- Fire alarm system classification
- Types of sounders used
- How modern systems work
- Notification methods
The sooner you or the rescue services are notified of a fire, the more likely it is to save lives, property and the home itself. In order to prevent the fire from leaving the controlled phase, it is necessary to use fire alarm and warning systems, which will be discussed in the article.
Modern technical means make it possible to recognize the signs of a fire almost instantly. To notify people in the room about a fire for their timely evacuation is the main goal of any system. Secondary purposes include automatic call of the fire brigade and transmission of accurate data on the nature and speed of fire propagation..
Fire alarm system classification
There are many technical subtleties that have given rise to such an abundance of alarm systems and even their entire families, but all systems can be characterized by a number of signs:
- The number of monitoring zones determines the number of sensors or their groups, the state of which can be monitored.
- Loop type is a compromise between speed, sensitivity and the number of sensors on one line.
- There are three types of notification methods: local, remote, or batch.
- Fire detection levels determine the number of different types of sensors in the complex: the more signs by which a fire can be determined, the more levels, which means the higher the probability of early detection.
- Performance depends on the perfection of electronic modules.
- The overall reliability indicator determines how reliable the system is, taking into account the hardware and software used, the percentage of false positives is taken into account.
It is important to remember: a fire alarm system is not a separate device, but a whole network, the quality of which also depends on the efficiency of the actions of the duty officer and the entire fire guard post..
Types of sounders used
There are not many precursors of fire, but they can be used to identify the source long before the fire enters an uncontrolled phase. The time difference between the appearance of the first signs of fire and the beginning of its uncontrolled spread is on average from 5 to 20 minutes. It is clear that every minute counts, so in any system several types of sensors should be used. But not only for timely detection, because by the time difference between the appearance of smoke and an open flame, you can say a lot about the nature of the fire and make its forecast.
The lowest level is human detection and pressing of the panic button. On a higher level are open flame detectors, in which the detection distance is inversely proportional to the magnitude and temperature of the flame. These detectors are called thermal fire detectors (TPI). They do well in small spaces, but large spaces would require too many of them, and their field of vision is limited by physical obstacles..
The harbinger of an open flame is smoke. Observations have shown that almost always the appearance of fire is preceded by intense smoldering for 5–10 minutes and abundant formation of smoke. The downside of smoke detectors is their high sensitivity, which reduces overall reliability due to multiple false alarms. Please note that this drawback is not devoid of a double meaning: it is smoke poisoning that is the main cause of death in a fire, in this regard, excessive sensitivity is only on hand.
The highest level of safety is highly sensitive thermal imaging sensors that can not only recognize a small focus of smoldering at a great distance, but also provide a complete summary of data on it: size, temperature, velocity and direction of propagation and direction of convection flows, which perfectly helps to plan localization activities and elimination of fire.
How modern systems work
The principle of operation of a fire alarm largely depends on the type of sensors. Regardless of the device, any sensor communicates with the control panel (PPC) through an electrical signal. It somehow changes the state of the input terminals, usually closing or opening the circuit. The internal analyzer of the control panel from time to time checks whether the current state matches the stored alarm patterns.
The frequency of polling increases with the improvement of electronic components, as a rule, with an increase in their fault tolerance. Modern control panels can check the state of the entire system several times per second. Sensors are also being improved: now they are not limited to two states and can transmit not only danger signals, but also warnings that put the system into an indefinite mode that requires human participation, or about a loop break. Legacy systems in such cases would give a huge number of false positives..
The most modern systems – analogue addressable – allow the exchange of packets of digital signals, which makes it possible to connect dozens of sensors on one line. There are still several connection lines to the control panel, but this is more likely to simplify the installation of standard wiring. Thus, the system divides the protected object into zones only conditionally: each sensor works individually, providing full coverage of the object.
The last key difference between fire alarm systems is the type of notification. Local (local) warning systems are implemented on a combination of alarm sound and light annunciators. In the domestic sector, these tasks are often assigned to the lighting lines (during a fire alarm, the lighting in the living rooms starts blinking) and hidden buzzers. This is how all systems are completed without exception, in particular, almost every fire detector has a built-in siren and a flashing red beacon.
The second method of notification – remote – is designed to report a fire to the control room and persons responsible for fire safety. For communication, telephone lines are used, including GSM transmitters. It is easy to guess that, in general, the quality of such a system depends not only on the installed alarm system. In many ways, the efficiency of work is determined by the quality of the organization’s infrastructure, which provides support and monitoring of the protected object..
Packet transmission implies two-way communication. Such systems are used in public institutions where it is not enough to simply report a fire to the rescue services: rapid smoke in an enclosed space requires people to be removed as quickly as possible. In this case, the system establishes data transmission with the fire brigade headquarters: it transmits the current status to the dispatcher in real time. The dispatcher responds accordingly:
- turns on emergency lights, guiding people along the optimal evacuation route;
- appropriately redirects ventilation flows to limit the spread of smoke;
- remotely switches on the installed fire extinguishing systems, if it is safe for people and property;
- cancels the alarm if it is false.