News
Rebreather 101 with Paul Toomer
How many of you have heard of Jacques Cousteau? All of you, right?
If you don’t know who he is, you need to be on the ‘Horse and Hounds’ or ‘Amateur Rambling in the Cotswolds’ website rather than Scubaverse. He invented SCUBA didn’t he? Didn’t he also write a book called the silent world?
Now, we all know he didn’t invent SCUBA; that was actually some geezer whose name we can’t remember and Mr C just stole all the glory, right?
Wrong! Well… partially wrong. Mr C stole the open circuit glory but not SCUBA. SCUBA is self contained underwater breathing apparatus and it was invented a long, long time ago. And it was a Closed Circuit Rebreather (CCR). That is why his world was SILENT. Open circuit is hardly bloody silent. If you don’t believe me, take a try dive on a rebreather and listen for when the hordes of wildebeest come charging past you blowing those confounded bubbles.
What is a Rebreather?
A rebreather is a closed breathing circuit (loop) enabling gas to be recycled, therefore giving the user an extended use of the limited gas that he/she carries. There are two primary problems that have to be overcome to make the rebreather work though. The first is the fact that we metabolise oxygen, and if we breathe too low an amount of oxygen it can cause unconsciousness, which could of course lead to an ultimately death. A by-product of oxygen metabolism is the creation of carbon dioxide, and this insidious gas can also lead to unfortunate circumstances, especially underwater (as I’m sure you can imagine).
The loop and how it works
When a diver exhales, his breath is forced through a non-return valve which forces the exhaled air through a carbon dioxide removal system known as a scrubber (I love that word). The scrubber is made up of a chemical called Sofnalime, which is primarily calcium hydroxide. The exhaled breath is scrubbed clean of carbon dioxide and the breath is now pushed through an area where oxygen analysers analyse how much oxygen is left in that cleaned breath. The analysers talk to a computer (the unit holds a constant PO2 or oxygen partial pressure) which then tells a solenoid to open and add oxygen to the loop if required. This can also be done manually of course in the event of any problems.
There are also counterlungs on the unit, which allow the diver to breathe gas around the loop. Without the counterlung the diver would be unable to breathe. It’s similar to trying to breath out of a glass bottle; it’s impossible. However, breathing out of a plastic bag is possible, although very unsafe. As the diver descends in the water hydrostatic pressure acts on the counterlung and compresses the gas within it. To enable the diver to breathe, diluent gas (a gas containing one or more inert gasses, normally air or trimix) is manually or automatically added to the loop.
Finally, due to the fact that the CCR holds a constant PO2, compared to open circuit where it’s optimum PO2 is only achieved at the Maximum Operating Depth, rebreathers will penalise the diver less in terms of decompression obligation. Another huge plus.
Gas, Gas, Gas!
Rebreathers work on metabolic rate and not surface air consumption rate. This means that if a diver uses 20 litres of air a minute but only metabolises 1 litre of oxygen, the rebreather is massively more effective at conserving gas. An example of this based on the above gas usage rates would be: An open circuit diver is at 30 metres on the Thistlegorm, for example, and is there for 30 minutes. He uses 20 litres/min x4 ata (30 metres) x30 minutes = 2400 litres of gas, or a full 12 litre cylinder pumped to 200 bar. If a CCR diver was at the same depth and for the same time he would use only 30 litres of oxygen. Therefore, if the CCR diver had a 2 litre cylinder filled to 200 bar, he would have 400 litres available. Based on a 1 litre metabolic rate that diver could stay on the Thistlegorm for 400 minutes or 6.66 hours.
6.66 hours compared to 30 minutes? A gigantic difference I am sure you’ll agree. This is the primary reason that deep technical divers prefer CCR. It’s all in the gas.
Aquatic Life
I took a CCR to the Maldives on a liveaboard a few years ago. I never went past 40 metres for the two weeks I was there and apart from the fact that I never had any decompression schedule, I was swamped by the aquatic life. I was chased by barracuda, nibbled by moray eels, had a 2 metre stingray push me down the reef as if I was not there. Mantas thought I was some kind of weird yellow box fish and finally, the sharks…..oh my God, it was unbelievable! I had white tips on a night dive try and beat me up, chewing my fins and rubbing themselves on me as they went passed, banging into me to see what I was….just incredible. It was one of the best dives of my entire life. This dive alone was enough reason to spend all that money on my unit.
Here is a little history for you:
- 17th century – the first rebreather was conceived by Giovanni Borelli
- 1878 – the first practical system produced by Henry Fleuss, who after diving his fully working unit swore he would never dive in the damnable thing ever again. He absolutely shit himself while doing some work in a flooded tunnel.
- 1881 – the first CO2 absorbent used by Khotinsky and Lake
- Prior to WWI – Dräger started produced rebreather systems. Mainly used for blowing the crap out of poor old Allies.
- WWII – Italian & British Navies used Oxygen & Nitrox systems. The Italian units were mainly used for long swims away from enemy lines back to Italy. The British units were primarily used for blowing the crap out of the Axis countries.
- 1990s – manufacturers launch many units including: Sentinel, Inspiration, Evolution, Megaladon, Ouroboros, Kiss, Optima, rEvo, Poseidon Mk 6, etc.
All that is left to do now is pick your unit, get some top end training and go and play. I assure you this is the future.
Next time we will look at some of the CCRs available, their features, recreational and technical CCR, and of course training options.
Please note that this article covers the basics of CCR. I really hope it gives you a little understanding of rebreathers, as I believe they are the way we will all dive in the future.
Paul is the Director of Training at RAID. To find out more about the courses that RAID offers, visit www.diveraid.com.
News
Spooktacular Underwater Adventure: Oyster Diving’s First Halloween Scuba Party at Mercers Lake
Last Thursday, Oyster Diving transformed Mercers Lake into a hauntingly unforgettable underwater realm for their inaugural Halloween Scuba Party. Approximately 20 intrepid divers plunged into the darkness, weaving through a mesmerising scene of spectral decorations, glow sticks, and eerie underwater pumpkins.
After the thrilling night dive, participants gathered to feast on a ghoulish spread of pumpkin soup, chilli con carne, and decadent fudge brownies, perfect fuel for the frightful festivities.
With a resounding success, Oyster Diving is excited to announce plans for this event to become an annual tradition. Next year, look forward to a fully licensed bar and live music, promising an even spookier celebration under the moonlit waters.
Join us next Halloween for an experience that promises to be a haunting delight!
Find out more about Oyster Diving at oysterdiving.com.
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
-
Blogs3 months ago
Gozo: An Underwater Treasure Trove in the Heart of the Mediterranean
-
News3 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
-
Marine Life & Conservation3 months ago
Book Review: Sharkpedia
-
Gear News1 month ago
DYNAMICNORD – New German diving brand enters the British market
-
News1 month ago
Exploring Cenote El Pit: A Diver’s Dream
-
Blogs3 months ago
Freediver Christian Redl Sets His 13th World Record at Lake Neufeld