What is Closed Circuit Scuba?
Closed circuit scuba, commonly referred to as rebreather technology, represents a significant advancement in underwater breathing apparatuses. Unlike traditional open circuit scuba systems, which release exhaled gases into the water, closed circuit rebreathers recycle the diver’s exhaled breath. This recycling process involves scrubbing carbon dioxide from the exhaled air and adding the necessary amount of oxygen to make the gas breathable again. Closed circuit systems are renowned for their efficiency in gas usage, allowing divers to stay underwater for extended periods. These systems are particularly favored in scientific research, military operations, and technical diving, where extended bottom times and reduced gas consumption are crucial.
Historical Development
The concept of rebreathing dates back to the early 17th century when inventors began experimenting with closed environments to recycle exhaled air. One of the earliest prototypes was created by John Baptiste Denys in the 1620s, which aimed to provide a constant oxygen supply while removing carbon dioxide. However, these early attempts were rudimentary and lacked practical application for underwater use.
Significant progress occurred in the 19th century with the invention of more sophisticated rebreathing apparatuses. Henry Fleuss, an English engineer, is credited with creating the first practical closed circuit rebreather in 1878. His device was initially intended for underwater construction work and later adapted for diving. Fleuss’s invention featured a rubber mask, breathing bag, and a soda lime canister to absorb carbon dioxide, laying the groundwork for modern rebreathers.
The 20th century saw substantial advancements in closed circuit scuba technology, particularly during and after World War II. The demand for stealthy and efficient underwater breathing systems for military operations accelerated rebreather development. Notable contributions came from Drägerwerk AG, a German company, and the U.S. Navy, both of which developed rebreathers for combat divers. These innovations significantly enhanced the safety and functionality of rebreathers, leading to their broader adoption in various diving disciplines.
Technical Overview
Closed circuit rebreathers operate on a sophisticated principle of gas management and recycling. At the heart of a rebreather system is the breathing loop, which comprises several key components. The diver inhales through a mouthpiece connected to a series of hoses and counter-lungs that hold the exhaled gas. The gas then passes through a scrubber canister filled with a chemical absorbent, typically soda lime, which removes carbon dioxide from the exhaled breath.
Once the carbon dioxide is scrubbed, the cleaned gas mixture is recirculated back to the diver. To maintain the appropriate oxygen level, the rebreather system adds a controlled amount of oxygen from an onboard cylinder. This process can be managed electronically or manually. Electronic closed circuit rebreathers (eCCRs) use sensors and a computer to automatically adjust the oxygen level, while manual closed circuit rebreathers (mCCRs) require the diver to manually inject oxygen based on the readings from the oxygen sensors.
One of the critical distinctions between open circuit and closed circuit systems is the management of the gas mixture. In open circuit scuba, exhaled gas, which contains unused oxygen, is expelled into the water. This leads to a significant waste of oxygen, especially at deeper depths where gas consumption increases. Closed circuit rebreathers, on the other hand, conserve oxygen by recycling the exhaled gas, making them much more efficient and suitable for longer underwater durations.
Types of Closed Circuit Rebreathers
Closed circuit rebreathers can be classified into three main types based on their technological design: electronic CCRs (eCCRs), manual CCRs (mCCRs), and hybrid systems. Each type has its unique features and applications.
Electronic closed circuit rebreathers (eCCRs) are the most advanced and popular type. They utilize a series of oxygen sensors and a microprocessor to monitor and maintain the optimal oxygen level within the breathing loop automatically. This automation allows divers to focus more on their underwater tasks rather than constantly managing their gas mixture. Popular eCCR models include the AP Diving Inspiration and the Hollis Prism 2, known for their reliability and user-friendly interfaces.
Manual closed circuit rebreathers (mCCRs), in contrast, rely on the diver’s manual intervention to maintain the correct gas mixture. Divers must periodically inject oxygen into the breathing loop based on readings from the oxygen sensors. While mCCRs require more attention and skill to operate, they are valued for their simplicity and reduced risk of electronic failure. The KISS Classic and the Pathfinder mCCR are notable examples of manual rebreathers.
Hybrid systems combine elements of both electronic and manual rebreathers, offering a balance between automation and manual control. These systems allow divers to switch between automatic and manual modes as needed, providing greater flexibility and redundancy. An example of a hybrid system is the rEvo rebreather, which offers both manual and electronic modes for enhanced safety and performance.
Advantages of Closed Circuit Scuba
One of the primary advantages of closed circuit scuba systems is their efficient use of breathing gas, which allows for significantly longer underwater durations compared to open circuit systems. By recycling exhaled gas and only adding the necessary amount of oxygen, rebreathers can extend dive times dramatically. This efficiency is particularly beneficial for technical and scientific divers who need to conduct prolonged underwater tasks without frequent resurfacing.
Another significant benefit of closed circuit rebreathers is the reduced risk of decompression sickness, commonly known as “the bends.” The precise control of the breathing gas mixture and the ability to maintain a constant partial pressure of oxygen (PPO2) help minimize the formation of nitrogen bubbles in the diver’s tissues. This advantage is crucial for deep and repetitive dives, where decompression management is critical.
Closed circuit rebreathers also offer a quieter and more discreet underwater experience. The absence of bubbles, which are a hallmark of open circuit systems, makes rebreathers ideal for wildlife observation and underwater photography. The silent operation reduces the disturbance to marine life, allowing divers to approach and observe creatures more closely without startling them.
Challenges and Limitations
Despite their numerous advantages, closed circuit rebreathers come with challenges and limitations. One of the primary challenges is the complexity of their operation and the need for rigorous training. Divers must be thoroughly trained in the use of rebreathers, including understanding the intricacies of gas management, emergency procedures, and routine maintenance. This level of complexity can be a barrier for recreational divers who may find open circuit systems more straightforward and user-friendly.
Maintenance and reliability concerns are also significant factors to consider with rebreathers. The systems require meticulous care and regular servicing to ensure they function correctly. Components such as oxygen sensors, scrubber material, and O-rings must be routinely checked and replaced to prevent malfunctions. Any failure in the rebreather system can be life-threatening, so diligent maintenance is paramount.
Instances of rebreather failures have been documented, underscoring the importance of proper training and maintenance. Common issues include sensor malfunctions, scrubber breakthrough (when the scrubber material is exhausted and no longer absorbs carbon dioxide effectively), and electronic failures in eCCRs. Divers must be adept at recognizing these problems and executing emergency protocols to mitigate risks.
Safety and Training Requirements
Given the complexity and potential risks associated with closed circuit rebreathers, specialized training and certification are mandatory for divers. Training programs are designed to equip divers with the knowledge and skills necessary to operate rebreathers safely. These programs cover various aspects, including the theory of gas management, equipment assembly and disassembly, emergency procedures, and in-water practice.
Key safety protocols for rebreather diving include thorough pre-dive checks to ensure all components are functioning correctly, continuous monitoring of oxygen levels and scrubber duration, and practicing emergency drills regularly. Divers must also be familiar with bailout procedures, where they switch to an open circuit system in case of a rebreather malfunction.
Regular maintenance of the rebreather unit is crucial for ensuring diver safety. This involves routine inspections, sensor calibrations, and replacing consumables like scrubber material. Manufacturers typically provide detailed maintenance schedules and guidelines, and adherence to these recommendations is essential for preventing equipment failure.
Key Takeaways
Closed circuit scuba technology has revolutionized underwater exploration, offering unparalleled efficiency and extended dive times. Despite its complexity and the need for rigorous training and maintenance, the benefits of reduced gas consumption, decreased decompression risks, and minimal environmental disturbance make closed circuit rebreathers a valuable tool for technical, scientific, and military divers. As technology continues to evolve, future advancements may further enhance the safety and performance of these sophisticated systems.
