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Flashcards in Ch. 21 Structural Collapse Deck (83)
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Structural collapse is ________ on the fireground.

One of the most feared occurrences
Large percentage of multiple-casualty incidents


Resistance to collapse per classes of construction:

Most resistant to least resistant
Class 1 fireproof
Class 4 heavy timber
Class 3 ordinary/standard brick and wood joist
Class 5 wood-frame
Class 2 noncombustible


Which class of construction has:
-up to 4 hr fire resistance
-skeletal framework, poured concrete or steel I-beams
-collapse is usually rather localized
-load being supported generally remains in place
-supposed to provide resistance to collapse to allow time for evacuation and fire control

Class 1 (greatest resistance to collapse)



Most severe collapse hazard in Class 1 bldgs is:

Poured-in-place concrete bldgs under construction
- fire involves wooden formwork
- pancake collapse


Second best construction type, as far as resistance to collapse is concerned:

Class 4, Heavy timber
-generally 12 x 12 columns and brick walls
-manual FFing long since shifted to exterior operations before danger of collapse
-exception is bldg has been scene of numerous repeated fires in same area
-advanced fires, apparatus removed (1 1/2 times collapse zone)


Third most collapse resistance:

Class 3, ordinary or standard brick and wood joist
-more prone to burn through than collapse
-flr/roof sheathing burn through long before floor joists fail
-FFs could be working underneath, unaware due to hung ceilings or smoke
-distinct danger=high floor loads and concentrated loads =roof-mounted AC


Fourth category in order or resistance to collapse is:

Class 5, wood frame
-dimensional lumber more prone to deck burn through
-only standard construction~doesn't apply to lightweight truss-construction


Least resistant to collapse:

Class 2
-large quantities of unprotected steel
-steel expands --> 100 ft expands 9.5 in. at 1000F
-at 1500F - lose its strength, will drop its load or twist/sag
-steel cooled, contract back to 100 ft while retaining distorted shape
-steel would shrink, end of beams no longer resting on original supports, collapse occurs


Hierarchy of structural components:

- Bearing walls
- Columns
- Girders (support beams)
- Beams and joists
- Floor or roof decking


Protected steel or concrete supporting system resist _____ collapse rather well.
These are called _______ since most of their weight is carried in the frame or skeleton.

Framed structures


Collapses that occur in framed structures are usually ________.

Very localized
*only area between two supporting members*


Structures with most of weight on bearing walls?

UNFRAMED structures
*failure of vertical member more serious than horizontal*


Wooden structural elements burn through at a rate of about:

1 in. for every 45 minutes of open-burning time
-fire attack standard 1 1/2 in. joist from TWO SIDES, burn through in less than 45 minutes


One of the most potentially dangerous situations is when columns support a ______ that carries the weights of upper-floor walls and floor joists when a __________ is removed to expand.

Ground floor wall


As little as ______ exerted laterally on a brick wall can topple it like a house of cards.

1 psi


Any location where _____ or _____ are stored demand tactics shift towards cautious, defensive operations.

Flammable gas


Biggest offender at fire operations concerning overloading of floors and roofs?

Runoff from hose streams
- also heavy loads - plumbing supplies, snow, etc. with no fire


One factor FFs have direct control over (cause of collapse) is:

Cutting of structural members during overhaul


If forced to operate in area where structural weakness is suspected:

Use methods and tools that produce little or no impact load or vibration
-use circular instead of axe or reciprocating
-can be external sources
-watch for elevated platforms


Examples of cause of collapse, miscellaneous

-high wind
-hose streams
-age of bldg


Indicators of collapse

12 of them
-each indicator separately might not raise SUFFICIENT ALARM
-when viewed as whole, signs bldg is in danger


Number One indicator-occupancy by problem business

Plumbing supply, appliance dealership, printing shops (P's)
Type of occupancy ALONE not reason to withdraw
-should trigger CAREFUL EXAMINATION for signs of collapse


Of all possible warning signs of collapse, only one more serious than truss construction

Structure that contains Explosives (rare and usually over before we arrive)
Number 2 collapse indicator


THE fire problem of 21st century

Fire in truss construction
-particle board I-beams deserve same technique


Prime indicators of bldg collapse (overloaded floors)

-heavy equipment
-water-absorbent stock
-built up water


Consider withdrawing forces if:

-Heavy fire obvious AND
-Not put out in 20 minutes


It is time to make decision about withdrawing forces when:

First members come out with low-pressure alarms ringing

Number 4 - fire more than 20 minutes


20 minutes rule begins

-not on arrival BUT
-when fire reaches open, flaming stage OR flashover AND begins to attack structural elements


20 minute not for lightweight construction, instead:

5 minutes


Cracks could mean collapse is imminent or could have been there for 40 years

Pay special attention to cracks that are EXPANDING or LENGTHENING
-indications of movement
-prompt evac if extensive