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An escape set (in German Tauchretter = "diver rescuer") is a breathing set, which lets its wearer survive for a time in an environment without (sufficiently) breathable air, in particular underwater, primarily or originally intending mainly to survive long enough to reach safety where the air is breathable.
The escape set was developed from such respirators and used to escape from a submarine submerged so long that its onboard air supply ran out, and for technical or military reasons the submarine could not surface: one example is the Davis Submerged Escape Apparatus. Escape sets were also used ashore, e.g. in the mining industry.
In language nowadays 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.
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.
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:-
- Das Boot (Johann das Gespenst stops water from breaking in under a diesel engine).
- Haie und kleine Fische (controlled exit from a sunk submarine).
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.
- 1903: Siebe Gorman started to make this breathing set in England; in the years afterwards it was improved, and later was called the Davis Submerged Escape Apparatus.
- 1905: An important innovation: metering valves to control the supply of oxygen. This was promptly adopted by other companies which made escape sets.
- 1907: Draeger of Lübeck invented the U-Boot-Retter = "submarine rescuer".
- Both systems were based on oxygen supply from a high-pressure cylinder with simultaneous absorption of carbon dioxide by an inserted cartridge filled with sodium hydroxide.
- 1916: The Draeger model DM 2 became standard equipment of the German Navy.
- 1926: Draeger displayed a rescue breathing apparatus that the wearer could swim with. While the previous devices served only for ascending to the surface and were designed also to develop lift so that the wearer arrived at the surface without swimming movements, the diving set had weights, which also made it possible to dive down with it, to search and rescue after an accident.
- 1939: Hans Hass developed from the escape set a type of rebreather with its bag on his back and two breathing tubes but no backpack box. These sets appear much in his movies and books.
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.
- Hermann Stelzner, Tauchertechnik - Handbuch für Taucher / Lehrbuch für Taucheranwärter. Verlag Charles Coleman, Lübeck 1943