This is taken from fireengineering.com from an article dated from January 1st, 1996, title The Dangers of High Rise Firefighting, section: Collapse:
"At the 1 New York Plaza high-rise fire in New York City in 1970, the major structural damage was floor collapse. Twenty thousand square feet of concrete and steel floor deck and 150 steel floor beams were replaced. The fire caused the floor above to buckle, crack, and heave upward. Floors and partition walls were slanted upward and sideways. No floor slab collapsed, but firefighters could not safely enter the floor area that was cracked and buckled upward because of the collapse potential.
The floor of a skeleton steel-frame high-rise structure is usually corrugated steel 10-foot by 12-foot sheets covered with two or three inches of concrete. This combination steel and concrete floor deck is supported by steel beams in a gridiron design. When the heat from a fire destroys the ceiling and heats up the underside of a floor`s corrugated steel, the section of concrete above will crack at the seams and buckle upward; then, a section of floor will sag as the steel beams below also warp, twist, and buckle.
At the Banker`s Trust Company Building fire in New York City in 1993, an officer reported that the floor above the fire he was searching was beginning to buckle and sag. He noticed file cabinet doors suddenly opening. Entire lengths of the file drawers rolled out of the cabinets. After the fire was extinguished, the cause of the file drawers` opening was found to be sagging and collapsing floors. As the steel and concrete sections of floor sagged, cabinet drawers slanted downward and rolled out.
At a high-rise fire in Montreal, Canada, that burned several floors, a 10-foot by 12-foot section of floor collapsed to the floor below.
Thus, be aware that a fire-resistive high-rise building can experience fire spread from floor to floor as well as collapse in a fire.
Wall collapse. At the One Meridian Plaza fire in Philadelphia, sections of the granite wall collapsed. Flames spreading upward from window to window on the outside of the structure heated the granite facade. Large chunks of heated granite weighing 20 to 30 pounds came crashing down on the sidewalk, narrowly missing firefighters. (Stone and concrete are subject to spalling--the collapse of masonry sections caused by the expansion of moisture inside the stone or concrete--when heated.)
Building collapse. At a five-alarm fire in 1990 in the Empire State Building, a reinforced concrete and steel structure, pieces of the concrete ceiling collapsed on firefighters advancing a hoseline. If a concrete structure does not have a drop ceiling, its ceiling will be directly heated by fire. Spalling will occur. Chunks of concrete ceiling will collapse on the helmets of firefighters advancing an attack hoseline. Concrete pieces weighing 10 to 20 pounds falling 10 feet can cause serious injury.
Suspended ceiling collapse. High-rises can have lightweight suspended ceilings. A thin metal and wire grid system holds removable panels. If flames heat the supports, the suspended ceiling can collapse. Firefighters can become entangled in the thin metal framework and suspension wire, or in falling electrical conduit, after a collapse, trapping them in a flaming room or hallway. Thus, the injury a firefighter receives from a suspended ceiling collapse may come not from being crushed but from smoke and burns following the collapse. When searching a floor at a high-rise fire, lift a panel of the suspended ceiling with a six-foot pike pole. Fire may be spreading in the space above the ceiling, over your head.
Fluorescent light fixture collapse. Even before spalling occurs, large, heavy, suspended fluorescent light fixtures can collapse during a fire. These fixtures can weigh 20 to 30 pounds and are suspended by wire or chain and fastened into the concrete ceiling by lead fasteners or anchors. The heat from a fire will quickly melt the lead fastenings, and the light fixture can fall. Concrete structures such as public schools, hospitals, and high-rise office buildings have these collapse dangers in their halls."
Source: http://www.fireengineering.com/articles/print/volume-149/issue-1/features/dangers-of-high-rise-firefighting.html
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