A fire escape is a special kind of emergency exit, usually mounted to the outside of a building or occasionally inside but separate from the main areas of the building. It provides a method of escape in the event of a fire or other emergency that makes the stairwells inside a building inaccessible. Fire escapes are most often found on multiple-story residential buildings, such as apartment buildings. At one time, they were a very important aspect of fire safety for all new construction in urban areas; more recently, however, they have fallen out of common use. This is due to the improved building codes incorporating fire detectors, technologically advanced fire fighting equipment, which includes better communications and the reach of fire fighting ladder trucks, and more importantly fire sprinklers. The international building codes and other authoritative agencies have incorporated fire sprinklers into multi-story buildings below 15 stories and not just skyscrapers. A fire escape consists of a number of horizontal platforms, one at each story of a building, with ladders or stairs connecting them. The platform and stairs are usually open steel gratings, to prevent the build-up of ice, snow, and leaves. Railings are usually provided on each of the levels, but as fire escapes are designed for emergency use only, these railings often do not need to meet the same standards as railings in other contexts. The ladder from the lowest level of the fire escape to the ground may be fixed, but more commonly it swings down on a hinge or slides down along a track. The moveable designs allow occupants to safely reach the ground in the event of a fire but prevent people from accessing the fire escape from the ground at other times (such as to perpetrate a burglary or vandalism). Exit from the interior of a building to the fire escape may be provided by a fire exit door, but in most cases the only exit is through a window. When there is a door, it is often fitted with a fire alarm to prevent other uses of the fire escape, and to prevent unauthorized entry. As many fire escapes were built before the advent of electronic fire alarms, fire escapes in older buildings have often needed to be retrofitted with alarms for this purpose. An alternate form of rapid-exit fire escape developed in the early 1900s was a long canvas tube suspended below