User Manual

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4.3 Smoke control
In education facilities smoke control should form an
integral part of the fire protection design process.
Customized smoke control systems should be designed to
restrict the spread of fire and smoke, and conduct the
heat and smoke through the installed ducting and smoke
vents into the external atmosphere (generally through the
roof of the building). To limit the amount of smoke
produced and the extent that it can spread, a fire must be
detected in its incipient stage and the smoke control
system should be activated immediately.
A properly designed automatic sprinkler system can make
an appreciable contribution to smoke control, by limiting
the growth of a fire and consequently the quantity of
smoke it generates. It can also help to cool the
atmosphere, thus taking energy from the smoke and
reducing its ability to move.
4.3.1 Objectives
Smoke presents the greatest danger to life in the case of
a fire. This is not only due to smoke inhalation injuries
and asphyxiation, but also due to smoke-filled corridors
and staircases, which make evacuation considerably more
difficult and raise panic levels. Consequently, an
important part of the risk assessment process is to
consider any measures which could restrict smoke to the
immediate locality of the fire and prevent it spreading in
an uncontrolled manner throughout the building.
The compartmentation measures discussed in Section 2.2
are largely responsible for restricting the spread of the
smoke; however it is the task of the smoke control system
to conduct the smoke out of the building in an efficient
and controlled manner. A smoke control system needs to
be activated during the early stages of a fire emergency
to maintain a tenable environment in the areas to be
protected. It has to be functional throughout the period of
evacuation and should not compromise any other life
safety systems.
The objectives of a smoke control system are as follows:
 Keep the escape routes as smoke-free as possible
during the time required for evacuation
 Control the migration of smoke from the locality
of the fire
 Provide conditions outside the fire zone that will assist
emergency response personnel
 in locating and controlling the fire
 in carrying out search and rescue operations
4.3.2 Smoke control systems
[6]
Smoke flow generally follows the overall air movement
within a building. Smoke can also spread to areas
adjacent to the smoke zone through openings such as
construction cracks, ducts and open doors. The principal
factors causing smoke to spread outside the smoke zone
are the temperature effects of the fire itself, the climatic
conditions (particularly wind and temperature) and
mechanical air-handling systems. These factors create
pressure differences across area partitions, and by
controlling and maintaining these pressure differences we
can have a direct influence on the way the smoke will
spread.
There are two kinds of smoke control systems – active and
passive systems.
Passive systems
Passive smoke control systems rely on the temperature
difference between the hot fire gases and the
surrounding air, utilizing the natural buoyancy of the
hotter fire gasses to convey the smoke out of the building.
However, variables such as outside temperature, wind
speeds, barometric pressure and pressure differentials
created by the HVAC system, have tended to limit the
appeal and practicality of this approach.
Active systems
These active mechanical systems fall into two categories:
pressurization and exhaust.
 Pressurization
The basic principle of a pressurization system is to
confine the smoke to the compartment where the fire
started (smoke zone) by creating a higher pressure in
the adjacent areas (smoke-free zones). Depending on
the building design and the protection goal, a smoke-
control zone can consist of part of a floor, an entire
floor, or even several floors.
 Exhaust
In large open spaces like malls and atria, it is generally
not practical to try to contain the smoke within the
area where the fire started. In such cases a mechanical
smoke extraction system would be the preferred
solution. In conjunction with motorized smoke
dampers such systems are able to maintain acceptably
low levels of smoke in both escape and rescue routes.
This greatly assists emergency response personnel in
their search-and-rescue, and extinguishing activities. It
also contributes to the protection of the building
structure and tangible assets.
4.3.3 Fire doors
As described above, buildings should be subdivided into
fire compartments by fire doors, fire-resisting walls and
floors. The tightness of the construction is a significant
issue in the effectiveness of a smoke-control system.
Openings around penetrations or poor construction may
permit excessive leakage so that adequate pressure
differences cannot be maintained. In this context, fire
doors play an important part. In normal situations they
need to permit the easy flow of traffic around a building,
however, in the event of a fire they need to fulfill two
important safety-related functions. When closed they
form a barrier to stop the spread of fire and when opened
they provide a means of escape. Smoke sealing (solid
core) fire doors help to provide a physical barrier that
impedes the spread of toxic fumes and smoke from one
room to another. Such doors also help to protect escape
routes allowing the occupants a safe passage when
evacuating the building during a fire alarm emergency.
A well designed timber fire door will delay the spread of
fire and smoke without causing too much hindrance
to the movement of people and goods under normal
conditions.