Fires
4. Fire Detection
We refer here to the automatic detection of fires.
Automatic fire detectors control one or more physical characteristics of the fire; i.e. those phenomena that develop during combustion (heat, radiation, fumes, etc).
Automatic fire detectors are basically composed of:
Detection sensor or simple detector:
Detects the source of the fire and transmit a signal to the centralised signals board.
Centralised signals board:
Evaluates received signals and provides information on the status of the installation. Abnormal conditions will be signalled by an alarm.
Alarm:
The alarm signal may be used to set off fire-fighting systems or simply as a warning using optical and/or acoustic signals.
Automatic fire detectors may be:
Flame detectors:
These measure the (infrared or ultraviolet) radiation given off by the fire. The alarm is set off when the sensitive photovoltaic cell receives a certain level of radiation.
Thermostatic detectors:
These react when the temperature reaches a certain level (e.g. 70º). The heat-sensitive device sets off the alarm.
Rate-of-rise detectors:
A device that is sensitive to the increase in temperature per unit of time, it sets off the alarm when the variation in temperature exceeds a certain value (e.g. 10º per minute).
Smoke detectors (based on ionization):
These work on the basis of the ionization of air inside a number of chambers via the action of a radioactive element. Ionization makes air a conductor and, if there is smoke, makes the conductivity of the air-smoke mixture vary. This variation in conductivity may be converted into an electric signal that sets off the alarm.
Smoke detectors (based on light diffusion):
Smoke particles diffuse the light of a special flashbulb depending on their concentration. The concentration of smoke may be obtained by means of photoelectric cells, and the alarm may be set off by this signal.
4.1. Maintenance of automatic fire detection and alarm systems
A) Operations to be carried out by the user:
Every 3 months:
- Check the correct functioning of the installations.
- Replace faulty pilot lights, fuses, etc.
- Maintenance of accumulators (cleaning terminals, topping up distilled water, etc.).
B) Operations to be carried out by specialised personnel from the manufacturing firm or the firm that installed the automatic detection system:
Every year:
- Comprehensive verification of the entire installation.
- Cleaning of the centralised equipment and accessories.
- Verification of threaded and welded joints.
- Cleaning and adjustment of relays.
- Regulation of voltages and intensities.
- Verification of alarm transmitting devices.
- Final testing of the installation with each source of electric power supply.
| EXTINGUISHER | |
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1. Extinguisher housing |
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