Automatic Fire Detection System
This article is based on the BS 420M Self Verify automatic fire detection system made by Autronica Fire and Security AS, Norway.
The fire detection alarm system is used for warning the ship’s staff when a fire or smoke takes place onboard. Appropriate countermeasures can be taken by the concerned person (with internal or external help) to counter the fire.
One of the most important features of these systems is that it is ‘Fail Safe’ type. All cables connected to the individual detectors/ sensors are fully supervised for short circuit or open circuit faults 24/7.
If the fault develops, an audio-visual alarm is enunciated on the control panel, showing the zone number/area. This audio alarm, however, is distinct from the Fire Alarm that is enunciated in case of actuation of sensors/detectors.
The system is consisting of the following:
- Main Control Panel – Main FDS panel with battery set
- Detectors: Smoke, Heat, Flame, Multi Detectors
- Manual Call Points
- FDS Repeater Alarm Panel
- Siren and Beacon
Features of the System
- Indicate the location of the incident
- Raise the alarm
- Cut off the ventilation and fuel supply
- Self-verifies every 24 hours
- All the alarms, fault indications & system status will be stored in Voyage Data Recorder (VDR).
- All the alarms, fault indications and system status will be indicated on the ship’s Integrated Alarm Monitoring & Control System and Light Column Controllers.
- All the alarms will be sounded via the ship’s Main Broadcast System.
The Types of Detectors of the Fire Detection System
1. Rate of Rise Cum Fixed Temperature Heat Detector
These detectors give an alarm on early detection of a sudden temperature change. These detectors also give an alarm when a pre-determined level of heat is reached in the proximity of the detector head.
Rate of Rise Cum fixed temperature heat detectors consist of 2 thermistors, whose characteristics change according to temperature, and suitable electronic circuitry. One of the thermistors is located outside the case and the other is inside. By comparing the difference in signal between the two thermistors, a rate of rise function is easily obtained.
The fixed temperature section operates when the temperature of the external thermistor is exceeding from predetermined temperature level.
Normally, the heat detectors are fixed inside the ship’s galley.
2. Optical Smoke Detector
The detector consists of an infrared LED and a Photodiode. The detector is working with the photoelectric and light scattering principle.
The IR LED pulses a beam of light every 10 seconds towards the photodiode. If there are any smoke particles in the chamber, they will scatter the IR light and it will sense by the photodiode. Then the photodiode sends a signal to the integrated circuit.
Normally, Smoke detectors are fitted inside compartments that contain more fabrics, papers or wood like accommodation areas and office rooms.
3. Infra-Red Flame Detectors
Two infrared sensors evaluate the heat spectrum in the compartment. When there is a fire, the detector will detect it at the initial stage of the flame using the infrared spectrum. Then the detector will initiate an alarm signal.
Generally, the flame detectors are fitted inside machinery compartments like engine rooms, and auxiliary machinery rooms.
4. Multi Detectors
Multi detectors consist of a combination of a photoelectric sensor and a thermister. Typically, multi-detectors are fitted in compartments having more electrical and electronic components like wires, switches and PCBs. Ex: Main Switchboard Room, Machinery Control Room.
Power Supply to the Fire Detection System
- Main Supply: 230VAC
- Alternate Supply: 230VAC (From a different Power Distribution Box)
- Emergency Supply: 24VDC by 2 No’s of batteries inside the FDS cabinet.
The sequence of Operation of the Fire Detection System
The main control panel (MCP) of 4 zones is installed for this particular installation along with smoke detectors, heat detectors, flame detectors, multi detectors, manual call points, sirens & Beacons and sounders.
- When one or more detectors actuate due to fire conditions, it generates a ‘fire Alarm’ on the main control panel, simultaneously indicating the zone number (Location) of the actuated detector.
- When the fire is noticed by a person in the vicinity, the glass on the nearest manual call point shall be broken by pressing the centre point on the glass on the manual call point.
- When a fire signal is initiated on the main control panel, it is initiated an audio alarm on the main control panel and external sounders will sound in all locations onboard. The main control panel’s audio alarm can be silenced by actuating the ‘mute’ push button provided on the main control panel. However, visual indication on the main control panel and the sounder will continue till such time a system is re-set by actuating the ‘Reset’ push button provided on the main control panel.
- A time delay circuit is also provided in the main control panel to give an alarm on the ship’s main broadcast after 2 minutes if any zone on MCP is activated with fire condition and this alarm is not acknowledged by ship staff within 2 minutes.
- In addition, when a fire signal is initiated on the main control panel, the following equipment will be tripped ‘Off’ in a particular logic as per the respective zone of detection of fire by the main control unit:
- Fuel Oil Purifiers
- Fuel Oil Transfer Pumps
- AVACAT (Aviation Carrier Turbine – Aviation Fuel) Transfer and Service Pumps
- Ventilation fans in the After Engine Room, Forward Engine Room, Auxiliary Machinery Room, Bow Thruster, Galley, and Emergency Diesel Generator Room.
- Fire Dampers of Air Handling Units
- Ship’s Galley
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