Basics of fire detectors

1. Fire Protection System - Automatic Fire Detectors
S.Sudha Velan B.E (Civil)

2. Fire Alarm System
• Designed to alert us to an emergency so that we can take action to
protect ourselves, staff and the general public.
• Fire alarms are found in Offices, Factories, and public buildings .
• Protection of life
• Protection of property

4. Conventional Fire Alarm Systems

10. Fire Detectors
• The Fire detectors are designed to detect one or more of following
threecharacteristics of a fire:
• Smoke
• Heat
• Radiation (flame)
• Choice of selecting a detector dependson the following
(i) The speed of response required.
(ii) Need to minimize false alarms
(iii) The nature of the fire hazard
(iv) Cost, suitability for environment, maintenancerequirement etc..

11. Types of Detectors
(A)Heat Detectors:
(i) FixedTemperature
(ii) Rate of Rise-Cum-fixedtemperature Detectors
(iii) Probetype high temperature Bi-MetalHeat Detector
(iv) LinearHeat Sensing Cables
(B) Smoke Detectors:
• Ionizationtype
(i) Opticaltype
(ii) Air Samplingtype
(iii) Multi-criteriaType
(iv) Photo-thermalType
(v) Beam Detector
(vi) CarbonMonoxide
(C) Spark / EmberDetector
(D) Ultraviolet(UV)FlameDetector
(E) Infra Red (lR) FlameDetector
(F) ThermalMulti-CriteriaDetector

12. Heat Detectors
• Fixed Temperature Detectors
•
A fixed temperature heat detector is designed to alarm at a set
temperature.
• Fixed temperature heat detectors can suffer from thermal lag when
fires build quickly may alarm when the room temperature is higher
than the set point.
• Application
• Used where the ambient temperature is likely to fluctuate rapidly
overshort period (kitchen, boiler room, D.G. Set room, Non-AC area
in building)

15. Rate of Rise-Cum-Fixed Temperature Detectors
• These detectors are designed to operate within a given time.
• When the rate of temperature rise at the detector exceeds a
predeterminedvalue regardless of the actual temperature.
• When temperature at detector exceeds a predetermined value.
• Application In areas subject to smoke, dust and dirt during normal
use, where smoke detectorscannot used.

18. Probe Type High Temperature Bi-Metal Heat Detector
• The detector are reset type and highly suitable to use above 80°C
where electroniccomponents cannot be used.
• Application: Generator Enclosure, turbine enclosures, oven and
furnace area etc.

20. Linear Heat Sensing Cables
• Continuous heat detector designed to detect heat along the length
of a sensor cable.
• Digital Sensor consists of two core cable in which the conductors are
separated by aheat sensitive insulator. When a specified temperature is
reached, the cable insulation breaks down and an alarm is activated.
• Analogue sensor, cores are separated by a negative temperature co-
efficient polymer whose resistance reduces in proportion to temperature
increase.
• Applications: Cable tunnels, trays and vaults ,material conveyors , bulk
storage mull - racked areas , rim seals of floating roof tanks storing
hazardous chemicals.

21. Digital Sensor Wires

22. Analogue Sensor Wires

31. Smoke Detectors
• Ionization type
• Good for invisible smoke detection. Due to use of radioactive element present in
it,the disposal is a great problem and can cause serious health hazard, hence
now slowly becomingobsolete, use of this detector may be avoided.

33. Optical Smoke Detectors
• The optical smoke detector is based on Light Scattering principle.
The LED (Light Emitting Diode) transmits light to the measuring
chamber where it is absorbed.
• Incase of fire, smoke enters the measuring chamber and the smoke
particle scatter thelight. The amount of light reaching to photo
diode is converted into a proportionalelectrical signal.
• On operation of detector when the electrical signal reaches a
predetermined threshold value it triggers the alarm on control panel.
• More suitable for smoldering fire which produces mainly larger
particle of smoke (burning of PVC)

35. Air sampling Type Detector
• Detector consists of apiping or tubing distribution network that
runs from the detector to the areas to beprotected.
• An aspiration fan in the detector housing draws air from the
protectedarea back to the detector through air sampling ports,
piping or tubing.
• At the detector, the air is analyzed for the products by the laser
based smoke detector.
• Use : Typical application of the system is in places where trace of
smoke needs to bedetected and high airflow can make traditional
smoke detector inadequate.

40. Multi-Criteria Type Detector
• Multi-criteria fire and CO detectors are plug-in,
addressable devices that provide both fire and carbon
monoxide (CO) detection. They combine four separate
sensing elements to sense multiple components of a fire:
smoke, CO, light/flame, and heat.

41. Photo-Thermal Type Detector
• Smoke and photoelectric thermal detector consists of
an optical chamber sensitive to light scattering and a
thermistor sensitive to heat.

42. Beam Detector
• Optical beam smoke detectors work on the principle of light
obscuration, where the presence of smoke blocks some of the
light from the beam, typically through either absorbance or
light scattering. Once a certain percentage of the transmitted
light has been blocked by the smoke, a fire is signalled.
• Beam detector provides excellent smoke detection compared
to standard optical detectors in large, open areas such as
warehouses, factories, arenas and airports.
• The range includes two options:
• up to 50 m (which has one reflector)
• up to 100 m (which has four reflectors in formation)
depending on the size of space.

46. Carbon Monoxide Detector
• Carbon monoxide detectors are the fastest way to prevent CO
poisoning. You can install a carbon monoxide detector in your
home. They work much like your fire or smoke alarm by
sounding a siren when they detect carbon monoxide.

49. Spark / Ember Detector
• This detector uses a solid-state photodiode or photo transistor to
sense the radiantenergy emitted by embers typically between 0.5
microns and 2.0 microns innormally dark environments.
• These detectors can be made extremely sensitive (microwatts) and
their responsetimes can be made very short (micro seconds)
• Applications
• The detectors are primarily installed to detect sparks and embers
that could, if allowed to continue to burn, can cause a much larger
fire or explosion.
• The detector is mounted on some form of duct or conveyor,
monitoring the fuel as itpasses by.
• It is necessary to enclose the portion of the conveyor where the
detectorsare located, as these devices generally require a dark
environment.

53. Ultra Violet (UV) Flame Detector
• It makes use of Ultra violet sensitive photocathode for detecting flame. It has
veryhigh sensitivityand low false alarm rate and is suitable for indoor application.
• The detector is not suitable for high ceiling as the radiation from fire is attenuated
bysmoke.
• The random UV radiation from sources such as lighting, the Arc welding etc.can
cause false alarms hence usagein such areas to be avoided.

54. Infra-Red Flame Detector
• Almost all the materials that participate in the flaming combustion
emit ultravioletradiation to some degree during flaming combustion
whereas only carbon containing fuels emit significant radiation at
4.35 micron (Carbon dioxide) band usedby many detectors to detect
a flame.
• This detector senses wavelength in the infrared spectrum.
• Application: High-ceiling, open-spaced buildings such as ware-
houses and aircraft hangers ,Outdoor or semi outdoor areas where
winds or draughts can prevent smoke from reaching a heat or smoke
detector.
• Where rapidly developing flaming fire can occur such as in
petrochemical production areas, storage areas, natural gas
installations, paint shops or solventareas.

56. Thermal Multi-Criteria Detector
• Multi-criteria fire and CO detectors are plug-in, addressable
devices that provide both fire and carbon monoxide (CO)
detection. ... They combine four separate sensing elements to
sense multiple components of a fire: smoke, CO, light/flame,
and heat.

59. Thanks & Regards
S.Sudha Velan