a caustic soda solution. working rebreathers henry fleuss, inventor of the rebreather the first commercially practical closed-circuit scuba was designed and built by the diving engineer henry fleuss in 1878, while working for siebe gorman in london. his self-contained breathing apparatus consisted of a rubber mask connected to a breathing bag, with (estimated) 50–60% o2 supplied from a copper tank and co2 scrubbed by rope yarn soaked in a solution of caustic potash; the system giving a duration of about three hours. fleuss tested his device in 1879 by spending an hour submerged in a water tank, then one week later by diving to a depth of 5.5 m in open water, upon which occasion he was slightly injured when his assistants abruptly pulled him to the surface. his apparatus was first used under operational conditions in 1880 by alexander lambert, the lead diver on the severn tunnel construction project, who was able to travel 1000 feet in the darkness to close several submerged sluice doors in the tunnel; this had defeated his best efforts with standard diving dress due to the danger of the air supply hose becoming fouled on submerged debris, and the strong water currents in the workings. in 1880 fleuss, used a rebreather to inspect seaham colliery in the uk after a gas explosion. fleuss and siebe gorban developed the proto breathing apparatus for mine rescue in 1911. fleuss continually improved his apparatus, adding a demand regulator and tanks capable of holding greater amounts of oxygen at higher pressure. sir robert davis, head of siebe gorman, improved the oxygen rebreather in 1910 with his invention of the davis submerged escape apparatus, the first practical rebreather to be made in quantity. 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, and as an industrial breathing set. davis submerged escape apparatus being tested at the submarine escape test tank at hms dolphin, gosport, 14 december 1942 the rig comprised a rubber breathing/buoyancy bag containing a canister of barium hydroxide to scrub exhaled co2 and, in a pocket at the lower end of the bag, a steel pressure cylinder holding approximately 56 litres of oxygen at a pressure of 120 bar. 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 1927. various industrial oxygen rebreathers such as the siebe gorman salvus and the siebe gorman proto, both invented in the early 1900s, were derived from it. professor georges jaubert invented the chemical compound oxylithe in 1907. it was a form of sodium peroxide (na2o2) or sodium superoxide (nao2). 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. hall and dr. o. rees of the royal navy in 1909. 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. in 1912 the german firm dräger began mass production of their own version of standard diving dress with the air supply from a rebreather. the apparatus had been invented some years earlier by hermann stelzner, an engineer at the dräger company, for mine rescue. rebreathers during world war ii a 1945 royal navy frogman with davis apparatus in the 1930s, italian sport spearfishers began to use the davis rebreather; italian manufacturers received a licence from the english patent holders to produce it. this practice soon came to the attention of the italian navy, which developed an extensively upgraded model designed by teseo tesei and angelo belloni that was used by its frogman unit decima flottiglia mas with good results during world war ii. during the second world war, captured italian frogmen's rebreathers influenced improved designs for british rebreathers. many british frogmen's breathing sets used aircrew breathing oxygen cylinders salvaged from shot-down german luftwaffe aircraft. 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 circular or 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. some british armed forces divers used bulky thick diving suits called sladen suits; one version of it had a flip-up single faceplate for both eyes to let the user get binoculars to his eyes when on the surface. the dräger rebreathers, especially the dm20 and dm40 model series, were used by the german helmet divers and german frogmen during world war ii. rebreathers for the us navy were developed by dr. christian j. lambertsen for underwater warfare. lambertsen held the first closed-circuit oxygen rebreather course in the united states for the office of strategic services maritime unit at the naval academy on 17 may 1943. during and after wwii, needs arose in the armed forces to dive deeper than allowed by pure oxygen. that prompted, at least in britain, design of simple constant-flow "mixture rebreather" variants of some of their diving oxygen rebreathers (= what is now called "nitrox"): scmba from the scba (swimmer canoeist's breathing apparatus), and cdmba from the siebe gorman cdba, by adding an extra gas supply cylinder. before a dive with such a set, the diver had to know the maximum or working depth of his dive, and how fast his body used his oxygen supply, and from those to calculate what to set his rebreather's gas flow rate to. post-wwii the diving pioneer hans hass used dräger oxygen rebreathers in the early 1940s for underwater cinematography. due to the military importance of the rebreather, amply demonstrated during the naval campaigns of the second world war, most governments were reluctant to issue the technology into the public domain. in britain rebreather use for civilians was negligible, and the bsac formally prohibited rebreather use by its members. 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. most high-altitude mountaineers use open-circuit oxygen equipment; the 1953 everest expedition used both closed-circuit and open-circuit oxygen equipment: see bottled oxygen. eventually the cold war ended, and in 1989 the communist bloc collapsed, and as a result the perceived risk of sabotage attacks by combat divers dwindled, and western armed forces had less reason to requisition civilian rebreather patents, and automatic and semi-automatic recreational diving rebreathers with oxygen partial pressure sensors started to appear. manufacturers and models industrial/rescue: blackett's aerophor – a nitrox semi-closed-circuit rebreather with liquid gas storage made in england from 1910 onwards for use in mine rescue and other industrial uses. sabre safety sefa (selected elevated flow apparatus) – an industrial oxygen rebreather formerly made by sabre safety with 2 hours duration on a filling. siebe gorman – british manufacturer of diving equipment and salvage contractor the savox was an oxygen rebreather with a use duration of 45 minutes. it had no hard casing and was worn in front of the body. siebe gorman salvus – industrial rescue and shallow water oxygen rebreather ida71 – russian military rebreather for underwater and high altitude use others: