This raises the question: Are you safe at 12,000 feet? There is a possibility that the answer to that question is a resounding yes. Again, it depends on your body's ability to tolerate the lower partial pressure of oxygen. If you live in Aspen, Colorado, which is situated in the Rocky Mountain range at nearly 8,000 feet, you may feel great at 12,000 feet for hours on end. However, if you are a relatively healthy sea-level dweller like myself, you will likely need oxygen somewhere between 8,000 and 10,000 feet. Blue says there are some people, particularly those with poor circulation, who need supplemental oxygen at as low as 6,000 feet. The FAA recommends oxygen use above 5,000 feet at night, because the eyes require even more oxygen for night vision.