Lukas Furtenbach, a well-known mountain guide, led a British team to climb Mount Everest very quickly, using a special xenon gas treatment. The team left London on May 16, reached the top on May 21, and came back home two days later. This xenon gas treatment, which is meant to help climbers avoid altitude sickness, has caused some disagreement and is now being looked into by Nepalese climbing authorities. The climbers got ready for the climb by training in special tents that simulate high altitude and by having xenon gas treatment at a clinic in Germany. Furtenbach believes that spending less time on the mountain could be better for the environment, for example, by reducing human waste. However, Furtenbach also says that the xenon gas was never used in Nepal, and he claims he can show it is safe for climbers.