CHECKING FOR FIRE SPREAD AT A HIGH-RISE FIRE
BY VINCENT DUNN
When searching the floor above a high-rise fire for fire extension, firefighters must know exactly where to look. It is not a hit-or-miss operation. You cannot wander around a 20,000-square-foot floor area that has 150 rooms, cubicles, and spaces smelling for smoke. There are specific areas to which fire has spread upward at previous high-rise fires. Fire officers must know these locations and quickly examine them for fire spread. If firefighters discover vertical fire spread, they must quickly notify the officer in command so a hoseline can be stretched to extinguish the fire.
WINDOW-TO-WINDOW FIRE SPREAD
The most common type of vertical fire spread in a high-rise building is from window to window above. Sometimes called “autoexposure,” flames lap out a window and flow upward, with heat cracking or melting the window directly above. Fire then spreads into the floor above through the broken window.
The window frame in a high-rise building may be constructed of aluminum, plastic, or stainless steel. The frame can melt when exposed to heat from a flame. Once the window frame is destroyed, large sections of glass fall out, and fire can enter and involve the whole floor. Or, fire can enter via radiant heat or through window cracks or smaller broken sections created by the heat.
Flames spread to the floor above through autoexposure ignite combustible curtains and ceiling tile near the broken window. Firefighters searching the floor above and discovering flames about to enter a window can take one of several actions once they have notified the incident commander.
If there are iron shutters in the open position on the outside wall, try to close them.
If the window is open, shut it.
Remove combustible shades, curtains, or drapes near the window.
If the ceiling near the window is combustible, pull it down with pike poles when the underside of the floor below is of noncombustible steel or concrete.
If there are combustible papers or boxes near the window, move them.
Stretch the hoseline from the standpipe, and wet down the area near the window.
If a sprinkler head is near the window, order the sprinkler siamese to be supplied with water.
CURTAIN WALL VOID
Skeleton steel high-rise buildings sometimes have an exterior curtain wall enclosing the structure as an outer skin. The curtain wall can be constructed of aluminum, stainless steel, glass, masonry, or plastic. It extends over the entire face of the building and is attached by bolts to the edge of the floor slabs on each level of the structure. However, there usually is a small space between the outer edge of the floor slab and the inside of the curtain wall through which flames and smoke spread to the floors above. Firefighters searching the floor above a high-rise fire must check this space for fire spread. If this concealed space is not firestopped with a noncombustible filler, fire and smoke can spread vertically. Open up the outer wall partitions below the window to check the void during search.
Older high-rises have a panel exterior wall–a nonbearing brick or stone wall that rests on the outer edge of the floor slab. It extends only one story and has no concealed spaces; thus, it does not have the avenue for fire spread that a curtain wall does.
UTILITY CLOSETS
Shafts containing electric power, communication cable, and water and sewer pipes extend upward throughout every floor of a high-rise. They sometimes are enclosed in small rooms called utility closets. The wire, cable, piping, and conduit rise up through holes in each floor level. These holes are known in the fire service as “poke-through holes” and allow vertical fire, heat, and smoke spread. Firefighters searching the floor above the fire must examine these holes for fire spread.
Fire spread in a utility closet is the most critical type for a number of reasons. Fire can extend 10 or 20 floors quickly if not stopped; also, the closet contains electric power, which must be shut off for extinguishment. And in some instances, the insulation of the wire or plastic piping is combustible and, once ignited, adds to flame spread.
Tests have shown that vertical fire spread in a utility closet containing conduit covered with combustible insulation will be as rapid as fire spread in a concealed space containing combustible lath and furring, as is found in ordinary or wood-frame buildings. For example, a fire in the World Trade Center in the 1970s spread into a utility closet containing telephone wire through louvered vents at the 11th floor. Flames ignited the electric wire`s combustible insulation and spread rapidly to the 41st floor. The lesson learned is, when you discover burning combustible insulation in a utility closet, you must check the utility closet on every floor of the high-rise. Flames that are burning insulation in a utility closet can skip several floors and then break out again. Also, flames can spread downward in a utility closet, so you must check all floors below the fire as well.
AIR-CONDITIONING PERIPHERY VENTS
When fresh air is supplied to a high-rise building through a central air system, it distributes air to a floor at the center of the floor area and at the periphery near the windows of the outer offices. Fresh air supply vents at the periphery of the floor come up from the floor below. Poke-through holes at the floor slab`s outer edges allow fiberglass ducts to extend up from the floor below. Periphery air is supplied to the outer offices through these ducts. During a fire on the floor below, the ducts sometimes burn away and smoke and flame–instead of fresh air–come up through the ducts. People trapped on the floor above may seek refuge in an outer office near a window, hoping to be rescued. They can be asphyxiated by smoke pushing up through the air ducts.
FLOOR COLLAPSE
Floor construction in a modern high-rise can consist of two inches of poured concrete on top of corrugated steel sheets. At a serious high-rise fire that burns uncontrolled for a long time, the suspended ceiling is destroyed and flames heat the underside of the floor above. The floor above the hottest part of the fire below buckles and heaves upward. Concrete on top of steel sheets cracks and heaves upward six inches or more. The floor cracks at the seams of the steel sheets, and flames can spread up through the cracks.
At the One Meridian Plaza Fire in Philadelphia in 1991, flames spread upward through cracks in the concrete floor. Here`s how an eyewitness observed fire spread: “First, the floor above the fire filled up with smoke, heat, and combustible gases. Next, a so-called `pilot` flame rose up through the middle of the cracked concrete floor. This flame rose up three or four feet, and suddenly the combustible superheated gases that had accumulated on the floor ignited. Floor after floor, this cycle occurred. The floor filled up with superheated combustible gases, then the `pilot` flame appeared, then sudden ignition.”
OPEN STAIRWAY
If, on entering the floor above a fire to search, you encounter large amounts of smoke and heat, consider the possibility of an open stairway connecting the fire floor to the floor you are about to search. In some high-rises where one company occupies several floors, the building code allows several floors to be connected with a decorative open stairway. Sometimes called an “access” stair, it allows an employee to go up or down several floors without having to go out of the office to use an elevator or exit stair.
These open stairways are extremely poorly designed from a fire protection standpoint. They render fire-resistive construction useless. Fire, heat, and smoke quickly spread up through an open stairway. Firefighters searching above a fire can become disoriented by smoke and fall down an open stair into the fire. When you encounter such a stair, immediately notify the IC.
CENTRAL AIR-CONDITIONING RETURN AIR DUCTS
One of the major avenues of fire spread at the First Interstate Bank Fire in Los Angeles in 1988 was up through a return air shaft of the central air-conditioning system that ran from the 12th to the 32nd floor. It was enclosed with 58-inch gypsum board and metal studs. The gypsum walls failed during the fire, and flames entered on the 12th floor and spread to the 13th and 14th floors by way of the return air shaft. Flames skipped floors 15 to 26 and spread from the shaft out to a storage room on the 27th floor. Fire spread into the return air shaft due to the collapsed gypsum and then spread from the shaft to the 27th floor through the dampers.
Firefighters searching above a fire must check the openings at the return air shaft to see if fire is spreading out of it onto the office floor. The return air shaft usually is located in the center core of the floor. Look on the floor plan for the exact location. The opening in the return air shaft is located above the suspended ceiling in the plenum and below the floor below. To examine this opening to the return air shaft, you have to remove the suspended ceiling near it. If fire or smoke is extending out of the return shaft through the opening, shut the damper manually (if possible) and notify the IC to ensure the central air system has been shut down.
A fire company assigned to search for vertical fire extension on the floor above a high-rise fire has an extremely dangerous assignment. Make sure you take certain safety precautions first.
Size up the fire you are going above. Are fire forces capable of extinguishment?
Use a stair clear of smoke and fire that is not being used by the attack line.
Assign a firefighter to warn of a fire increase that may cut off your escape route.
Notify the IC when you go above the fire and when you safely return.
You may need forcible entry tools to gain access.
Use a search rope–for quick exit if smoke suddenly increases and visibility is reduced or to quickly stretch a hoseline to an area where flame is spreading.
Use lights, masks, and portable radios. n
