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Fire System
Fire Alarm Strobes
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Fire Alarm System
The fire alarm system is used to generate alarms whenever there is any occurrence of fire. All the alarm signals can be linked to a central location where humans can carry out activities to handle the fire. There are many designs. The main functions of all these Fire Control designs are:
- Indicate fault signals triggered by:
- Sprinkler flow switches
- Break glasses
- Smoke detectors
- Heat detectors
- Fire pump operation
- Air conditioning AHU operation
- Smoke spill and ventilation fan operation
- CO2 system operation
- Indicate the location or zone of the signal
- Provide intercom communication from it to each floor
- Provide public address announcements
- Acknowledgement of alarm signals
- Provide a printout of the alarm signal
- Provide direct alarm signal link to the local Fire Brigade
- Provide direct telephone communication with the local Fire Brigade
A typical Main Fire Alarm system for a high rise commercial center is designed as described below:
- A fire control room fitted with a Central Processing Unit ( CPU ) and a mimic panel. The panel uses LED to display the location and state of sensors
- Sixteen (16) Remote Panel Processing Units ( RPPU ), mainly located at the staircases. They collect signals from sensors and also dispatch signals to actuators.
- The CPU collects incoming signals from all the RPPU and dispatches outgoing signals to actuators through the RPPU
- All the signals are 24 Volts D.C.
- The main alarm system is normally operating on AC supply. In case of power supply failure, stand-by batteries are provided for a 72 hours operation
- The input signals coming from the sensors are the Breakglass, Flow switches, Smoke detectors. The latter are located at the staircases and in the AHU rooms. These signals are collected in the RPPU before being sent to the CPU to indicate a normal status, a line fault, or an alarm.
- The output signals are sent to the actuators. These can be contactors or motors to stop AHU, lifts, activate roller shutters, alarm bells, pressurization fans, smoke spill fans, and fire dampers.
- These signals are controlled by the CPU before being dispatched through RPPU to the correct location
Activation of fire alarm
When the fire alarm panel is activated by either breakglass, smoke detector or sprinkler flow switch, the following will occur immediately:
- The printer will print out the exact location and time the event occurred
- A LED will blink on the mimic panel indicating both the floor concerned and the kind of the sensor responsible for the alarm activation.
- The fire control room buzzer will start.
- The CPU will send signals to:
- Stop the AHU on the floor the alarm occur
- Start all the smoke spill fans and open the motorized fire dampers on the concerned floor and close those on the other floors
- Start the Pressurization fans for all the lift lobbies and regulate the pressure in the lift lobbies of the concerned floor using the lift lobby differential pressure device and the associated motorized fire damper.
- Start the alarm bell continuously for the concerned floor and intermittently for the floor above and below.
- Close the roller shutters of the concerned floor after three minutes time.
- Indicate the signals sent on the fire alarm display panel with LED
Acknowledgement of the alarm
A person on duty should then acknowledge the alarm by pressing a push button at the fire control room. The buzzer will then stop but the alarm will still be active. Action needs to be taken to determine whether the fire is real or not.
For a false alarm, the choice will be to isolate the sensor alarm in order to stop all signals and interrupt the fire sequence.
If it is a real fire, the signal will come again after 5 minutes. A general alarm sounds automatically. The CPU will send signals to start the alarm bells continuously for all the floors of the building. The general alarm can also be manually activated through the Manual Evacuate switch.
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