Rebreather - Wikipedia, the free encyclopedia. Rebreather. Acronym. CCUBA (closed circuit underwater breathing apparatus); CCR (closed circuit rebreather), SCR (semi- closed rebreather)Uses. Breathing set. Related items. Davis apparatus. A rebreather is a breathing apparatus that absorbs the carbon dioxide of a user's exhaled breath to permit the rebreathing (recycling) of the substantially unused oxygen content of each breath. Oxygen is added to replenish the amount metabolised by the user. This differs from an open- circuit breathing apparatus, where the exhaled gas is discharged directly into the environment.
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- Compulsory Specification for Breathing apparatus. 1.1 This specification covers the following types ofbreathing apparatus for personal respiratory protection: a).
Rebreather technology may be used where breathing gas supply is limited, such as underwater or in space, where the environment is toxic or hypoxic, as in firefighting, mine rescue and high- altitude operations, or where the breathing gas is specially enriched or contains expensive components, such as helium diluent or anaesthetic gases. Rebreather technology is used in many environments: Underwater - as a self- contained breathing apparatus, where it is sometimes known as .
High altitude reduces the partial pressure of oxygen in the ambient air, which reduces the ability of the climber to function effectively. Mountaineering rebreathers provide a higher partial pressure of oxygen to the climber. Submarines, underwater habitats, and saturation diving systems use a scrubber system working on the same principles as a rebreather. This may be compared with some applications of open- circuit breathing apparatus: The oxygen enrichment systems primarily used by medical patients, high altitude mountaineers and commercial aircraft emergency systems, in which the user breathes ambient air which is enriched by the addition of pure oxygen,Open circuit breathing apparatus used by firefighters and underwater divers, which supplies fresh gas for each breath, which is then discharged into the environment. Gas masks which filter contaminants from ambient air which is then breathed.
The recycling of breathing gas comes at the cost of mass, bulk, technological complexity and specific hazards, which depend on the specific application and type of rebreather used. General concept. Base metabolism requires about 0. L/min of oxygen from a breathing rate of about 6 L/min, and a fit person working hard may ventilate at a rate of 9.
L/min but will only metabolise about 4 L/min of oxygen . Exhaled air at sea level still contains roughly 1. The situation is even more wasteful of oxygen when the oxygen fraction of the breathing gas is higher, and in underwater diving, the compression of breathing gas due to depth makes the recirculation of exhaled gas even more desirable, as an even larger proportion of open circuit gas is wasted.
Continued rebreathing of the same gas will deplete the oxygen to a level which will no longer support consciousness, and eventually life, so gas containing oxygen must be added to the breathing gas to maintain the required concentration of oxygen. However, if this is done without removing the carbon dioxide, it will rapidly build up in the recycled gas, resulting almost immediately in mild respiratory distress, and rapidly developing into further stages of hypercapnia, or carbon dioxide toxicity. A high ventilation rate is usually necessary to eliminate the metabolic product carbon dioxide (CO2). The breathing reflex is triggered by CO2 concentration in the blood, not by the oxygen concentration, therefore even a small buildup of CO2 in the inhaled gas quickly becomes intolerable; if a person tries to directly rebreathe their exhaled breathing gas, they will soon feel an acute sense of suffocation, therefore rebreathers must chemically remove the CO2 in a component known as a carbon dioxide scrubber. By adding sufficient oxygen to compensate for the metabolic usage, removing the carbon dioxide, and rebreathing the gas, most of the volume is conserved.
To re- oxygenate the air inside it, he likely generated oxygen by heating saltpetre (potassium nitrate) in a metal pan to emit oxygen. Heating turns the saltpetre into potassium oxide or hydroxide, which absorbs carbon dioxide from the air. That may explain why Drebbel's men were not affected by carbon dioxide build- up as much as would be expected. If so, he accidentally made a crude rebreather more than two centuries before Saint Simon Sicard's patent. This early rebreather design worked with an oxygen reservoir, the oxygen being delivered progressively by the diver and circulating in a closed circuit through a sponge soaked in limewater.
Sir Robert Davis, head of Siebe Gorman, perfected the oxygen rebreather in 1. While intended primarily as an emergency escape apparatus for submarine crews, it was soon also used for diving, being a handy shallow water diving apparatus with a thirty- minute endurance. The cylinder was equipped with a control valve and was connected to the breathing bag.
Opening the cylinder's valve admitted oxygen to the bag and charged it to the pressure of the surrounding water. The rig also included an emergency buoyancy bag on the front of to help keep the wearer afloat. The DSEA was adopted by the Royal Navy after further development by Davis in 1. It was a form of sodium peroxide (Na.
O2) or sodium superoxide (Na. O2). As it absorbs carbon dioxide in a rebreather's scrubber it emits oxygen. This compound was first incorporated into a rebreather design by Captain S. S. Rees of the Royal Navy in 1. Although intended for use as a submarine escape apparatus, it was never accepted by the Royal Navy and was instead used for shallow water diving. The apparatus had been invented some years earlier by Hermann Stelzner for mine rescues.
This practice soon came to the attention of the Italian Navy, which developed its frogman unit Decima Flottiglia MAS and was used effectively in World War II. The earliest of these breathing sets may have been modified Davis Submerged Escape Apparatus; their fullface masks were the type intended for the Siebe Gorman Salvus, but in later operations different designs were used, leading to a fullface mask with one big face window, at first oval and later rectangular (mostly flat, but the sides curved back to allow better vision sideways). Early British frogman's rebreathers had rectangular counterlungs on the chest like Italian frogman's rebreathers, but later designs had a square recess in the top of the counterlung so it could extend further up toward the shoulders. In front they had a rubber collar that was clamped around the absorbent canister. Rebreathers for the US Navy were developed by Dr.
Lambertsen for underwater warfare. In Britain rebreather use for civilians was negligible . The Italian firms Pirelli and Cressi- Sub at first each sold a model of sport diving rebreather, but after a while discontinued those models. Some home made rebreathers were used by cave divers to penetrate cave sumps. With the end of the Cold War and the subsequent collapse of the Communist Bloc, the perceived risk of attack by combat divers dwindled.
Western armed forces had less reason to requisition civilian rebreather patents, and automatic and semi- automatic recreational diving rebreathers started to appear. System variants. Oxygen rebreathers can be remarkably simple designs, and they were invented before open- circuit scuba. They only supply oxygen, so there is no requirement to control the gas mixture other than removing the carbon dioxide. One is constant flow; the other is a manual on- off valve called a bypass valve; both feed into the same hose which feeds the counterlung.
This will add gas at any time that the counterlung is emptied and the diver continues to inhale. Oxygen can also be added manually by a button which activates the demand valve. Military and recreational divers use these because they provide better underwater duration than open circuit, have a deeper maximum operating depth than oxygen rebreathers and can be fairly simple and cheap. They do not rely on electronics for control of gas composition, but may use electronic monitoring for improved safety and more efficient decompression.
Semi- closed circuit equipment generally supplies one breathing gas such as air, nitrox or trimix at a time. The gas is injected into the loop at a constant rate to replenish oxygen consumed from the loop by the diver. Excess gas must be constantly vented from the loop in small volumes to make space for fresh, oxygen- rich gas. As the oxygen in the vented gas cannot be separated from the inert gas, semi- closed circuit is wasteful of oxygen.
A portion of the respired gas is discharged that is in some way proportional to usage. Generally it is a fixed volumetric fraction of the respiratory flow, but more complex systems have been developed which exhaust a close approximation of a ratio to the surface respiratory flow rate. These are described as depth compensated or partially depth compensated systems. Gas addition is triggered by low counterlung volume. The simple case of a fixed ratio discharge can be achieved by concentric bellows counterlungs, where the exhaled gas expands both the counterlungs, and while the larger volume outer bellows discharges back to the loop when the diver inhales the next breath, the inner bellows discharges its contents to the surroundings, using non return valves to ensure a one- directional flow. The amount processed during each breath depends on the tidal volume of that breath.
Towards the end of inhalation the bellows bottoms out and activates an addition valve, in much the way that a regulator diaphragm activates the demand valve, to make up the gas discharged by the inner bellows. This type of rebreather therefore tends to operate at a minimal volume. The fixed ratio systems usually discharge between 1. As a result, gas endurance is from 1. Oxygen fraction in the loop depends on the discharge ratio, and to a lesser extent on the breathing rate and work rate of the diver.