Security systems / | All about fire alarm |
The Journal №3 this year (p. 66-70) was published "A brief sketch of the fire automatics." To meet the wishes of readers, we decided to write a fairly lengthy story about the fire alarm "Beginners." We hope that it will allow future owners of fire alarm systems to understand how they work, to determine a first approximation with the equipment that is necessary to buy and to "speak the same language" with potential sellers of equipment and installers who have a license for the establishment of systems of fire automatics. In addition to the information you need to know the future owners of fire alarm systems, we provide some data on most of the designers, because even a layman, familiarized with them, get an approximate idea of how complex alarm systems, ensuring their system, and it is useful to take into account when designing the (reconstruction) of the object. In the future, it will prevent the need to "hollow wall" or take unscheduled loan from the bank to "debugging" the fire alarm system, fire inspection if you refuse to issue a permit to start work.
Assigning part of a network of fire alarm Fire
alarm system - a set of technical tools for the detection and notification of sunbathing place of its origin. It includes detectors (sensors), receiving devices, communication lines and power supply.
Smoke detectors are devices for applying an electric signal to a fire at point guard. Distinguish sensors manual closing and sensors that respond to factors associated fire (smoke, heat or light radiation). Depending on what the factor of fire they react distinguish heat, smoke detectors, flame detectors and fire detectors special purpose. Perceiving information about changing any settings (for example, the temperature in the protected area) Detectors convert it into electrical signals. On the Structure and principle of operation of sensors of various types described below. Fire detectors may be part of the security alarm system; in which case it is called a guard-fire.
Receivers fire alarm systems are used to receive signals from the fire smoke detectors, display rooms of the protected object from which the signal is received, and the sound (light) alarm is an alarm for remote turn-fire automation, and broadcast an alarm in the fire brigade.
Terminology
«legal" terms and definitions used in the fire alarm system are given in Annex A to the DBN V.2.5-13-98 Engineering equipment buildings and structures. Fire automation of buildings and structures. Apart from the ideal definition given there, yet let me quote some of them.
Sensor technology - measuring device that converts the factors associated fire, and generates a signal about a fire in an electrical signal used in fire-fighting systems and alarms.
The detector address - an automatic fire detector, which responds to factors related fire, in place of its installation, and continuously or intermittently active generates a signal on the status of fire in the protected space and a private performance with an indication of their numbers (addresses).
unaddressed detector - automatic fire a detector responsive to factors related fire in the place of installation and generates a signal on the occurrence of a fire in the protected area without their numbers (addresses).
Note that address fire detectors are sometimes called "addressable" and unaddressed - "unaddressed ».
room staff on duty - the point situated on the protected object, a clock duty personnel, equipped with means of displaying information on the status of the fire-extinguishing and fire alarm systems as well as communication with the fire protection of the object (of the village) and facility management services .
network fire alarm - a set of lines for the input-output, channel switching and transmission of signals from fire alarms to the alarm control devices and control devices.
connecting lines - lines connecting distribution (connection) boxes with cross (defensive line box) or by the control panel.
Fire alarm loop - the electric circuit connecting the output circuits of fire detectors, includes auxiliary (outrigger) elements (diodes, resistors and so on. p.) and connecting wires and intended for delivery to the alarm control panel fire alarm and fault, in some cases, to supply power to the detectors.
Circle line - the line of the loop, beginning and end of which is connected to the alarm control unit.
Working smoke detectors
reiterated that the work of all types of fire detectors is based on the discovery of certain signs of fire: smoke, heat or thermal radiation. Hand-held detectors are triggered as a result of closure of the electrical circuit when actuated button or switch.
Smoke detector. Smoke detectors work on the principle of detection of smoke in the air, that is. E. The smallest particles formed during the incomplete combustion of substances and materials. There are two types of smoke detectors: ionization and optical.
Optical smoke detector can operate on the principle of control of light scattering or on the principle of monitoring the transmitted light. The first type includes fire detectors are connected with the outside camera, which is installed an infrared light source (LED) and protected by a screen photodiode. The chamber walls are made of materials with a high degree of blackness, in the normal state and almost all the light emitted by the LED is absorbed by them. In case of contact with the camera smoke particles scatter the light begins to them, resulting in the flow picked up by the measuring optics, amplified, and provided they exceeded a certain value is generated signal "Fire". It is believed that these detectors are able to detect signs of combustion in the early stages, for example, already in the event of corruption. Their possible false alarm if condensation of water vapor in the chamber as well as in case of contact with it dust.
Job sensors operating on the principle of the control transmitted light based on a comparison of the intensities of the two light fluxes from the single LED, one of which passes through the hermetically a closed chamber, and the second - through chamber communicating with the air of the protected space. In the normal state, both the beam completely fall on the measuring optics, and the presence of smoke particles occurs scattering of light passing through an "open" chamber. If the difference between the intensity of the two streams exceeds a certain limit, the sensor is triggered and triggers an alarm. It should be noted that today's sensors, which are based on the principle described, equipped with tricky devices to take account of the amendment on the gradual contamination of the sensor, the aging of materials and even temperature fluctuations. Experts say that such sensors equally well react to smoke particles having different parameters (size, color, chemical composition), resistant to a variety of disturbances, their false positive - a rare phenomenon.
Least flattering reviews of ionization smoke detectors, rather, their universality: such good detectors detect small particles of smoke resulting from the burning fiery, but of little use to detect decay processes, which resulted in the formation of large particles, as well as the detection of combustion processes plastics, accompanied by the formation of electrically charged particles of smoke. Measuring chamber smoke detectors of this type are placed between two metal plates that are permanently energized. Between the plates installed power (α-radiation which ionizes the air in the chamber. As a result, there occurs an ionic current. Particles of smoke enters the chamber, "stick" ions, whereby the speed of movement of the latter decreases, ie. E. Reduced ion current. If it falls below the level of an alarm.
Optical smoke detectors are unsuitable for signs of burning substances, if not produced smoke (eg, gas, polar organic liquids, a number of mixed solvents). Since emissions (α-particles, which under external influence does not cause harm to the person, accompanied by "pervasive» γ-radiation. Ionization smoke detectors are not recommended for use in areas with a permanent presence of people, and in many cases their use is prohibited (this is discussed below).
Heat detectors. Heat detectors, depending on the application of the principle of work contained in its structure one or two heat-sensitive semiconductor element and are triggered when the temperature exceeds a certain value or when its rate of growth in excess of a certain amount. These are called thermal detectors and maximum differential respectively. Differential heat detectors are more sensitive and can give a false alarm when significant temperature fluctuations due to technological reasons, the maximum heat detectors in a considerable temperature fluctuations over short periods of time, working more stable. The maximum thermal detectors are chosen such that the temperature of their operation exceed the maximum allowable temperature in the protected area (more precisely, at the installation location of the sensor) 10 ... 30 ° C or more, the greater the difference, the lower the probability of false positives . At the same time, it increases the probability of detection is reduced sunbathing at the earliest stages.
As a rule, the use of thermal fire detectors, which are generally cheaper than other types of fire detectors, the most expedient in those cases where, for one reason or another it is impossible to use smoke detectors and flame detectors. At the same time, in accordance with current regulatory documents, in many cases, there are multiple options preference is supposed to give a heat fire detectors. When installed in rooms with high ceilings, heat detectors in most cases give an alarm when the fire is already quite advanced and it is difficult to put out using the primary means of fire. It goes without saying that the use of the maximum heat detectors in areas with a high enough temperature - not the best solution.
Fire Flame Detectors. Flame detectors can respond to infrared or ultraviolet part of the spectrum of its light sensors that react to the appearance of a ray of the visible spectrum of radiation of flame, it is fairly rare. Flame detectors responsive to an open flame much faster than other types of fire detectors, so their use is most expedient in those cases where flaming combustion occurs in the initial stages of a fire (such as by combustion or liquids). At the same time, the flame from the fire detectors are of little use if a fire starts with corruption. The sensors responsive to the ultraviolet part of the spectrum, are ineffective unless accompanied by intense burning smoke generation because ultraviolet radiation is absorbed by the active solid particles of smoke.
Infrared flame detectors react to the part of the light spectrum, the most characteristic of the flame. At the same time capture the radiation, current flame detectors can analyze the frequency of its flicker operation in order to eliminate the impact of infrared radiation emitted by other sources (the sun, heaters, process equipment, incandescent lamps, and so on. D.). Matches wavelength and flashing frequency with the given values, the detector should give a signal of fire. IR flame detectors suitable for detecting combustion both in the presence of smoke generation, and in the case of smokeless combustion, wherein the detecting efficiency is practically independent of the distance between the sensor and the source of the combustion flame (of course, within the monitoring area). Infrared Flame Detectors are typically used to control the places of storage and processing of flammable liquids and materials, in order to avoid false alarms they are not allowed to be installed in locations of devices Incandescent.
UV flame detectors react to short-wavelength ("hard") ultraviolet radiation present in the spectrum flame. Rays of this wavelength is almost completely trapped when passing through the Earth's atmosphere, so ultraviolet flame detectors do not respond to normal daylight. The sensor is triggered, if the frequency of the discharge pulses in the measuring chamber exceeds a predetermined value. In addition to the thick smoke, the fire ultraviolet flame detectors interfere with various layers of the touch surface (soot, dirt, grease, etc.), Impeding flow of ultraviolet rays. False alarm UV flame detectors can cause a variety of sources "hard" ultraviolet radiation, such as the working gas and electric welding machines, flash, etc., Tue. h. situated at a respectful distance from them.
Perfect smoke and heat fire detectors and flame detectors, not yet invented. Therefore, to protect important installations sometimes use several types of sensors that respond to different fire factors. There are also combined fire detectors capable of responding to two or three factors and is rarely used.
Regulations
Recall that the main document, which lists the objects to be automatic fire-fighting equipment and fire alarm systems, It is mentioned in the previous article "List of objects of the same type intended to be automatic fire extinguishing equipment and fire alarm system." The requirements apply to this list designed, built, maintained, reconstructed and technically re-equip and extensible objects. It summarizes the requirements for buildings, structures and premises, which are most prevalent in various industries. Detailed lists of the premises subject to the equipment automatic fire extinguishing and fire alarm systems, developed for specific industries (most of existing instruments were also mentioned in the "brief sketch of the fire automatics"). The demands put forward by the fire alarm systems are set out in the previously mentioned construction norms DBN V.2.5-13-98.
According to "the List", public buildings and facilities, which are located in warehouses, banks, administrative, economic and everyday life, a variety of production and so on. d. shall be, at best, a fire alarm system equipment. A lot of cases where there is no escape their fire suppression systems hardware, but now it's not about that. After reading this document, generally difficult to think of any public building or structure, and production, where we could do without alarm systems or fire extinguishing.
Signaling alarm
According to para. 1.1.2 The DBN .2.5-13-98, "automatic fire alarm system is to work around the clock." Signals from smoke detectors, as already mentioned, should act on the alarm control panel. According to para. 1.1.7 DBN V.2.5-13-98, "If it is technically possible signals from the alarm control panels of fire-extinguishing and fire alarm systems bring to the remote centralized monitoring of fire protection." Typically, the presence of this "technical capability" is defined bodies of a legally. In fact, such a possibility can be provided practically always.