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63-495: The air handling function of a PLSS is similar to that of a diving rebreather , in that exhaled gases are recycled into the breathing gas in a closed loop. When used in a microgravity environment, a separate propulsion system is generally needed for safety and control, since there is no physical connection to a spacecraft. The portable life support system used in the Apollo lunar landing missions used lithium hydroxide to remove

126-459: A 279 watt-hour battery. For the extended missions of Apollo 15 through 17, the EVA stay time was doubled to 8 hours by increasing oxygen to 1,430 pounds per square inch (9.9 MPa), lithium hydroxide to 3.12 pounds (1.42 kg), cooling water to 11.5 pounds (5.2 liters), and battery capacity to 390 watt-hours. An emergency backup was provided in case the main system failed, by a separate unit called

189-550: A fire hazard, so the more successful applications have been for space-suits, fire-fighting and mine rescue. A liquid oxygen supply can be used for oxygen or mixed gas rebreathers. If used underwater, the liquid-oxygen container must be well insulated against heat transfer from the water. Industrial sets of this type may not be suitable for diving, and diving sets of this type may not be suitable for use out of water due to conflicting heat transfer requirements. The set's liquid oxygen tank must be filled immediately before use. Examples of

252-417: A large range of options are available depending on the specific application and available budget. A diving rebreather is safety-critical life-support equipment – some modes of failure can kill the diver without warning, others can require immediate appropriate response for survival. A helium reclaim system (or push-pull system) is used to recover helium based breathing gas after use by the diver when this

315-404: A loop configured machine has two unidirectional valves so that only scrubbed gas flows to the patient while expired gas goes back to the machine. The anaesthetic machine can also provide gas to ventilated patients who cannot breathe on their own. A waste gas scavenging system removes any gasses from the operating room to avoid environmental contamination. One of the functions of a space suit

378-474: A lower pressure in the suit which gives the wearer better freedom of movement. Submarines , underwater habitats , bomb shelters, space stations , and other living spaces occupied by several people over medium to long periods on a limited gas supply, are equivalent to closed circuit rebreathers in principle, but generally rely on mechanical circulation of breathing gas through the scrubbers. Flow measurement Too Many Requests If you report this error to

441-405: A maximum of about 30 minutes of emergency oxygen for breathing and cooling. This could be extended to 75 to 90 minutes with a "buddy system" hose that used the other astronaut's functional PLSS for cooling (only). This allowed the vent valve to be partly closed to decrease the oxygen flow rate. The PLSS was 26 inches (66 cm) high, 18 inches (46 cm) wide, and 10 inches (25 cm) deep. It

504-550: A naturally hypoxic environment. They need to be lightweight and to be reliable in severe cold including not getting choked with deposited frost. A high rate of system failures due to extreme cold has not been solved. Breathing pure oxygen results in an elevated partial pressure of oxygen in the blood: a climber breathing pure oxygen at the summit of Mount Everest has a greater oxygen partial pressure than breathing air at sea level. This results in being able to exert greater physical effort at altitude. The exothermic reaction helps keep

567-435: A number of hoses and electrical cables twisted together and deployed as a unit. This is extended to the divers through the diver umbilicals. The accommodation life support system maintains the chamber environment within the acceptable range for health and comfort of the occupants. Temperature, humidity, breathing gas quality, sanitation systems, and equipment function are monitored and controlled. An atmospheric diving suit

630-454: A pendulum rebreather. Breathing hoses can be tethered down to a diver's shoulders or ballasted for neutral buoyancy to minimise loads on the mouthpiece. A mouthpiece with bite-grip , an oro-nasal mask , a full-face mask , or a sealed helmet is provided so that the user can breathe from the unit hands-free. A store of oxygen, usually as compressed gas in a high pressure cylinder, but sometimes as liquid oxygen , that feeds gaseous oxygen into

693-468: A rotary separator. The removed water is stored and used to supplement the water supply used in the LCVG. The sublimator also cools the remaining oxygen to about 55 °F (13 °C). A flow sensor monitors the flow rate. Extra oxygen is added to the flow from a storage tank as necessary, downstream of the flow sensor. The oxygen is then returned to the suit at the back of the head, where it flows down over

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756-425: A wide enough bore to minimise flow resistance at the ambient pressure in the operational range for the equipment, are usually circular in cross section, and may be corrugated to let the user's head move about without the tube collapsing at kinks. Each end has an airtight connection to the adjacent component, and they may contain a one-way valve to keep the gas circulating the right way in a loop system. Depending on

819-435: Is a small one-man articulated submersible of roughly anthropomorphic form, with limb joints which allow articulation under external pressure while maintaining an internal pressure of one atmosphere. Breathing gas supply may be surface supplied by umbilical, or from a rebreather carried on the suit. An emergency gas supply rebreather may also be fitted to a suit with either surface supply or rebreather for primary breathing gas. As

882-502: Is added to replenish the amount metabolised by the user. This differs from open-circuit breathing apparatus, where the exhaled gas is discharged directly into the environment. The purpose is to extend the breathing endurance of a limited gas supply, while also eliminating the bubbles otherwise produced by an open circuit system. The latter advantage over other systems is useful for covert military operations by frogmen , as well as for undisturbed observation of underwater wildlife. A rebreather

945-402: Is calcium hydroxide, which is relatively cheap and easily available. Other components may be present in the absorbent. Sodium hydroxide is added to accelerate the reaction with carbon dioxide. Other chemicals may be added to prevent unwanted decomposition products when used with standard halogenated inhalation anaesthetics. An indicator may be included to show when carbon dioxide has dissolved in

1008-413: Is generally understood to be a portable apparatus carried by the user. The same technology on a vehicle or non-mobile installation is more likely to be referred to as a life-support system . Rebreather technology may be used where breathing gas supply is limited, such as underwater, in space, where the environment is toxic or hypoxic (as in firefighting), mine rescue, high-altitude operations, or where

1071-420: Is important, such as in space stations and space suits. Lithium peroxide also replenishes the oxygen during the scrubbing reaction. Another method of carbon dioxide removal occasionally used in portable rebreathers is to freeze it out, which is possible in a cryogenic rebreather which uses liquid oxygen. The liquid oxygen absorbs heat from the carbon dioxide in a heat exchanger to convert the oxygen to gas, which

1134-613: Is less of a problem. The Soviet IDA71 rebreather was also manufactured in a high altitude version, which was operated as an oxygen rebreather. Anaesthetic machines can be configured as rebreathers to provide oxygen and anaesthetic gases to a patient during surgery or other procedures that require sedation. An absorbent is present in the machine to remove the carbon dioxide from the loop. Both semi-closed and fully closed circuit systems may be used for anaesthetic machines, and both push-pull (pendulum) two directional flow and one directional loop systems are used. The breathing circuit of

1197-427: Is more economical than losing it to the environment in open circuit systems. The recovered gas is passed through a scrubber system to remove carbon dioxide, filtered to remove odours, and pressurised into storage containers, where it may be mixed with oxygen to the required composition for re-use, either immediately, or at a later date. The life support system provides breathing gas and other services to support life for

1260-399: Is sufficient to freeze the carbon dioxide. This process also chills the gas, which is sometimes, but not always, desirable. A breathing hose or sometimes breathing tube on a rebreather is a flexible tube for breathing gas to pass through at ambient pressure. They are distinguished from the low-, intermediate-, and high-pressure hoses which may also be parts of rebreather apparatus. They have

1323-427: Is the earliest type of rebreather and was commonly used by navies for submarine escape and shallow water diving work, for mine rescue, high altitude mountaineering and flight, and in industrial applications from the early twentieth century. Oxygen rebreathers can be remarkably simple and mechanically reliable, and they were invented before open-circuit scuba. They only supply oxygen, so there is no requirement to control

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1386-522: Is then available again to react with more carbonic acid. 100 grams (3.5 oz) of this absorbent can remove about 15 to 25 litres (0.53 to 0.88 cu ft) of carbon dioxide at standard atmospheric pressure. This process also heats and humidifies the air, which is desirable for diving in cold water, or climbing at high altitudes, but not for working in hot environments. Other reactions may be used in special circumstances. Lithium hydroxide and particularly lithium peroxide may be used where low mass

1449-427: Is to provide the wearer with breathing gas. This can be done via an umbilical from the life-support systems of the spacecraft or habitat, or from a primary life support system carried on the suit. Both of these systems involve rebreather technology as they both remove carbon dioxide from the breathing gas and add oxygen to compensate for oxygen used by the wearer. Space suits usually use oxygen rebreathers as this allows

1512-421: Is usually necessary to eliminate the metabolic product carbon dioxide (CO 2 ). The breathing reflex is triggered by CO 2 concentration in the blood, not by the oxygen concentration, so even a small buildup of CO 2 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 , so rebreathers must remove

1575-542: 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

1638-419: The decompression status of the diver and record the dive profile . As a person breathes, the body consumes oxygen and produces carbon dioxide . Base metabolism requires about 0.25 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 95 L/min but will only metabolise about 4 L/min of oxygen. The oxygen metabolised is generally about 4% to 5% of

1701-447: The CO 2 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. The endurance of a rebreather, the duration for which it can be safely and comfortably used, is dependent on the oxygen supply at the oxygen consumption rate of the user, and

1764-755: The Earth weight of 3.1 kg) on the Moon). Similar systems have been used by Space Shuttle astronauts, and are currently used by International Space Station crews. The primary life support system for the EMU suit used on the Space Shuttle and International Space Station is manufactured by Hamilton Sundstrand . It is mounted to the back of the Hard Upper Torso (HUT) assembly. Oxygen (O 2 ), carbon dioxide (CO 2 ) and water vapor are drawn from

1827-574: The Oxygen Purge System (OPS), mounted on top of the PLSS, immediately behind the astronaut's helmet. The OPS maintained suit pressure and removed carbon dioxide, heat and water vapor through a continuous, one-way air flow vented to space. When activated, the OPS provided oxygen to a separate inlet on the pressure suit, once a vent valve on a separate suit outlet was manually opened. The OPS provided

1890-551: The air that the staff breathe, and at high altitude, where the partial pressure of oxygen is low, for high altitude mountaineering. In aerospace there are applications in unpressurised aircraft and for high altitude parachute drops, and above the Earth's atmosphere, in space suits for extra-vehicular activity . Similar technology is used in life-support systems in submarines, submersibles, atmospheric diving suits , underwater and surface saturation habitats, spacecraft, and space stations, and in gas reclaim systems used to recover

1953-419: The ambient pressure breathing volume components, usually called the breathing loop in a circulating flow rebreather, and the make-up gas supply and control system. The counterlung is an airtight bag of strong flexible material that holds the volume of the exhaled gas until it is inhaled again. There may be a single counterlung, or one on each side of the scrubber, which allows a more even flow rate of gas through

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2016-441: The ambient pressure breathing volume, either continuously, or when the user operates the oxygen addition valve, or via a demand valve in an oxygen rebreather, when the volume of gas in the breathing circuit becomes low and the pressure drops, or in an electronically controlled mixed gas rebreather, after a sensor has detected insufficient oxygen partial pressure, and activates a solenoid valve. Valves are needed to control gas flow in

2079-475: The astronaut's face. By delivering oxygen to the helmet and drawing gas from the extremities, the suit is designed to ensure that the suit occupant breathes the freshest possible oxygen. The operating pressure of the space suit is maintained at 4.3  psi (30  kPa ) (0.3 atm ~ one third of Earth atmospheric pressure ) during extravehicular operations , and 0.7 psi (4.8 kPa) relative to external pressure while in intravehicular mode ( i.e. , inside

2142-470: The breathing gas is a mixture of oxygen and metabolically inactive diluent gas. These can be divided into semi-closed circuit, where the supply gas is a breathable mixture containing oxygen and inert diluents, usually nitrogen and helium, and which is replenished by adding more of the mixture as the oxygen is used up, sufficient to maintain a breathable partial pressure of oxygen in the loop, and closed circuit rebreathers, where two parallel gas supplies are used:

2205-713: The breathing gas is specially enriched or contains expensive components, such as helium diluent or anaesthetic gases. Rebreathers are used in many environments: underwater, diving rebreathers are a type of self-contained underwater breathing apparatus which have provisions for both a primary and emergency gas supply. On land they are used in industrial applications where poisonous gases may be present or oxygen may be absent, firefighting , where firefighters may be required to operate in an atmosphere immediately dangerous to life and health for extended periods, in hospital anaesthesia breathing systems to supply controlled concentrations of anaesthetic gases to patients without contaminating

2268-692: The breathing volume, and gas feed from the storage container. They include: Oxygen sensors may be used to monitor partial pressure of oxygen in mixed gas rebreathers to ensure that it does not fall outside the safe limits, but are generally not used on oxygen rebreathers, as the oxygen content is fixed at 100%, and its partial pressure varies only with the ambient pressure. Re breathers can be primarily categorised as diving rebreathers, intended for hyperbaric use, and other rebreathers used at pressures from slightly more than normal atmospheric pressure at sea level to significantly lower ambient pressure at high altitudes and in space. Diving rebreathers must often deal with

2331-406: The capacity of the scrubber to remove carbon dioxide at the rate it is produced by the user. These variables are closely linked, as the carbon dioxide is a product of metabolic oxygen consumption , though not the only product. This is independent of depth, except for work of breathing increase due to gas density increase. There are two basic arrangements controlling the flow of breathing gas inside

2394-401: The carbon dioxide absorbent: 4KO 2 + 2CO 2 = 2K 2 CO 3 + 3O 2 . A small volume oxygen cylinder is needed to fill and purge the loop at the start of use. This technology may be applied to both oxygen and mixed gas rebreathers, and can be used for diving and other applications. Potassium superoxide reacts vigorously with liquid water, releasing considerable heat and oxygen, and causing

2457-454: The carbon dioxide from the breathing air, and circulated water in an open loop through a liquid-cooled garment , expelling the water into space, where it turned to ice crystals. Some of the water was also used to remove excess heat from the astronaut's breathing air, and collected for dumping into the spacecraft 's wastewater tank after an EVA. The PLSS also contained a radio transceiver and antenna for communications, which were relayed through

2520-416: The complications of avoiding hyperbaric oxygen toxicity, while normobaric and hypobaric applications can use the relatively trivially simple oxygen rebreather technology, where there is no requirement to monitor oxygen partial pressure during use providing the ambient pressure is sufficient. Rebreathers can also be subdivided by functional principle as closed circuit and semi-closed circuit rebreathers. This

2583-473: The diluent, to provide the bulk of the gas, and which is recycled, and oxygen, which is metabolically expended. Carbon dioxide is considered a waste product, and in a correctly functioning rebreather, is effectively removed when the gas passes through the scrubber. There have been a few rebreather designs (e.g. the Oxylite) which use potassium superoxide , which gives off oxygen as it absorbs carbon dioxide, as

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2646-439: The diver continues to inhale. Oxygen can also be added manually by a button which activates the demand valve. Some simple oxygen rebreathers had no automatic supply system, but only the manual feed valve, and the diver had to operate the valve at intervals to refill the breathing bag as the volume of oxygen decreased below a comfortable level. All rebreathers other than oxygen rebreathers may be considered mixed gas rebreathers, as

2709-411: The extremities of the suit by the liquid cooling and ventilation garment or LCVG , which sends the gas to the PLSS. When gas enters the PLSS, activated charcoal removes odors and lithium hydroxide (LiOH) removes carbon dioxide. Next, the gas passes through a fan which maintains a flow rate of about six cubic feet per minute. A sublimator then condenses water vapor, which is removed by a "slurper" and

2772-410: The gas composition other than removing the carbon dioxide. In some rebreathers the oxygen cylinder has oxygen supply mechanisms in parallel. 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. Others are supplied via a demand valve on the counterlung. This will add gas at any time that the counterlung is emptied and

2835-435: The granules by size, or by moulding granules at a consistent size and shape. Gas flow through the scrubber may be in one direction in a loop rebreather, or both ways in a pendulum rebreather. The scrubber canister generally has an inlet on one side and an outlet on the other side. A typical absorbent is soda lime , which is made up of calcium hydroxide Ca(OH) 2 , and sodium hydroxide NaOH. The main component of soda lime

2898-475: The inspired volume at normal atmospheric pressure , or about 20% of the available oxygen in the air at sea level . Exhaled air at sea level contains roughly 13.5% to 16% oxygen. 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

2961-401: The intermediate reaction, the carbonic acid reacts exothermically with sodium hydroxide to form sodium carbonate and water: H 2 CO 3 + 2NaOH –> Na 2 CO 3 + 2H 2 O + heat. In the final reaction, the sodium carbonate reacts with the slaked lime (calcium hydroxide) to form calcium carbonate and sodium hydroxide: Na 2 CO 3 + Ca(OH) 2 –> CaCO 3 + 2NaOH. The sodium hydroxide

3024-435: The internal pressure is maintained at one atmosphere, there is no risk of acute oxygen toxicity. This is an underwater diving application, but has more in common with industrial applications than with ambient pressure scuba rebreathers. Different design criteria apply to SCBA rebreathers for use only out of the water: Mountaineering rebreathers provide oxygen at a higher concentration than available from atmospheric air in

3087-534: The large volumes of helium used in saturation diving . The recycling of breathing gas comes at the cost of technological complexity and specific hazards, some of which depend on the application and type of rebreather used. Mass and bulk may be greater or less than open circuit depending on circumstances. Electronically controlled diving rebreathers may automatically maintain a partial pressure of oxygen between programmable upper and lower limits, or set points, and be integrated with decompression computers to monitor

3150-400: The personnel under pressure in the accommodation chambers and closed diving bell. It includes the following components: The life support system for the bell provides and monitors the main supply of breathing gas, and the control station monitors the deployment and communications with the divers. Primary gas supply, power and communications to the bell are through a bell umbilical, made up from

3213-402: The photo, benefit from easier field repair if a tear or hole while helical corrugations allow efficient drainage after cleaning. Breathing hoses are usually long enough to connect the apparatus to the user's head in all attitudes of their head, but should not be unnecessarily long, which will cause additional weight, hydrodynamic drag , risk snagging on things, or contain excess dead space in

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3276-403: The pressurized spacecraft). Technologies being considered for application in future PLSSs include pressure swing adsorption (PSA), a process by which CO 2 can be separated from gas more efficiently, and through a repeatable process, as opposed to the current LiOH canisters, which become saturated with each use, and are limited to around eight hours. By regenenerating the sorbent during EVA,

3339-418: The rebreather, known as the pendulum and loop systems. In the pendulum configuration, the user inhales gas from the counterlung through a breathing hose, and exhaled gas returns to the counterlung by flowing back through the same hose. The scrubber is usually between the breathing hose and the counterlung bag, and gas flow is bi-directional. All of the flow passages between the user and the active absorbent in

3402-467: The scrubber are dead space – volume containing gas which is rebreathed without modification by the rebreather. The dead space increases as the absorbent is depleted. Breathing hose volume must be minimised to limit dead space. In the loop configuration, the user inhales gas through one hose, and exhales through a second hose. Exhaled gas flows into the scrubber from one side, and exits at the other side. There may be one large counterlung, on either side of

3465-621: The scrubber contents from freezing, and helps reduce heat loss from the user. Both chemical and compressed gas oxygen have been used in experimental closed-circuit oxygen systems – the first on Mount Everest in 1938 . The 1953 expedition used closed-circuit oxygen equipment developed by Tom Bourdillon and his father for the first assault team of Bourdillon and Evans ; with one "dural" 800l compressed oxygen cylinder and soda lime canister (the second (successful) assault team of Hillary and Tenzing used open-circuit equipment). Similar requirement and working environment to mountaineering, but weight

3528-463: The scrubber, or two smaller counterlungs, one on each side of the scrubber. Flow is in one direction, enforced by non-return valves, which are usually in the breathing hoses where they join the mouthpiece. Only the flow passage in the mouthpiece before the split between inhalation and exhalation hoses is dead space, and this is not affected by hose volume. There are some components that are common to almost all personal portable rebreathers. These include

3591-436: The scrubber, which can reduce work of breathing and improve scrubber efficiency by a more consistent dwell time . The scrubber is a container filled with carbon dioxide absorbent material, mostly strong bases , through which the exhaled gas passes to remove the carbon dioxide. The absorbent may be granular or in the form of a moulded cartridge. Granular absorbent may be manufactured by breaking up lumps of lime and sorting

3654-442: The service, they may be made of a flexible polymer, an elastomer , a fibre or cloth reinforced elastomer, or elastomer covered with a woven fabric for reinforcement or abrasion resistance. If the woven layer is bonded to the outside surface it protects the rubber from damage from scrapes but makes it more difficult to wash off contaminants. Breathing hoses typically come in two types of corrugation. Annular corrugations, as depicted in

3717-409: The size and weight of the sorbent canister can be greatly reduced. PSA accomplishes this by venting CO 2 and water vapor into space. Rebreather 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, and unused inert content when present, of each breath. Oxygen

3780-580: The spacecraft's communication system to Earth. PLSS controls were provided in the Remote Control Unit (RCU) mounted on the astronaut's chest. Oxygen and water were rechargeable for multiple EVAs from the spacecraft's environmental control system. Lunar surface EVA times for the first four missions (Apollo 11 through 14) were limited to 4 hours, with oxygen stored at 1,020 pounds per square inch (7.0 MPa), 3.0 pounds (1.4 kg) of lithium hydroxide, 8.5 pounds (3.9 liters) of cooling water, and

3843-416: The type include: A cryogenic rebreather removes the carbon dioxide by freezing it out in a "snow box" by the low temperature produced as liquid oxygen evaporates to replace the oxygen used. This may be compared with some applications of open-circuit breathing apparatus: The widest variety of rebreather types is used in diving, as the consequences of breathing under pressure complicate the requirements, and

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3906-425: The water of the soda lime and formed carbonic acid, changing the pH from basic to acid, as the change of colour shows that the absorbent has reached saturation with carbon dioxide and must be changed. The carbon dioxide combines with water or water vapor to produce a weak carbonic acid: CO 2 + H 2 O –> H 2 CO 3 . This reacts with the hydroxides to produce carbonates and water in an exothermic reaction. In

3969-598: Was tested at the Houston Flight Center by James P. Lucas, working for Hamilton Standard , and by various astronauts in neutral buoyancy tanks at Dallas. It was tested in space for the first time by Rusty Schweickart in a stand-up EVA in Earth orbit on Apollo 9 . His PLSS weighed 84 pounds (38 kg) on Earth, but only 14 lb (equivalent to the Earth weight of 6.4 kg) on the Moon. The OPS weighed 41 pounds (19 kg) on Earth (6.8 lb (equivalent to

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