All rebreathers have specific complexities which introduce forms of risk not experienced by open circuit divers. The fundamental difference between open-circuit scuba and rebreather systems is that while utilizing scuba, the diver mixes a specific gas for a maximum depth. When CCR is used, the gas is constantly changing.Gas in the ccr loop is a “dynamic” one, constantly changing. The oxygen fraction may drift out of life-sustaining range within the course of a single dive. it is possible that the diver may breathe-up all of the oxygen in the breathing loop before the oxygen addition valve is triggered, thus leaving only nitrogen.
Problems can be largely avoided if the gas supply rate of
rebreathers is adjusted carefully and the breathing loop is flushed
with fresh gas prior to an ascent. In closed circuit models multiple redundant oxygen sensors and oxygen control systems are incorporated for additional safety. Unfortunately, symptoms associated with hypoxia and oxygen toxicity cannot be regarded as a reliable precursors to black-out. Therefore it is ultimately up to the diver to take steps to ensure a continuous life-sustaining gas mixture in the breathing loop at all times. This level of discipline requires a great deal of discipline and training. Thus rebreather divers must have a higher dedication to equipment maintenance and operation than is generally required for open-circuit divers. Furthermore, rebreathers are generally more complex devices than open-circuit scuba gear, which also accounts for why they require more training time.Another disadvantage of rebreathers is monetary expense. Even low-end rebreather designs can cost several thousand dollars, and sophisticated closed-circuit rebreathers range between $7,200. and $15,000 or more. After the initial purchase price, however, operational expenses are not significantly greater than they are for conventional scuba and do use substantially less gas. This can amount to significant savings when using helium mixes.Training for semi closed ranges from 400. to 600. Closed circuit courses range from 1000. to 1500. plus consumables.Consumables are those items that are used short term such as; batteries to operate the microprocessors and O2 inject solenoid, scrubber material to remove carbon dioxide, oxygen, air and helium.
Sensors should be considered an annual maintenance requirement, their cost is about 80. each which amounts to 240. for most CCR’s.
see CCR MaintenanceType, Model and ManufacturerWhen comparing rebreathers; ALL rebreathers have advantages and disadvantages. And a “try dive” is not often going to make you aware of the minor shortcomings of a particular model. This is why it is important to discuss with your instructor what type of diving you are presently doing, as well as your near term goals (say 3 – 5 years out)