The balloon ascent of Sivel and Croce-Spinelli, who carried with them a considerable quantity of oxygen and made observations at heights of up to 21,000 feet. In the Spring of 1875 Gaston Tissandier joined forces with two other experienced aviators, Joseph Croce-Spinelli and Th矇odore Sivel, the latter two of whom were interested in studying the effects of breathing oxygen at great heights to prevent asphyxiation. Early experiments were promising, and on April 16 the trio took off from Paris to study meteorological phenomena of the upper atmosphere. The trio of balloonists attained the altitude of 26,000 feet, above which is known in mountaineering as the "death zone" because the oxygen levels are not enough to sustain human life. They attained the altitude of 26,000 feet, but all three aviators were overwhelmed by the thinness of the air before they could get to their bagged oxygen. Sivel and Croce-Spinelli died from asphyxiation. Tissandier survived both the asphyxiation and the fall, but became at partially deaf as the result of the disastrous expedition.