What is Fire Alarm System?
A fire alarm system is number of devices working together to detect and warn people through visual and audio appliances when smoke, fire, carbon monoxide or other emergencies are present. These alarms may be activated automatically from smoke detectors, and heat detectors or may also be activated via manual fire alarm activation devices such as manual call points or pull stations. Alarms can be either motorized bells or wall mountable sounders or horns. They can also be speaker strobes which sound an alarm, followed by a voice evacuation message which warns people inside the building not to use the elevators. Fire alarm sounders can be set to certain frequencies and different tones including low, medium and high, depending on the country and manufacturer of the device. Most fire alarm systems in Europe sound like a siren with alternating frequencies. Fire alarm sounders in the United States and Canada can be either continuous or set to different codes such as Code 3. Fire alarm warning devices can also be set to different volume levels. Smaller buildings may have the alarm set to a lower volume and larger buildings may have alarms set to a higher level.
Fire Alarm Devices
Automatic Detection
Components of a fire consist of:
• Smoke (particulate and aerosol)
• Heat
• Light Radiation
• Fire detection devices are built to detect one or a combination of these components. While all components are necessary for a fire to exist, all components may not exist at a detectable threshold. Detectors will be selected that will detect the elements that may exist in a fire for the ambient conditions that are present. It also should be realized the similar non-fire components might exist in the same ambient conditions, which could cause unfavorable false alarm conditions.
• Devices used for fire detection include smoke detectors, thermal detectors, flame detectors, fire-gas detectors, and other devices.
• Smoke detectors sense visible or invisible particles of combustion generated by burning, smoldering, or the incipient stage of combustion. These devices fall into two categories — photoelectric and ionization.
• Thermal detectors sense the high temperature or the temperature rise caused by a fire.
• Flame detectors sense the radiation produced by a fire.
• Fire-gas detectors sense the gases produced by a fire.
• Other detectors sense some phenomenon other than smoke, thermal, flame, or fire-gas to detect a fire.
Smoke Detectors:
There are three types of smoke detectors: Ionization, photoelectric, and combination.
Ionization:
The ionization smoke detector is widely used. Its capability to detect smoke originating from fire is best utilized for clean-burning fires that produce small particles during combustion.
The ionization smoke detector consists of an alpha particle producing a radioactive source, a smoke chamber, and charged detector plates.
• The alpha source causes the air within the smoke chamber to become ionized and conductive
• As smoke particles enter the smoke chamber, the smoke particles attach themselves to the ionized air molecules and the air in the chamber becomes less conductive
• When the air conductivity within the chamber drops below a predetermined level, the alarm is triggered
Advantages of Ionization Smoke Detectors:
• Detects invisible products of combustion — It can detect fires that are in the incipient stage or detect other aerosol-type smoke products
• Quick acting – Provides for earlier detection than other types of smoke detectors or thermal detectors
• Disadvantages of Ionization Smoke Detectors:
• May provide false detection if used where volatile solvents, conductive material dusts, or high humidity are present
• Detects the presence of smoke only, not toxicity
• Has a potential for high false alarm rate
• Typical locations or hazards for ionization detection:
• Clean rooms
• Computer rooms
• Mechanical air ducts
• Locations where sensitive detection methods are needed.
Photoelectric:
A photoelectric smoke detector is the most common smoke detector used today. It detects smoke by using either the principle of light obscuration or light scattering. Its capability to detect smoke originating from fire is best utilized for fires that produce large particles during combustion.
Spot type photoelectric smoke detectors using the light obscuration principle have a light emitting device, usually a light-emitting diode (LED), a smoke chamber, and a photosensitive device that receives the light directly from the light source and produces a monitored current.
Smoke that enters the smoke chamber reduces the intensity of tech light reaching the photosensitive device, which reduces the monitored current. When the intensity drops below a certain level, the sensor control circuitry detects a drop in the current produced by the photosensitive device. When the current falls below a preset threshold, the smoke alarm is triggered.
Spot type photoelectric smoke detectors that use the light scattering principle are constructed similarly to the detectors that use the light obscuration principle except that the photosensitive device is set so that it cannot see the light source directly. When smoke enters the chamber, the smoke particles reflect the light from the source into the photosensitive receiver. When sufficient light intensity is detected, the alarm is triggered.
Advantages of Photoelectric Smoke Detectors:
• Sensitive to visual particles of smoke
• Detects smoldering low heat fires
• Provide early warning
Disadvantages of Photoelectric Smoke Detectors:
• Early contamination by dust causing reduced sensitivity
• Detects presence of smoke, not toxicity
• Must be cleaned on a regular basis
• Has a potential for high false alarm rate
• Typical locations or hazards for photoelectric detection:
• Office areas
• Clean rooms
• Raised floor spaces
• Atriums and corridors
• Meeting rooms
• Computer rooms
• Telecommunications rooms
• Electrical equipment rooms
• Sleeping rooms
• Storage closets
Beam Detector:
Beam smoke detectors are line-type photoelectric detectors consisting of a separate light source and photosensitive receiver. These devices are usually installed in large open areas where there is an unobstructed line of sight between the light source and the receiver and where the use of spot-type detectors would be economically unfeasible due to the number of detectors required.
Advantages of Beam Smoke Detectors:
• Cover a large area economically
• Quick acting
• Disadvantages of Beam Smoke Detectors:
• Unobstructed Loss between the light source and the receiver
• Correct alignment needs to be maintained
• Typical locations or hazards for beam detectors:
• High atriums
• Manufacturing spaces
Fire Alarm Devices
Automatic Detection
Components of a fire consist of:
• Smoke (particulate and aerosol)
• Heat
• Light Radiation
• Fire detection devices are built to detect one or a combination of these components. While all components are necessary for a fire to exist, all components may not exist at a detectable threshold. Detectors will be selected that will detect the elements that may exist in a fire for the ambient conditions that are present. It also should be realized the similar non-fire components might exist in the same ambient conditions, which could cause unfavorable false alarm conditions.
• Devices used for fire detection include smoke detectors, thermal detectors, flame detectors, fire-gas detectors, and other devices.
• Smoke detectors sense visible or invisible particles of combustion generated by burning, smoldering, or the incipient stage of combustion. These devices fall into two categories — photoelectric and ionization.
• Thermal detectors sense the high temperature or the temperature rise caused by a fire.
• Flame detectors sense the radiation produced by a fire.
• Fire-gas detectors sense the gases produced by a fire.
• Other detectors sense some phenomenon other than smoke, thermal, flame, or fire-gas to detect a fire.
Smoke Detectors:
There are three types of smoke detectors: Ionization, photoelectric, and combination.
Ionization:
The ionization smoke detector is widely used. Its capability to detect smoke originating from fire is best utilized for clean-burning fires that produce small particles during combustion.
The ionization smoke detector consists of an alpha particle producing a radioactive source, a smoke chamber, and charged detector plates.
• The alpha source causes the air within the smoke chamber to become ionized and conductive
• As smoke particles enter the smoke chamber, the smoke particles attach themselves to the ionized air molecules and the air in the chamber becomes less conductive
• When the air conductivity within the chamber drops below a predetermined level, the alarm is triggered
Advantages of Ionization Smoke Detectors:
• Detects invisible products of combustion- It can detect fires that are in the incipient stage or detect other aerosol-type smoke products
• Quick acting- Provides for earlier detection than other types of smoke detectors or thermal detectors
• Disadvantages of Ionization Smoke Detectors:
• May provide false detection if used where volatile solvents, conductive material dusts, or high humidity are present
• Detects the presence of smoke only, not toxicity
• Has a potential for high false alarm rate
• Typical locations or hazards for ionization detection:
• Clean rooms
• Computer rooms
• Mechanical air ducts
• Locations where sensitive detection methods are needed
Photoelectric:
A photoelectric smoke detector is the most common smoke detector used today. It detects smoke by using either the principle of light obscuration or light scattering. Its capability to detect smoke originating from fire is best utilized for fires that produce large particles during combustion.
Spot type photoelectric smoke detectors using the light obscuration principle have a light emitting device, usually a light-emitting diode (LED), a smoke chamber, and a photosensitive device that receives the light directly from the light source and produces a monitored current.
Smoke that enters the smoke chamber reduces the intensity of tech light reaching the photosensitive device, which reduces the monitored current. When the intensity drops below a certain level, the sensor control circuitry detects a drop in the current produced by the photosensitive device. When the current falls below a preset threshold, the smoke alarm is triggered.
Spot type photoelectric smoke detectors that use the light scattering principle are constructed similarly to the detectors that use the light obscuration principle except that the photosensitive device is set so that it cannot see the light source directly. When smoke enters the chamber, the smoke particles reflect the light from the source into the photosensitive receiver. When sufficient light intensity is detected, the alarm is triggered.
Advantages of Photoelectric Smoke Detectors:
• Sensitive to visual particles of smoke
• Detects smoldering low heat fires
• Provide early warning
Disadvantages of Photoelectric Smoke Detectors:
• Early contamination by dust causing reduced sensitivity
• Detects presence of smoke, not toxicity
• Must be cleaned on a regular basis
• Has a potential for high false alarm rate
• Typical locations or hazards for photoelectric detection:
• Office areas
• Clean rooms
• Raised floor spaces
• Atriums and corridors
• Meeting rooms
• Computer rooms
• Telecommunications rooms
• Electrical equipment rooms
• Sleeping rooms
• Storage closets
Beam Detector:
Beam smoke detectors are line-type photoelectric detectors consisting of a separate light source and photosensitive receiver. These devices are usually installed in large open areas where there is an unobstructed line of sight between the light source and the receiver and where the use of spot-type detectors would be economically unfeasible due to the number of detectors required.
Advantages of Beam Smoke Detectors:
• Cover a large area economically
• Quick acting
• Disadvantages of Beam Smoke Detectors:
• Unobstructed LoS between the light source and the receiver
• Correct alignment needs to be maintained
• Typical locations or hazards for beam detectors:
• High atriums
• Manufacturing spaces
Air Sampling Smoke Detectors:
For environments where detection of smoke is most critical, an air-sampling system provides the earliest possible detection. An air sampling or aspirating type fire detection system is a self-contained smoke detection package compromised of five primary components:
• Air-sampling system
• Aspiration system
• Filter assembly
• Detector
• Control system
It uses a network of pipes to continuously draw air samples and direct them to a central smoke detector.
The system operates with a network of sampling pipes that extend into the protected area. The pipes are usually made of a thermoplastic material. An internal aspirator continuously draws air into the piping network. The systems use either a filter assembly or laser particle counting technology to filter out airborne dust and debris particles, which helps to eliminate false readings.
Typical locations or hazards for Air-Sampling smoke detectors:
• Telecommunications areas
• Computer rooms
• Data centers
• Hospitals
• Clean room environments
• Atriums
• Cold storage areas
• Power stations
• Mines
• Paper and timber mills
• Museums
• Art Galleries
• Cathedrals
Thermal Detectors
Fixed Temperature
• Fixed Temperature Thermal Detectors can respond to:
• Fixed temperature limit
• Rapid rate of change of the temperature in the protected area
• Combination of these types of detection
Typical fixed temperature spot-type smoke detectors contain a bimetallic switch element that closes at a specified temperature limit. The switch is normally composed of two metals, each having a different temperature coefficient of expansion. As this bimetallic element heats the metal with higher coefficient of expansion, it causes the switch to bend or curve, closing the switch; thus indicating an alarm condition.
Line type thermal detectors are cables that detect heat along their entire length. A line type thermal detector may consist of two wires that are separated by an insulator. After the heat builds to a certain level the insulation melts, allowing the wires to touch and current to flow, initiating an alarm.
Bimetallic spot and coaxial style thermal detectors are self restoring. Fusible link and melting insulation types of line thermal detectors are not self-restoring.
Advantages of Fixed Thermal detection:
• Lower cost than smoke detector units
• More reliable than smoke detector units
• Not affected by dusty or dirty environments
• Minimal maintenance
Disadvantages of Fixed Thermal detection:
• Slower to respond than smoke detectors
• Will not detect products of combustion
• Only suitable for protection of property
Rate of Rise
Rate-of-Rise Thermal Detectors measure the rate at which the air temperature changes during a fire event. Measuring the change in temperature provides a faster alarm response than measuring the temperature level in a space.
The rate-of-rise detector measures the change in the temperature of the space through the use of a differential pressure switch. This switch contains an air chamber separated for the air in the ambient space by a flexible diaphragm. As air in the ambient space changes temperature, the air pressure increases, creating a differential pressure across the diaphragm.
The air chamber is constructed with a calibrated leak so that normal temperature and pressure fluctuations within the room space adjust across both sides of the diaphragm and will not cause the alarm contacts to close. During a fire, the air temperature rises at a rate faster than normal, causing an increase on the room side of the diaphragm diaphragm. The leak cannot compensate, and therefore the diaphragm moves and closes the detector contacts.
Combination rate-of-rise and fixed temperature thermal detectors are also manufactured and have both technologies built in.
Advantages of Rate-of-Rise Thermal detection:
• Responds faster than the fixed temperature detector
• Not affected by dusty or dirty environments
• More reliable than smoke detector units
• Less expensive than smoke detector units
• Minimal maintenance
Disadvantages of Rate-of-Rise Thermal detection:
• Slower to respond than smoke detectors
• Will not detect products of combustion
• Only suitable for protection of property
Rate Compensated
Rate-compensated thermal detectors are devices that are designed to activate at a predetermined temperature in a space regardless of the rate at which the temperature in the space increases. This is accomplished by compensating for the thermal lag between the room temperature and the interior of the device.
Construction consists of an outer metal tube that expands at a fixed rate. Within this tube, alarm contacts close when a certain expansion distance is reached, but this expansion is opposed by another metal device.
At a slow rate-of-rise in temperature, the outer tube expands drawing the contacts closer together. The inner metal device exerts a counter force, keeping the contacts separated until the entire device has been heated to its rated temperature.
At a rapid rate-of-rise in temperature, the outer tube expands faster than the inner device can compensate. Therefore, the alarm contacts close when the entire device has been heated to a lower level, thus compensating for thermal lag.
Advantages of Rate Compensated Thermal detectors:
• Responds accurately and positively to fire threats
• Virtually eliminates false alarms
• Not affected by dusty or dirty environments
• More reliable than a smoke detector
• Less expensive than smoke detector units
• Minimal maintenance
Disadvantages of Rate Compensated Thermal detectors:
• Slower to respond than smoke detectors
• Will not detect products of combustion
• Only suitable for protection of property
Flame Detector:
Flame detectors are used to detect the light radiation component of a fire. Typical detectors of this type detect the wavelength of either IR or UV or a combination of the two. These detectors are extremely fast acting and are used in areas where rapidly occurring fires or explosions could occur.
Advantages of Flame Detection:
• Extremely fast acting
Disadvantages of Flame Detection:
• Narrow field of vision
• Expensive
• Requires unobstructed field of view
• Difficult to maintain
Typical Uses:
• Fuel loading docks
• Industrial process spaces
• Other hazardous areas where a fast developing fire could occur
Fire-Gas Detector:
These detectors respond to the various gases produced during the combustion process.
• Carbon monoxide
• Carbon dioxide
• Steam
• Other elements
The Fire-Gas detector employs two types of technology to predict the fire. One method uses a semiconductor material that changes the metals conducting potential in a fire situation. The other method uses a catalytic element encased in an aluminum bead.
Advantages of Fire-Gas Detection:
• Detects products of combustion
• Sensitive enough to detect levels of gases produced between the occurrences of detectable particulate levels and detectable heat levels
• Detects gases prior to reaching lethal levels
Disadvantages of Fire-Gas Detection:
• Can be prone to false alarms
• Must be mounted at a low level, leaving it susceptible
to damage
• Can be poisoned
• Not suitable for areas where CO and CO2 and produced as part of the functions within the area
• Cannot be considered as a universal replacement for smoke and/or thermal detectors
• High cost
CONVENTIONAL FIRE ALARMS…
Fire Alarm Panels
* Fire Alarm Panel LF/CP Series
* Fire Alarm Repeater Panel LF/RP Series
* Gas Extinguishing Panel LF/EX Series
Fire Alarm Detectors
* Optical Smoke Detector LFPE 60
* Rate of Rise Heat Detector LFHD 60
* Detector Base LFB 60
* UV Flame Detector LFFD 60
* Optical Smoke Detector W/Relay LFPE 50
* LF/GD Gas Detector
* Battery Operated Smoke Detector W/Alarm LFSD 40
Fire Alarm Accessories
* Manual Call Point
* Remote Indicator
* Manual Call Point (w/cvr)
* Sounder
* Siren
* Siren with Strobe
* Xenon Beacon
* LF/AS Abort Switch
* LF/EL Emergency Light
* LF/RS Manual Release Station
* LFB6/LFB8 Alarm Bell
Fire Alarm Control Panel:
Fire Alarm Control Panel
Fire Alarm Control Panel
* Fire Alarm Panel 8000C
* Fire Alarm Panel 3002
* Fire Alarm Panel FAP/IAP 2001
* Fire Alarm Panel 8007
* Fire Alarm Panel 8008
* Fire and Extinguising Panel 8010
Fire Alarm Detectors
* Fire Detector 9000 Series
* Intelligent Fire Detector 9200
* Ex-detector
Fire Alam Accessories
* TEDIS Remote Diagnosis System
* IBM GPAX Bldg. and Info. System
