SOMETHING FOR EVERYBODY
BY FRANCIS L. BRANNIGAN, SFPE
High-strength concrete is currently being widely used. It appears to be subject to explosive spalling, which would be hazardous to firefighters and greatly reduce the fire resistance of the structure, possibly leading to collapse.
I am working on the subject. In the meantime, I urge that you contact the building department, determine those buildings built of high-strength concrete, and note this in preplans. The possibility of a hot sustained fire in cargo was not anticipated in the planning of the English Channel Tunnel. A large area of concrete tunnel simply spalled out of existence. Fortunately, it was in solid chalk at the point of the fire.
The spalling of concrete will expose the steel “reinforcing,” which provides tensile strength to the composite concrete. This is particularly dangerous in tensioned concrete. The steel tenons totally fail at 8007F.
“MY WAY OR THE HIGHWAY”
The ranks of the imperial fire chief whose solution for any problem was to shoot the messenger are thinning, but the species is not extinct. We reported earlier the successful (approximately) $500,000 civil suit by Seattle`s former safety officer against the city.1 Fire Control Digest (April l998) reports that the State Department of Labor and Industries fined the city $45,000 for failing to tell line firefighters about arson threats against the warehouse, where four firefighters died, and to require that firefighters activate personal alarms and wear breathing apparatus. A $25,000 fine was for obstructing Safety Officer Rodney Jones.
NEW YORK CITY ACTS ON WOODEN I-BEAMS
The hazard of wooden I-beams was brought forcefully to the attention of New York City firefighters in the “near miss” collapse related in Building Construction for the Fire Service, Third Edition (BCFS3, (p. 552). Builders are now required to inform the fire department when wooden I-beams are used so the information can be included in the CIDS system, which provides critical information at the time of dispatch.
A builder who failed to do so was taken to the Board of Standards and Appeals, which ordered the building sprinklered.
WOODEN I-BEAMS ARE “GOOD” FOR YOU!
Lieutenant Chuck Wehrli of the Naper-ville (IL) Fire Department sent me a promotional tape from Truss Joist McMillan, a manufacturer of wooden I-beams (I-joists), which extols the economic and ecological benefits of wooden I-beams and stresses the need for fire departments to inspect and preplan, although it never says exactly why.
It equates the reluctance of some firefighters years ago to adopt breathing apparatus, which might save your life, with reluctance to accept wooden I-beams, which might cost you your life.
It doesn`t point out that experience gained in sawn-joist structures is not applicable to wooden I-beams, which do not have the “FAT” (structurally unneeded wood along the sides of the beam which prolongs the fire/life of a sawn beam), and doesn`t draw the reasonable conclusion that if these early-failure I-beams are in place, the building should be so marked visibly and owners and occupants should be warned that the probability of early failure once the beams are involved requires surrender of their building to the fire. The owners of many of the fancy new houses with sauna baths, exercise rooms, and heated toilet seats would be astonished to learn that the life expectancy of their Taj Mahal in the event of a structural2 fire is about equal to that of a Marine Corps 2nd Lieutenant in combat.
The statement that one-hour fire resistance is achieved with gypsum board is made by an unidentified male dressed in fire turnouts. There is no reference to my many disclosures that this claim is extremely questionable and certainly not valid as an argument for firefighter safety. (BCFS3, pp. 232, 538) A firefighter mentions that they have five minutes if the fire gets to the attic. By the time fire in an attic is visible from the exterior, the five minutes have most likely expired.
Sprinklers are also mentioned as providing protection without noting the real problems of coverage of deep long-span wooden I-beams (BCFS3, p. 552) or that “residential” sprinkler systems do not cover the combustible wooden voids. (BCFS3, p. 548)
It appears to me that this tape was made to fend off any attempt by fire departments to restrict construction with I-beams and to make the argument “We told them to be careful” should there be a lawsuit. Unfortunately, it may be seized on by the “Charge of the Light Brigade”3 segment of the fire service to argue that those who respect the deadly nature of wooden I-beams, trusses, unprotected steel, and concrete under construction are “paranoid.”
ANOTHER HAZARDOUS METAL BABBITT
Babbitt is an alloy of tin, copper, and antimony that can be poured when melted and solidifies when it cools. It is used to secure elevator cables inside socket baskets on elevators. In WNYF,4 (third issue, 1997), Battalion Chief Dennis J. Moynihan reports on two elevator collapses. Fire was found on an elevator. As the shaft door was forced, the elevator fell to the basement. The Babbitt metal had melted. Another elevator had collapsed similarly.
The recommended precaution is not to enter or straddle the car but to remain on the safe landing.
CHESAPEAKE, VIRGINIA, CHANGES
In 1996, two Chesapeake firefighters died in the collapse of a long-span parallel chord truss roof on a commercial occupancy.5 The recently appointed acting chief announced that the department has identified 3,088 buildings that require special warnings such as for trusses and other hazardous conditions. This information will be computerized and be made available to the incident commander (IC) on a laptop computer. Why not get your fire department into such a program before the funerals?
LIGHTWEIGHT WOOD TRUSSES
By now you may be tired of reading about the hazard of lightweight trusses and trusses in general. It might be useful for you to be able to explain specifically in technical terms why the truss is so inferior to wooden beams when the argument is offered, “We all know that wood burns–what`s the difference?”
Compare a lightweight wooden parallel-chord truss with a sawn beam. In Chapter 2, BCFS3 (p. 52), we learn that in an ordinary beam, the top of the beam is in compression and the bottom is in tension. The greatest compression is at the top, gradually lessening as the neutral plane is approached. The greatest tension is in the bottom, gradually lessening as the neutral plane is approached. There is a continuum in the loading of the beam. The loss of some material, therefore, is not necessarily fatal.
In the truss, all the compressive load is carried on the top chord, typically a light member such as a 2 2 4. Loss of wood can precipitate crushing failure in compression. All the tensile load is carried on the bottom chord. Except for quite short trusses, the bottom chord is made up of two or more pieces of wood, joined end to end with metal gusset plates. The loss of a gusset plate would cause the tensile load to pull the truss apart. For additional information, see Chapter 12, BCFS3.
Tactically, we must seriously reconsider the traditional practice of the headlong rush into the fire building, which in today`s construction environment is as sensible as diving into a pool at the shallow end. Maybe we need to take a leaf from the Air Force: There are old pilots, and there are bold pilots, but there are no old, bold pilots.
CONCRETE OVER WOOD
Captain John Norman of the City of New York Rescue Company 1 and author of Fire Officer`s Handbook of Tactics6 provides much valuable information in WNYF (first issue 1997) on “Masonry-Covered Floor Collapse.” I have drawn on his article and my own material for this item.
Heavy dead-load concrete can be placed over wooden floors for a variety of reasons. Although the wood floor may be able to sustain the load under ordinary conditions, the loss of wood to a fire burning below the concrete may cause sudden collapse of the floor without warning.7
Apparently, concrete was added to wood floors to provide “fireproofing” in the early development of this technology.
A thin layer of concrete can be laid over a plywood floor to provide a smooth surface for the wall-to-wall carpeting (see “Preplanning Building Hazards,” Fire Engineering, November 1994, 65).
A thicker layer of concrete may be found on some “fire rated” floor assemblies. I am not sure of its purpose, but it probably slows down heat transfer to the surface during the test, thus lengthening the time before the limiting temperature is reached. The serious deficiencies of rating wood and gypsum assemblies as “fire resistive” are fully covered in BCFS3, pp. 223-232.
A tile floor surface may be required by the code in occupancies subject to health regulations for ease of cleaning. The tile must be set in concrete. One practice is to remove the wood floor, cut the beam down the desired depth, add ledger boards of 2 2 4 along the beams, install floor boards, and pour sufficient concrete so that when the tile is installed the floor will be at the same level as before. To further add to the hazard, this floor will be single thickness vs. the double thickness of the usual subfloor-finish floor combination in older buildings. When the wood burns away, the concrete falls; it has no tensile strength.
Sergeant John Carter, District of Columbia Fire Department, died in November 1996 when a grocery store with nine layers of tile collapsed and plunged him into the basement.
Bathrooms often have tile floors. Expensive houses may have tile or stone floors in the entry hall. A typical “dash in the front door” attack on a cellar fire may be fatal. I recall a house fire in the Midwest in which a firefighter went through the floor to his death at the front door on the initial attack. In 1966, 12 New York firefighters fell through a tile floor on 23rd Street–the greatest single loss in the department`s history.
In 1976, Philadelphia firefighters were seeking the source of smoke in a lunch-eonette. The fire was in the basement, but the smoke from the fire was passing through a hole in the basement wall to the next occupancy. There was an old barbecue pit in the next basement, and the smoke was exiting through the stack. Four firefighters died when the floor collapsed.
Laundromats pose a particular hazard. A 12-inch slab is required to resist the torque of washers and dryers. If there is a basement, it is highly probable that the support is unprotected steel and a few thin studs, or there may be no special support for the huge added dead load. These floors will collapse “without warning.” The warning is obtained by getting out and examining every masonry floor in the district to determine the method of support. Incorporate this information in a system that will make it available to the IC even 50 years from now. Buildings are forever.
Read the ads for homes firefighters cannot afford. Look for features such as “tile or stone foyer.” Look at the support for bathroom floors, heavily loaded with plumbing features.
In one case, the fire was all up through the walls, a new experience for the fire department that had its live fire training in a typical burn structure that would not collapse and presented no hidden fire. The second alarm was sent 90 minutes after the first, but no one realized that the hidden fire was eating up the building`s structure and destroying the gravity-resistance system. When overhauling, a firefighter was ordered to stand up on a bathtub to pull down a smoking remnant. The floor under the tub gave way. Fortunately for the firefighter, the tub fell vertically, enfolding him like an Egyptian mummy. He was unharmed.
Four Pennsylvania firefighters died when unprotected steel supporting a concrete floor failed. The building was very close to the fire station but had never been looked at critically.
Units operating at a fire in a building with tile or concrete floors should stay out of the collapse area until the stability of the support system has been evaluated. Most likely, there will be no sagging warning.
Home improvement shows on television often present new ideas in building construction. In a recent program, I noted a very dangerous hazard to firefighters making an initial attack or search. There is no interior wall finish. Instead of rough studs, good quality white pine 2 2 4s are used on two-feet spacing with two cross-braces, accurately finished and discretely nailed between each stud. This increases the load-carrying capacity of the studs (see BCFS3, p. 65). The wood may be finished with a combustible finish.
The second floor is of two-inch tongue-and-groove spruce, exposed to give a wooden ceiling supported on 2 inch 2 10 inch solid sawn beams a heavy load even before furniture is added. What`s the problem? There is no semblance of fire protection for the structural studs that are supporting this very heavy load, which the studs can handle because of the cross-bracing. A fire of any size will start to eat away immediately at the structural strength of the studs. A contents fire will be a structural fire from the beginning. Because of the all-wood interior, the room will be totally involved in moments.8 Just picture the room fire in the NFPA videotape “Countdown to Disaster,”9 which develops from a smoldering chair to a backdraft in two minutes, occurring in this “delightful” house. Such shows are popular, so keep an eye out for such “advanced ideas” in the construction in your area.
Two Stockton, California, firefighters died when a wood stud wall failed under the load of heavy beams supporting a dance studio above.
The log cabin is back. Usually such houses have a wooden interior finish. The entire surface can be involved in a few minutes. Keep that big line handy; you may need it on an “ordinary house fire.” n
1. Ol` Professor, Fire Engineering, July 1997.
2. By structural, I mean that the structure, the gravity-resistance system, is involved in the fire.
3. In the Crimean War, a British Army Light Cavalry Brigade “gallantly” charged Russian artillery with sabers. Generations of school children have recited Alfred Lord Tennyson`s poem celebrating this criminally stupid action.
4. WNYF is the official training publication of the City of New York Fire Department.
5. See the excellent article “Two Firefighters Fall in Chesapeake,” by Curtis Massey, a former officer in the department, in Fire Engineering, August 1996, 56.
6. The new second edition is available from Fire Engineering.
7. Concrete over the wooden floor is shown in the sketch of the area where four firefighters died in a Seattle fire in Ol` Professor, March 1996. The concrete may have been a replaceable wear surface or required because it was a food processing plant. In any case, the firefighters believed they were on the first floor, unaware of the floor below. The concrete may have helped to deceive them. One young firefighter made a note to ask the officer why the floor, which they assumed was on ground, got so hot.
8 In Ol` Professor, June 1996, I summarized a letter from Captain John Norman about a fire that went from a mattress to full involvement in a few minutes. The entire interior surface was wood.
9. “Countdown to Disaster” should be seen by every firefighter as part of the training to head off flashover and backdraft disasters.
n FRANCIS L. (FRANK) BRANNIGAN, SFPE, recipient of Fire Engineering`s first Lifetime Achievement Award, has devoted more than half of his 56-year career to the safety of firefighters in building fires. He is well known for his lectures and videotapes and as the author of Building Construction for the Fire Service, Third Edition, published by the National Fire Protection Association. Brannigan is an editorial advisory board member of Fire Engineering. He may be reached at (301) 855-1982.