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Automatic Fire Detectors

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Automatic Fire Detectors
Do we really need a detector
Kerosene
Kerosene
Speed & Aftermath of Fire
Yes
Fire Detectors
detect fires at
their earliest
stages and
sound a loud
warning to
help you
get out
safely
Detection
• Typical room
• Typical room
Alarm bell
Corridor
Stair pressurisation fan
Fire escape stair
Fire AlarmPanel
Bell
• Typical room in hotel
Alarm bell
Corridor
Stair pressurisation fan
Fire escape stair
Fire AlarmPanel
Bell
Detector
Sprinkler
• Fire starts in room
•
•
•
•
Smoke detector activates alarm
Smoke fills guest room
Alarm sounds in rooms and at lobby
Stairway fan pressurisation begins
• Occupants make way to stairwell
• Smoke slowly spills into corridor
• Stairwell provides SAFE egress
path to outside of building
• Sprinklers in room operate,
discharging water, controlling and
extinguishing fire
• Occupants exit from building
• Occupants leave building to safe area
• Smoke is discharged from building
Detection
 Detectors sense the existence
of a fire
 Fire Panels
acknowledge the detectors,
test the system,
check for faults
operate the alarms
 Alarms inform the occupants
of a fire and assist the
evacuation
1. Concentration of energy
Ignition
and fire
growth
2. Source of oxygen
3. Spontaneous oxidation at
surface of combustible
material
4. Release of particles into
atmosphere
5. Exponential propagation of
chain reaction
6. Release of energy in the
form of light and heat
Fire Growth
VISIBLE SMOKEFLAMING FIRE INTENSE HEAT
STAGE 1
STAGE 2
SMOKE DENSITY AND HEAT OUTPUT
INCIPIENT STAGE - NO VISIBLE SMOKE
TIME
STAGE 3
STAGE 4
Detectors Smoke
Flame
Heat
CO
Smoke
Detector
 Detects the presence of
smoke particles
 Inexpensive, early
detection for
smouldering fires
 No need for line of sight
 Indoor applications only
 Subject to occassional
false alarms
Smoke
Detector
 Ionisation
 Optical
 Beam
 Sampling
 Installed
every 10m
Ionisation
Smoke
Detector
ION-CHAMBER SMOKE
Alpha source
Collector
Battery
Chamber cover
Working of Ionisation Detector
Smoke
Detector
Double Chamber
Ionization
Detector
OPTICAL SMOKE
Insect
Screen
Insect
Screen
Fins
Smoke Path
Sampling
Volume
Optical
Detector
Light Scatter Type
Optical
Detector
Obscuration
Type
Sampling
Detector
What is an Air Sampling System?
Air samples are drawn
into the sampling pipe
and carried through to the
Detector by the aspirator.
Detail of
Sampling
point
Sampling pipe
Sampling point
Air samples
VESDA
Very Early Smoke Detection Apparatus
Display
Air enters detector
Inlet manifold
Ultra pure air is used
to keep optical surfaces clean
Laser
Chamber
Air sample is
moved through
the laser chamber
via the aspirator
and filter
The signal is then
passed to the
Dual Stage Filter
processor card for
and onto the Display
Dust is filtered Module
out
Aspirator
®
Operation of the VESDA Detector
Radiation / Flame Detectors
Forms of radiant energy produced by a fire
 Detects radiation from
flame
Flame
Detector
 Analyses one or more UV
or IR frequencies
 Extremely fast on flaming
fires
 Long range, line of sight
 Sophisticated and
expensive
 Suitable for high risk,
liquid and gas hazards
Infra-red (IR)
Radiation Detector
Scanning Infra-red (IR)
Radiation Detector
Ultra-violet (UV)
Radiation Detector
FALSE ALARMS
• Ultra Violet
–Welding
–X-ray
–Lens contamination
–High power consumption
• Infra Red
–sunlight
Heat
Detector
 Senses temperature or
temperature change
 Immune to false alarms in
most cases
 Reliable, fairly slow
detection
 Fire must be near detector
 Low maintenance
 Inexpensive
Heat
Detector
 Fixed temperature
 Rate-of-rise
Heat
Detector
Expansion of
single metal
strip
Heat
Detector
Expansion of
single metal
strip
Heat
Detector
Expansion of
bi-metallic
strip
Heat
Detector
Expansion of
gases
Heat
Detector
Expansion of
gases
Heat
Detector
Linear
Heat Detecting
Cables
Optical Fibre
Distributed Temperature Sensing
• Technology provides continuous profiles of
temperature using a single optical fibre as the
sensing element
• An instrument containing an Optical Time
Domain Reflectometer and signal processing
software
• Monitors hundreds of points in seconds
• Sensor is insensitive to EMI
• Sensor is Intrinsically safe
Beam
Detectors
Effects of Flame
on IR Beam
Effects of Smoke
on IR Beam
Carbon
Monoxide
Detector
 CO is a toxic gas
 CO is the major cause of
death in fires
 CO detectors sense slow
smouldering fires before
smoke detectors
 Best option for hotels,
hospitals, nursing homes
CARBON MONOXIDE
SOMETHING NEW
IN
FIRE DETECTION?
FACTS
Carbon Monoxide Gas
– Produced in fires
– Odourless
– Colourless
– Travels more freely than smoke
– Makes victims lethargic,
disoriented
– Brain damage, death at high ppm
FACTS
Slow Smouldering Fires
– Vast quantities of CO before
flaming
– Cause of many deaths
– Difficult to detect using traditional
Ion- or Optical based detectors
– Cause of backdraft?
Fire Growth
INCIPIENT STAGE - NO VISIBLE SMOKE
VISIBLE SMOKEFLAMING FIRE INTENSE HEAT
STAGE 1
STAGE 2
STAGE 3
STAGE 4
SPRINKLER
SMOKE DENSITY AND HEAT OUTPUT
BEAM
PHOTO
VESDA
ION
TIME
FLAME
HEAT
Call
Points
 Allow manual alarm of fire
 Different types include:
Breakglass
Push button
Lever
 Located at exits and
throughout risk
Panels
 Panels are the “Brains”
that receive the detector
inputs and decide the
action or output
response
 The panels and detectors
are configured into
SYSTEMS
 There are two types of
system configurations:
 CONVENTIONAL and
ADDRESSABLE
Conventional
systems
• Simple installation
• Detectors and
inputs are
grouped into
ZONES
2 Core
• Each detector and
input is individually
Addressable identified
Systems • One wire connects
different types of
inputs
2 Core
Outputs
• Alarms
• Bells
• Sirens
• Lights
• EVAC systems
• Voice commands for
regulated evacuation
• Drivers for control
• Suppression system
• Shutdown of air
handling
• Control of doors
 Prevention issues
Selecting
Detectors
Life safety,
Business interruption,
Asset protection,
Explosion prevention
Tolerable damage levels
?
 Fire issues
Slow or rapid development
Smouldering or flaming
Solids or liquids
Analyse relative importance of:
 Speed of response
Selecting
Detectors
 Range of response
 Sensitivity and discrimination
 Reliability
 General immunity to false alarm
sources
 Immunity to specific radiation
sources
 Electronic interface
 Cost
Early Detection
leads to
Life Safety
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