COLLAPSE INDICATORS DURING OPERATIONS
BY TOM BRENNAN
Last month we discussed some of the signs that show stress to the structural integrity of the building during the firefight. When I mentioned puddles on the floor, I meant that the puddle is more than an inconvenience to firefighters wearing shoes instead of boots. The floor is overloaded–tension stress is building to the max! (The beams are bending.) Collapse can take the form of lean-to if supports on one side of the floor let go, “V” if the beams crack in the middle, and pancake if the whole floor lets go (remember, no floor below is ever designed to take the “hit” of the floor above it).
If you are ever in doubt, open the base of the interior finish on the bearing walls and look at the position and condition of the beams and surfaces that support them.
Another indication of collapse is if you notice new flooring material near the baseboard and it`s quarter round molding. Why would there be clean, bright, new-looking floor finish against a wall? Simple–either the floor is moving away from the wall or the wall is leaving the floor. In any event, it is a major collapse indicator.
Finished interior wall movement. In older construction, plaster slides off the lath or falls from the ceiling. In new construction, plasterboard buckles as the studs holding it move. This may be accompanied by a noise louder than other collapse signs. Regardless, report it and prepare to retreat.
The lesson here is that these subtle signs have been present at many collapses in the past. The sad case is that they were reported during the critique phase of the operation–after the building collapsed. All firefighters must be trained to recognize and report interior collapse signs.
Elastic steel beams. Steel moves! As I have said here before, this is the single most serious reason that a masonry wall will begin to bulge during firefighting operations. The steel will elongate eight inches in 100 feet of span. No doubt, if it bulges the wall, that is one sign. But what happens if the wall is too strong? The eight inches is developed in the twisting of the beam, and it begins to drop its load of beams and rafters. Steel exposed to fire is itself a collapse indicator.
It is worth repeating a myth that firefighters still find confusing when asked: If a steel beam is glowing, do you hit it with the cold stream from the nozzle? YES! Steel is elastic, and you will stop the expansion factor. According to the books, it may begin to retake its original shape. The confusion comes from old writings in dealing with cast iron support columns, which cautioned that heated cast iron would shatter if you applied cold hose streams. And that, according to Frank Brannigan (Building Construction for the Fire Service), was only if it was a poor cast. Hit the hot steel and check for other indicators.
While we are still inside the building–one more thought. All building materials have a different coefficient of expansion (and contraction). This is a tricky mathematical phrase that means all materials move, when heated, at different rates. As fire exposure time goes on, get used to looking at all areas of structure support. Metal window lintels and brick support points, corbeling and parapets, stair stringers and walls–everything was connected before the fire, and it all is moving at its own pace.
Outside streams. What are the collapse factors? One that never gets “play” is complacency–once we are outside and defensive, firefighters tend to believe that the safety threat is over. More members are injured from collapsing structures outside buildings than inside. Remember the collapse zones.
Someone should keep track of how many and the length of time large-caliber streams have been operating. Water weighs eight-and-one-half pounds per gallon, and a 750-gallon stream “dumps” three tons of weight into a weakened structure every minute. Where is it? If it is running out and down the street, fine. If it is not, the building is dangerously overloaded.
Today`s tower streams pack a wallop. As a matter of fact, the job of a highly maneuverable tower ladder stream is to do interior damage–tear down the ceilings, plow through interior partition and bearing walls to get at hidden fire. There is an old adage: “One pound per square inch of pressure can knock over a 12-inch brick wall.” Watch for additional structural damage during aggressive defensive firefighting–you may be forced to take another position once collapse is forecast during outside stream operations. A pretty good rule is that once the building is turned over to tower ladders, keep moving them until they finish the job! The practice of always going back inside with hose streams after the towers shut down is unsafe nonsense.
Remember, the wall that the towers are most effective on for interior access is the weakest of the four enclosure walls–the one with the most openings: the front of the building.
High rack stacking of stock is a subtle collapse indicator. The fire burns, unaccessible and hidden for longer periods of time–longer periods for the heat to attack structural integrity. Handlines become difficult to maneuver rapidly–again, longer heating time. This type of storage also provides for an unusually high likelihood of injuries because of local collapse (including of the rack itself).
So you see, with all these signs, how can we say the collapse was a surprise? All these indicators were factors in collapse operations time and time again, only they were not recognized! Or recognized and not reported! Or reported and not recorded! n
TOM BRENNAN is chief of the Waterbury (CT) Fire Department and a technical editor of Fire Engineering. He spent more than 20 years in some of the world`s busiest ladder companies in the City of New York (NY) Fire Department. He is co-editor of The Fire Chief`s Handbook, Fifth Edition (Fire Engineering Books, 1995).
