Element C3

Element C3.3

Fire Detection and Alarm Systems

and Procedures

Categories of Alarm and Detection

Systems

Property risk / protection

P1

Systems installed in all parts of the building.

Earliest possible warning of fire

Minimise time between ignition and arrival of fire fighters

P2

Systems installed only in defined parts of building

Early warning of fire in areas of high fire hazard level or

areas which risk to property or business continuity from fire is

high

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Categories of Alarm and Detection

Systems

Life risk / protection

M

Manual systems – call points and sounders only

No automatic detectors

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Categories of Alarm and Detection

Systems

Life risk / protection

L Automatic detection for protection of life

Sub categories…

L1 All areas of building

Earliest possible warning of fire

L2 Defined parts of building

Early warning of fire in specified areas

L3 Early warning to enable safe escape

L4 Systems installed in escape routes comprising corridors and stairways

Provide warning of smoke within escape routes

L5 Satisfy specific fire safety objective

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Common Fire Detection Equipment

Can detect fires at each of the 4 stages of a fire’s

development:

Invisible products of combustion (CO detectors etc.)

Visible smoke

Heat

Flame

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Common Fire Detection Equipment

Smoke detection

Optical smoke detectors

IR light refracting off smoke particles entering detection

chamber, onto a light sensor which triggers alarm

Good for large particles of smoke

Smouldering fires, fabrics, furnishings

Prone to false alarms caused by steam or dusty

environments

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Common Fire Detection Equipment

Smoke detection

Beam detectors

Transmitter and receiver

TX emits IR beam to RX

Detects obscuration by smoke

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Common Fire Detection Equipment

Smoke detection

Ionisation detectors

Smoke particles pass between 2 electrodes

Causes ionisation of surrounding air and a small current flow

Added weight of smoke particles slows down transmission

rate, alarm triggered

Fast faming fires, small particles of smoke

False alarms from burning odours

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Common Fire Detection Equipment

Heat detection

Rate of rise heat detector

Responds to rapid increase in temperature

Use where smoke detector is undesirable

i.e. flammable liquids

Fixed temperature heat detector

Sensing element at fixed temperature

Triggers alarm

Kitchens or boiler rooms – rate of rise no good

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Alarm Systems

Purpose

Increase safety of occupants by encouraging them to

escape to place of safety

Increase possibility of early extinction of fire

Reducing loss or damage

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Alarm Systems – Design Features

Method of raising alarm

Hand operated

Hand bell or whistle

Limitations – size of building, portable (lost)

Call points

1.4m above floor level

On escape routes

Max distance to travel = 30m direct / 45m actual

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Alarm Systems – Design Features

Wiring

Mineral insulated copper clad

PVC conduit

Pirelli F P 200

Lower standards may be acceptable for certain

components of a modern system

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Alarm Systems – Design Features

Control panel

Must show state of system

Normal, fault, fire

Sited in area of low fire risk

Ground level near to entrance

Visible to fire and rescue service in event of fire

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Alarm Systems – Design Features

Power supplies

Normal = public mains system

Standby = battery with auto charger ( 4 yrs life)

Or battery with standby generator

Standby should be able to maintain power for 24

hours

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Alarm Systems – Design Features

Radio link systems

Advantages

No wiring needed

Easy, cheap, quick install

Can be extended beyond single building

No damage to building surfaces

Disadvantages

Interference

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Alarm Systems – Design Features

Signals

Audible signals

Bells or sirens

In event of short circuit, at least one sounder will

continue to sound

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Alarm Systems – Design Features

Signals

Sound levels

65 dB(A) or + 5 dB (A) above other noise

75 dB(A) for sleeping persons

Special provisions to be made for hearing impaired

Visual signals, recorded messages

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Alarm Systems – Design Features

Signals

Single stage alarm

Through whole building – calls for total evacuation

Two-stage alarm

Large / high rise buildings

Evacuate higher risk first

Closest to fire / above it

Evacuation signal and alert signal for others

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Alarm Systems – Design Features

Signals

Staff alarms

Public premises

Controlled evacuation

Prevent distress etc.

Coded announcements, contact by radio

Sufficient training for staff

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Alarm Systems – Design Features

Zones

No confusion as to point of origin of fire

Sub-divide building into zones

Careful zoning minimises search distance

Distance travelled to visually determine position of a fire

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Alarm Systems – Design Features

Testing

Daily Panel check – indicates normal operation.

If not, fualt and action taken must be recorded in the log book

Weekly One detector, call point, end of line switch to be operated to check

controls and indicating equipment, as well as to test sounders

Annual / after fire By competent person (installation engineers)

Standby power Visual check on batteries, oil, fuel, coolant on generators.

Defects remedied and logged

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Manual Systems

Should always be opportunity for building occupants

to raise alarm themselves

Breaks glass- electrical contact made, alarm triggered

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Automatic Systems

Majority of serious fires occur at night

Automatic detection with 24 hour monitoring

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