CAN HIGH-RISE COLUMNS FAIL?
Two recent fires in high-rise buildpings—One Meridian Plaza in Philadelphia and the First Interstate Bank in Los Angeles—have presented the fire service with the unthinkable problem of a multifloor raging fire in an unsprinklered high-rise building. It is reasonable to assume that there will be other such fires.
Both fires were fought by fire departments with great resources. Only a handful of departments could mount and sustain such operations. All fire departments, particularly those without such resources, should press vigorously for full sprinkler protection for all high-rise structures.
The duration and intensity of the two fires focused attention on the possible loss of strength and stability of the structural frame. In both eases, the structural steel frame endured the fire. Can we draw’ from these experiences that we need not fear collapse-even in a raging high-rise fire? I believe the answer is a resounding no.
In First Interstate, the steel was protected with a cementitious coating. In One Meridian, the steel was protected with sprayed-on mineral fiber with a cement binder and some asbestos (the columns were finished with gypsum board, but this was not part of the rated fire-resistant system). Over the years, many methods for insulating steel have been used, and some are more reliable than others.
INDIVIDUALLY APPLIED FIREPROOFING
When it was first recognized that despite its noncombustibility, steel still can be damaged by fire, the insulating system —called “fireproofing”— was devised and required to be incorporated in buildings where steel is used. “Fireproofing” was a bad word choice and created problems that were compounded by calling buildings with such insulation “fireproof.” Many buildings of this type still exist. It is important, therefore, to consider the type of protection provided for the structural system when preplanning a highor low-rise monumental building.
Tile, concrete, gypsum board enclosures, and spray-on fireproofing are examples of individually applied fireprtxjfing—each steel member is individually protected.
Brick unci tile. The first “fireproof” building had brick segmental arches “sprung” between unprotected steel beams. loiter, flat arches of terra-cotta tile were used. When failures of buildings made it evident that the steel must be protected from the fire, “skewback” tiles were developed to provide protection to the bottom flange of the steel beams.
Concrete. Early high-rise structures were fireproofed in whichever manner the designer thought best. The still-standing columns in the Government Printing Office in Washington, D.C., were surrounded by a brick box. Concrete was poured into the box from a substantial height. This probably caused the aggregate to sink to the bottom, making the concrete’s ability to hold doubtful should a fire occur. The circular cast iron columns of New York’s Parker Building were “fireproofed” with three terra-cotta blocks. The then-new electrical conduit was concealed behind the tile. The fire that occurred in 1908 elongated the conduit and caused it to rip the tile off the columns. There was a massive interior collapse. The building was destroyed, and three firefighters died. Buildings of this era are still in use.
The Parker Building fire; the 1912 Equitable Building fire, also in New York; and the 1904 Baltimore conflagration, which involved many “fireproof’ buildings, convinced all concerned that there was a dire need to develop standards and test procedures for “fireproof’ construction and that the growing concern about column stability was warranted. (See sidebar on page 67.)
Fireproofing for high-rise steel buildings prior to World War II was usually concrete cast in place around the columns. Floors also were of cast concrete. The wooden forms used for the concrete provided many spectacular fires, such as those involving the Sherry Netherlands Hotel in New York and the Statler (now the Hilton) in Washington, D.C. The heavy concrete fireproofing added substantial weight, which required that heavier steel be used. Steel was the only suitable material, so the added costs were accepted. Concrete fireproofing once in place is most likely to stay in place.
After World War II, designers turned their attention to cheaper reinforced concrete for the frames of high-rise buildings. Some steel companies developed superior reinforcing rods that made concrete-framed high-rises practical. Some concreteframed high rises are several hundred feet high. Often the decision to use a material rests on economics. Some buildings may appear to be identical, but one could be steel-framed and the other concrete-framed.
Concrete has an advantage. In listing the costs of a steel-framed building, “fireproofing” is an identified line item. No such item appears in the cost breakdown for concrete buildings. Fire resistance is achieved in the formulation of the concrete. The decrease in the use of structural steel caused the steel industry’ to look for lighter, cheaper ways to protect steel.
Asbestos. Spray-on asbestos fireproofing then became widely used and created many problems. During testing, for example, the column was washed with carbon tetrachloride before the protective material was applied; this was never done in the field.
A West Coast insurance executive took pictures during the spraying process used at a building owned by the state of California. The contractor was sweeping up overspray material, placing it on the lower flange of beams, and spraying over it. A fire in that building caused serious structural damage. It cost as much to repair the building as it did to construct it.
An engineer and I found that all the fireproofing had been removed from columns on the 30th floor of the Bank of America building by the plasterers. Sprayed asbestos material is easily removed by any of the trades that find it inconvenient. At another fire, hose streams stripped the fireproofing material. Firefighters were forced to retreat, and the steel was heavily damaged.
On more than one occasion, sprayed fireproofing has been found generously applied to all exposed steel surfaces in a building, including the sprinkler system.
An insurance engineer rated a Las Vegas high-rise hotel as unprotected steel because of the poor fireproofing. This raised the cost of insurance considerably. After objections, the building was reinspected and rated fire resistive.
Asbestos, because of the health hazards it presents, is no longer used and is being removed from many buildings. It still, however, represents a hazard to firefighters and fire investigators. After the Du Pont Plaza fire in Puerto Rico, it was learned that many guests had returned home with what probably was contaminated baggage. When an asbestos-covered steam main blew up in New York, a number of pieces of apparatus were contaminated, and concerns about firefighters’ exposure to asbestos particles were raised.
The fire department should know what is being done to replace the originally required fireproofing after the asbestos is removed. The bottom line is that for a fire in any building fireproofed with asbestos, the firedepartment should (1) prepare for aggressive heavy attack to suppress the fire as early as possible; (2) evacuate the building if the fire cannot be suppressed; and (3) be very aware of the contamination potential.
Gypsum board. This material is a component of some listed systems, and when used in structures it is important that it be applied in accordance with a listed system. Some inspectors or tradesmen do not realize that taping joints and covering nails is a vital part of the fire resistance system. They consider these actions cosmetic touches that should be applied only to surfaces to be painted.
MEMBRANE FIREPROOFING
This type of fireproofing encompasses assemblies. Membrane fireproofing uses a suspended ceiling that provides a membrane under the areas to be protected. The membrane may be cement plaster on wire lath. In recent years, the use of a suspended acoustical tile ceiling as the membrane has become more prevalent. The steel structure requiring protection is left bare.
Unprotected columns. Failures that would involve sections of a floor or an entire floor are serious enough, but there is a much more serious condition permitted by some building codes that might result in a catastrophic partial or total structural collapse of a supposed fire resistive building
Some codes permit the omission of fire protection for columns as they pass through the plenum (void) space. The concept is that the bare areas of the column are protected by being within the rated fire resistive floor assembly. The deficiencies cited above conclusively demonstrate that this concept is dangerously defective.
There is a clear warning contained in Fire Protection Through Modern Building Codes, published by the American Iron and Steel Institute, Washington, D.C. (5th edition, p.126). that protective materials should extend to the full column height. There should be no discontinuities— either by cutoffs at the ceiling lines or at other constructions that may abut the column.
Fhe removal of one tile near an unprotected column in a high fire load area could be the most serious hazard, since the heat output of the fire would be concentrated at a single vulnerable point. Imagine the huge volume of fire pouring out the windows of the First Interstate Bank Building in Los Angeles being concentrated on an unprotected steel column. The whole column need not be heated; the heating of a foot or two would be sufficient to cause buckling of the column.
A single 50-vear-old temporary wooden platform burned in the i2nd Street subway station in New York City. Serious failure of the unprotected columns resulted in the collapse of the street above. Similar damage to a high-rise building might well cause catastrophic collapse.
In some observed cases, the column protection in the plenum consists of gypsum board enclosures. True to the widespread erroneous trade belief that the taping of joints and nail-setting is merely cosmetic, the nail heads and joints sometimes are left untaped. Exposed to fire, such incomplete assemblies will fail rapidly-
The fire department should be aware of all buildings in which the columns are bare or inadequately protected in the hidden area of the plenum. This information must be available to the fireground commander for use at a serious fire. The information cannot be kept in the files of the Building Department or Fire Prevention Office, where it will surface only after a disaster has occurred.
It is not sufficient to say that there has been little bad experience with rated ceilings. The potential for serious problems exists. Experience is not the best teacher, but it certainly can be the most expensive. There are dangers, and the fire department must be prepared to present its point of view to code authorities, to train its own personnel, and to educate the owners and occupants of membrane fireproofed buildings.
Concrete columns. Whether or not a concrete column is adequately fire resistive depends entirely on its being properly formulated. The only test is a serious fire.
When I built a Navy firefighting school in Panama during World War II. there was no steel available for a tank. A concrete foreman who had built fire resistive structures built a tank that survived hundreds of fires. Another foreman, supposedly following the first foreman’s instructions, built a pit. It spalled violently during every fire.
The term “reinforcing” rod is a misnomer. Steel provides the tensile strength, and concrete the compressive strength. Together, the steel and concrete form a “composite element”; any failure of the bond between the steel and concrete means that the structural element has failed. In the case of columns, in addition to dealing with tensile loads, the vertical rods are columns in their own right, carrying part of the compressive load. The compressive strength of steel is about nine times that of concrete. In some columns in the lower floors of high-rise buildings, there is so much steel so close together that chemicals are added to the concrete so that it will flow between the rods.
Any sign of vertical rods breaking out a column indicates severe distress and justifies immediate evacuation of the building. A few buildings have post-tensioned columns. The tendons used for post-tensioning are cold drawn steel that loses its tensile strength at 800°F. Any such building should be carefully monitored. Unlike beams and floors, which may fail gradually and give warning, column failures are “sudden and catastrophic” — to quote one expert.
HAZARDS OF FLOOR-CEILING ASSEMBLIES
Buildings with floor-ceiling assemblies, particularly where the columns passing through the plenum space above the ceiling are unprotected, can represent a serious menace to the safety of firefighters who are, in the main, completely unaware of the dangers. A few of the deficiencies are
- Builders sometimes disregard detailed instructions, particularly when they do not understand them or find them inconvenient. A fire inspector found aluminum wire being used to support the ceiling channels. “What’s the matter with aluminum?” asked the mechanic.
- The value of laboratory listing is contingent on the assembly being accomplished exactly as performed in the laboratory. Few building inspectors have sufficient expertise and time to follow and examine each item.
- Owners, managers, and occupants—even of buildings where fire protection equipment is well maintained—usually are totally unaware of the significance of the absolute integrity of the ceiling system. A common practice is to remove tiles from the
- storeroom (who needs a fancy ceiling in the storeroom?) to replace tiles in locations seen by the public. Tiles are damaged by water leaks. Tiles arc removed by tradesmen. Holes are cut through tiles. Displays are hung from the metal grid (floor-ceiling systems are not tested with superimposed loads). Where the plenum space is part of the air-conditioning supply, smart employees soon learn that displacement of a tile improves airflow at their location.
As far as I know, codes do not require that the membrane protection be maintained. Even if the code stipulated such maintenance, it would be difficult to enforce.
- There is no guarantee that a supply of replacements such as light fixtures will be identical to those tested. This probably would be unnecessary though, since it is most unlikely that the building owners and contractors realize that exact replace-
- ments are necessary to preserve the structure’s fire resistant system.
- The term fire rated is used quite often in the fire protection and building construction fields. By itself it is nonspecific and therefore meaningless. With respect to ceiling t.ks, for example, it may refer to tiles that merely have met the requirements for flame spread or tiles that are part of a listed fire resistance system.
- The laboratory fire tests are necessarily conducted under a slight negative pressure to remove smoke and fumes. Fires generate positive pressure, and lay-in ceiling tiles may be easily displaced by fire pressures. When a tile is displaced by a mechanic, it often is just dropped back down into place without any restraint to upward motion.
- The addition of insulation not part of the specifications of the listed roof-and-ceiling assembly can significantly affect the fire performance of the assembly. The insulation will cause heat to be retained in the channels supporting the tiles, making them fail earlier than expected.
- By its nature, a membrane protection system must be perfect. The failure of even a single tile is the equivalent of a pinhole in a condom.
- Some codes provide for firestopping, but the use of the plenum space for various services makes it probable that the firestopping wall be ineffective. The use of deep, long-span truss-
We noted earlier that in effect there is a cockloft between the ceiling and the floor. In one incident I investigated, a fire that started in one room traveled across a hallway above the ceiling and came dow n through joints in the tile ceiling of another room to ignite books on a top bookshelf. Only alert firefighting prevented the full involvement of the floor.
i es to provide clear floor areas creates plenum spaces several feet high — high enough for a person to walk upright. It is simple to provide access to this interstitial space and use it for storage. The fire load has been placed adjacent to vulnerable unprotected steel, in a location in which firefighting will be almost impossible *
