2. Objective
Main objective of Fire & Gas detection
system is to ensure safety of personnel,
protection of environment, Plant &
Production
3. F&G Requirement
• Early detection & alarm
• Provide visual & audible alarms at
strategic location in the field and control
rooms
• Initiate preventive/shutdown actions at an
early stage to mitigate the consequences
of fire and gas release
• Alert personnel to danger
• Initiate suppression system (if required)
5. Selection of the detectors
• Suitable for type of hazard
• Area/span to be covered/protected
• Sensors calibrated for type of gas /
vapour or nearest likely to be present
• Fast Response
• Poision resistant
• Self diagnostic
• Low maintenance
6. Locating the detectors
• High density gases/vapours - Near
ground level
• Low density gases/vapours - At higher
elevation
• On downwind of credible leak.
• No obstruction infront of detector
7. Locating the detectors
• Point source detector close to credible
leak
• Open path detector on plant perimeter /
wide area coverage.
• Away from likely steam leaks & frosting
• No obscuration / blind eye due to
sunlight
• Easily accessible and visible
8. Detectors for Detecting Fire
• Manual Call Point.
• Optical Smoke Detector
• Ionization Smoke Detector
• Rate of Rise Heat Detector
• Linear Heat Detector.
• IR Flame Detector.
• UV Flame Detector.
• UV/IR Flame Detector.
13. • Works on light scattering principle.
• Consist of an emitter and a photo
detector with baffles.
• Emitter produces narrow beam of light,
which doesn’t reach to photo detector
as baffles are provided.
Working Principle
14. • When smoke is present in sampling
volume, proportional light scatters and
reaches to the photo detector.
• Hence light reaches to photo detector is
proportional to the smoke density, which
is converted into analogue signal and
can be send to give an alarm.
Working Principle
15. Smoke Detector - Ionisation
Location
PIBs, Control Rooms,
Sub Stations
17. • Ionization principle to detect smoke.
• Radioactive source (Americium 241)
ionizes the air inside chamber & causes
small current to flow between source &
cover.
• Ionisation causes small current to flow
between source and cover which have a
fixed voltage applied between them.
Working Principle
18. • The chamber has electrode (collector)
with some potential.
• When smoke enters the chamber,
potential of the collector will increase.
• Magnitude of this change in potential
can be used to indicate smoke density.
Working Principle
20. Working Principle
• Senses steady rise in temperature.
• It uses two matched thermistors in
bridge configuration.
• Any change in temperature of sensing
thermistor w.r.t reference thermistor will
cause change in voltage.
22. Working Principle
Alarm line high resistance sensor cable
senses temperature variations by way
of continuous monitoring resistance of
specially doped NTC polymeric
insulation, by its associated interface
unit.
24. Working Principle
• Works on the flame-flicker principle
• Detector uses IR sensors, Filters, Micro-
processor.
• Microprocessor analyses the waveform taken
by more than one wavelength from IR
spectrum.
• Generates alarm by means of co-relation
techniques.
27. Toxic Gas Detectors Types
• H2S (Hydrogen Sulphide) Gas Detector
• SO2 (Sulphur Di-oxide) Gas Detector
• Cl2 (Chlorine) Gas Detector
28. Occupational Exposure Limits
(OELs)
• Threshold Limit Value (TLV) - Time
Weighted Average (TWA) represents the
time weighted average concentration of a
toxic substance over a normal 8-hour
workday and 40 hour work week , to which
nearly all workers may be repeatedly
exposed , day after day ,without adverse
health effects.
29. Occupational Exposure Limits
(OELs)
• Short Term Exposure Limit(STEL) is a 15
minutes time weighted average exposure
which should not be exceeded during the
workday even if the 8 hour TWA is within
the TLV.
• Exposures at the STEL should not be
repeated more than four (4) times per day.
30. Alarm Setting
Low Gas Alarm : TLV of reference gas
High Gas Alarm : STEL of reference gas
32. Working Principle
• Senses presence of toxic gas conc.
and variation of oxygen in air.
• It consists of two electrodes immersed
in common electrolyte (gel).
• when gas enters the chamber, it reacts
with the electrolyte resulting in small
current to flow which is linear to gas
concentration.
33. Combustible Gas Detectors
Types
• Combustible Gas Detectors (Methane,
Propane, Butane, Pentane, Benzene,
Xylene, Octane, Toluene) -Hydrogen
Gas Detector (DGH)
• Open Path Gas Detector
35. Lower Explosive Limit (LEL)
• This is the ratio between the flammable
gas/vapour and the oxygen that is just
‘rich’ enough to ignite
• L.E.L. Value is different for each type of
gas/vapour .
Example : LEL of Methane (in air) : 5 vol%
36. Lower Explosive Limit (LEL)
• Flammable gas detection is normally
carried out in the range 0-100 % L.E.L.
0 5 15
VOL%
0-100 % LEL (Measurement Span)
L.E.L. U.E.L. (Methane)
39. Working Principle
• Infrared absorption principle.
• Light passes through the sample
mixture at two wavelengths, one is
set at the absorption peak of the gas
to be detected
• These beams are reflected back by a
retro-reflector
40. Working Principle
• Detector compares the signal
lengths of sample & reference
beams.
• Difference of sample & reference
gives measure of gas
concentration.
42. • Electro-catalytic type metallic coil
sensor (Pellistor) coated with alumina
on inner surface and catalyst on outer
surface.
• When combustible gas/air mixture
passes over the hot catalyst surface,
combustion occurs
Hydrogen Gas Detector
43. • Increase in temperature of pellistor due
to combustion results change in
resistance of Platinum coil.
• The resistance change is measured
through bridge configuration which is
directly proportional to the gas
concentration.
Hydrogen Gas Detector
44. • Green - Healthy Status of Detector
• Yellow - Fault Status of Detector
• Red - Fire Detector in Alarm
• Blue - Toxic Gas leak alarm
• Amber – Comb. Gas leak alarm
• Grey - Detector Inhibit status
• White - Detector Over Range
• Violet – Analyser House Common Alarm
Interpretation of Alarms
50. Dual Counter Rotating Ring
Master/ Slave Relationship
The Lowest Node Address
Becomes The New Master
51. Do’s and Don’ts
• Ensure devices are protected from dust
and moisture.
• Ex proof Junction Boxes are properly
closed.
• Flammable & Toxic gases are used for
calibration and testing of Detector
sensors. While calibration, handle these
gases carefully.
