Download Fireground Support Operations (1st Edition)

Fireground Support Operations (1st Edition)
Chapter 9 - Special Ventilation Operations
Test Review
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Challenges presented by high-rises include: large numbers of offices/apartments, heavy occupant loads, falling
glass/debris, smoke/fire spread through vertical shafts, locked doors, low water pressure, and crew exhaustion
(climbing stairs).
Most fire departments attack high-rise fires from the floor below the fire floor.
Never walk into a high-rise empty-handed (carry extra equipment).
Low-rise elevators serve lower floors of a building, while high-rise serve upper floors, and mid-rise serve
floors between the low- and high-rise elevators.
Express elevators serve only the upper floors and ground floor.
Freight elevators serve only the ground floor and uppermost floor.
It is less likely to overload freight elevators than passenger elevators.
Elevators that serve the fire floor should not be used by occupants or firefighters unless the officer in charge on
the fire floor authorizes it.
Personnel assigned to Lobby Control should bring all elevators to ground level and lock them there.
Elevators that do not serve the fire floor or above and have manual fire department control may be used for
occupant evacuation and fire personnel/equipment shuttling.
Fire behavior in high-rise buildings is most affected by stack effect and mushrooming.
Stack effect is the natural vertical movement of heat/smoke (convection) in tall structures.
The greater the difference between outside and inside temperature, and taller the building, the greater the stack
effect.
If temp inside a high-rise is hotter than outside temp, airflow will be inward at the bottom and outward at the
top (no airflow if temps are equal, reversed if temps are reversed).
As smoke rises in a high-rise and temp equalizes, smoke loses its buoyancy and begins to stratify (can occur
below the top floor).
If smoke ceases to rise in a high-rise, it will start to spread laterally and bank down (AKA reverse stack effect).
Elevator shafts should not be used for ventilation (creates fall hazard when doors are left open).
Top ventilation of high-rises prevents or reduces mushrooming on upper floors and does not promote lapping.
Using aerial devices is the preferred method of reaching the roof of a high-rise for ventilation.
One of the most direct means of moving personnel/equipment to a high-rise roof and removing occupants
stranded on the roof, is with a helicopter (weather/smoke permitting).
Venting a stairwell above the fire floor must be done only after occupants above the fire floor have been
evacuated.
In a closed compartment, pressure will be higher near the top of the compartment than near the bottom.
Somewhere near vertical midpoint of a closed compartment is the neutral pressure plane, where interior
pressure is equal to pressure outside the space.
Pressure is positive above the neutral pressure plane and negative below it (negative = inward pull, positive =
outward flow).
Forced ventilation creates a negative pressure within a space causing fresh air to be drawn in and contaminants
to be pushed out.
Wind produces a positive pressure on the windward side of a building (RAISES neutral pressure plane) and
negative on leeward side (LOWERS neutral pressure plane).
Wind blowing across the top of a roof can increase the stack effect if a vent opening is present.
Ventilating horizontally BELOW the neutral pressure plane causes air to be drawn IN, while ABOVE it cause
an OUTFLOW of air.
Ventilating below the fire floor may be necessary when reverse stack effect conditions are present.
Ventilating above the fire floor is most effective if started at the top of the building working downward.
Modern HVAC systems have controllable dampers to prevent fire gas/smoke spread.
High-rise electricity should not be shut down arbitrarily with fire in the building.
Guidelines for using HVAC to control smoke movement include: operation by qualified engineer, may assist
in fire seat location, may limit smoke/fire extension, should not be allowed to spread smoke/fire beyond point
of origin, and should provide fresh air.
Smoke detectors should be present in HVAC ducts to automatically shut down the system.
Some heavy-duty HVAC system can assist in removing cold smoke.
Roof vents and curtain boards are most common in large buildings having wide, unbroken floor space.
Roof vents/curtain boards limit fire spread, release heated fire gases, and reduce smoke damage.
Automatic roof vents release heat/smoke to the outside before mushrooming occurs (may eliminate need for
further ventilation by fire personnel).
FireNotes.com®
Fireground Support Operations (1st Edition) – Chapter 9
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Automatic roof vents are activated by smoke detectors or fusible links (old).
Heat-activated roof vents may not open if sprinkler heads in the area discharge near them.
Large atriums, in many high-rise hotels and office buildings, lend themselves to the stack effect, therefore are
required to have automatic atrium vents to release heat/smoke.
Areas enclosed by curtain boards are generally critical industrial processes and/or concentrations of flammable
liquids or other HazMat with high fire potential.
Underground structures usually require forced ventilation (natural ventilation sometimes possible).
IDLH atmospheres are of greater likelihood in underground spaces.
SCBA must be worn when below grade.
PPV can effectively ventilate a basement or cellar.
Structures of balloon-frame construction must be monitored closely with basement fires.
Windowless buildings increase the likelihood of backdraft conditions.
Pre-incident planning is a must with highly secure buildings.
During remodeling of a building, companies during inspection should note changes to bearing walls, roof/floor
assemblies, and other structural elements that might affect stability.
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Fireground Support Operations (1st Edition) – Chapter 9
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