Rebreather facts for kids

Quick facts for kids
Rebreather

A fully closed circuit electronic rebreather (AP Diving Inspiration)
Acronym	CCUBA (closed circuit underwater breathing apparatus); CCR (closed circuit rebreather), SCR (semi-closed rebreather)
Uses	Breathing set
Related items	Davis apparatus, Self-contained breathing apparatus, Escape hood

A rebreather is a special breathing device that lets a user breathe the same air over and over. It works by taking out the carbon dioxide from your breath. Then, it adds fresh oxygen to replace what your body used. This is different from regular breathing gear, like a scuba tank, which just lets your exhaled breath go into the environment.

The main idea behind a rebreather is to make a limited gas supply last much longer. It also stops bubbles from coming out, which is great for secret military missions or watching underwater animals without scaring them away. Rebreathers are usually small enough to be carried by the person using them. Bigger versions, like those on submarines, are called life-support systems.

Rebreather technology is useful when there isn't much fresh air or gas available. This includes being underwater, in space, or in places with bad air like during a fire or in a mine. They are also used when the breathing gas is special or expensive, like gas mixed with helium.

You can find rebreathers in many places:

• Underwater: Diving rebreathers are a type of self-contained underwater breathing apparatus. They have both a main and an emergency gas supply.
• On land: They are used in industrial jobs where poisonous gases might be present or where there's no oxygen.
• Firefighting: Firefighters use them to work safely in dangerous air for longer times.
• Hospitals: Anaesthesia machines use similar systems to give patients special gases without letting them spread into the room.
• High altitudes: Climbers use them on tall mountains where the air has less oxygen.
• Space: Space suits use rebreather technology for astronauts doing spacewalks.

Using a rebreather is more complex than other breathing systems. It also has its own risks. Electronically controlled diving rebreathers can automatically keep the oxygen level just right. They can also work with decompression computers to track a diver's safety during a dive.

How Rebreathers Work

When you breathe, your body uses oxygen and makes carbon dioxide. Even when you're resting, your body uses a small amount of oxygen. When you work hard, you breathe more, but you still only use a small part of the oxygen you take in.

Regular breathing gear, like open-circuit scuba, wastes a lot of oxygen. This is especially true underwater, where the gas is compressed due to depth. Rebreathers help save this gas.

If you just kept breathing the same air without cleaning it, the oxygen would run out. Also, carbon dioxide would quickly build up. Too much carbon dioxide makes you feel like you're suffocating. It can quickly become dangerous. Your body's breathing reflex is triggered by carbon dioxide levels, not oxygen levels. So, rebreathers must remove carbon dioxide. They do this using a part called a carbon dioxide scrubber.

By adding enough oxygen and removing carbon dioxide, rebreathers save most of the gas. This means you can breathe the same gas over and over.

How carbon dioxide levels affect your body over time.

How Long Can You Use It?

How long a rebreather can be used safely depends on two things:

• How much oxygen it has, and how fast the user breathes it.
• How well the scrubber can remove carbon dioxide.

These two things are connected because carbon dioxide is made when your body uses oxygen. The depth you are at doesn't change how long the rebreather lasts, but breathing gas becomes thicker at depth, making it harder to breathe.

Rebreather Design

How rebreathers are built: pendulum vs. loop systems. * Mouthpiece with dive/surface valve * Two-way breathing hose * Exhalation hose with non-return valve * Inhalation hose with non-return valve * Scrubber * Counterlung * Automatic make-up valve * Manual bypass valve * Breathing gas storage cylinder * Cylinder valve * Regulator first stage * Cylinder pressure gauge * Over-pressure valve

There are two main ways rebreathers are designed for gas flow: pendulum and loop systems.

Pendulum System

In a pendulum system, you breathe air in and out through the same hose. The scrubber, which cleans the air, is usually between the hose and a bag called a counterlung. Air flows both ways through the scrubber. This design can have more "dead space," which is air that gets breathed again without being cleaned.

Loop System

In a loop system, you breathe in through one hose and out through another. The exhaled air goes into the scrubber from one side and comes out clean on the other. This system usually has one or two counterlungs. Air flows in only one direction, thanks to special one-way valves. This design has less dead space.

Main Parts of a Rebreather

An oxygen rebreather (KIP-8) showing its inside parts.

Outside view of a Russian firefighting rebreather (KIP-8).

Most portable rebreathers have similar main parts. These include the parts that hold the breathing air and the system that adds fresh gas.

Counterlung

The counterlung is a strong, flexible bag that holds the air you breathe out until you breathe it in again. Some rebreathers have one large counterlung, while others have two smaller ones. This helps the air flow smoothly through the scrubber, making it easier to breathe.

Scrubber

The scrubber is a container filled with a material that absorbs carbon dioxide. This material is usually made of strong chemicals called bases. The air you breathe out passes through this material to get rid of the carbon dioxide.

A common absorbent is soda lime. It's mostly made of calcium hydroxide and sodium hydroxide. These chemicals react with carbon dioxide to clean the air. This process also makes the air warmer and more humid, which can be nice for diving in cold water or climbing in cold mountains. Some scrubbers have a special indicator that changes color when the material is used up, telling you it's time to change it.

Breathing Hoses

A dive/surface valve with mouthpiece and breathing hoses.

Breathing hoses are flexible tubes that carry the breathing gas. They are wide enough to let air flow easily. They are often corrugated (like a flexible straw) so they don't collapse when you move your head. Each end of the hose connects tightly to other parts of the rebreather. Some hoses have one-way valves to make sure the air flows in the right direction.

Mouthpiece or Facemask

You need a way to breathe from the rebreather hands-free. This is usually a mouthpiece you bite onto, a mask that covers your nose and mouth, a full-face mask, or a sealed helmet.

Oxygen Supply

Rebreathers have a supply of oxygen, usually in a high-pressure tank. This oxygen is added to the breathing air. It can be added constantly, when you press a button, or automatically when sensors detect that the oxygen level is too low.

Valves

Valves control how gas flows in the rebreather.

• One-way valves: These make sure air flows in only one direction in loop systems.
• Dive/surface valves: On diving rebreathers, these stop water from getting in when you take the mouthpiece out or breathe surface air.
• Gas supply valves: These let high-pressure gas flow from the oxygen tank.
• Overpressure valve: This releases extra gas, especially important in diving rebreathers when a diver goes up and the gas expands.

Oxygen Sensors

Oxygen sensors are used in mixed gas rebreathers to check the oxygen level. This makes sure the oxygen doesn't go too high or too low, which could be dangerous. Simple oxygen rebreathers usually don't need these sensors because they only supply pure oxygen.

Types of Rebreathers

Rebreathers can be grouped by where they are used (underwater or on land/in space) or by how they work.

Oxygen Rebreathers

A simple oxygen rebreather used for mine rescue (Siebe Gorman Proto 1).

This is the oldest type of rebreather. Navies used them for escaping submarines and for shallow diving. They were also used for mine rescue, high-altitude climbing, and in factories. Oxygen rebreathers are quite simple and reliable. They only supply oxygen, so there's no need to control the gas mix, just remove the carbon dioxide.

Mixed Gas Rebreathers

A mixed gas electronically controlled closed circuit diving rebreather.

All rebreathers that aren't pure oxygen rebreathers are called mixed gas rebreathers. Their breathing gas is a mix of oxygen and other gases that your body doesn't use, like nitrogen or helium.

• Semi-closed circuit rebreathers: These constantly release a small amount of gas and add fresh gas to the loop. They need a supply of both oxygen and the other gases.
• Closed circuit rebreathers: These use two separate gas supplies: one for the main gas (diluent) which is recycled, and one for oxygen, which your body uses up.

Rebreathers That Make Oxygen

A Russian multipurpose rebreather (IDA-71) with its lid open. One part can be filled with a special material that makes oxygen.

Some rebreathers use a special material, like potassium superoxide, that creates oxygen as it absorbs carbon dioxide. These are often used in space suits, for firefighting, and in mine rescue because they are lightweight and efficient.

Rebreathers Using Liquid Oxygen

An Aerorlox liquid oxygen rebreather in a coal mining museum.

Some rebreathers use liquid oxygen. This is very cold and needs good insulation. A special type, called a cryogenic rebreather, freezes out the carbon dioxide using the cold from the liquid oxygen.

Where Rebreathers Are Used

• Underwater: As a self-contained breathing apparatus for divers. They are also used in surface-supplied diving to reclaim expensive gases.
• Mine rescue and industry: Used where poisonous gases are present or oxygen is missing.
• Firefighting: For firefighters who need to work in dangerous air for long periods.
• Crewed spacecraft and space suits: Outer space has no oxygen, so rebreathers are vital.
• High-altitude mountaineering: To provide more oxygen than the thin mountain air has.
• Medical anaesthesia systems: To give patients controlled amounts of gas during surgery and save expensive gases.
• Life-support systems: In submarines, underwater habitats, and space stations, which are like big rebreathers for many people.

This is different from:

• Oxygen systems for medical patients or aircraft emergencies, which just add oxygen to the air you breathe.
• Open-circuit breathing gear (like regular scuba), which releases all exhaled gas.
• Gas masks that filter bad stuff from the air around you.

Diving Rebreathers

A SIVA Underwater Mine Countermeasures (MCM) Diving Apparatus (oxygen rebreather).

Diving rebreathers are the most varied type because breathing under pressure adds many challenges. They are critical safety equipment. If they fail, it can be very dangerous for the diver.

Gas Reclaim Systems for Surface Diving

These systems are used to get back expensive helium-based breathing gas from divers. The gas is cleaned to remove carbon dioxide and then reused. This saves a lot of money compared to just letting the gas go.

Life-Support Systems for Saturation Diving

These systems provide breathing gas and other services for people living under pressure in special chambers or diving bells. They include:

• Equipment to supply, clean, and recycle breathing gas.
• Systems to control temperature and humidity.
• Monitoring and communication tools.
• Fire safety systems.
• Sanitation.

Atmospheric Diving Suits

A US Navy atmospheric diving suit.

An atmospheric diving suit is like a small, human-shaped submarine for one person. It lets a diver work deep underwater while staying at normal air pressure inside. The breathing gas can come from the surface or from a rebreather built into the suit. Since the inside pressure is normal, there's no risk of oxygen toxicity.

Industrial and Rescue Rebreathers

Mine rescue rebreathers in a Czech museum.

Rebreathers used on land, like for firefighting or mine rescue, have different design needs:

• The air pressure around them doesn't change.
• Cooling the gas inside the rebreather might be needed, as the scrubber creates heat.
• They need to be tough and protected from heat and impacts for firefighters.
• Being lightweight and comfortable to carry is important, especially in tight spaces.
• They often use simple oxygen rebreather technology, which is very reliable.
• Some can provide a slight positive pressure to prevent bad outside air from leaking in.
• They might have features like drinking water access, radio communication, and alarms for low gas or no movement.

Mountaineering Rebreathers

Mountaineering rebreathers give climbers more oxygen than the thin air at high altitudes. This helps them work harder. They need to be light and work well in extreme cold. The heat from the scrubber reaction helps keep the system from freezing.

Anaesthesia Systems

Anaesthetic machines can be set up like rebreathers. They give oxygen and special gases to patients during surgery. A scrubber in the machine removes carbon dioxide. This helps save expensive gases and keeps the operating room air clean for staff.

Space Suits

Buzz Aldrin on the Moon in 1969, showing his portable life support system.

An Orlan space suit during a spacewalk from the International Space Station, with its life-support cable visible.

Space suits provide astronauts with breathing gas. This gas can come from the spacecraft or from a portable system on the suit. Both systems use rebreather technology to remove carbon dioxide and add oxygen. Space suits often use oxygen rebreathers. This allows for lower pressure inside the suit, making it easier for astronauts to move around.

Habitat Life-Support Systems

Submarines, underwater habitats, and space stations are like very large closed-circuit rebreathers. They use similar principles to keep the air breathable for many people over long periods. They usually use fans to circulate the air through scrubbers.

Safety with Rebreathers

Using rebreathers has several safety concerns, especially for diving.

Dangers

Some dangers come from how the equipment works, and others from the dangerous places where rebreathers are used.

Low Oxygen (Hypoxia)

This can happen if the rebreather doesn't have enough oxygen or if the system isn't properly prepared. For example, if an oxygen rebreather isn't "purged" (flushed with fresh oxygen) at the start, old air with less oxygen can stay in the system.

Carbon Dioxide Buildup

Carbon dioxide will build up if the scrubber isn't working right, is empty, or is packed badly. Your body usually notices high carbon dioxide levels quickly. However, if you keep using a rebreather with a bad scrubber, the carbon dioxide can become toxic. This will lead to extreme breathing problems, unconsciousness, and eventually death.

Leaks of Bad Gases

Industrial rebreathers are often used in places with toxic air. If the rebreather isn't perfectly sealed, bad gases from outside can leak in, especially during inhalation. This is a big concern around the edges of a full-face mask.

Fire Risk with High Oxygen

High levels of oxygen greatly increase the risk of fire. Many materials that don't burn easily in normal air will burn quickly in high oxygen. This is more of a risk for land-based uses like firefighting than for diving.

Caustic Cocktail

This happens in diving rebreathers if water gets into the scrubber. The water mixes with the carbon dioxide absorbent, which can be a harsh chemical. If this mixture reaches the mouthpiece, it can taste bad or cause a burning feeling. This tells the diver to switch to a different breathing gas and rinse their mouth. Many modern diving rebreathers are designed to prevent this "caustic cocktail" from forming.

How Rebreathers Can Fail

Scrubber Failure

"Break-through" means the scrubber stops removing enough carbon dioxide. This will happen if it's used too long. It can also happen early if:

• The absorbent material is completely used up.
• Gas bypasses the absorbent because it's not packed tightly or seals are missing. This is called "tunneling."
• For deep diving, the scrubber needs to be bigger because gas molecules are packed more tightly, making it harder for carbon dioxide to reach the absorbent.
• If the scrubber gets wet, it works less well and can cause early break-through.
• In very cold conditions, wet scrubber chemicals can freeze, stopping them from working.

Other Ways Rebreathers Can Fail

• Flooding: In diving rebreathers, water can fill the breathing parts.
• Gas leaks: Gas can leak in or out. This is most dangerous if the outside air is toxic.
• Oxygen monitoring failure: In mixed gas diving rebreathers, sensors can fail, leading to wrong oxygen levels.
• Gas injection system failure: Also mainly a problem for mixed gas diving rebreathers. Oxygen rebreathers usually have strong gas injection systems that can be controlled manually if they fail.

History of Rebreathers

Early Ideas

Around 1620, a scientist named Cornelius Drebbel found that heating a chemical called saltpetre could make oxygen.

The first basic rebreather idea was patented in France in 1808 by Pierre-Marie Touboulic. His design used an oxygen tank and a sponge soaked in limewater to absorb carbon dioxide. He called it Ichtioandre (Greek for 'fish-man'). There's no proof that a working model was ever built.

In 1853, Professor T. Schwann showed a rebreather at the Belgian Academy of Science. It had a large oxygen tank and two scrubbers with sponges soaked in a strong chemical solution.

Working Rebreathers

Henry Fleuss, who invented the first practical rebreather.

The first truly practical closed-circuit scuba was designed by Henry Fleuss in 1878. He worked for Siebe Gorman in London. His device had a rubber mask, a breathing bag, and a copper tank with oxygen. It used rope soaked in a chemical to remove carbon dioxide and could last about three hours. Fleuss tested it himself in 1879, even diving to 5.5 meters (about 18 feet) underwater.

His device was first used in a real job in 1880 by Alexander Lambert. He was a diver working on the Severn Tunnel and used it to go 1000 feet into a dark, flooded tunnel to close some doors. This was too dangerous with regular diving gear. In 1880, Fleuss also used a rebreather to check a coal mine after a gas explosion.

Fleuss kept making his rebreather better. Sir Robert Davis, who led Siebe Gorman, improved the oxygen rebreather in 1910. He created the Davis Submerged Escape Apparatus, which was the first rebreather made in large numbers. It was meant for submarine crews to escape, but it was also used for shallow diving and as an industrial breathing set.

The Davis Submerged Escape Apparatus being tested in a submarine escape tank in 1942.

This gear had a rubber bag with a carbon dioxide scrubber and a steel oxygen tank. The British Royal Navy adopted it in 1927. Other industrial oxygen rebreathers, like the Siebe Gorman Salvus and Proto, came from this design.

In 1907, Professor Georges Jaubert invented a chemical called Oxylithe. This material released oxygen as it absorbed carbon dioxide. The British Royal Navy tried to use it in a rebreather for submarine escape in 1909, but it was only used for shallow diving.

In 1912, the German company Dräger started making their own rebreathers for divers. These were based on a design by Hermann Stelzner for mine rescue.

In the 1930s, the United States Navy started using simple rebreathers called Momsen lungs for submarine escape. These were used until the 1960s.

Rebreathers in World War II

A British Royal Navy frogman in 1945 with a Davis Submerged Escape Apparatus.

In the 1930s, Italian spearfishers started using the Davis rebreather. The Italian Navy then developed a much better version, designed by Teseo Tesei. Their frogman unit, the Decima Flottiglia MAS, used it very successfully during World War II.

After World War II, captured Italian rebreathers helped the British make better designs. Many British frogmen used oxygen tanks from shot-down German planes. The Dräger rebreathers were used by German divers and frogmen during the war. Dr. Christian J. Lambertsen developed rebreathers for the US Navy for underwater warfare. He taught the first closed-circuit oxygen rebreather course in the US in 1943.

During and after WWII, armies needed to dive deeper than pure oxygen allowed. This led to the design of simple "mixture rebreathers" (now called "nitrox") by adding an extra gas tank. Divers had to calculate the right gas flow for their dive depth.

After World War II

The famous diving pioneer Hans Hass used Dräger oxygen rebreathers in the early 1940s for making underwater films.

Because rebreathers were so important to the military, most governments didn't want to share the technology with the public. In Britain, civilian use was very low. However, after the Cold War ended in 1989, the risk of sabotage by combat divers seemed less. Then, automatic and semi-automatic rebreathers with oxygen sensors started to become available for recreational diving.

See also

• Carbon dioxide scrubber
• Escape set
• Primary life support system, also known as Portable Life Support System
• Self-contained breathing apparatus (SCBA) (surface-only (industrial) breathing sets including rebreathers)