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On the other hand,a low fire risk may
not justify the cost,complexity and
extent of such a system.
For example,the single occupant of a
small bungalow might be adequately
protected by the installation of one
mains powered smoke alarm,whereas
the risk to which families in a six storey
house in multiple occupation are
exposed would warrant much greater
expenditure on a more complex and
comprehensive system.
This sort of common sense approach
permeates the Code and this, coupled
with its acknowledgement of economic
constraints,makes the Code particularly
simple to adhere to.
The design of the system - which
includes considerations such as the
number of and siting of alarms, and the
form of power supply required should
take the following factors into account:
1. The probability of fire occurring
2. The probability of injur y or death of
occupants if fire occurs
3. The probability of the system operating
correctly at the time of a fire
4. The probability of early detection
and warning to occupants in the
event of fire
Points one and two combined define
the ‘fire risk’,while point three relates to
system reliability. The fourth point is
defined by the standard as ‘a form of
success rate for the system’.
The Code recommends that fire risk be
assessed by taking into account a
number of different factors. These are
now to be found in Annex A of the
2004 Code.
Firstly,it recommends that each room in a
dwelling be assessed for its own particular
fire risk,taking into account current
statistical information. How likely is it that
a fire will start in a living room,for
example? Or a bedroom? What are the
possible sources of ignition in that room?
Statistically,what are the chances of
injury or death to an occupant if a fire
does break out in that type of room?
ASSESSING FIRE RISKThe Code discusses the generally
relevant factors in carrying out a fire risk
assessment to determine the most
appropriate design of fire detection and
fire alarm system. However,it also notes
that the lifestyle of the occupants may
require a change to the assessment.
The Code looks at where fatal fires
typically break out and where occupants
may be at the time.
First and foremost,it notes that the
greatest impediment to escape in the
event of a fire is smoke obscuring the
escape route. Any fire which starts in a
circulation area - or spreads to a
circulation area - needs to be detected
as soon as possible. The Code says that
“smoke detectors need to be installed in
the circulation areas of all dwellings”.
SYSTEM DESIGN - FIRE RISKASSESSMENTHow can a system be designed to
meet the latest standards?
The Code recommends that a system is
designed – where reasonably
practicable - based on a fire risk
assessment of the property.
This needs to take into account:
• The probability of fire
• Ignition sources
• Possible fire prevention methods
• The lifestyle of the occupants
• The probability and extent of harm
• Means of escape
• Number of storeys in the dwelling
• Flammable materials (e.g. smoking)
• The age, physical condition and socio-
economic nature of the occupant
Fire risk then is essentially a combination
of the probability of fire occurring and the
magnitude of the consequences of fire.
In this way,the Code is recognising that
you don’t have to buy the most
expensive fire detection system available.
You must,however,ensure that the system
is adequate for the risks involved.
A high fire risk demands high reliability
to ensure early detection of fire and
warning to occupants,regardless of
where the fire starts,and high
reliability on the part of the system to
operate correctly when required.