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There are two basic types of stairs in high-rise buildings. They are referred to as "return-type" and "scissor-type." In return-type stairs, entry to and exit from the stairshaft is made from relatively the same location on each floor level. Scissor-type stairs consist of two sets of stairs in a common stairshaft. In this type of stairs, the access point for each set of stairs in the shaft is usually at opposite locations on adjacent floors. Some sets of scissor stairs alternate floors with each set of stairs in the stairshaft (one set may serve odd-numbered floors only, the other set serves even-numbered floors).
Though there may be many sets of stairways in high-rise buildings, they are not designed for total building evacuation. Firefighters should have a working knowledge of the different types of stairways in high-rises:
- The fire tower (sometimes called the Philadelphia Tower) is a stairway that has access to outside air. An open-air balcony protected by self-closing fire doors separates the stairs from the hallways on each floor. Any smoke entering this hallway is ventilated to the exterior, preventing smoke from entering the stairs.
- There are stairshafts that contain a vestibule between the hallway and the stairs that will exhaust any smoke that enters into a vent shaft preventing the contamination of the stairs.
- The enclosed stairway.
- There may be unprotected open stairs between floors in older buildings. A common example is a large open stairway connecting a lobby area with a mezzanine floor.
- Access stairs that connect floors of individual business concerns. These private stairs permit an employee access to multiple floors without entering public stairs or elevators. This allows a degree of safety and convenience.
- Some stairshafts may be pressurized. This pressurization in stairshafts prevents smoke migration into the stairways and is excellent for firefighting. In buildings that contain multiple stairshafts, all stairshafts may not be pressurized.
Stairwell pressurization can be accomplished through various methods. The basic premise is to introduce outside air through fans to create pressure within the stairway. This pressure will prevent the smoke on a fire floor from entering the stairway. The outside air can be introduced either at the top, bottom, or at various levels throughout the stairshaft.
The system can function in a variety of ways. One method has an exhaust fan that allows for constant air changes, removing any smoke that may enter the stairs. This occurs at a rate to maintain pressurization. Other systems work similar to a relief valve on a pumper. When the pressurization reaches a certain level, some air is exhausted to maintain the correct amount of pressure in the stairshaft.
Too much pressurization in a stairway would make it difficult to open doors. Likewise, if too many doors are propped open to fight the fire or evacuate floors, the stairwell pressurization can be negated.
There has been success in setting up positive-pressure fans at the base of enclosed stairways to pressurize them.
Use Of Elevators
The only practical method of movement in a high-rise building is by using elevators. During a fire in a high-rise building, this can be dangerous. Many fire departments forbid the use of elevators until units have reached the fire floor and can ensure their safe use. Some fire departments in their standard operating procedures (SOPs) or standard operating guidelines (SOGs) dictate when an elevator may be used.
A common rule is that the elevator should not be used by firefighters if the fire is located on the first seven floors. This rule recognizes the danger involved in the use of elevators and that firefighters can safely arrive at a fire location in a reasonable amount of time by climbing stairs. If a fire is located above the seventh floor, the use of the elevators is at the discretion of the incident commander.
If the decision is made to utilize an elevator, the elevator should have fireman's service and the firefighters must be familiar with its emergency operation. This will enable the firefighters to have control over the elevator car. A factor to consider is whether the elevator services the fire floor. If it does not service the fire floor, it would be much safer to use.
In taller buildings there are often split banks of elevators using different shafts. A typical example would be a 30-story building with three banks of elevators. The lower bank would service the first 10 floors, the mid-bank would service floors 11 to 20 and the upper bank would service floors 21 to 30. A fire on the 23rd floor could be reached by using the mid-bank to the 20th floor and walking up from that point. This would save a tremendous amount of time while providing a safety factor for the firefighters.