Basic Fire Alarm Systems

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Basic Fire Alarm Systems
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ALARM INPUTS
OUTPUTS
Bells
Detectors
Strobes
Supervisory Inputs
Horns
Manual Pull Stations
Speakers
Gate Valve
Auxiliary Devices
Waterflow Switches
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CPUs
1. Brains of the system. 2. Controls power
to the system. 3. Receives the input
data. 4. Processes the data
5. Transmits data to outputs.
6. Monitors integrity of system.

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CLASS B IDC N/O Initiating Contacts
End of Line Resistor (EOL)
1. In normal operation current flows out through
the EOL on one leg and returns to the
control panel on the other leg. In this way the
circuit is being supervised for any opens or
ground faults. 2. If one of the initiating
devices goes into alarm the contacts close,
shorting the circuit. 3. The increased current
flow will be seen as a alarm condition at the
control panel.
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Class A Initiating Device Circuit
1. No EOL Resistor. 2. Circuit is returned to the
panel after last device. 3. Will continue to
operate properly with a single open or
ground. 4. Under Normal conditions 'supervisory'
current is flows through IDC circuit.
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If a break occurs, and a detector goes into Alarm


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1. Current will flow out the other wire, through
the detector, and return to the panel. 2.
Panel detects the current and indicates an
alarm. 3. Class A circuits provide a higher
reliability than Class B.
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Single Action, Single Stage
Dual Action Single Stage
MANUAL PULL STATIONS
Single Action Single Stage Break Glass
Single Action Dual Stage
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Wet Pipe Sprinkler System Vane Switch
1. Detects waterflow in the sprinkler pipe. 2.
Vane Switch device 3. When water flows, the vane
turns closing a dry contact switch. 4. Dry
contact closure is monitored by an input
module. 5. Activation of the input module results
in an alarm condition.
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Sprinkler System Valve Tamper Switch
1. Monitors the water supply valves on the
building sprinkler system. 2. When these valves
are shut, that part of the sprinkler system will
not operate. 3. Switches are normally
monitored by input modules or zones of a fire
alarm System. 4. When valve is closed, the
switch dry contacts close, activating the input
module or device. 5. A supervisory signal is
sent to the control panel, notifying personnel
that one of the sprinkler gate valves is being
tampered with.
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Heat Detectors

• Not a Life Safety Device.
• Activates when surrounding temperature
• reaches a preset temperature.
• Typical 135 degrees F.

Two methods of Heat Detection 1. Spot Type -
Detects temperatures at a specific location. 2.
Line Type - Detects temperatures of an area along
its specific length.
Example of a line type is a length of two wire
insulated cable with power applied and zigzagged
across an area or equipment. Heat from a fire
would melt the wire insulation allowing the two
wires to short. The short would indicate the
off-normal condition. Used often in large open
warehouses and storage areas.
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Thermistor Type Heat Detector
Fixed Temperature - Thermistor has a negative
temperature coefficient. As Heat rises,
resistance decreases, allowing more current flow.
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Heat Detector Application
1. Not a life safety device. 2. Used where smoke
detectors would cause a high rate of nuisance
alarms. 3. May be used where flames may occur
instantly.

• Characteristics
• Slowest reacting detector
• Main disadvantage is Thermal Lag
• May be restorable or non-restorable

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Heat Detectors

• Rate-of-Rise Heat Detectors
• Signal an alarm when the rate of temperature
  increase exceeds a
• predetermined value.
• Typically 12 degrees to 15 degrees rise per
  minute
• Do not respond well to a slow building fire.
• Fixed Temperature/Rate-of-Rise Heat Detectors
• Rate-of-Rise compensates for thermal lag.
• Fixed Temperature compensates for slow fire
  expansion
• All Heat Detectors remain the slowest in response
  to alarm conditions.

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Photoelectric Smoke Detectors
Signals an alarm condition when it senses visible
smoke particles in the air. Responds to larger,
visible smoke particles Reacts to a minimum
concentration of visible smoke. Used where
materials present enter the smoldering stage
rapidly.
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Projected Beam Photoelectric Detection
Light Obscuration Method
Normal Condition
Transmitter
Receiver
Emits Light
Converts Light to electricity.
Fire Condition
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Photoelectric Spot Type Smoke Detector
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Light Scattering Method
During normal conditions 1. Light emitting from
LED is absorbed by the black matte in
inside of chamber. 2. Little light falls on the
receiver. 3. Electrical output is very low.
During an alarm condition 1. Smoke enters the
chamber. 2. The visible particles of smoke
reflect the light onto the receiver. 3. Increased
light, increases the electrical output to
the alarm threshold.
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IONIZATION SMOKE DETECTORS
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Ionization Detector
Sensing Chamber
Reference Chamber
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Vs
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VsVr

Normal
Vr
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Vs
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VsltVr

Vr
Alarm Condition
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Detector History

• 2-Wire and 4-Wire Smokes
• Non-intelligent
• No communication skills
• Any response was an alarm
• Frequent nuisance alarms

• Signature Intelligent Smokes
• Intelligent
• Advanced communications
• Use Artificial Intelligence
• fuzzy logic
• Individually identifiable
• Multi-element detectors
• Decide and communicate
• their condition
• Drastic reduction in
• nuisance alarms
• Substantially faster, more
• accurate response.

• Analog Addressable Smoke
• Semi-intelligent
• Basic communication skills
• Analog output based on environment
• Did not decide their condition
• Control panel determined status
• Trouble
• Normal
• Maintenance
• Alarm
• Individually identifiable
• Reduced nuisance alarms

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Notification Appliance Circuits
NACs

• 1. Visual or audible signals for warning
  occupants of an alarm condition.
• Bells, horns, buzzers, sirens, or chimes
• Speakers for audio
• Strobes or rotating beacons
• 2. NACs are all output devices in the fire alarm
  system.
• 3. In a General Alarm system, any alarm will
  cause all of the NACs to be activated.

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Typical Class B Notification Appliance Circuit
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1. This NAC circuit could be audible with horns,
bells, chimes or visual with strobes or
rotating beacons. 2. To accomplish supervision
without activating the devices, diodes are
placed on the devices. 3. In the condition shown
current would flow from negative to positive
through the EOL without activating the device. 4.
In an Alarm condition, the polarity is reversed
at the control panel which allows current to
flow through the devices. 5. A single open in the
circuit would make those devices down stream
of the break inoperative.
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Class A Notification Appliance Circuit
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1. Operates in the same manner as Class B. 2. A
single break in the wiring, will not affect the
normal operation of this system.
Most NACs operate on DC Voltage, normally 24VDC.
An exception to this is audio systems, which
operate on AC. In this case, Reverse Polarity
circuits are not necessary. Their supervision
remains DC, which does not effect the speaker
circuits.
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Emergency Voice/AlarmCommunications
Provides dedicated facilities for originating
and distributing live or recorded voice
instructions in addition to alert and evacuation
signals to building occupants.