Flashcards in Ch. 12 Ops Ltwght Bldgs Deck (32):
______ are the deadliest style of roof construction per incident (Ch. 12 Ops in Ltwght Bldgs)
Wooden bowstring truss roofs
Collapse zones at end walls that have rafters resting on a truss and bearing wall should be at least ______ times the height of the wall.
Flat timber truss is variation of:
Flat timber truss more dangerous than bowstring in one way:
No visual hint; preplanning is critical
Bowstring and flat roof typically found in ____ and ____; there is ________ _________ of a civilian life hazard in these occupancies.
Industrial and storage
Styles of lightweight trusses (3)
1) short scraps of 2x4s joined by gusset/gang nail plate (MOST COMMON)
2) 2x4 or even 2x3 top and bottom chords connected by tubular steel webs
3) very thin pieces of sheet metal stamped into gusset plates on the ends, acting as web members of truss
Lightweight trusses biggest drawback is:
Lack of mass
______ by far the most easily recognized type of lightweight construction in use.
Several flaws for trusses from FF standpoint
1) lack of mass compared to standard beam
2) connectors (conduct heat and/or fail)
Of all those types of buildings that firefighters may have to OPERATE in, those built with ______________ are the most dangerous.
Any of the lightweight construction methods
Two problems exist that make such operations dangerous in today's buildings:
New lightweight construction
This type of roof or floor has several drawbacks from an ARCHITECTS point of view: (2)
Area that can be spanned (about 25 ft)
They are expensive
Danger of truss exists _______.
Only in fire conditions
Greatest danger to firefighters is: a truss depends on _______________.
Every one of its pieces AND the connections to hold it together.
Of all the modern styles, ____________ are the deadliest style of roof construction PER INCIDENT. If heavy fire is present, ___________.
Wooden bowstring truss roofs
All personnel must be removed from roof and from interior operations IN THE VICINITY of the truss roof.
Size of boards, bowstring truss vs flat timber truss
BS-2x10 with spaces between alternate boards, 20 ft spacing
FT-2x8 or 2x10 (chords), 2x4 or 2x6 web members, 20 ft spacing
Gusset plate penetrates wood
About 1/4 in.
Pin drilled into steel tube and wood chord has two effects
Drilling hole weakens 2x4
Steel pin and hole allow fire to attack from both inside and outside chord
A concern common to all PARALLEL-chord 2x4 trusses is ______________.
Risk of penetrating the top chord with a POWER saw blade during ventilation or overhaul (only covered with 1 in. of roofing and plywood)
While not a truss, poses many of the same problems
Top/bottom chord of 1 1/2 x 2 in. plywood with a web of 3/8 in. plywood
Plywood I-beam (parallel-chord beam)
Open web steel bar joists supporting corrugated metal deck
Bending steel bar in a repeating Z pattern
Up to 60 ft long and spaced 6 ft apart
ANOTHER style steel I-beam shapes with large hexagons cut out of the web
Metal deck roofs
MAIN drawback of open web steel bar joists and steel I beam shapes with hexagons cut out of webs is:
Lack of fireproofing and the way unprotected steel behaves when exposed to temperatures of a structural fire (collapse after few minutes)
Roof decking of metal deck roofs
1/16 in. thick, 3 ft wide and 20 ft long
Layer of tar
Insulating material, fiberglass or rubber, 3 in. thick
PRIMARY hazard to roof FFs with metal deck roofs is
Danger of falling into ventilation hole while cutting
Steel truss roofs when failing
Sag rather than snap
Fail in less than 5 minutes with heavy fire BUT don't fail without warning
Ample warning to FF's on top (below may not be able to see)
Fire in metal deck roof bldg/store
Use reach of large hose stream to cool unprotected joists
Start 3 stores over from fire store
Vent exposed store and stop fire advance
Three problems with metal deck
Falling in vent hole
Sudden catastrophic collapse
Metal deck roof fire
In metal deck roof fire, first step is to:
Cut through insulation and expose burning tar
2 x 2 ft section to determine which direction CORRUGATION runs
The long 2 ft strips perpendicular to the corrugations
2 1/2 in. stream
The great danger is that FF's will look at the building and ________________.
Take it at face value, utilizing tactics appropriate for original building
If roof ventilation isn't possible then:
Aggressive interior operations must ALSO CEASE
Lightweight roofs and floors
Life hazard with and without heavy fire attacking structural elements
Without heavy fire-offensive operations justified
With heavy fire-safest, most direct route. May involve exterior hose/approach (VES)
*key element is potential for saving lives. Still savable?"