National Geographic : 2012 Apr
Bundled in their down suits, Ralf Dujmovits and Kaltenbrun- ner study the route up toward Camp IV and the beginning of the "death zone." That is the point, above 8,000 meters, at which mountaineers who opt to climb without bottled oxygen face the limits of the human body. "What makes a difference in not having oxygen is your ability to fend off cold," Dujmovits says. "You freeze yourself from the inside out, because you can't burn enough fat to stay warm."