompt words:
F – FLOW
Ambient pressure gas flow around the rebreather in a single correct direction. Tested with the Mushroom (One Way) valve check as part of Pre Assembly. This should be tested prior to each dive as stray granules of absorbent etc could compromise a Mushroom Valve.
High pressure and intermediate pressure gas flow around the rebreather. Slowly turn on the cylinder valves and then add Diluent and Oxygen manually, inflate and check dumps on BCD/wing, check that the ADV and BOV function and ensure the solenoid can inject oxygen where applicable to each specific type of rebreather.
L – LOOP
Conduct a negative loop test and a positive loop test where appropriate to each style of rebreather.
A negative test is conducted on a completely assembled rebreather by placing the mouthpiece in the rebreather or closed circuit position and breathing in through the mouth (To empty the loop) and out through the nose until the loop is empty and then closing the mouthpiece. A suitable period of time (A minimum of 1 minute) is allowed to pass and the rebreather should maintain that negative i.e. not leak air into to rebreather.
Indications of a good negative can include, crushed breathing hoses, ADV diaphragm remaining concave or in, a lower PO2 than ambient (e.g. Pre negative mouthpiece open PO2 0.21, during negative mouthpiece closed 0.19) and a strong ‘gasp’ or sucking sound when opening the mouthpiece at the end of the check.
A positive test is conducted on a completely assembled rebreather by placing the mouthpiece in the rebreather or closed circuit position and breathing in through the nose and out through the mouth until the loop is full and then closing the mouthpiece. A suitable period of time (A minimum of 1 minute) is allowed to pass and the rebreather should maintain that positive i.e. not leak air out of rebreather.
Indications of a good positive can include rigid inflated counter lungs.
A – ANALYSE
The Rebreather although containing Oxygen sensors must not be used to analyse the gases used within the rebreather.
All gases, Oxygen, Diluent and all bailouts should be analysed and labeled prior to being assembled into the rebreather or as bailouts with an Oxygen or where required an Oxygen/Helium analyser.
Many rebreathers are calibrated by flushing them completely or flushing a sensing chamber where the sensors sit with Oxygen at Ambient pressure, if this were completed with a gas supply other than specified (i.e. Oxygen) then the calibration would be inaccurate and therefore the PO2 incorrect during the dive.
G – GAUGES
Test the contents of all required cylinders, Oxygen, Diluent and all required bailout and check for leaks.
Turn on (Slowly) cylinder valves and note the reading of pressure.
Turn off cylinder valves and leave off for 1 minute.
Check contents pressure has not dropped (If the pressure has dropped there is an HP or IP leak to be located and resolved)
S – STACK / SENSORS
The rebreather should be tested for basic function by the Pre Breathe detailed below.
The purpose of this check is to watch the 3 sensor outputs for stabilisation, correct reading and change on prompt i.e. whist breathing add Oxygen and note a rise in PO2 and then add Diluent and note a drop in PO2 from set point.
If fitted during the Pre Breathe a Carbon Dioxide sensor can be monitored for a rising figure.
Again if fitted on the specific rebreather a thermal activity monitor ‘Temp Stick’ can be monitored to ascertain the exothermic reaction of the sofnolime absorbing Carbon Dioxide causing thermal sensors within the stack to register a rise in temperature.
Pre-Breathe
The fully assembled Pre Dive checked rebreather should be breathed for an adequate time to assure the user of systems functionality.
This is the period when the above Stack/Sensors tests are performed.
Current research would indicate that a part used, over used, poorly packed, incorrectly fitted or even absent stack may not give enough signs or symptoms of Hypercapnia during a 3-5 minute Pre Breathe to ensure a diver notices and considers the rebreather unfit for use.
Quick Pre Jump Confirmation
Many training agencies provide Pre Jump quick check prompt cards that can be attached to the Rebreather.
Steps on these include but are not limited to:
- Cylinder valves fully open on Oxygen, Diluent, Single supply gas and bailout?
- Electronics on and safe breathable PO2 displayed?
- BCD inflated?
- Mouthpiece in mouth and in rebreather position?
These Pre Jump checks are NOT considered a full Pre Dive check and are in no way meant to replace full Pre assembly, Pre Dive and Pre Dive checks. The Pre Jump is intended to be used in addition to normal checks as a last check just prior to water entry.
Find out more about Phil at www.philshorttechnical.co.uk.
Marine Life & Conservation
Shark Trust launches Oceanic 31 Shark Art Auction
After a two-year tour of UK art galleries, community spaces and aquariums, the Shark Trust’s acclaimed Oceanic31 exhibition takes its final bow at the Royal Geographical Society later this month. And the unique collection of artwork, depicting 31 species of oceanic sharks and rays, donated by 31 artists, is now open for bids from art lovers and shark enthusiasts. The online auction, launched today, will close on the 7th December at 8pm (BST). The money raised will support the Shark Trust Oceanics Programme.
People can now bid on 27 of the artworks by visiting this website:
https://superstars-auctions.com/sharktrustauction
It is a chance to own a beautiful piece of original art and to support the Shark Trust. The timing of the auction also means that these would make a very special Christmas gift for any shark-lover.
The diversity of pieces mirrors that of the sharks and rays they represent. You can bid on paintings, digital creations, sculptures, mixed media and more. You can pick your favourite artist or species of shark. Or you can select the perfect artwork to make a statement in your home or office. Whichever you choose, you will be supporting the work to protect these amazing animals.
One of the pieces of art has been selected to be auctioned live by Steve Backshall at the For the Love of Sharks event at the Royal Geographical Society in London on the 29th November. In addition to this, two further pieces will be raffled at this event, giving people a chance to win an incredible piece of shark art. For the Love of Sharks is the Shark Trust’s flagship evening. A night to celebrate sharks. Steve Backshall is the headline speaker at this event that will see other prominent shark advocates join him on stage.
Tickets for the event can be snapped up here:
https://thesharktrust.org.uk/Event/flos24
Those that would like to see the Oceanic 31 exhibition have one final chance. It is being displayed at the Pavilion at the Royal Geographic Society from 26th November until the 7th December. Entry is free.
Find out more here:
https://www.rgs.org/events/upcoming-events/oceanic-31
Paul Cox, Shark Trust CEO, Said “This exhibition has given us the opportunity to reach out to a new audience. And inspire more people with the wonderful sharks and rays on which our Big Shark Pledge campaign is based. We are immensely grateful to the 31 artists who have worked so hard to create these works.”
Bid for your favourite Oceanic 31 artwork here:
https://superstars-auctions.com/sharktrustauction
Banner Image: Smooth Hammerhead by Alicia Hayden
Gear News
Introducing the RS Series Drysuit from DYNAMICNORD
Cozy and warm in cold water.
It’s drysuit season all year round. With the new RS series premium drysuits from DYNAMICNORD, divers are perfectly equipped for all cold waters.
The sophisticated cut of the RS drysuits allows complete freedom of movement, providing maximum comfort. The high-quality 350 g/m² ripstop material with double ripstop zones on the elbows, knees, and crotch protect ensures extreme robustness as well as long life.
The suit’s features leave nothing to be desired: A high-quality TiZip zipper, easily adjustable inlet and outlet valves, upgradeable with electrically heated underwear, HP bottleneck cuffs made of high-strength latex on the wrists, a 3mm neoprene neck cuff for maximum comfort, a 7mm hood with air outlet and 3mm boots made of double-sided, cross-layered neoprene with ankle straps and fin strap stoppers and a protective but very flexible sole.
Noteworthy is the Molle fastening system, which can be used in a variable and compatible manner. This way, the two detachable leg pockets can be attached easily, safely and comfortably.
Alterations of boots to a different shoe size or adjustments to neck or wrist cuffs are done free of charge at the own DYNAMICNORD service centre in Germany in only a couple of days.
The matching Dynaskins made with high-quality Polartec® technology are available in various designs. As an undersuit under the drysuit, as a single suit in warm waters or as a two-piece suit. Polartec® technology’s main features are neutral buoyancy, breathablilty and quick-drying.
Dynaskins are made largely from recycled plastic bottles.
The drysuit RS-351 for men and RS-352 for women are now available at your DYNAMICNORD dealer and in the online store.
Colors men and women: Black-Blue and Black-Burgundy
Sizes men: XS-4XL incl. intermediate sizes MS, MT, MLS, MLT, LS, LT, XLS, XLT, 2XLS, 3XLS, 4XLS
Sizes Women: XS-XL incl. intermediate sizes MS, MT, LS, XLS
DYNAMICNORD – Your Outdoor Companion.
-
Blogs3 months ago
Gozo: An Underwater Treasure Trove in the Heart of the Mediterranean
-
News2 weeks ago
Iconic SS United States to become the World’s Largest Artificial Reef
-
Blogs2 months ago
NovoScuba’s Game-Changing Approach for Dive Store Owners: WE PAY YOU!
-
News1 month ago
Book Review – 52 Assignments: Underwater Photography
-
News3 months ago
Treasures, Shipwrecks and the Dawn of Red Sea Diving by Howard Rosenstein available now
-
Marine Life & Conservation2 months ago
Book Review: Sharkpedia
-
Gear News1 month ago
DYNAMICNORD – New German diving brand enters the British market
-
News4 weeks ago
Exploring Cenote El Pit: A Diver’s Dream