Should You Switch? Pros and Cons of Closed-Circuit Rebreathers

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Closed-circuit rebreathers (CCRs) have revolutionized technical diving over the past two decades. Once the exclusive domain of military and elite deep divers, CCRs are now a mainstream option for technical divers seeking longer bottom times and better gas efficiency. But as with any tool in technical diving, CCRs are not without their trade-offs.

If you are considering making the switch to a rebreather, it is critical to understand both the advantages and the challenges before investing your time, money, and training into this technology. In this article, we will take a deep dive into the pros and cons of closed-circuit rebreathers - helping you decide whether this advanced equipment is the right choice for your diving goals.

What Are Closed-Circuit Rebreathers?

At their core, closed-circuit rebreathers are breathing systems that recycle exhaled gas. Instead of venting carbon dioxide-rich exhaust into the water, a CCR "scrubs" CO₂ from your exhalation using a chemical absorbent and adds oxygen back into the loop to maintain a breathable gas mix. This closed-loop design means almost no bubbles and remarkable gas efficiency, especially on deep or long dives.

In contrast, open-circuit technical diving simply dumps your exhaled gas into the water, wasting expensive helium mixes and limiting dive time. For technical dives involving significant decompression, overhead environments, or long penetrations, the efficiency of CCRs becomes a huge advantage.

The Advantages of Closed-Circuit Rebreathers

1.     Improved Gas Efficiency

One of the most obvious benefits of CCRs is their efficiency. Because the system recycles exhaled gas and only adds oxygen to match metabolic needs, gas consumption is no longer dictated by depth.

The human body consumes the same amount of oxygen per minute at the surface as it does at any depth, provided work rate remains constant. The only way to increase oxygen usage is to up the workload. 

As we only replace the metabolized oxygen in the range of 0.5 to 3L of oxygen per minute, a 3L cylinder could last between 20 and 3 hours. On deep dives that use expensive helium trimix, this efficiency can make otherwise cost-prohibitive dives more affordable and longer.

For example, a diver at 90 meters on open circuit might burn through several large cylinders of trimix during a single dive. A CCR diver on the same profile might use only a fraction of a small cylinder. This is why closed-circuit rebreathers are often the preferred choice for expedition-class exploration dives. 

2.     Extended Bottom Times

On open circuit, your dive time is usually limited by gas supply. On CCR, your bottom time is much more likely to be limited by decompression obligations, thermal endurance, or mission constraints. 

This is particularly valuable for wreck exploration, scientific documentation, or mapping projects, where time at depth is essential. CCRs allow you to stay longer, collect more data, and reduce the logistical burden of carrying multiple open-circuit stage cylinders.

See how CCRs unlock legendary wrecks: Diving the HMHS Britannic 

3.     Optimized Decompression

CCRs allow you to maintain a nearly constant partial pressure of oxygen (PPO₂) throughout the dive. This means you can keep a higher average PPO₂ than is practical with open circuit, optimizing your on-gassing and off-gassing, and potentially reducing decompression times.

On long technical dives, this benefit can save precious minutes (or even hours) of decompression while staying within safe oxygen exposure limits. It also provides flexibility in managing deco obligations in the event of an emergency or unexpected profile changes.

4.     Minimal Bubble Signature

For underwater photographers, videographers, or anyone working in delicate marine environments, CCRs' bubble-free operation is a major advantage. Marine life often reacts less to CCR divers, allowing closer approaches and better observational opportunities.

This "quiet" operation also benefits military, scientific, and conservation work, where bubbles can disturb sensitive ecosystems or alert observers.

Curious where these advantages come into play? Explore SSI's Top 12 Must-Visit Dive Destinations for Tec Divers

The Challenges of Closed-Circuit Rebreathers

While the benefits are compelling, CCRs come with significant challenges - and they are not for every technical diver.

1.     Higher Complexity and Workload

CCRs are mechanically and electronically more complex than open-circuit scuba. Divers must constantly monitor their PPO₂, scrubber time, bailout options, and other life-support parameters throughout the dive.

This added mental workload is not trivial and demands a higher level of training, discipline, and situational awareness. Unlike open circuit, a lapse in attention or poor pre-dive checks can quickly escalate into a life-threatening emergency.

2.     Greater Risk of Equipment Failure

CCRs introduce potential failure points not found in open circuit: oxygen sensors, electronics, solenoids, CO₂ scrubbers, and oxygen delivery mechanisms. Many CCR incidents can be traced to mechanical or human error - highlighting the importance of regular maintenance, thorough pre-dive preparation, keeping skill levels high, and careful redundancy planning.

An undetected hypoxic, hyperoxic, or hypercapnic event can lead to unconsciousness underwater. However, with proper training, disciplined procedures, and routine upkeep, these risks can be effectively managed, making CCR diving a safe and reliable choice for well-prepared divers.

3.     Cost

CCRs are expensive - often several times the cost of an open-circuit technical rig. Beyond the initial purchase price, there are ongoing costs: replacement sensors, scrubber material, battery packs, oxygen and diluent fills, and periodic servicing.

This cost barrier is one reason many divers choose to continue on open circuit even at advanced levels. What you save in Helium can offset some of the cost, but CCR diving properly is never cheap.

4.     Learning Curve and Training Requirements

Becoming a competent CCR diver requires a significant investment in training and practice. Even experienced technical divers often report feeling "like a beginner again" when first transitioning to CCR.

In addition to the basic CCR certification, many divers will also complete specialized training for Deep Trimix, cave diving, or technical wreck diving on CCR.

Ready to go deeper? Explore SSI's Best Ultra-Deep Technical Dive Sites.

5.     Bailout Planning

Like all technical dives on CCR, you also cannot simply surface if something goes wrong. Bailout planning is a critical part of every CCR dive and often involves carrying multiple open-circuit bailout cylinders, adding to the complexity and weight of the dive.

Is CCR Right for You?

Closed-circuit rebreathers are not a magic bullet - they are a highly specialized tool. If your diving goals include deep exploration, long bottom times, minimal bubble disturbance, and greater efficiency at depth, CCR might be the right choice.

CCR demands a higher level of commitment, rigorous training, and constant awareness. Many technical divers successfully dive for decades without switching to CCR and still achieve remarkable exploration and personal goals.

If you are considering CCR, start by talking to an SSI Extended Range Instructor or dive center. Many offer CCR Try Dives or orientation programs that let you experience the gear and skills in a controlled environment before committing to a full certification course.

Your Path to CCR Diving

SSI offers a full progression of Extended Range programs, including training on closed-circuit rebreathers for technical diving. Whether you are exploring deeper wrecks, intricate caves, or long decompression profiles, SSI's CCR courses teach you the theory, skills, and mindset required for safe and effective closed-circuit diving.

Start with Extended Range Foundations to build solid technical skills on open circuit. Then progress to CCR-specific training:

• CCR Diving - learn to dive a closed-circuit rebreather within recreational depth limits.
• CCR Extended Range Trimix - expand your capabilities for deeper, longer technical dives now with decompression.
• CCR Technical Extended Range - master advanced skills for demanding environments, including multiple bailouts and greater depths up to 60m.
• CCR Hypoxic Trimix - reach the pinnacle of rebreather technical diver training, exploring depths up to 100 meters using hypoxic gas mixes.

With each step, you gain greater confidence and access to more challenging and rewarding dives.

Ready to Get Started?

Find your nearest SSI Extended Range Training Center and take the first step toward mastering closed-circuit rebreathers today.