This document summarizes various methods of fire detection, including smoke, flame, and heat detection. It describes the phases of fire and how different sensor types detect fires at different phases. Smoke detectors use ionization chambers or photoelectric sensors. Flame detectors use spectral analysis to detect flickering frequencies unique to flames. Heat detectors include fixed temperature types and rate-of-rise types. Other detection methods discussed are air aspiration systems and gas sensors.

1. Fire, Flame & Smoke Detectors
Presented By
Akaash Sahoo
Roll No- 210114001
M.Tech in Process Control & Instrumentation

2. Contents
• Phases of fire
• Smoke detection
• Flame detection
• Heat detection
• Other methods of fire detection
• References

3. Phases of fire

4. • Incipient Phase: Warming causes the emission of invisible but
detectable gases like- CO2 , CO
• Smoldering Phase: Smoke is formed in this phase.
• Ignition Phase: Ignition temperature is reached and flames are
present and therefore they emit radiation: mainly in UV or IR region.
• Heat release Phase: heat is released; the temperature of the space
starts to rise rapidly.

5. Smoke Detection
Two types:
 Ionization Chamber Sensor
• Used in the incipient stage for early warning.
• It’s inexpensive & better at detecting smaller amount of smokes produced
by flaming fire.
• Response is very fast but also causes a lot of false alarm.
 Photoelectric Sensor
• It is effective in the smoldering stage.
• It must be maintained so that dust and dirt accumulation doesn’t cause
false alarm.

6. Ionization Chamber Detectors
•It contains two electrodes at different potential & alpha particle source that
ionizes air in the chamber.
•The sensing part of the detector consists of two chambers - an open, outer
chamber and a semi-sealed reference chamber within.

7. • A low activity radioactive foil of Americium 241 is mounted in the reference
chamber which is an emitter of alpha particles.
• This enables formation of ion-pairs & causes current to flow between the
inner and outer chambers when the detector is powered up.
• As smoke enters the detector, particles become attached to the ions, causing
a reduction in ion-pairs and consequently current flow in the outer chamber.
• the drop in the ionization current is constantly monitored and an alarm is
triggered when it reaches a set point.
•The ionization current reflects air composition & rises as combustible gas
concentration rises.

8. Photoelectric Detectors
In the normal case, the light from the
light source on the left shoots straight
across and misses the sensor
When smoke enters the chamber,
however, the smoke particles scatter the
light and some amount of light hits the
sensor.

9. Flame detection
• Basis of detection: Spectral band analysis, Flickering frequency, Radiation
intensity threshold and detection algorithm.
• Flame flickering frequency (5-25cps) is different from ambient light
sources and bulbs, tube (120cps) which helps in discrimination of the
radiations.
• Mounting location should be carefully selected so that it has an
unobstructed vision.
• Flame detectors are used when combustible gases or flammable liquids
are present & ignition is instantaneous.
• The cone of vision of detectors and the fuel source is specified generally so
that it does not detect potentially background noises.

10. Advantages/disadvantages
• Detection distance
• Sensitivity
• Speed of response
• Range of applications
• False alarms
• High Cost
• Blinded by thick smoke,
vapors, grease and oil
deposits on the
detector’s window

11. Types of Flame detector
 UV Detectors- Detection is based on Geiger-Muller tube. When the
counted pulses exceeds the threshold value fire alarm is activated.
1. Good for H2 and CH4 fuelled flames. It’s unaffected by hot objects.
2. It’s prone to false alarm and it’s blinded by thick smoke, oil droplets etc.
 IR Detectors- Good for hydrocarbon based flames.
> Some IR detectors have flicker and statistical analysis algorithms to
minimize the effects of black body sources, a false alarm source.
 UV/IR Detectors- Both UV “AND” IR sources must be present and
exceeding their threshold levels to activate the alarm in one configuration.
> In other, UV “OR” IR source presence can trigger the alarm.
• Dual IR- Have longer detection ranges than UV or IR sensors and are more
fuel specific in their applications.

12. > Desensitized by high background levels of IR, reducing their ability to
detect a fire
• Multispectrum IR- These detectors offer greater detection ranges and
give fewer false alarms.
> Different manufacturer uses different flame detection algorithm.
• Closed Circuit Television- Only sensitive to the red-green-blue spectrum
and are not suitable for blue/translucent flames from such fuels as
hydrogen and methanol.
User is able to verify the presence of a fire before taking any action
.

13. Heat Detection
• Oldest type of automatic fire detection.
• They have the lowest false alarm rate but they are slow in response.
• They can’t differentiate between heat of fire and that of furnace.
• Used in confined place where rapid fire is expected or in places where
other methods fail.
Heat
Detection
Fixed
temperature
type
Rate of rise
type

14. Fixed temperature heat detectors
• Detectors are designed to alarm when the temperature of the operating
elements reaches a specific predefined air temperature.
• They cover a wide range of temperature
• Types of fixed temperature heat detectors:
 Electro-mechanical heat detectors- Contains a bi-metallic strip as a part of
electric circuit, that completes the circuit when a particular temperature is
reached.

15.  Fusible link type- An eutectic alloy is used, which is fixed on a spring. It
changes from solid to liquid at a particular temperature and acts as a
solder.
> This enables the spring to release & actuate alarm.

16.  Opto-mechanical type- Modern variation of electro-mechanical
type.
>It contain one or more fiber optic cables separated by a heat
sensitive insulator.
> A focused light signal is passed through the fiber optic cable.
When exposed to heat, the heat sensitive insulator changes state
from a solid to a molten state which has the effect of
discontinuation of the focused light signal.
> This actuates the alarm.

17. Rate of rise heat detector
• As an effect of flaming fire the air temperature rises rapidly
• The detector functions when the rate of rise in air temperature exceeds a
preset value; generally (12-15)F/minute.
• Rate-of-rise detectors are designed to compensate for the normal changes
in ambient temperature that are expected under non-fire conditions.

18. Electro-pneumatic type heat detector
•It’s a rise-of-rate type heat detector.
•Electro-pneumatic heat detectors comprise a controlled vented
chamber containing a diaphragm that moves due to a pressure
differential according to the rate of change of the ambient
temperature.
•When the ambient temperature changes faster than the calibrated
rate which the vent has been designed to release, the diaphragm
moves sufficiently to create an electrical circuit to indicate an alarm.
•Electro-pneumatic heat detectors operates at a range of
temperatures because they respond to the rate of change in
temperature, not at a fixed temperature only.

19. Other detection methods
• Air aspirating system- It draws air draws an air sample into the
detection chamber, via the pipe network.
1. The sample is analyzed for the existence of smoke, and then returned to
atmosphere.
2. If smoke is present in the sample, it is detected and an alarm signal is
transmitted to the main fire alarm control pane
• Gas Sensors- New systems are being developed that can analyze the
concentration of particular type of gases like- CO, CO2
> When the concentration exceeds a limit the alarm is triggered.

20. References
• Process Measurement and Analysis- Volume1, by Bela G. Liptek
• Heat Detectors – Principle and Operation
http://firewize.com/page/training/heat-detectors-principle-operation
• Techniques of fire detection - Richard W. Bukowski, Center for Fire
Research, National Bureau of Standards
• Flame detection types (ppt)