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Dunn > Chapter 8-Timber Truss Roof Collapse > Flashcards

Chapter 8-Timber Truss Roof Collapse Flashcards

1
Q

A timber truss roof can be built in a variety of shapes?

A

a. inclined plane truss (gable shaped roof)
b. parallel Chord truss (flat roof)
c. bowstring truss (arch roof)

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2
Q

Most common shape of Timber truss roof is?

A

BOWSTRING TRUSS ROOF

-entire truss section may fail as soon as the smallest web member weakens

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3
Q

During Fire conditions, the truss is only as strong as its?

A

WEAKEST MEMBER

-the strength and stability of truss depends upon the smallest web member

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4
Q

Truss construction is…?

A

MOST DANGEROUS roof condition

  • known to collapse during EARLY STAGES of fire
  • often cause subsequent collapse of the front masonry enclosure wall of the building
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5
Q

Why do front walls collapse more OFTEN than rear walls?

A

rear walls are more stable and have few openings

front walls have MORE OPENINGS-less able to resist any movement of sloping roof joists

openings weaken load bearing capabilities and permit fire spread

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6
Q

High decorative parapet walls can…?

A

CONCEAL roof shapes

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7
Q

FF discovering any type of Truss , shall immediately notify ?

A

INCIDENT COMMANDER

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8
Q

Large space created by the concave arched underside of the bowstring truss roof acts as a ?

A

HEAT SINK- allows the flow of large amounts of heat/smoke upward from the fire floor below

a serious fire in a building with a bowstring truss roof might allow firefighters to enter the structure, walk upright to the rear of the occupancy and become trapped under a collapsing roof

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9
Q

3 size up indicators of a truss roof in a building?

A

a. large open space without columns, indicates long span roof support, such as truss
b. bowstring truss roof only- MOUNDED roof shape
c. certain occupancies frequently use truss construction- supermarkets, bowling alley, garages, theaters, places of worship, auto dealerships, armories, piers

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10
Q

Fire strategy for Timber Trusses…

A
  • timber truss roof supports are often visible from the floor level, because often, NO CEILING EXISTS…this absence of ceiling greatly assists firefighters because:
  • it allows identification of trusses from inside
  • gives interior hose stream an open path to extinguish fire in timber truss roof quickly
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11
Q

What is more dangerous…truss roof concealed by ceiling or without ceiling?

A

CONCEALED is much more dangerous

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12
Q

TIMBER TRUSS concealed strategy ?

A

NO EXTINGUISHMENT FROM BELOW THE BURNING TRUSS THROUGH A TRAP DOOR IN CEILING

NO EXTINGUISHING A FIRE IN A TRUSS SPACE FROM ABOVE

-when fire extends to a timber truss attic space, prepare for a DEFENSIVE OUTSIDE ATTACK and protect exposures

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13
Q

Timber Truss NOT concealed by a ceiling?

A
  • first engine attack fire directly with large diameter hose line
  • powerful stream, capable of reaching 50 feet , will be needed for upper portion of trusses

-if first stream does not control flames within the FIRST FEW SECONDS OF WATER DISCHARGE, and fire will increase, interior fire fighting should be discontinued

if 1st line is successful- then stretch 2nd line to back up (large diameter hose)- this line should sweep underside of roof, if necessary

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14
Q

If web members are enclosed …trusses will appear like curtain boards ?

A

if collapse of this compartmented roof occurs, timber truss roofs will fail one at a time

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15
Q

if web members are UNENCLOSED, on one side…not covered with fire retardant ?

A

entire truss roof will fail at once, with all timber trusses failing at the same time

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16
Q

Timber Truss Roof Vent?

A

-if roof stability is ASSURED and roof venting is needed- FF’s can sometimes open the skylights or scuttle covers quickly and leave roof immediately

17
Q

Roof Vent: using vent opening in the sloping front or rear portion of the roof…

A

if SMALL fire exists-overheated motor/electric wiring in bow string truss roof structure and concealed by ceiling -access ladder can’t be found….quick access can be obtained by:

making a roof cut opening at the SLOPING ENDS of the roof deck

  • hose line can be directed into a truss roof area through this roof cut opening, if the small normal access opening cannot be located
  • to quickly determine if a fire has spread to the roof space of a bowstring truss, a triangular cut may be made in the sloping front or rear portion of the roof from an aerial platform
18
Q

Truss identification will only be observed from the roof shape when the truss is ?

A

BOWSTRING TRUSS ROOF

-parallel chord or gable truss roof will not be identified by the roof shape

19
Q

FF’s ordered to evacuate should retreat in a direction ?

A

PERPENDICULAR to the roof trusses

same goes for members inside the building

20
Q

FF’s operating initial hoseline should be?

A
  • positioned behind a truss section, next to the one involved in fire
  • reach of a powerful stream will allow them to be out of the collapse zone of a single truss
21
Q

Truss is discovered?

A

notify INCIDENT COMMANDER

22
Q

Places of worship?

A

-often most unstable structures

TOWER and STEEPLE most unstable

23
Q

Church fire?

A
  • large fires/lack of partitions
  • as soon as flames are knocked down, walls and attics should be checked
  • if 2 lines do not extinguish, withdraw to defensive position
24
Q

Rose Window?

A
  • PRIMARY ventilation at front of church or temple
  • large stained glass window
  • where first TL should operate
  • vent entire window
  • notify IC if unbreakable glass is encountered
  • LCS through Rose Window may extinguish fire at the upper peak near ceiling
25
Q

Primary venting also includes stained glass windows near fire on sides of building…

A

-if interior must be vented for hoseline attack, vent stained glass windows nearest to fire on both side (after Rose Window)

26
Q

During initial stages portable ladders shall be positioned?

A

side of stained glass windows near the fire, where FF’s are operating hoselines

Dunn (5 decks)

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