Ch. 21 Structural Collapse Flashcards Preview

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Flashcards in Ch. 21 Structural Collapse Deck (83):

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


Sign roof pulling away from wall

Relatively clean wood on ends of beams


One of LAST warning signs BEFORE collapse

OBVIOUS sagging of floors or roofs


Sponginess (roofs) calls for:

Further evaluation
-natural condition - inverted roof


Too late to reach safety

-obvious movement of floors, walls or roofs


Sign of partial collapse in remote area of structure

Deep rumbling


Plaster sliding off of walls and distortion of door and window frames

Subtle movement of structure (plaster)
Result of being pushed over (doors/Windows)
-prevalent in class 5 construction


____ is usual means of initiating the withdrawal.
Additional means of communicating for those not equipped or may not have heard is _____.

Turn all audible devices for 30 SECONDS


Masonry walls weigh:

80-130 lbs. per cu. ft.


Ladders or platforms must avoid positioning themselves:

-Any closer to bldg horizontally than they are vertically
-from top of bldg to lowest part of their device


Obvious instance where 1 1/2 times height of wall is too short:
(Ch. 21)

Collapse initiated by an Explosion


"Rafters resting on a truss" collapse zone

2 1/2 times the height of the wall


If 2 1/2 times collapse zone not possible then:

-flanking positions off to sides of threatening wall OR
-position above wall, as in basket of elevating platform


Beware of ____, ____, and ____ that could be brought down by primary collapse

Trees, telephone poles, overhead power lines


(Elevating platform) When roofs collapse, huge fireball:

Some cases 50-60 ft high
-make sure platform isn't perched directly over


5 types of collapse

V-shape - class 3/5 (overloaded, center support gone, burned away)
A-shape - common in explosions
Supported lean-to - supported each end
Unsupported lean-to - floor/roof joist dangling in mid-air
Pancake - appear to be unstable-not the case, lowest level examined, numerous rescues in class 3/5, locating victims somewhat simpler


Individual voids formed by a series of strong objects AND are found in:

ANY type of collapse


Appears unstable but is not the case:



This type of collapse has a severe danger of further collapse:

Unsupported lean-to
-because low end is totally unsupported


First priority if FF is trapped or disabled in vicinity of fire:
(Collapse rescue ops, ch. 21)

Keep them from burning to death
-one of first actions is to bring as many streams to bear in that area
-nothing compares to Tower Ladder


Other use of tower ladder at collapse rescue:

Boom as tie-off point for hoisting objects (full working load=1,000 lbs)
-remove extra weight-jettisoning everything
-brace boom with cribbing/planking
-only as fixed anchor point


The place for the best you've got available (rescuing downed members)

RIT, specially selected and equipped
-heavy rescue company, paramedic level firefighters


5 stages of collapse rescue

Recon - intelligence gathering
Surface victims (accounting for/removal)
Searching voids
Selected debris removal/tunneling
General debris removal


___ is search while ____ is actual rescue.

Void exploration
Selected debris removal


During tunneling, ______ could increase chances of success.

Two or more approaches


If threat of secondary collapse, several options:

Rope off area/deny access (not possible if survivors)
Shore up area
Tie off debris to substantial object
Pull debris over where it does no harm


Most gruesome task yet

General debris removal


Critical actions of first-alarm units:

Street management
Fire control


Street management hampered by:

Scope of destruction
Crowd of spectators
Sheer volume of responding personnel


First-alarm engine company PRIORITIES at collapse

Fire actively burning within rubble (highest priority).
Exposure protection (next).
Extinguishment of burning VEHICLES


Collapse operations - first 4 engine ASSIGNMENTS

1st and 2nd engines = separate hydrants OUTSIDE the block on SEPARATE MAINS
3rd and 4th engines = similar positions at REAR of structure


Frozen Zone for:

-major incidents
-no non-emergency vehicles
-reduce vibration (secondary collapse)
-preserve evidence


During collapse operations, rotate personnel:

Every half hour or less (30 or less)


Causes of collapse
Collapse indicators



Building permit usually ensures that ______________ has at least reviewed the design for any obvious weaknesses.

An architect or structural engineer


Lightweight steel bar joists can lose strength in 5-10 minutes of fire exposure. Thicker pieces take longer to heat up but when they _____________, their failure is just as assured as the lightweight ones.

Reach 1,500F


Steel usually ____ prior to total failure.



It's ability to be readily cast in a mold and then bolted together in sections made it the first material to be used for _________ .

Cast Iron
Prefabricated buildings (late 1800's)


Cast iron has great compressive strength but almost no shear strength, therefore cast iron it was once a favorite material for ______ but unsuitable for _____.

Columns and prefab walls


Overloading of floors
Large quantities of material that absorb water, such as ____, _____, and _____. Two effects that threaten collapse: _______ and _______.

Newsprint, baled rags, baled cotton

First is weight (absorb their full weight in water)
Second effect is as they absorb water, they swell


Collapse rescue operations
SEARCH team should bring

Spare SCBA or RIT-pak for each victim
At least one member of SEARCH should be EMT


Best chances of locating victim occur when you know which area to start looking. This is part of:

Recon or intelligence gathering


One difficulty in controlling utilities at collapse scenes is:

Controls may be buried under debris


Surface victims (2) can be done simultaneous with:

Recon (1)
Searching voids (3)


Done to take advantage of natural openings remaining in the debris, LEAST labor and time consuming, victims with greatest chance of survival

Search of voids


Immediately designate an officer to:
Keep track of who leaves or are removed
-name and where located.
-if time permits, escape route.
Noting any injuries.
If victims transported, what hospital.

Victim Tracking Coordinator


No matter what type of building is involved, ________ such as ____ and _____ must be forbidden at this stage. Although a MANUAL operation is time consuming, it is _____________.

Large, power demolition equipment
-Backhoes and cranes

Necessary as long as you suspect there are survivors


Once you get close to the victim, all work should ______________.

Proceed with only hand-powered tools, unless object and victim are visibly clear and no injury is likely.


Tools that produce no _______ are preferable. Tools that perform a task _______________ are usually preferable to those that do.

Exhaust fumes
Without producing showers of sparks


Once all of the live victims have been removed, the ______________.

Selected debris removal operation should cease


This task should also be performed at any fast-moving fire that results in early collapse since there may be persons present who haven't yet been missed

General debris removal


Street Management-
It is up to the _____________ of each and every vehicle approaching the scene to take the proper actions to ensure continued smooth access to the site.

Officer AND driver


_______ should also be kept away from the front of the building. The positions in front of the collapsed structure should be taken by __________. In close proximity but not directly in front of the building should be ___________.

Aerial ladders

Elevating platforms (telescoping type-tower ladders)

One or more heavy-rescue apparatus and /or specialized collapse shoring vehicles


The ________________ will likely begin triage and initial treatment. Position them ___________, __________ but ___________ and _________.

First two or so ambulances

In proximity to the structure
Visible from the scene
Out of way of rescue/firefighting operations
Out of secondary collapse zone