The Untold Threat of High-Rise Fires
Fighting of high-rise fires has not been very successful. The main reason is that many of these fires occur on floors that are beyond the reach of fire department ladders and cannot be attacked with streams of water from the outside. For the same reason, it is very difficult to evacuate personnel and remove victims. Experience shows that extinguishing the fire takes about two hours of firefighting for each affected floor.
Vincent Dunn, the former deputy chief of New York Fire Department, says the best kept secret in America's fire service is that firefighters cannot extinguish a fire in a large open floor area in a high-rise building. Although such buildings have been classified as fire-resistant, actually most of them are not. Central air-conditioning systems are particularly conducive for spreading flames and smoke between floors. For example, fire and smoke spreading through the air-conditioning system at a hotel fire in Las Vegas killed 85 people.
Because of the size of the high-rise buildings, it takes the fire departments much longer to get to the source of the fire. It takes 15 minutes or more to get in place and further delays may be caused by failed elevators. A New York City study showed that elevators failed in about a third of major fires. This requires firefighters to carry their gear up many floors while the fire has time to spread.
The key to successful firefighting in high-rise buildings is the standpipe system which pumps water to the higher floors. Chief Dunn points out that in too many cases, the system does not work. In some of the major fires on record, the system was shut down for repairs at the time of a fire, the building fire pumps were not operating, the outlet valves melted or were set at an inadequate pressure.
The result is that high-rise fires that involve an entire floor or more of a building, are subjected to what the fire departments call "controlled burning". That means that firefighters maintain a defensive position until all the combustible contents have been burned. Large numbers of firefighters are needed to control the fire and keep it from spreading to adjoining buildings, but they are not always available.
While much discussion has focused on fighting the fire, the effects of smoke can be even more devastating, especially to the building occupants. Because these buildings do not have windows that can be opened, large volumes of heat and smoke become trapped inside the structure. This is called the "stack effect" which results from the temperature difference between the inside and outside of a sealed high-rise building. The stack effect causes uncontrollable smoke movement within the building that cannot be reliably contained through ventilation.
The standard instructions for the occupants of a burning building are to stay in place until ordered to evacuate. Chief Dunn says that this does not work and the occupants will attempt to leave the building anyway. In the case of the 1993 explosion at the World Trade Center, 50,000 people left the building without instructions. More than 300 jumped to their death. Part of the reason was that the building communications system was damaged and people were on their own. But even in normal situations, the communications gear carried by the firemen does not work above the 65th floor and transmission within steel structures is problematic. Special antennas are now being installed in some buildings to deal with this situation.
The question can be asked whether it is ethical to follow the so-called "defend-in-place" strategy whereby a fire is fought with most of the occupants remaining inside the building. In the past, there was no alternative. More recently, however, various companies have developed techniques, such as slides, chutes and descenders that permit the escape of occupants through windows, balconies or from the roof.
The use of such systems introduces a new set of problems. If windows are broken, the falling glass may injure or kill personnel and cut the fire department hose lines. Uncontrolled mass evacuation outside the building could interfere with fire department operations.
There is no question that use of personal escape systems would save lives in some circumstances. In most cases, however, the defend-in-place strategy may be more appropriate. In the best of all worlds, individual escape procedures would be coordinated with the overall firefighting operation. This would be easy in office buildings that have designated fire marshals on each floor. They would authorize individual escapes upon coordination with the fire chief. Specific windows could be set up to open for egress and avoid breaking glass in an emergency.
The situation in residential buildings is different. While the number of occupants in such buildings is typically smaller, communication with them may often be impossible. Matters are further complicated by the fact that many apartments have only one door. When it is blocked by fire or smoke, exiting directly to the outside may be the only chance to escape. In such situations, the occupants would have to decide for themselves when to use any unconventional escape technique they have available.
(For the full story by Vincent Dunn go to http://vincentdunn.com)
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