Types of Fire Alarm Systems
It is important to understand that a hotel fire alarm and detection system should provide early detection of the source of ignition and at the same time guarantee a nearly complete absence of false alarms – to avoid the financial and reputational losses, not to mention human casualties. This article dwells on the problem of choosing a right fire alarm system, fire detectors and their arrangement based on particular features of a property we want to protect.
Conventional Fire Alarm
In general, an efficiency of fire protection is determined by a selected type of a fire alarm system. Conventional systems have limited capabilities. Major drawbacks of conventional systems are instability of an alarm sensitivity of detectors, an absence of monitoring of actual performance and a high level of false alarms. With a ‘Fire’ signal indicated on a control unit, one can only identify a circuit number of a fire detector activated. Naturally, a great deal of precious time is inevitably lost for defining of an area that a specific fire alarm circuit protects and a room where the fire has been detected.
Within 1 or 2 years the alarm threshold of a conventional smoke detector may differ significantly from the factory setting. Dust deposits forming on the walls of the smoke chamber increase a threshold and lead to false alarms. On the other hand, an aging of electronic components leads to a loss of a threshold level. Within a few years a reduction of LED brightness of the optic coupler can almost turn a fire detector into a dummy that does not react to the presence of smoke.
Moreover, these processes occur simultaneously in all the devices of one production lot and regardless of the number of detectors in the room the efficiency of an alarm warning system is festered by the fact that in most structures they do not test fire detectors. The reason is that first there are no regulatory requirements for maintenance, and secondly there are cost savings. In most cases it is not clear when and at what density of smoke a smoke detector will be activated and whether it is going to work at all.
It is also necessary to consider the significant costs of equipment, installation and maintenance of conventional systems and to take into account the required installation of no less than 3 conventional detectors in every room. The costs of even a relatively small conventional system nearly equals that of a intelligent addressable system if we consider the installation costs of 3 mounting bases for conventional detectors compared to a just one single intelligent detector.
These drawbacks are getting even worst with increasing of a number of detectors and a number of protected areas and floors of a hotel. With large conventional systems there may occur a lot of expenses on loop cables and their installation. If in an intelligent system a capacity of one loop covers several hundred smoke detectors and modules; in a conventional system every 20–30 detectors constitute a separate loop and are connected to a control panel with a separate cable. Thus, in large systems the costs of the cable and a construction of the circuit increase significantly.
In addition, maintenance costs are significant too. They imply periodical cleaning of smoke chambers and testing of detectors. According to requirements of manufacturers every smoke detector has to be disassembled and cleaned of dust every six months or once a year. At very important sites this rather time-consuming procedure is performed on a regular basis; whereas, at smaller sites detectors are only cleaned after false alarms start to occur.
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TEXT : IGOR NEPLOKHOV, Fire Alarm Engi neering Director at Pozhtechnika Group of Companies,
Ph.D. in Technical Sciences