FIRE BREAKS DOWN CONCRETE
FIRE REPORT
An intense fire in an industrial section of Chicago causes massive structural damage to a fire-resistive concrete building.
(Photo by Chicago Fire Department.)
(Photo by Chicago Fire Department.)
IN CHICAGO on the afternoon of Friday, April 14, 1989, a fire involving thousands of old automobile and truck tires illegally dumped in a vacant building resulted in unusually severe structural damage to a sevenstory industrial building. Tire fires are notorious throughout the fire service for being extremely hot, smoky, and difficult to extinguish, but even by fire service standards this fire was exceptional. Before it was over, seven alarms were struck and overhaul continued for more than a week.
The fire buildings were located in a row of large industrial structures that extended for more than one city block. Some of the buildings were in use as manufacturing or warehouse facilities. This industrial section was bounded by a railroad embankment to the east, the Chicago River to the west, and other commercial stuctures to the north and south.
The fire originated in or adjacent to a one-story, combustible, sprinklered* warehouse constructed of exposed steel frame and built in 1956. It was used for the storage of thousands of old tires. The warehouse adjoined an older, seven-story, fire-resistive building, formerly used as a printing plant, on the exposure 2 side. That building’s basic structure was of steel-reinforced con-
*Sprinklers were not in service; the building was vacant for several years and the fire department was unable to locate the Siamese.
Crete, built to accommodate heavy printing machinery. Each floor in its “flat slab” floor system was approxi mately 18 inches thick and was support ed by 28-inch-diameter concrete col umns approximately 18 feet on center The 90-foot-high building was con structed in two sections in 1921 and 1927; the older section measured approximately 100 by 225 feet and the newer section, adjacent to the original fire building, was about 125 by 225 feet. These sections were separated by a fire wall with openings protected by sliding steel fire doors, most of which did not operate. Tires were scattered about the first floor of this building and also outside on the ground.
The fire rapidly involved the entire one-story tire warehouse, then quickly communicated to the first floor of exposure 2, fueled by tires carelessly dumped there. It became the kind of hot, smoky, stubborn fire typical of burning tires. It burned long into the night, generating an enormous column of smoke. Fire also developed on the upper floors, but this was attributed to combustible partitions in vacant office areas. Fortunately, the bulk of the fire was contained in the newer section of former printing plant, but by the time it was finally extinguished it hadn’t left much. Ultimately, even the gravity tank burned.
What made this fire noteworthy was the extent of structural damage sustained by the fire-resistive occupancy. After the fire was controlled it was discovered that the burning tires had generated enough heat to cause failure of the massive interior columns. The columns spalled extensively, exposing the inner steel-reinforcing bars to the intense heat of the fire. This, in turn, resulted in the structural failure of the concrete floor slabs over the fire and progressive failure of the columns and floor slabs on the upper floors. Floors two through seven —the entire structure-had either collapsed entirely or sagged several feet.
(Photos above and right by author.)
This fire presents an interesting case study of two opposing elements: a massive fire-resistive structure and the enormous thermal energy produced by burning rubber. The value of fire-resistive construction is the structural integrity it provides under fire conditions. This structural integrity permits bolder tactical firefighting than in non-fire-resistive structures. This is especially true with respect to steel-reinforced concrete structures. The concrete serves as a noncombustible insulator to protect the reinforcing steel within. The concrete floor slabs act as excellent barriers to the vertical passage of fire unless they have been penetrated.
Where concrete structural systems fail under fire conditions is typically due to spalling. Spalling results from deterioration of the concrete due to expansion of moisture locked within the concrete as it hardens. When the concrete spalls, the reinforcing steel is exposed to the fire, resulting in its failure. However, this occurs only under very severe fire conditions.
Rubber has a heat of combustion close to that of gasoline. Ironically, rubber is also a waterproof material. These two characteristics make rubber fires extremely hot and deep-seated under any conditions. In this industrial fire, the heavy concrete floor areas acted to confine a large amount of heat within the structure. The building, in effect, became a huge oven. Stream penetration was limited. The heat forced the firefighters to work from a distance, and then it quickly vaporized the water.
Fortunately, the incident commander was able to call the Chicago Fire Department’s fireboat into service early in the incident. Although the boat is stationed some 20 miles from the fire scene and took some time to get there, events proved the decision to be a good one. The fireboat is capable of pumping 12,000 gpm —and where tire fires are concerned, there is no such thing as too much water.
(Photo by author.)
