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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?

Poseidon course 1Now, 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.

rebreathers-inspiration-xpd-evp-evo-apdiving1There 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!

MKVI 2Rebreathers 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.

RebreatherAll 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.

RAID_Concepts_vFPaul is the Director of Training at RAID. To find out more about the courses that RAID offers, visit

After living in South Africa for 23 years, Paul moved to the UK, where he discovered diving. Within months of learning to dive he had his own centre in London and rapidly progressed to Course Director before finding his passion for technical diving. Paul is an avid wreck, cave and rebreather diver, and has worked as an Instructor and Instructor Trainer for PADI, IANTD, and TDI. Paul recently held the position of Director of Technical Training for SSI, but moved on when he was offered the chance to co-own and run his own training agency. Paul now holds the role of Director of Diver Training at RAID International.

Marine Life & Conservation

Go Fish Free this February



There are no longer plenty more fish in the sea! Fish Free February challenges you to help protect our oceans by removing seafood from your diet for 28 days and helping to raise awareness of the issues caused by intensive fishing practices.

Our oceans are in a state of global crisis, brought about by ocean warming, acidification, pollution, and habitat destruction. However, the biggest immediate threat to ocean life is from fisheries. Each year an estimated 1-2.7 trillion fish are caught for human consumption, though this figure does not include illegal fisheries, discarded fish, fish caught to be used as bait, or fish killed by not caught, so the real number is far higher. It is no wonder then, that today nearly 90% of the world’s marine stocks are fully exploited, overexploited or depleted. If we do not act fast, overfishing and damaging fishing practices will soon destroy the ocean ecosystems which produce 80% of the oxygen in our atmosphere and provide three billion people with their primary source of protein.

Fish Free February, a UK-registered charity, is challenging people around the world to take action for marine life in a simple but effective way. Take the Fish Free February Pledge and drop seafood from your diet for one month, or beyond. Fish Free February wants to get people talking about the wide range of issues associated with industrial fishing practices and putting the well-being of our oceans at the forefront of dietary decision-making. A third of all wild-caught fish are used to create feed for livestock, so Fish Free February urges us to opt for plant-based dishes as a sustainable alternative to seafood, sharing our best fish-free recipes on social media with #FishFreeFebruary and nominating our friends to do the same.

“Not all fishing practices are bad” explains Simon Hilbourne, founder of Fish Free February. “Well-managed, small-scale fisheries that use selective fishing gears can be sustainable. However, most of the seafood in our diet comes from industrial fisheries which often prioritise profit over the well-being of our planet, resulting in multiple environmental challenges. In some cases, the fishing industry has even been linked to serious human rights issues such as forced labour and human trafficking! Fish Free February hopes to shed more light on fishing practices, create wider discussion around these issues, and offer solutions to benefit people, wildlife, and the natural environment.”

To learn more about these issues and to take the Fish Free February pledge visit

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The Diver Medic introduces new DEMR course



The Diver Medic has developed a course suitable for every diver, or even surface support officer out there. The course will instil confidence and understanding of the subject your instructor may not have had the knowledge and skills to teach you unless they were DEMR trained themselves.

The Diver Medic DEMR Course – Diving Emergency Medical Responder Course is approved and written by Chantelle Newman – The Diver Medic Course Director and Founder.

The main objective is to ensure divers get the right treatment in the event of an accident or diving emergency, whether inland or in a remote location.

The Diver Medic is Agency neutral and their mission is to support all Agencies in the quest for better medical training and safety for all divers.

Is this course for you?

This qualification is for people who have a specific responsibility at work, or in voluntary and community activities to provide pre-hospital care to patients requiring emergency care/treatment.

For example, Liveaboard crew, Skippers, Captains, Dive Boat Crew, Dive Schools, Instructors, DiveMasters, Course Directors, CoastGuard, RNLI, Police Divers, Public Safety Divers, Tenders, Scientific Divers, Military Divers, Recreation, Technical, Cave, CCR Divers, Freediver, Surface support staff, Freediver competition crew, Lifeguards, ThemePark Divers, Aquarium staff, Explorers, Nurses, Doctors, EMS and more.!

Entry Requirements

Learners must be at least 18 years old on the first day of training. CPR and AED certified, basic understanding of First Aid Training


If you are interested in becoming a TDM Diving Emergency Medical Responder Instructor you can apply to The Diver Medic by emailing with your resume and an introductory letter explaining why you should be considered you as an Instructors.

For more information visit

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E-Newsletter Sign up!


This is the perfect start to your 2021 diving season… and at an incredible lead-in price of just £885 per person.

Jump on board the latest addition to the Emperor fleet and enjoy diving the famous sites of the Red Sea with this fantastic special offer. This itinerary takes in the wonderful South & St Johns from 26 February – 05 March 2021.  

Subject to availability – limited flight seats at this price so don't delay!

Call Diverse Travel on 01473 852002 or email to book your spot!

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