Escape set

An escape set (in German "Tauchretter" = "diver rescuer") is a breathing set that allows its wearer to survive for a time in an environment without (sufficiently) breathable air.
Early escape sets were rebreathers and were typically used to escape from submarines with a depleted air supply that, for technical or military reasons, were unable to surface. One example is the Davis Submerged Escape Apparatus. Escape sets were also used ashore, e.g. in the mining industry.
Naming.
Currently, language in German as in English, "tauchen" = "diving" only means in water. Until the middle of the 20th century the German word "tauchen" = "to dive" also meant "to stay in unbreathable atmosphere". Thus around 1900 a water-cooled fire protection hood with air supply for firefighters was called in German a "Feuertaucher" (= "fire diver"), and still into the 1940s in German a man with a breathing apparatus for use in unbreathable atmosphere was called a "Gastaucher" (= "gas diver"). But as escape sets were used more for rescue from sunken submarines and as light diving equipment, the German word "tauchen" was restricted to underwater meanings.
Function.
Chemical.
Normal breathing air contains about 20% oxygen. In normal breathing the body uses about 4% and replaces it with carbon dioxide. A certain volume of air can be "breathed deeply" several times, until its oxygen portion is exhausted. However, each breath becomes heavier, since carbon dioxide accumulates and oxygen is used up. Therefore, this accumulating carbon dioxide must be removed from the breathing cycle.
For the general function of this sort of breathing set, see rebreather.
The absorbent used is almost always sodalime, or a material based on sodalime, but in former times slaked lime or quicklime or caustic soda was sometimes used.
Submarine escape sets had a mouthpiece, so the user had to also wear a noseclip to avoid breathing water through his nose. The working time of an escape set depended upon depth of submersion, between 15 and 45 minutes.
Use during submarine rescue.
If an emergency made exit from a submarine necessary, first the crew had to wait until the air inside the submarine was compressed by pressure of entering sea water until the remaining air pocket was at the same pressure as outside. The lower end of the escape hatch had therefore to be low enough so that the remaining air inside the submarine could not escape when the hatch was opened. Then the crew could step out. The set's user had to breathe continually to avoid pulmonary barotrauma. Escape sets are used in these films:
History.
Development of the first militarily useful submarines before the First World War raised briefly the question about rescue possibilities if the submarine sank. First, often deadly attempts were started with simple "breathing bags", which were useful as a very short-period assistance, but often did not contain enough oxygen to survive the whole ascent. Robert Henry Davis and Henry A. Fleuss developed a rebreather, which was useful in the mining industry and under water.
Further developments of the escape gear.
Later developments contained a suitable breathing mixture, automatically proportioned by a valve, instead of an oxygen or compressed air cylinder, which makes possible deeper use possible of these diving breathing sets.
Oxygen rebreathers are technically simpler than mixture breathing sets, but limits use to shallow water. Oxygen cycle devices are much liked by combat divers and underwater photographers, as they make far fewer bubbles than aqualung-type (open circuit) sets, and those bubbles could betray the diver.
Another operational area is fire protection, for instance in chemical industry or rescue in the mining industry, where need for a long use duration forbids use of compressed air sets. Advancements in rebreather design include special more-or-less complex gas proportioning and control devices, allowing use even deeper and even longer, for work divers, than emergency breathing sets and the type of sport diving called technical diving. Today's escape sets are combined with lifejackets and protection hoods to protect the head and breathing organs from being overpowered by water. They are used with thermal protection suits similar to the well-known scuba diving drysuits. Use is nevertheless limited to comparatively small depths; escape capsules and rescue submarines and emergency lift devices and droppable ballast provide safety in deeper water.
The original German model of escape set from the Second World War is still used now in Leopard 2 tanks, as emergency safety devices in operations submerged in rivers.