Windsor JS, McMorrow RC, Rodway GW. Oxygen on Everest: the development of modern open-circuit systems for mountaineers. Aviat Space Environ Med 2008; 79:799–804.The use of supplemental oxygen on Mt. Everest is now commonplace. From 1990 to 2006, more than 95% of those summiting the mountain did so using supplemental oxygen at some point during their ascent. The open circuit systems currently in use can be traced back to the device first used by George Finch on Mt. Everest in 1922. Wearing equipment weighing 33 lb (15 kg), Finch and his colleague Geoffrey Bruce set a world altitude record by reaching a height of 27,250 ft (8175 m). However, it would be with a lighter system weighing just 22 lb (10 kg) that Sir Edmund Hillary and Tenzing Norgay made the first ascent of the mountain in 1953. In the years since then considerable improvements in weight, comfort, and efficiency have been made; however, the original “open” principles first used by Finch almost a century ago still remain steadfastly in place.