From the location of their final camp (discovered in 2001), a summit climb may be estimated to have taken them around 11 hours. Assuming they took two cylinders each, they had only about eight hours of oxygen available, although this depends on the flow rate, which could be controlled and was not necessarily full flow. The oxygen would almost certainly have run out before they reached the summit. The two flow rates available on those oxygen sets were 1.5 and 2.2 L/min. Both are low rates for active climbing, and the two are unlikely to have used the lower flow rate. One of their oxygen bottles was found some short of the First Step, which enables their speed of climbing to be calculated (about 275 vertical ft/h; Hillary and Norgay climbed at 350 vertical ft/h at this altitude). At best, they might have reached the base of the Second Step with 1.5 hours of oxygen remaining each. Given the vertical distance remaining (about 800 vertical ft), the climb to the summit after the Second Step at the same climbing rate would be 3 hours, but climbing speed drops quickly with altitude (Hillary and Norgay managed only 150 vertical ft/h above 28,000 ft). Thus, even if Mallory had taken Irvine's oxygen, he would not have had enough oxygen to reach the summit.