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In page Steelmaking:

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The basic oxygen process was developed in 1948 by Robert Durrer, as a refinement of the Bessemer converter that replaced air with (more efficient) pure oxygen. It reduced plant capital costs and smelting time, and increased labor productivity. Between 1920 and 2000, labour requirements decreased by a factor of 1000, to 3 man-hours per thousand tonnes.[citation needed] In 2013, 70% of global steel output came from the basic oxygen furnace.[1] Furnaces can convert up to 350 tons of iron into steel in less than 40 minutes, compared to 10–12 hours in an open hearth furnace.[2]