FOCUS FIRE SAFETY
PROTECTING ESCAPE ROUTES
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Smoke control systems are
designed to protect escape
routes for occupants to evacuate
safely and unimpeded by the
e ects of smoke; assist fire fighters
entering the building to find and
tackle the fire quickly; protect
stock and machines and loss of
production capacity; and reduce
risk of explosions and roof collapse.
It is important to understand the
distinction between smoke clearance
and smoke control. Smoke clearance
uses a notional amount of ventilation
to assist the firefighting operations,
allowing firefighters to clear smoke
from the relevant building or part
of the building, o en a er a fire has
been extinguished. Therefore, smoke
clearance o… ers a limited benefit
during the actual event of a fire or the
building evacuation and as a result,
smoke clearance has a much more
simplified design process.
Smoke control, on the other hand,
is designed to help during the actual
event of a fire. It is designed to
remove and restrict the movement of
smoke while the fire is still burning,
thereby assisting occupants with a
safe escape. It primarily does this by
extending the amount of time that a
building’s occupants have to safely
evacuate, without being overcome by
the e… ects of the smoke.
In order to do this e… ectively, it
is usually necessary to estimate
the amount of smoke that will be
produced, and how much heat will
be generated. Therefore, smoke
control system design requires
careful consideration and expert
maintenance.
TYPES OF SMOKE CONTROL
SYSTEMS
Natural extraction systems:
Have fail safe operation
Are self-compensating
Operate silently
Have no time or temperature limits
Are lightweight
Are sensitive to wind e… ects
Mechanical extraction systems:
Are not wind-pressure sensitive
Are suitable for ducting
Have a fixed extract volume
Require noise and weight
considerations associated with
them
Have a dedicated air inlet
Have a standby unit in case of fan
failure
Natural ventilation has the benefit of
not requiring any power or any other
functionality to work, (apart from
the vents being open) as the smoke
just escapes under its own buoyancy.
They also have the added benefit of
being ‘self-compensating’, meaning
the hotter the smoke gets, the more
e… ective the ventilators work, due
to the increase in smoke buoyance
caused by the heat. Mechanical
systems extract at one rate only, so
regardless of the amount of smoke,
it will be extracted at a steady
pace. Mechanical systems are also
designed to extract smoke at a certain
temperature for a set amount of
time, e.g. 300 degrees Celsius for one
hour. With natural ventilation, these
constraints do not apply.
Mechanical systems have the
benefit of not being sensitive to wind
e… ects, as natural ventilators are.
Plus, mechanical ventilators can be
ducted, which allows them to be used
in multi-level buildings. It must be
noted that because of the powerreliance
that mechanical systems
have, it is standard practice to provide
fire-rated wiring for them, a standby
power supply and a stand-by unit, in
case of fan failure.
Common building types that need
specialised smoke control systems
designed and installed are:
Large single storey buildings, such
as factories and warehouses
Shopping centres
Multi-storey buildings – residential
and otherwise
Buildings with atria
Car parks where gas and fume
extraction are required
As with many fire safety systems,
the concepts of smoke clearance
and smoke control are quite
straightforward. However, as
life-safety systems, they must be
robust and comprehensive. The
design and equipment must be
specific to the building-type and the
installation and maintenance of the
equipment must also be carried out
by a very competent team to ensure
the systems work properly when
required.
SAFE MAINTENANCE
Smoke control systems are o en
looked a er by fire security
companies, who may sub-contract
this to independent “AOV” or “smoke
vent” operatives. But a maintenance
provider who isn’t fully aware of the
intricacies of maintaining smoke
control systems may not know exactly
what ‘warning signs’ to look out
for or what tests to run to resolve
them. All too o en, a simple smoke
test is deemed as enough evidence
that a smoke control system is
working properly for this very reason.
However, if your service provider
is not doing full motor resistance
and load tests, then your system is
not being tested to work at maximum
duty, which is precisely when it
does need to function properly.
If they are not testing to the cause
and e… ect, battery charge rates, etc.,
then you will not know if the system
will function properly in the event of
a fire.
46 FEBRUARY 2022