PREPLANNING BUILDING HAZARDS
FRANCIS L. BRANNIGAN
Editor`s note: For further reference, consult Building Construction for the Fire Service, Third Edition. Page numbers are included after each caption for your convenience.
(Top) When an excavation is dug, except in solid rock, the earth around it is trying to shear sideways into the hole. If it does, the buildings surrounding the hole will go with it. This steel excavation bracing is as light as possible. The cylindrical shape of the “rakes” permits the heaviest load with the thinnest steel. In addition, codes generally permit loads as much as twice as normal because the bracing is “temporary” (perhaps more temporary than anticipated). The heavier the load, the lower the temperature at which the steel will fail. The steel, therefore, is very vulnerable to early collapse in a fire. The excavation may be loaded with fuel, plywood, flammable gases, etc. This steel must be cooled immediately. Buildings in the collapse zone should be evacuated. Apparatus must be clear of the collapse zone.
Ask the engineer in charge how far the collapse might extend if the steel should fail. Such a collapse has never happened, but all the elements for a collapse are present. Know the possibilities and act on them. Waiting for experience will be disastrous; fire experience is “blood and tears.”
If the steel is inaccessible to hoselines, it would be prudent to have pipes installed with spray nozzles or perforations or to fireproof the steel. Such precautions certainly will be required after a massive collapse disaster. (Ref. p. 278)
(Middle) Buildings under construction often are enclosed in plastic to retain heat in cold weather, to protect fresh concrete, or to just provide comfort. Liquefied petroleum gas often is used under unsafe conditions, such as the freestanding gas cylinders without being supported, in the presence of open flame burners. Mass-burn casualties and collapse are real possibilities. Are your resources adequate to handle such a disaster? (Ref. p. 351)
(Bottom) Lightweight steel trusses are strong but very subject to early failure from heat. The failure can be accelerated by loads improperly placed on the lower chord of the trusses. The trusses are tied together for wind resistance; a failing section can bring down trusses not directly affected by fire. Cooling the steel from a safe location is imperative. If fire is sufficient to heat the steel (less fire than you might think), collapse may be imminent. (Ref. p.283)
FRANCIS L. BRANNIGAN, SFPE, a 52-year veteran of the fire service, began his fire service career as a naval firefighting officer in World War II. He`s best known for his seminars and writing on firefighter safety and for his book 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.
