Chapter 7 - Ventilation Systems Flashcards
What is a fire department’s first concern at a high-rise fire?
Getting people out of the path of danger.
What kills most people in high rise fires?
Smoke.
What is one of the most crucial elements of managing high-rise fires?
Understanding smoke movement. p117
What are the three big shafts that were most concerned with?
Stairwells.
Elevator hoistways.
Ventilation shafts.
What is the most obvious natural force that moves smoke into shafts and other floors?
The pressure generated by the fire.
What is the force that causes air to move up in buildings on cold days or down on hot days?
Stack effect.
On cold days the air moves which direction?
From the bottom of the building to the top.
Stack effect has greater velocity on what type of day?
Colder days.
Temperature difference is much greater.
What is the point halfway up the building where air neither enters nor exits the building?
The neutral pressure plane.
If the openings in the bottom half of the building are increased, the neutral pressure plane will what?
Drop to a lower level.
Where is the personnel staging floor usually located?
Usually two floors below the fire.
What is something that is highly instrumental in increasing stack effect?
Open stairwell doors.
What is important to monitor in reverse stack effect situations?
Carbon monoxide.
What is a particular problem when a fire is above the neutral pressure plane?
Reverse stack effect.
Stairwell doors have what dimensions for smoke to get through?
18 square inches.
Through the evacuation process what is very important?
For all doors to be kept closed as much as possible.
Chances for a safe evacuation by stairwells are greatly diminished if what happens?
If the stairs are not pressurized.
A closed elevator hoistaway door has a leakage area of approximately what?
0.6 square feet.
What is the most common method to keep smoke out of elevator shafts?
Enclose elevator lobbies on each floor with normally open doors that close automatically upon alarm.
What is one of an incident commander’s best tools in regards to ventilation systems?
An elevator riser diagram showing each hoist way and the floors each elevator opens on.
Smoke spread through ventilation shafts is largely limited to where?
The involved zone.
The shutting down a ventilation systems is usually what?
Best avoided.
Most fire alarm systems are carefully designed to prevent fans from doing what?
Spreading smoke to other floors.
In most AHU systems the coils are cooled by what?
Passing cold water through them.
What is a very common HVAC system?
Has one AHU on each floor each in a mechanical room.
In regards to controlling smoke which system is best?
Type 1 because there are no slab penetrations.
Why is there no danger of smoke migrating from floor to floor in a type 1 system?
There is no outside air shaft.
What are the two different types of dampers?
Motorized.
Fusible link
Where are fusible link dampers usually found?
Return air openings in demising walls.
Openings to air shafts.
What is the difference in type 2 system versus type 1?
The way the AHUs get fresh air.
Most buildings do what at night and on weekends
Turn off their ventilation systems.
What fan doubles as the smoke removal fan
The toilet exhaust fan.
All smoke removal systems do their job by what type of manipulation?
Fan and damper manipulation.
What system does not have air handlers or mechanical rooms on each floor?
Type 3.
What type of system combines large supply and return fans located together and functioning as a unit on a main mechanical floor?
Type 3
In a type 3 system there are often how many AHUs per ventilation zone?
Two or more.
In a type 3 system the supply fan uses what percentage fresh air to pressurize the floors adjoining the alarm floor?
100%.
What type of fans are usually unaffected by the alarm system?
Ancillary fans
Originally all smoke removal systems were what type?
Automatic.
What is a major problem with the automatic ventilation systems?
They can interfere with evacuation of the fire floor.
What makes it difficult for some people to push stairwell doors open to escape the fire floor?
Negative pressure on the inside and positive pressure on the outside b
While the fire is burning the objective of smoke control should be what?
Isolate the fire floor by closing all dampers.
Which damper should be closed on the fire floor?
Both the supply and exhaust.
The supply dampers on non-fire floors should be what?
Open.
What type of damper is a motorized damper
Combination smoke/fire
What type of damper is a fusible link damper
Fire damper
Where are the two places fusible links are typically found
Return air openings in demising walls
Openings to air shafts.
What system usually has no operable dampers
Type 2 system without smoke removal system
When does The fresh Air fan shut down automatically
Only if smoke reaches its intake side
