Model of the London Bridge Tower, 2006.

UNITED KINGDOM - OCTOBER 04: Standing over 300 meters tall, and with more than 70 floors, �The Shard of Glass� will be the tallest building in Europe when it's completed in 2010. Due to its height, fire safety has been a priority. One of the biggest dangers in a fire is the smoke. Tall staircases can act as chimneys, drawing smoke from one floor up into the staircase. In a building as tall as this, the stairs have to be protected from smoke for a long time to allow everyone to evacuate. Fresh air will be forced into the stairwells to prevent smoke flowing in and to keep the air clear. The doors will be self-closing and fire-resisting, and there will always be two of them arranged like an air lock to add to the protection. Stairs won't be the only way to get out of London's tallest building. In a first for the city, double-decker lifts form part of the evacuation plan. (Photo by SSPL/Getty Images)