Chap 3 FF Problems/ Structural Hazards Flashcards
In low rise fire resistive construction smoke spreads by ?
Heat
Convection currents
Fire pressure
And wind
In high rise you also have smoke spread by HVAC system
What is the major FF PROBLEM with fire-resistive construction
The central AC system
Commercial buildings (offices and hotel ) usually have one or multiple HVAC systems
One large HVAC
These systems penetrate every fire barrier in the building which flame and smoke can spread
Central HVAC eliminates the concept of compartmentation (called passive fire resistance )
Fire resistive apartment houses
Formerly did not have central AC now they are being constructed with central ac
May connect the public halls on several floors with ducts and vents
May spread heat and smoke through the fire resistive building possibly to floors above and below
The major collapse hazard at a fire resistive constructed building ?
Lies in the concrete
Two basic types of fire resistive buildings are
Reinforced concrete and structural steel buildings
Structural failure in reinforced concrete buildings ?
Is caused by spalling ( the rapid expansion of heated moisture inside the concrete )
Collapse in reinforced concrete buildings
Heated concrete ceilings can collapse on top of FFS
OCCURS IN type of building without suspended ceiling where the concrete ceiling above the fire is directly exposed to flame
Internal pressure can cause heavy sections of the concrete to crack away form ceiling and collapse down
Collapse in steel Skelton buildings
Underside of floor is not concrete
Each floor consists of a light gauge steel sheet(fluted metal deck)which supports several inches of concrete floor
The heat reaching the fluted metal deck is conducted through to the concrete floor directly above
The bottom of the concrete cannot collapse downward because of supporting steel so the expanding moisture explodes the concrete upward . The floor cracks and erupts several inches
If fire is severe, the steel beams supporting the fluted metal deck start to sag and bow downward causing the concrete above to also sag and bow downward
When heated a concrete floor can crack and allow heat, smoke, and flame to spread to floor above
At a serious fire In a fire resistive building the composite concrete and the fluted metal deck floors will be damaged because the steel expansion is greater than the concrete when heated by fire. The composite concrete and the fluted metal deck is a collapse danger
The major FF problem in Non-combustible/ limited combustible construction.
The flat ,steel deck roof covering that can ignite during fire
The major collapse problem at non-combustible/limited combustible construction is
Roof cave-in from the use of open web steel joists
Collapsing material is the I protected steel open web bar joist
Light weight steel bar jousts is non-combustible but is susceptible to damage from fire can fail if Un-protected within 5-10 min when exposed to fire
Heavy Snow falls collapse these roofs and not designed for weights of ffs
None of these buildings after 911
When a fire occurs in a non-combustible/limited combustible building the IC should,
ASAP after the fire is darkened down have FF check the roof covering above the fluted metal deck for fire extension as heat may have conducted through the metal roof deck and ignited the combustible roof covering
After the fire is extinguished the IC should order a company to the roof to,check the combustible asphalt roof covering as heat may have conducted through the steel fluted roof deck and ignited the roof covering
What are the three basic types of non-combustible/limited combustible construction buildings
- The “steel building” - metal frame structure covered by metal exterior walls
- Metal frame structure enclosed by concrete block , non- bearing exterior walls
- Concrete block bearing walls supporting a metal roof structure
Note on all three types the steel roof support system may be either :
Steel girders and beams
Light weight open web bar joists
Or combo of both
The major fire problem in brick and joist construction
Fire and smoke spread throughout concealed spaces
These concealed spaces contain large amounts combustible materials
ASAP after fire is extinguished ff must be directed to open ceiling above and nearby walls for fire spread
If fire discovered in concealed space than cockloft must be check before leave scene
The largest and most serious concealed space at brick and joist construction
The common cockloft
The major collapse potential at brick and joist construction
Parapet wall
Note the front of these fire buildings is dangerous ffs are urged to move inside the doorway or away from the front building altogether at these types of fires
Major firefighting problem at heavy timber truss is
The large wooden interior timber framework
For a building to qualify as heavy timber
A wood column cannot be less than 8 inches thick
A wood girder cannot be less than 6 inches thick
The major collapse hazard for heavy timber truss construction is
Falling masonry walls which crash to ground and spray bouncing chunks of brick and mortar along street
The major firefighting problem in wood frame construction. Is
Combustible outside wooden walls
Only construction that has exterior wooden walls
Consider 6 sides of building for possible extension
A 7th side must be considered the combustible exterior walls
Outside hoseline is often required to prevent exterior fire spread
The major collapse hazard At wood frame buildings is
The combustible bearing walls composed of 2x4 inch studs
The bearing walls of wood frame structure are usually the
Two side walls
Fires coming out the side walls are more dangerous than those coming out the front windows
3 ways a masonry wall can collapse
- 90 degree
- Curtain
- Inward/ outward
What is the most common collapse at masonry wall fire failures
90 degree
The wall falls straight out and the top of the collapsing wall strikes the ground a distance equal to the height of the falling section measured from the base of the wall
Bricks and steel lintels may bounce even further
Examples of how 90 degree collapse may occur in masonry wall
- The lateral force from rubble from interior wall collapse
- A free standing wall of burning structure during cold weather becomes unstable
- The force of LCS of water directed at the inside of free-standing wall can cause wall to collapse outward on street
- Masonry walls can can separate from other enclosing walls where they intersect
- vertical cracks can allow walls to separate Nd fall at a 90 degree angle
