PD ch 1 Flashcards
2.1PD’s Originally built for one or two family occupancy, these structures are usually one to three stories in height. They may be attached, semi-attached or detached. The interior of split level homes however, may have as many as five levels within a three-story building. An open and unenclosed stairway is the major weakness from a firefighting and fire protection standpoint.
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New Construction on PD’s
Many newly constructed dwellings are incorporating wooden I beams, metal “C” joists and lightweight wooden trusses into their construction. These lightweight construction systems are used in place of both conventional floor joists and/or roof rafters. Floor collapse can be as serious a threat as a roof collapse. When fire extends from the building contents to the structure, early collapse can be expected. Any building with lightweight construction must be entered into the CIDS program.
ï¨ Laminated wood “I” beams consist of a top and bottom chord and web. The chords are made of 2”x3”, 2”x4”, or two-3/4” CDX or pressed plywood glued together. The web is usually made of 1/2” plywood. Contractors may have bored holes to route electric, plumbing etc., compromising the strength of this beam. If not properly sealed, fire can extend from one bay to another.
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ï¨ Metal “C” joists are constructed of lightweight steel, approximately 1/16” thick, and may have predrilled holes for plumbing and electric lines. Cross braces may prevent twisting.
ï¨ Lightweight wood trusses are made of 2”x3”s or 2”x4”s, which are held together with sheet metal gang nails or gusset plates. Gang nails penetrate only 1/4” to 1/2”. When exposed to high heat, fire, or prolonged moisture, gang nails may pull away causing the failure of that truss. The failure of one truss may initiate a domino effect on adjoining trusses. When lightweight wood trusses are used as joists, fire can spread horizontally unimpeded.
Lack of a secondary means of egress from upper floors. Interior stairs are often narrow and sometimes winding. Landings are small; thus restricting movement of the operating forces and making an interior attack more difficult. CONTROL AND MANAGEMENT OF THE INTERIOR STAIRS IS CRITICAL TO A SUCCESSFUL OPERATION.
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