Abstract
Closed circuit rebreathers will revolutionize the underwater diving industry. Individuals will enjoy extended underwater experiences and be more comfortable while diving. Instead of hearing bubbles, individuals will enjoy the natural sounds of hundreds of fish and turtles that surround them. Being engulfed with clouds of fish, they will forget that they are actually diving. Safety features built into the rebreather eliminates the risk of nitrogen narcosis when operated within recreational limits. This frees individuals to enjoy the diving experience, which was unheard of before the invention of the rebreather. By controlling and maintaining the partial pressure of the gasses, one breathes at depth, thus restricting the nitrogen loaded into his or her system. After the dive, the circulatory system is cleaner than when the diver entered the water. The air all humans breathe contains 21% oxygen, 79% nitrogen, and slight trace gases. Circulatory systems maintain these averages. However, when using a rebreather, it changes these parameters to 45% oxygen and 55% nitrogen at a prescribed depth. Imagine the consequences; divers will no longer have a "NO-FLY" restriction after diving, so the long- anticipated diving vacation can be enjoyed right up to the time the flight leaves. The only thing that stands between them and experiencing the Closed Circuit Rebreather diving vacation is training.

Closed Circuit Rebreather Closed circuit rebreathers will revolutionize the dive industry. Individuals will experience a longer, more comfortable diving experience, with safety features that can eliminate nitrogen narcosis when diving within recreational limits. Before the invention of the rebreather, all divers experienced nitrogen narcosis in some form. The latest evolution to be introduced into the Self Contained Underwater Breathing Apparatus (SCUBA) diving market is the "Rebreather." A rebreather is a mechanical device that is designed with electronic components to monitor, clean, or recondition exhaled gas so it can be reused for a finite number of times, hence the name rebreather. So in essence, one would be breathing his or her own recycled air. These devices are now termed as closed circuit rebreather (CCR), and divers who use this equipment are called CCR divers. When diving CCR, as the name infers with closed circuits, there are no bubbles. However, open circuit (OC) is the terminology dive professionals use when referring to open circuit diving. As a diver breathes, his or her breath is exhaled into the open ocean. An example of this process can be seen at the Newport Aquarium in northern Kentucky. On a scheduled basis, divers will be tasked to clean the walls of the exhibit. The diver, in most cases, will be using open circuit SCUBA diving equipment, meaning the bubbles that an onlooker sees are from the diver exhaling his or her breath into the water. The potential energy that remained in the exhalation is now lost and cannot be reused, thus limiting the air supply. Rebreathers are classified into two categories: semi-closed circuit rebreather (SCR) and closed circuit rebreather. The difference between the two is in the design. In the closed circuit rebreather, all the divers exhausted gases remain trapped within a loop. In the semi-closed rebreather system, there is no scrubber in place to clean the carbon dioxide (CO²) from his or her exhalation, and therefore, it vents a portion of gas routinely. Gases are continuously replaced with a breathing gas specific for that depth. Generally, all rebreathers are similar in that they serve the same purpose. They recycle either all or some portion of divers' exhaled gases, increasing the efficiency and the time they can remain at depth. However, before a diver can rebreather this gas, it must go through a chemical scrubber to remove the carbon dioxide, while simultaneously adding a small portion of inert gas in order to replace the amount of oxygen that was consumed. This comes with some inherent risks. The diver must remain within a safe oxygen partial pressure (PPO²) limits at all times. Furthermore, the rebreather must provide the diver with a reasonable breathing volume. This means there must be ample volume of gas within the breathing loop so the diver may breathe comfortably and not be short of breath. In open circuit diving, the volume of gas will change as the individual changes his or her depth within the water column. This is because of the external water pressure on the divers body, which reduces the volume of gas within his or her lungs. As a diver exhales, the volume of gas within his or her lungs decreases then causes buoyancy to decrease. The diver will then begin to sink within the water column. However, breathing in increases the gas volume, thus increasing the buoyancy, and the diver will rise. Buoyancy becomes a very important issue for all divers. Without buoyancy, the diver risks damaging the delicate underwater reefs structure. To maintain neutral buoyancy, the diver must add a small amount of gas to the buoyancy control device (BCD) to remain steady in the water column. On the other hand, in closed circuit diving, once neutral buoyancy is established, the volume of gas will only change for a few reasons. For instance, when one exhales into the open ocean and not into the closed loop, it will drastically reduce the volume of gas in the divers' counter-lungs, thus decreasing the divers' buoyancy, and limiting the available breathing gas in the loop. Additionally, if a diver damages the external counter-lung and loses breathing gas, this will change the buoyancy of the unit and effectively turn the highly technical and expensive rebreather into an open circuit SCUBA unit, creating a very serious emergency condition. The CCR diver must end the mission immediately, employ all the safety procedures, decompression stops, and take any additional steps required which were learned in training, to safely surface without endangering him or herself and the dive team. However, when an individual establishes neutral buoyancy with his or her BCD and breathes within the closed loop, the divers buoyancy will remain constant. Divers can breathe normally without rising or falling in the water column. This becomes one of the biggest changes an open circuit diver has to overcome. The experienced OC diver is accustomed to simply inhaling deeply to rise above the obstruction in one's path and continue with the dive. The closed circuit diver has to change his or her buoyancy by adding gas to the BCD to rise above the same object or simply swim around it. These procedures are accomplished manually with the rebreather. Neutral buoyancy is one of the key elements to safe diving. Bozanic (2002) said a possible "unexplained buoyancy loss may be due to two failures, either the buoyancy compensator (BC) or the breathing loop (or both!) losing their integrity" (p. 271). This is one possibility that could happen with either semi-closed or closed circuit rebreathers. However, the primary advantage that rebreathers provide is the recirculation of breathing gases. Bozanic (2010) states that "Gas efficiency is generally cited as the primary advantage to using SCR or CCR apparatus. Along with gas efficiency comes reduced or eliminated bubble noise, as the bubbles are either reduced (with SCR) or eliminated (with CCR)" (p. 7). A remarkable experience for many new rebreather divers is that they find themselves surrounded with marine life, as the fish are not scared off by any noise from the exhaust gases. This is because it remains within the loop. The noise is the occasional firing of the solenoid adding a minuscule amount of oxygen to the breathing loop. Many divers have exclaimed that CCR diving has become a whole new experience that opened a window into an underwater world only briefly touched by open circuit diving. It is important to remember that not all rebreathers are manufactured equally. Different companies offer unique components that have advantages over their competitors. It depends on what type of diving will be done. There are two distinct types of rebreather diving. The first is recreational diving, and it is all inclusive. The second is technical diving, which is limited only to a select few individuals who are well equipped, experienced, and determined divers. It depends on what the diver expects to get out of his or her chosen course of study. It is an endless process that requires years of in depth-study of the physiological demands that are inherently present with technical closed circuit rebreather diving. However, if one has an interest in purchasing a rebreather, there are as many choices to consider as there are colors of the rainbow. Some manufactures boast that their units are smaller, lighter weight, and more manageable, which can be an advantage. If one's intention is to travel the world and dive the Red Sea, the size and weight of a rebreather may be of concern. Conversely, the technical diver may require the ability to remain at depth up to six hours at a time. This may require a larger and less maneuverable unit with two, six-liter cylinders and a vastly larger scrubber to meet mission requirements. There are manufacture styles, cylinder size, mixed gas units, No Decompression Limit (NDL), software considerations, and, of course, price points will enter into the decision making process. Most units start between eight thousand and ten thousand dollars. Some reach as high as twenty thousand dollars for the unit and may or may not include the training for the specific type of rebreather. The current cost of training is substantial, because no manufactures will sell a unit without proper training, documentation, and certification. Training is type specific for each piece of equipment either for recreational or technical diving limits. The advanced level certifications that specific demands to be considered. One must determine whether or not the rebreather purchased has the capability of performing at depths for technical diving. For example, one may ask if a unit can operate at depths between three to five feet. World War II wrecks in Thailand can be found at these depths. This type of dive would require advanced closed circuit rebreather technical diving instructions and dive planning. Mount, Sawatzky, & Hess (2005) learn dive planning: Dive planning is the process by which divers determine and clarify the objectives of a proposed dive, rehearse the specifics of the dive plan, and review their proposed actions in order to eliminate or minimize the associated risk. To accomplish these goals, four important processes must occur: information gathering, group planning, personal planning, and contingency planning for personal and environmental unknowns (p. 5). Another critical course that requires certification is the CCR Trimix. This is important because oxygen becomes poisonous at depths greater than 220 feet.
Clark (2009) stated: As the deeper the resulting pressure of each gas increase's leading to physiological consequences on the diver. As the oxygen pressure increases the diver will ultimately reach a point where they experience CNS toxicity or a seizure. As the nitrogen pressure increases the diver will start to lose the ability to reason, sometimes leading to inability to recognize or deal with reason, eventually leading to inability to recognize or deal with emergency situations. Unfortunately, we cannot remove oxygen or nitrogen without adding something back to make a whole mixture. We want to reduce the oxygen, so we can go deeper without experiencing a seizure. We also want to reduce the nitrogen, so we can be safer, and continues on to say, Due to the physiological properties of helium we can take out some oxygen and nitrogen from our breathing mixture and add in helium. Now a diver can go deeper within our desired PO² limits and PN² limits [sic] (p. 6). Primarily, these problems occur with the Central Nervous System (CNS) oxygen toxicity when partial pressure of oxygen excess 1.6 ATA. Recreational divers never approach these limits, which makes it unbelievably safe for the recreational diver. After exploring one's depths of desire and taking into consideration training to safely dive this equipment, training can range in upwards of ten thousand dollars, which may or may not include travel and accommodations. One can now see that this is a very intense and demanding training scenario. Individuals must be dedicated to his or her studies before considering this hobby because of all the dangers involved. No matter how safe the dive industry portrays the sport, there is always the occasional person who will challenge even the most basic of skills and create a situation that will put his or her abilities to the test. Brylske (2011) believes: Learning how to use open-circuit SCUBA is generic. Although some of the features may differ, all recreational SCUBA systems operate, more or less, the same way. So, the skills are easily transferable, and any open water SCUBA diver course offered by any SCUBA training organization will give him or her required skills to dive with any standard open circuit system. Not so with rebreathers. Aside from fundamental features like SCR versus CCR design, each unit has many unique aspects. Given the complexity of learning all the design of a particular system, training must be, likewise, customized to specific models. While there are common elements for all closed circuit training programs, each course involves learning a particular unit; and additional training is required before using a different system (p. 41). Initial Rebreather Training with Bozanic (2010) states that: Many recreational SCUBA diving agencies offer rebreather training. Rebreather training in the recreational sector began with the technical diving agencies, and later was offered by the larger, more generic open water training agencies. As rebreathers become more common, it is expected that additional organizations will develop and offer training. While not all courses are structured identically, there are basic similarities. Some agencies offer a single rebreather course, while others offer several types of rebreather training. There are certification courses that train divers on either SCR or a CCR system. In addition, rebreather training may be further divided into multiple levels for introductory and advanced use (pp. 9, 10). Now several agencies permit beginner divers to start dive training using rebreathers rather than using the more traditional open circuit. There are no prerequisites that require an individual to be certified first as an open circuit diver. Agencies that require no experience will cover additional skills and information in future courses and these courses may take additional time to complete. Bear in mind that rebreathers are all different and each requires a distinct type certification. The cost of training can be overwhelming with the number of various units and manufactures. This can range well upwards of six thousand dollars per class type. Do the research and ask questions from diving professionals who are certified in one of the many different types of semi-closed and closed circuit rebreathers. Let them help assist through all the nuances and then limit the number to just a couple. Pick the one that will serve in the most diverse diving environments. Remember, sport diving, like many other sports, can be very expensive. At some point there will be something new on the market that will be a must have item. Always investigate all new products. Making the best decision will save the hard earned dollars in the long term. The education process for technical, deep, rebreather diving can take months to complete and years of intense diving before an individual poses enough diving skills to be considered as advanced as a top rated instructor. One small mistake in a chain-of-events can lead to another, which leads to yet another, and this can endanger the life of the diver and, most assuredly, the instructor's life as well. Instructors are very cautious with students and take responsibility very seriously. This type of diving is on the cutting edge of technology. Only the most committed divers even consider this type of diving because there is very little data to support new theories. Data has been gathered daily from people that enjoy the sport and take the time to share one's diving data with the experts. They do this in the hopes of making a difference that will ensure a safer sport for recreational divers around the world. As rebreathers become less expensive, and more commonly accepted, they will replace the open circuit equipment. Because, when diving within recreational limits, the diver will no longer be loading nitrogen into his or her systems, eliminating nitrogen narcosis, more commonly known as the "Bends." Today divers are required to remain at sea-level for a 24 hour surface interval before flying home from a fabulous dive resort. This time is needed to off-gas the nitrogen that has built-up in divers' systems. However, when on closed circuit, and within recreational limits, the diver does not build up nitrogen in his or her system because of the constant PPO² he or she maintains in the rebreather. So, in essence, a CCR diver can dive in the morning, get straight out of the water, and take a flight home within the same hour, safely. A diver will no longer have to endure a “NO-FLY” restriction after diving. While the rebreather diver can enjoy diving right up to the time of his or her flight, the OC diver has to observe the mandatory surface interval. The main barrier that stands between open circuit and closed circuit is the initial cost of training. This discussion focused on two types of divers, OC and CCR. In the future, training will only include closed circuit. This will eliminate several hours of classroom instruction. In-water instruction will be slightly longer, with additional safety drills and procedures. Closed circuit rebreathers will revolutionize the dive industry. Individuals will experience a longer, more comfortable dive with safety features that can eliminate nitrogen narcosis while diving within recreational dive limits. This has never been heard of before the invention of the rebreather. As the prices of technology come down with time, more people will enjoy the experience of closed circuit rebreather diving.

References
Bozanic, J. (2002). Understanding rebreathers. Flagstaff, AZ: Best Publishing Company.
Bozanic, J. (2010). Mastering rebreathers. (2nd ed.). Flagstaff, AZ: Best Publishing Company.
Brylske, A. (2011, February). The ultimate recyclers. Dive Training, p. 35.
Clark, D. M. (2009). Ccr trimix simplified. Everett, WA: Silent, LLC.
Mount, T., Sawatzky, D., & Hess, J. (2005). Tek closed circuit rebreather: ccr technical diving - normoxic trimix - cave - wreck. Miami Shores, FL: IANTD, Inc.