Fire is a combustion process producing heat, light, and smoke, with stages including incipient, smouldering, flame, and decay. Various fire detectors exist, including heat, smoke, and flame detectors, each designed to function optimally in specific situations and environments. Historical advancements in fire detection include the first electric alarm patented in 1890 and subsequent innovations in thermal detection technologies.

2. FIRE
 A process in which substances combine
chemically with oxygen from the air and
typically give out bright light, heat, and
smoke; combustion or burning.
 In this process always fuel gets
exhausted.
 Product of combustion is flame with
enormous heat, end product of the fuel
and mixture of exhausted gases.

3. STAGES OF FIRE
 INCIPIENT STAGE(Initial stage)
 SMOULDERING STAGE(Developing
stage)
 FLAME STAGE(Fully developed stage)
 DECAY STAGE
For predicting the fire in every stages we
need to install different types of detectors.

4. STAGES OF FIRE

5. FIRE DETECTORS

6. Detector Act As
 A sensor/ device.
 Respond to Fire and initiate an alarm.
 To alert occupant and Fire department.
Functions of detectors
Prime function of a fire detector is to detect one or
more changes in the protected environment
indicating the development of a fire.
Types of fire detectors
1. Heat Detector
2. Some Detector
3. Flame Detector

7. History
The first automatic electric fire alarm was patented
in1890 by Francis Robbins Upton an associate of
Thomas Edison George Andrew Darby patented the
first European electrical heat detector in1920 in
Birmingham England.
Definition:-
Thermal detectors are light detectors Which is used
to rise induced temperature, they are suitable for
wide wavelength infrared spectral region.

8. FIRE DETECTORS
 IONISATION DETECTOR
 PHOTOELECTRIC DETECTOR
 INFRARED DETECTOR
 THERMAL DETECTOR
IS 2189 : 2008
Reviewed In : 2018
Selection, installation and maintenance of
automatic fire detection and alarm system
code of practice

10. HEAT DETECTOR
 These are suitable for use in most
buildings in general they have a greater
resistance to adverse environmental
condition than other types.
 Where fire can occur in which heat is
evolved rapidly, with little some, they
may give more rapid fire detection than
a smoke detector.

11.  Fixed temperature and rate of rise
detectors should fixed temperature heat
detectors are not suitable in cold stores
where ambient temperatures are
abnormally low.
 Combined be avoided if rapid changes in
ambient temperature are likely.
 In situation such as furnace rooms, where
very high ambient temperature occurs, and
heat detectors to BS544: part8 should be
used.

12. TYPES OF HEAT
DETECTORS
 FIXED TEMPERATURE
It is one that responds only when a
predetermined temperature is reached.
 RATE OF RISE
It is one that responds when temperature
rises is abnormally rapid.

13. PRINCIPLE:
 Thermal detectors contain a small active
element on which radiation is focused.
 By blackening and insulating the element by
minimum the size of the element , temperature
change and detector response is maximised.
 Temperature change is approximately
proportional to the exposed surface area of the
element.
 As the intensity of the radiation increases the
temperature the temperature change on the
element of the detector increases.

14. THERMAL
DETECTORS

15. TYPES OF THERMAL
DETECTORS
 THERMOCOUPLE
 THERMISTORS (Pyroelectric detector)
 PNEUMATIC (Golay cell)

17. THERMOCOUPLE
 Two dissimilar metals like antimony and bismuth.
 Two ends are called hot junction and cold
junction.
 The surface at the junction of wire is coated with
black metallic oxide.
 IR radiation falls on hot junction by heat source
change in temperature at the junction between
the metallic wires causes electric potential to
develop between the wires.
 The potential difference between the unjoined
ends of the wires is amplified and measured.
 Cold junction is not exposed to IR.

18. ADVANTAGES OF
THERMOCOUPLE
 The Thermocouple device is cheaper than the
other temperature measuring device
 The thermocouple has fast response time.
 It has wide temperature range.

19. DISADVANTAGES OF
THERMOCOUPLE
 The thermocouple has low accuracy.
 The recalibration of the thermocouple is
difficult.
 Nickel-alloy, platinum/rhodium alloy,
Tungsten/rhenium-alloy, chromel-gold,
iron- alloy are the name of the alloys
used for making the thermocouple.

20. THERMISTORS:
 Thermistors are the devices that have an
electric resistance that is higher temperature
dependent.
 The materials used in thermistors are sintered
oxide of cobalt, Manganese, Nickel.
 A constant potential is applied across the
thermistor and the difference in current flow
between an illuminated thermistor and a non-
illuminated thermistor is measured using a
differential operational amplifier.
 As the temperature of mixture increases, its
electrical resistance decreases.
 Response time is 80 m/sec.
 It should be operated at a frequency of less than
12Hz.

21. PYROELECTRIC
DETECTORS:
 Pyroelectric detector contains a noncentrosymmetrical crystal, it
exhibits an internal electric field along the polar axis.
 Pyroelectric effect depends on the rate of change of the detector
temperature rather than on the temperature itself.
 These detectors operate with a much faster response time and makes
the choice for fourier Transform Spectrometers where the response is
essential.
 MATERIALS USED IN PYROELECTRIC DETECTORS:
1. Triglycine sulphate (TGS)
2. Deuterated triglycine sulphate(DTGS)
3. Lithium niobate(LiNbO3)
4. Lithium tantalate(LiTaO3)

23. ADVANTAGES:
 Uses at room temperature.
 Low power requirement.
 Relatively fast response.
 Low cost material.
 Faster than Thermocouple.

24. DISADVANTAGES:
 Complex structure.
 Difficulty of scanning elements.
 Used for short distance applications.
 Devices are not allowed to move around while
transmission is in progress.

27. GOLAY CELL
 Golay cell consists of a small metal cylinder closed by
a rigid blackened metal plate.
 Pneumatic chamber is filled with xenon gas.
 At one end of cylinder a flexible silvered diaphragm
and at the other end infra red transmitting window is
present.
 When IR radiation is passed through IR transmitting
window the blackened plate absorbs the heat. By this
heat the xenon gas causes expand.
 The resulting pressure of gas will cause deformation
of diaphragm. This motion of diaphragm detects how
much IR radiation falls on metal plate.
 Light is made to fall on diaphragm which reflects light
on photocell.
 Response time is 20m/sec.