Aico Smoke Alarm Manual: Comprehensive Guide on System Design and Fire Risk Assessment

SYSTEM DESIGN - FIRE RISK ASSESSMENT

How 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.

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 injury 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 RISK

The 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”.

BALANCE BETWEEN FIRE RISK & SYSTEM RELIABILITY & SUCCESS RATE

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