Inadequacy of Primary Evacuation Methods
In the event that a fire occurs in a high-rise building, the only way to ensure the complete safety of all its occupants is by conducting a full-scale evacuation. However, because the primary evacuation systems present in most high-rise buildings today are inadequate, this seemingly simple, yet essential, task can be dangerous and problematic. The primary methods of evacuation in high-rise buildings today fail to provide occupants with a timely, safe, and effective egress.
A building's passenger elevators, in the event of a fire, are automatically returned to its main level and shut down to await reactivation by firefighters ? unusable for egress.vii A building?s stairways, typically designed according to the evacuation needs of their respective floor populations rather than the evacuation needs of the entire building, are not intended to handle the cumulative effect of fleeing occupants ? congestion.viii Congested stairways, by inhibiting occupant egress and firefighter ingress, increases the risk of injury and death to both: When combating a building fire, the standard practice for firefighters is to tap into the building's internal water system, known as a standpipe, located in the stairwell below the fire, and then drag a hose upstairs with which to douse the flames.ix A congested stairway full of fleeing occupants inhibits firefighter access to the standpipe and their moving between floors. The result: A greater amount of structural damage inflicted onto the building, possibly enough to induce complete or partial collapse, and a greater likelihood of incurring occupant fatalities from smoke inhalation.
Another inadequacy of the primary evacuation systems found in today?s high-rise buildings is their design flaws. Elevators are typically grouped in a convenient central location on all floors ? the "elevator lobby" or "sky lobby" layout. It is this layout that makes them vulnerable to compromise. If a fire were to originate or spread into the elevator lobby, the heat and choking smoke would prevent occupant access to the elevators on the floor. As a result, occupants would be forced to negotiate the stairway down to the floor below or subsequent floors below in order to gain access via a clear elevator lobby; this assuming, of course, that the elevators are even operational. However, relying on a building?s stairways to provide occupants with a safe method of egress is dangerous in itself due to the combination of the Stack effect and the Breaking-of-the-Seal effect.
"[The] Stack effect is a natural phenomenon affecting air movement in tall buildings. It is characterized by a draft from the lower levels to the upper levels, with the magnitude of the draft influenced by the height of the building, the degree of air-tightness of exterior walls of the building, and temperature differential between inside and outside air."x
Thus, during a fire, smoke and toxic gases are carried upward through a building in a natural air draft that causes the upper floors to be contaminated first, with smoke then proceeding downwards, contaminating the subsequent floors down to the fire floor.10
Even in buildings that are compartmentalized to contain the spread of smoke and fire, the stairwells can quickly become the most dangerous place for occupants to be. As occupants on lower floors begin evacuating the building, opening doors to corridors and stairwells in the process, smoke, due to the Stack effect, naturally diffuses into stairwells and begins rising towards the upper floors. Occupants on higher floors, therefore, become unable to use the stairways for egress due to their rapid contamination. This Breaking-of-the-Seal effect, the opening of doors that results in the loss of smoke containment, is one reason why occupants are told never to wait to evacuate until the fire department arrives: When firefighters enter a burning building, they unavoidably prop open the building?s hallway and stairwell doors with their hoses and other equipment. Smoke, as a result, rapidly spreads and contaminates the passageways and stairwells of the buildingxi making the prospect of successful evacuation even less likely and more dangerous. In situations such as this, "protecting in place," or securing oneself against smoke contamination in a room or office, is the recommended course of action.