Other means to escape
The search for escape solutions that do not require major structural changes has been going on for years. Since 9/11, a score of proposals have gained attention:
Helicopter. A rooftop heliport located a safe distance from antennas, mechanical installations and other hazards will allow landings to effect rescue. When smoke, flames or dangerous updrafts prevent landings, a basket can be lowered to hoist evacuees to safety. However, not every building can have a heliport and evacuees, especially the disabled, cannot always get to the roof. Besides, the helicopter pilot needs to be trained in a technique known as "vertical reference flying". Consequently, this is not a practical method for mass evacuation.
Parachutes. Several companies are offering parachutes, similar to the extreme sport of BASE-jumping. While this approach will work only if the jumper is athletic, experienced and high enough, such as on the 10th floor or above, at least six companies are selling escape parachutes. Because of crosswinds, obstacles such as flagpoles, and the need for considerable training, this method is considered highly hazardous.
Slides. Similar to the chutes used in airplane evacuation, slides have been listed as an alternate means of egress in the building codes of several US cities. Such slides, however, may not be feasible above the height that is reachable by fire department ladders. Also, a chute requires setting up the anchor on the ground and trained personnel on hand during the emergency. Using a separate chute for each floor would make the set-up very cumbersome.
Wires. Another proposal requires wires stretched between buildings so that people can slide from one affected building to another. Clearly, this would cause a morass of wires across city streets. Furthermore, experience on drilling rigs, where such wires are sometimes used, shows that the descent requires considerable courage and may result in serious injury.
Flying platforms. Such a machine would approach the building at any given floor and pick up passengers. Clearly, this is a very expensive solution and would only be available to a limited number of people. Platforms operated from the ground have also been considered.
Tubes. A vertical tube of flexible material has been installed in some buildings in Asia and Europe. It can serve multiple floors, but unless it is located outside the building, it may be subject to the same hazards as stairways and elevators. Abrasions and minor injuries may be likely.
Collapsible elevators. Such a system, developed in Israel, requires the installation of collapsible cubicles on the roof of the building. In an emergency they deploy along a rail on the outside of the building and stop to load evacuees. New York City has denied a permit for the system because of the potential bottlenecks as people try to enter the cubicles. Since each cubicle is fixed in a series with others, there is also danger that a cubicle may stop at a fire level while another accepts or discharges passengers.
Descenders. Similar to those used by mountaineers, firemen and the military, most descenders use a rope in conjunction with some type of a simple mechanism to control its movement. This method, known as rappeling, is not suited for escaping from a high-rise buildings. The useful length of the rope is limited by its bulkiness and weight, and if the descent requires going through a fire area, the rope may burn and break. Most importantly, to descend at a sufficient speed requires a physically fit person and considerable training. Since this approach is not practical in its traditional form, several improvements have been introduced.