Scott Scuba Services CCR Diving

What is Closed-Circuit Rebreather Diving and Why Should You Learn?

For the divers who are looking to push the boundaries further, to linger longer and explore deeper, there’s an advanced technique waiting for you: closed-circuit rebreather (CCR) diving. It’s not just a step up in your diving journey; it’s a leap into a whole new realm of underwater exploration. Book CCR courses with expert instructor Scott.

What is Closed-Circuit Rebreather Diving?

When we talk about closed-circuit rebreather diving, we’re discussing a sophisticated approach to scuba diving that allows divers to maximise their time underwater. Unlike traditional open-circuit scuba, where you breathe in from your tank and exhale bubbles into the water, CCR systems recycle the air you exhale.

And here’s the kicker: because the system recycles gas, it conserves your oxygen supply dramatically. This means CCR divers can enjoy significantly longer dive times compared to traditional open-circuit dives. Longer dives? More time to explore the underwater marvels!

How do CCR systems work?

The components of a CCR system are fascinating. You’ve got your oxygen cylinders, of course, but the real stars are the CO2 scrubbers and the complex electronics that monitor and adjust the gas mix. These systems ensure that you’re always breathing the right mix for your depth and exertion level.

The magic of a CCR system lies in its ability to recycle the exhaled breath. Here’s a closer look at how it works:

  1. Breathing Loop: When you exhale in a CCR system, the gas is directed into a closed loop. This loop begins with a ‘counterlung’, which acts as a reservoir for the exhaled breath.
  2. CO2 Scrubbing: The exhaled gas contains carbon dioxide, which is harmful if rebreathed. It passes through a CO2 scrubber, typically filled with a substance like soda lime, which absorbs the carbon dioxide, effectively ‘scrubbing’ the gas clean.
  3. Oxygen Monitoring and Addition: The cleaned gas, now low in oxygen, circulates back towards the diver. Along the way, sophisticated electronics continuously monitor the oxygen levels. Based on these readings, the system automatically adds oxygen from a small cylinder to maintain an optimal breathing mix.
  4. Optimal Gas Mixtures: The objective is to maintain a partial pressure of oxygen (PPO2) that is safe and efficient for the depth and duration of the dive. Typically, the PPO2 in a rebreather system is maintained between 0.7 and 1.4 bar, depending on the diver’s depth and the specific dive plan. This precise control over the gas mixture allows for safer, longer, and deeper dives.
  5. Diluent Gas: In addition to oxygen, a CCR system also includes a ‘diluent’ gas – usually air or a helium-based mixture like trimix. This gas is used to maintain the appropriate pressure in the loop and is particularly crucial during deeper dives.

By recycling the exhaled gas and optimising the oxygen level, a CCR system dramatically reduces gas consumption.

How do the CO2 scrubbers in CCR work?

The CO2 scrubber is a critical component in a closed-circuit rebreather (CCR) system, and it plays a vital role in ensuring the safety and efficiency of the dive. Let’s delve into how it works and the maintenance it requires:

How CO2 Scrubbers Work

  1. Absorbing Carbon Dioxide: The primary function of a CO2 scrubber is to remove carbon dioxide (CO2) from the exhaled breath of the diver. When a diver exhales into the rebreather system, the exhaled gas contains a high concentration of CO2. If this CO2 is not removed, it would rapidly accumulate to dangerous levels, posing a serious risk to the diver.
  2. Soda Lime Canisters: The scrubber typically consists of a canister filled with a substance like soda lime. Soda lime is a granular chemical compound that has a high affinity for CO2. When the exhaled gas passes through the soda lime, a chemical reaction occurs, wherein the CO2 is absorbed and neutralized.
  3. Chemical Reaction: The reaction in the soda lime is essentially a process of converting CO2 and water (which is also a component of exhaled breath) into calcium carbonate, a harmless compound. This reaction generates heat, which can sometimes be noticeable as a slight warmth in the breathing loop.

Maintenance and Replenishment

  1. Regular Replacement: The soda lime in the CO2 scrubber doesn’t last indefinitely. Over time, its ability to absorb CO2 diminishes. Therefore, it’s crucial to replace the soda lime regularly to ensure the rebreather functions safely and effectively. The frequency of replacement depends on factors like the type of soda lime used, the duration and depth of dives, and the breathing rate of the diver.
  2. Indicators of Exhaustion: Some soda lime products include an indicator dye that changes colour when the material is exhausted and can no longer effectively absorb CO2. However, not all soda lime has this feature, so divers should not solely rely on this as an indicator. Instead, following manufacturer guidelines and best practices for replacement intervals is essential.
  3. Risks of Overused Soda Lime: Using soda lime beyond its effective lifespan can lead to a dangerous condition known as “breakthrough,” where CO2 is no longer being adequately absorbed. This can result in the diver breathing harmful levels of CO2, leading to symptoms like headaches, dizziness, or in severe cases, loss of consciousness.

What is a Counterlung in CCR diving?

The counterlung acts as a flexible reservoir for the breathing gas in the rebreather system. It compensates for the volume changes that occur during the breathing cycle. Essentially, it mimics the function of the lungs, expanding and contracting as the diver breathes in and out.

Typically, counterlungs are positioned either on the diver’s chest (front-mounted) or back (back-mounted), or sometimes at both locations. The positioning can affect the diver’s buoyancy and trim in the water.

How Does the Counterlung Work?

  1. Breathing In: When the diver inhales, the counterlung contracts as the volume of gas inside it decreases. This contraction creates a slight negative pressure in the system, which opens a valve allowing the diver to inhale the gas from the breathing loop.
  2. Breathing Out: Conversely, when the diver exhales, the counterlung expands. This expansion accommodates the volume of gas exhaled by the diver. The CO2 in this exhaled gas is then processed by the CO2 scrubber before the gas is recirculated.
  3. Volume and Pressure Regulation: The counterlung is critical in maintaining a constant volume and pressure within the rebreather loop. This is important for maintaining proper buoyancy and ensuring the efficient function of the CO2 scrubber.
  4. Buoyancy Control: Since the counterlung changes volume with the diver’s breath, it also impacts buoyancy. Divers need to be skilled in managing their buoyancy with subtle breath control, which can be more nuanced in CCR diving compared to open-circuit diving.
  5. Safety Considerations: The counterlung must be carefully monitored and maintained as part of the rebreather system. Overexpansion (due to ascending or incorrect gas management) or underexpansion (due to descending or breathing issues) can lead to potential problems, including buoyancy control issues or damage to the system.

In summary, the counterlung in a CCR system serves as a flexible gas reservoir that compensates for the volume changes during the breathing cycle. Its role in maintaining the volume and pressure of the breathing loop and aiding in buoyancy control is vital for the safe and effective operation of a rebreather. Understanding and managing the counterlung’s function is a key skill in CCR diving.

The Benefits of CCR Diving

One of the most appealing aspects of CCR diving is the extended bottom time it offers. With the efficient use of gas, CCR divers often enjoy longer dives and reduced decompression requirements, making those elusive deep wrecks and reefs more accessible.

But it’s not just about spending more time underwater. CCR diving has a gentler footprint on the marine environment. The lack of exhaled bubbles means less noise and disturbance, allowing divers to get closer to marine life – it’s like being a fly on the wall in an underwater ballet!

Also, with specialised training and equipment, CCR diving opens up opportunities to dive deeper than ever before. For those with a thirst for exploration, this means accessing dive sites that are out of reach for traditional scuba divers.

Training and Safety Considerations

Diving with a CCR isn’t something to take lightly. It requires comprehensive training and a solid understanding of the system. Getting certified in CCR diving involves learning a host of new skills – from mastering buoyancy in a completely different setup to managing potential emergencies with a calm and knowledgeable approach.

Maintenance plays a huge role too. A well-maintained rebreather is a reliable rebreather. This means regular checks and care of all components, especially the CO2 scrubbers and oxygen sensors.

Safety in CCR diving is paramount. The risks are real, but they can be effectively managed with proper training and respect for the equipment and procedures. It’s a blend of technology, knowledge, and skill that makes CCR diving a rewarding challenge for those willing to undertake it.

Book a CCR training course today with Scott who runs courses across the East of England and is one of the most experienced instructors on the platform. He also runs CCR Try Dives if you are unsure whether to commit to a full course.

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Co-founder and Chief Adventurer

I am Max, the co-founder and CEO of adventuro. We are on a mission to help you get into the sports you have always wanted to try, or develop in the sports you love, exploring new skills and locations. We do this by partnering with the best instructors, guides, and activity centres to get a great spread from beginner all the way to instructor training.

For too long, it has been way to confusing to find your next steps, or even to know where to start when getting into adventure sports. I am an experienced and/or qualified paraglider, skydiver, scuba diver, freediver, power boat driver, snowboarder, kitesurfer, kayaker, mountain biker, surfer, dirt biker, wakeboarder, and sailor.

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