FIRE ALARM SYSTEM

By :MUHMMAD FARID, AHMED MUHAMMAD, MUHMMAD ZARIA, MAHMOUD AFEFY

Overview Fire alarm system is installed for

protection of life, property and mission. In order to a fire alarm system to be useful, it must be able to perform these functions:

Detect the presence of a fire. Notify the occupants. Notify the fire department

BASIC FIRE ALARM TECHNOLOGY

Secondary (DC)

Primary (AC)

Outputs

Inputs

1.Main Controller (control panel)

Fire Alarm

Detectors

Automatic

Electronic

Flame

infrared

ultraviolet

heat smoke

visible invisible

Electromechanical

2. Classifications of fire alarm detectors

3. Selection For Detectors Stage OneIncipient: Products of Combustion particles are produced (<0.3 microns). No visible smoke or detectable heat. May occur for milliseconds or days.

Use ionization detectors

Stage TwoSmoldering: Visible smoke particles are produced (>0.3 microns). Little visible flame or noticeable heat.

Use Photoelectric Detectors

Stage ThreeFlame: Rapid combustion produces radiant energy in the visible, and invisible (IR, UV) spectrums. Heat begins to buildup at this stage

Use Spark or Flame Detectors

Stage FourHigh Heat: Uncontrolled combustion is caused by the heating of nearby combustibles to their ignition point.

Use Heat Detectors

4. Notification Appliances (outputs) Bells: Used if they are only

for fire, or have a distinctive sound from other bell signaling devices. Often used as an external gong to indicate the flow of water in the sprinkler system.

Horns: Loud and distinctive output. Often used in high-noise environments, such as manufacturing plants.

Sirens: Extremely loud devices generally limited in use to outdoor or heavy industrial areas.

Speakers: Audible devices used in conjunction with voice

SMOKE DETECTOR

SMOKE DETECTOR A smoke detector is a device that senses

smoke, typically as an indicator of fire. Smoke detector consists of two parts:

A sensor to sense the smoke An electronic horn to horn the people

Two basic types of smoke detectors are used today ionization and photoelectric.

IONIZATION SMOKE DETECTOR

IONIZATION SMOKE DETECTOR

IONIZATION SMOKE DETECTOR

Advantages of Ionization Smoke Detectors1. Detects invisible products of combustion. It can detect fires that are in the incipient stage2. Provides earlier detection than other detectors such thermal detectors Disadvantage of Ionization Smoke Detectors1. Has a potential for high false alarm rate, so may

provide false detection if used where dusts, or high humidity are present 

PHOTOELECTRIC SMOKE DETECTOR The photoelectric type detector utilizes light as a

detection mechanism. A photoelectric, or optical, smoke detector

contains a source of infrared, visible, or ultraviolet light, a lens, and a photoelectric receiver (typically a photodiode).

There are two types of photoelectric smoke detectors:Light sensing(scattering)Light obscuring(blocking)

LIGHT SCATTERING SMOKE DETECTOR

Advantages of Light Scattering Photoelectric Smoke Detectors• Sensitive to visual particles of smoke• Detects smoldering low heat firesDisadvantages of Light Scattering Photoelectric Smoke Detectors• Early contamination by dust causing

reduced sensitivity• Must be cleaned regularly

LIGHT OBSCURING SMOKE DETECTOR (BEAM SMOKE DETECTOR)

Advantages of Beam Smoke Detectors• Cover a large area economically• Quick acting in high atriums

Disadvantages of Beam Smoke Detectors• Correct alignment needs to be maintained

PHOTOELECTRIC SMOKE DETECTOR CIRCUIT

COMPARISON SENSOR TYPE IONIZATION SENSORS PHOTOELECTRIC SENSORS 

USAGEIonization sensors are designed to recognize fast-burning, flaming fires through the small amounts of smoke they produce.

Photoelectric sensors are better at detecting smoldering fires that generate lots of smoke.

Price $2.48 to $24.32 $14.90 to $106.91 

Typical locations Clean rooms Computer rooms Mechanical air ducts Locations where

sensitive detection methods are needed

 

Cargo Handling Areas, loading Bays etc. Atriums and

corridors Computer rooms Photographic Rooms

(Dark/Developing/Copying) Lift Shaft Electrical equipment rooms Warehouses

PLACEMENT OF SMOKE DETECTORS Smoke detectors should either be placed in the

center of the ceiling, or on the wall 6-12 inches below the ceiling

DETECTOR SPACING

PEAKED OR SLOPED CEILINGS

FLAME DETECTOR

Flame Detector Designed to detect & respond to the presence of a

flame or fire. It can include sounding an alarm, deactivating a

fuel line and activating a fire suppression system. A flame detector can often respond faster and more

accurately than a smoke or heat detector.

Flame Detector Circuit

Optical flame detectors

1. Ultraviolet Detectors UV often included to minimize false alarms which can be

triggered by other UV sources. Emitted at the instant of ignition within 3–4

milliseconds.

2. Infrared False alarms can be caused by other hot surfaces and

background thermal radiation in the area. The usual response time of an IR detector is 3–5 seconds.

3. Infrared Thermal Cameras Infrared (IR) cameras can be used to detect heat and with

particular algorithms can detect hot-spots within a scene. These cameras can be used in complete darkness and operate

both inside and outside.

4. UV/IR

These detectors are sensitive to both UV and IR wavelengths.

Detect flame by comparing the threshold signal of both ranges.

This helps minimize false alarms.

5. IR3 flame detection Triple-IR flame detectors compare three specific

wavelength bands within the IR spectral region. IR3 detectors can detect at up to 65m (215ft) in

less than 5 seconds. Most IR detectors are designed to ignore

constant background IR radiation.

Applications Hydrogen stations. Gas-fuelled cookers. Industrial heating and drying

systems. Domestic heating systems. Industrial gas turbines.

Advantages Detection distance Sensitivity Speed of response Reliability

Disadvantages Narrow field of

vision. Expensive. Difficult to maintain.