FOTObank 
Infrared linear smoke detector, consisting of an emitter and a receiver 
SYSTEM SENSOR
Linear laser smoke detector with receiver and transmitter - in one housing - and reflector 
Optical open flame detectors "Pulsar" from KB "PRIBOR" with a sensor built into the control device 
with remote sensor 
Pointless smoke detectors of domestic production: (IP 212-3SU, DIP 54-T, DIP 3-M3) 
Domestic thermal addressless detectors (MAK-1, IP 101-1A, IP 103-31) 
SYSTEM SENSOR
Point smoke "smart" detector series "Profi" 
150 years ago, the tower was the most effective means of detecting a fire 
SYSTEM SENSOR
Combined smoke-heat detectors - addressable 
SYSTEM SENSOR
intellectual 
SYSTEM SENSOR
unaddressed 
SYSTEM SENSOR
Thermal maximum differential addressless detector of the "Eco" series 
Non-address manual call points with "button" and rotary knob 
SYSTEM SENSOR
Addressable analog manual call point "Eco" series 
Non-addressable smoke and thermal maximum detectors from APOLLO 
SYSTEM SENSOR
Addressable analog detectors - point smoke; 
SYSTEM SENSOR
maximum differential Domestic autonomous smoke detectors signaling scheme based on autonomous smoke detectors 
: (IP 212-50, Agat, IP 212-43M) 
(Agate) 
Scheme of addressless fire alarm 
The panel for measuring and controlling the parameters of "smart" sensors 
SYSTEM SENSOR
Laser tester for remote testing of "intelligent" smoke detectors
In the previous issue of the magazine, we talked about the primary means of fire extinguishing. But they should be activated only after detecting a fire. And what happens if a fire that is starting is not detected in time? That's right, a big and irreparable trouble will happen. Therefore, today we will talk about modern means of automatic fire detection at the earliest stage of its occurrence - fire alarm systems.
Who should detect a fire?
About 150 years ago, the fire tower, the tallest building in the city, was the most effective means of detecting a fire. It was even easier with warning devices - run out into the street and shout loudly: "Fire!" Everyone who hears was OBLIGED to run to extinguish it - "some with a hook, some with a bucket."
Naturally, these funds are far in the past. In order to capture a fire at its earliest stage, when it is called a fire, modern detection systems and fire alarm systems (FSS) are now used. They are designed to monitor the protected facility around the clock and alert the owner of the first signs of fire or smoke. To create such systems, the following are used: detection devices - fire sensors (it is more correct to call them detectors), signal processing devices (control panels - PKP) and actuating equipment (alarm devices). They are produced by such companies as ESSER (Austria), Texecom and PYRONIX (Great Britain), System Sensor (Italy), Securiton (Switzerland), ESMI (Finland), Napco (USA), ADEMCO - a division of Honeywell (USA), as well as domestic "RUBEZH" (Saratov), "IVS-Signalspetsavtomatika" (Obninsk), NVP "BOLID" (Korolev), "ARGUS-SPEKTR" and "IRSET-CENTER" (St. Petersburg), Siberian Arsenal (Novosibirsk), Radiy (Kasli), etc.
Fire detectors
They are the main elements of fire detection systems. First of all, the efficiency of the system depends on their sensitivity and noise immunity. In private housing, smoke, heat and open flame detectors are commonly used. As a rule, all of them are "threshold", that is, they are triggered if the controlled parameter exceeds the set value.
Smoke detectors. Smoke is the most characteristic sign of a fire at its earliest stage. By measuring the concentration of smoke in the air, the sensor "concludes" that there is a fire. Smoke detectors are divided into point and linear.
Point measured in the place where they are installed. In private housing, only photoelectric ones are used from point detectors. Inside such a device, a measuring chamber with a light source and a photodetector is hidden. Smoke particles entering the chamber change the light transmission of the air and scatter the light flux. These changes are captured by the photodetector. But in different designs in different ways. In some, it captures the overall attenuation of the luminous flux (if it is located strictly opposite the light source). In others, flow scattering (the photodetector is located at right angles to the light source). The first of the devices described are more sensitive, but less resistant to interference (for example, dust) and require frequent maintenance. The latter are slightly less sensitive, but more noise-resistant. It is they who are mainly used in the creation of ATP in private housing. They are usually mounted under the ceiling, as hot gases and smoke rise up. The area controlled by one smoke detector can be up to 80 m 2 . Even if the footage of the room in which the sensor is installed is much less than this value, at least two fire detectors should be installed in it to increase the reliability of fire detection. When using false ceilings and laying power wiring behind them, it is necessary to protect the space above the ceiling with separate smoke detectors.
Let's discuss these issues using point smoke detectors as an example. The sensitivity of sensors can be high, medium and low, but must necessarily be in the range from 0.05 to 0.2 dB / m work if smoke in the place of its installation causes a weakening of light at a distance of 1 m by 1.1-4.5%). Some detectors have the ability to adjust the sensitivity, which is performed by a special switch mounted on the rear wall. It can be either two-position (switches from the upper immediately to the lower limit) or three-position (switches from the upper limit to the lower through the middle, for example, in the "Profi" and Leonardo series from SYSTEM SENSOR). It is better to choose a detector with a three-position regulator. Why? Set to the upper sensitivity limit, the device reacts to the minimum smoke content in the air and can "trigger" not only when smoking in the room, but also when frying meat or using a toaster in the kitchen (practically these are the same "false positives"). The minimum sensitivity may not be enough - it seems to you that the sensor should work, but it stubbornly "is silent". Most likely, you will be satisfied with the average level of sensitivity. And the sensor with a two-position regulator is deprived of it. Sensors of any type need periodic maintenance, more precisely, maintenance. Why is it necessary? It is clear that fumes and dust will settle on appliances located under the ceiling. Moreover, these "charms" settle not only on the cases, but also inside the measuring chamber, weakening the luminous flux to which the device is tuned, and causing the so-called false alarm. The sensor reacts to dust particles that have not settled (hovering in the air inside the chamber) in the same way as to smoke. "False alarm" - a rather unpleasant phenomenon for the owners: nothing is on, and the sensor stubbornly signals: "FIRE!" At the same time, the owners are nervous and rack their brains: “What if something really burns in the house, but we don’t notice?! We should check everything again!” To prevent dust from getting inside the measuring chamber, manufacturers enclose it with a rather complex, almost labyrinthine structure and complicate the geometry of the housing, thereby reducing the likelihood of "false positives". Settled dust, of course, must be periodically removed. But if it costs nothing to wipe dust from the case, then it can be quite difficult to remove it from the “labyrinth” enclosing the measuring chamber. And to wipe the optics, and even more so - overdoing it, you can violate the alignment (optics in this case is used very tiny). In general, it is better to entrust care to specialists who will periodically come to your home.
Linear smoke detectors. They consist of two elements that outwardly resemble CCTV cameras - an emitter and a receiver-converter. They are installed opposite each other on opposite walls of the room ("IPDL" from Poliservice, price - $ 95; "SPEK-2210" from "SPEK", price - $ 230; "6424" from System Sensor, price $ 540). Recently, models have appeared in which both elements are combined in a common housing - in this case, there is a reflector opposite the emitter ("6200" and "6500" from System Sensor). The emitter can be either infrared or laser, operating in the visible range of red light. The appearance of smoke in the space between the transmitter and receiver (or between the transceiver and reflector) causes a weakening of the received light flux. The value of this attenuation is fixed by the receiver-converter. And if the set threshold is exceeded, it generates a “Fire” signal.
Such sensors are beneficial only for large rooms, since they detect smoke in a zone with a length of 10 to 100 m and a width of 9 to 18 m (that is, they provide control of an area from 90 to 1000-2000 m 2). In general, one linear detector is quite capable of replacing a dozen point detectors, which can be beneficial not only economically, but also in terms of room design. But there are also disadvantages. The response time of the devices depends on the volume and even the configuration of the room. "False alarms" can cause sudden changes in direct and reflected light, lightning flashes, as well as a change in the relative position of parts.
Thermal fire detectors. Sensitive elements of heat detectors can be: bimetallic plates (for example, in IP-103-5 from KomplektTroyservice; IP 101-1A from Siberian Arsenal), semiconductor thermistors, etc.
According to the principle of operation, heat detectors are divided into passive (contact) and active (electronic). Passive ones do not consume electricity and function as follows: when the temperature in the room reaches a critical one (about 70 C), the sensing element either generates a certain signal (due to the thermoelectric effect), or breaks / closes the contact of the electrical circuit, thereby giving an alarm. Active devices consume electricity, but they provide information not only about reaching the critical temperature in the protected area, but, most importantly, about changes in the rate of temperature increase. They are called differential detectors. Inside their case there is not one sensitive element, but two - one is in direct contact with the external environment, the other is hidden inside the case. If the temperature rises rapidly during a fire, the device records the difference in the readings of the sensitive elements and sends an alarm signal to the control panel ("MAK-DM" from NPP "Specinformatika", Moscow, price - 215 rubles; "IP 115 - 1" from " Magneto-Contact", Ryazan, price - 315 rubles; "5451E" from System Sensor). If the temperature rises slowly (then the temperature of the elements changes equally), the device detects that it has exceeded the threshold value and also sends an alarm signal.
As a result, if passive heat detectors are only suitable for detecting fires with an open flame, accompanied by a sharp increase in the temperature threshold (they work when something is already burning), then differential heat detectors give an alarm when there is still no open flame, and the temperature has just begun. grow, but at an "unacceptable" rate. This explains the fact that passive sensors have recently been used in alarm systems less and less (and this despite their low cost - 15-20 rubles). Consumers prefer sensors, albeit more expensive, but triggered at an earlier stage of the fire - differential. They are usually used where smoke detectors would give false alarms, such as kitchens, showers, smoking rooms, etc. For rooms such as boiler rooms, where rapid temperature rises are common, threshold detectors at 70 C are more suitable - differential detectors will give false alarms here.
Optical open flame detectors. It is clear that any combustion site is a source of optical radiation in the range from infrared to ultraviolet. The detection of such radiation using a photodetector having a high spectral sensitivity in the ultraviolet or infrared region, but insensitive to the visible part of the spectrum, is the task of optical open flame detectors.
On sale you can find mainly infrared optical devices (for example, a series of sensors "Pulsar" from KB "Pribor", Yekaterinburg, the price is from 1360 to 2200 rubles; "Spectron" from NPO SPECTRON). The sensor in them can be either built into the receiver-converter or remote. In the latter case, the sensor is installed directly in the monitored area and connected to the receiver installed outside it with a fiber optic cable (length up to 20 m).
Optical detectors are low-inertia devices with a minimum time for detecting a fire. Detection angle - 90-120, range - from 13 to 32 m. They can detect both smoldering hearths and open flames. Their disadvantage is that if the source of combustion is obscured by building elements or furniture, the detector will not detect it. Such devices are indispensable where a quick flame without smoke is possible (garages, storerooms, rooms with electrical appliances). For example, in garages where gasoline and other petroleum products can ignite, at least two such devices should be installed so that the car in the center does not block the flame.
Combined detectors are a combined device of two sensors in one housing, controlled by one microcircuit. For example, the "IP212/101-2" detector of the "Eco" series from SYSTEM SENSOR (price - 320 rubles) combines the functions of an optical-electronic smoke detector and a thermal maximum differential detector, due to which it works in case of any fire (both accompanied by smoke, and and smokeless, but with an increase in temperature). It should be noted that combined detectors of this type have recently become increasingly popular, since they relieve consumers of the need to install two types of sensors in the same room - smoke and heat (such a need often arises, for example, in garages). Such a device, of course, costs more than a separate smoke or thermal device, but cheaper than both combined (smoke "IP212-58" - from 227 rubles, thermal "IP101-23" - from 217 rubles).
On the one hand, a combined detector is a good thing, because it allows you to detect fires of various types - both smoldering and open flames, but smokeless. And in general, the fewer devices installed, the less they need to be serviced. On the other hand, as is known, the reliability of any combined devices is always lower than that of monofunctional ones. So if you purchase a combined sensor, then it is highly reliable and from a well-known company.
Manual call points- these are "panic buttons" that serve to signal a fire "manually" (for example, if it is detected before the "activation" of the alarm system sensors). They are installed on escape routes (in corridors, walkways, stairwells, etc. at a height of 1.5 m from the floor level) at least one for each of the routes, and if necessary - in separate rooms. In multi-storey buildings, manual call points must be on all landings of each floor (NPB 88-2001 *). Places of their installation must have artificial lighting.
Autonomous detectors. You can create an elementary fire alarm by installing autonomous smoke detectors, for example, one for each room (if they are small). These devices are called autonomous because inside each of them there is an independent power source (battery type "Krona", "Korund" - 9V), which must be changed periodically (about once a year). But the system is absolutely independent of the presence of a supply voltage in the network (it is simply not necessary). In addition to the battery, a sensitive element (smoke sensor) and an annunciator (siren) are hidden inside the case, emitting a sound with a volume level of 85-120 dB. The siren, after the sensor is triggered, will "scream" until you intervene or the battery runs out. Despite the fact that autonomous detectors are somewhat more expensive than conventional ("traditional") detectors, in which there is neither a power source nor a siren, a fire alarm system based on autonomous sensors has a minimal cost, since it does not have wires, control devices and the necessary operation of the backup power system. The only type of maintenance that autonomous detectors require is periodic dust blowing. The downside is that each sensor works on its own, and if you're at the far end of the house, you may not hear the alarm.
Until recently, only foreign-made autonomous detectors were on sale: Dicon, BRK (both US) - $ 20-25, as well as several Chinese models - about $ 15. Currently, their serial production has also been mastered by the domestic industry: " IP212-50M" from "RUBEZH" (Saratov), price - 420 rubles; "DIP-47" from "Agata" (Obninsk), the price is 435 rubles, etc. Moreover, according to experts, these models are not inferior in quality to imported ones and even surpass them in some ways. For example, the device "IP212-43" ("DIP-43") from "IVS Signalspetsavtomatika" emits not one, but several types of light and sound signals - "Attention", "Fire", "External alarm", which can be used quite objectively assess the situation without seeing what happened. In addition, it gives a signal that the battery is low. Also on sale you can find autonomous co-produced detectors. For example, the firms "KrilaK" (Yekaterinburg) and Kidde safety (USA) produce an autonomous fire detector "PE-9", the price is $ 18.
More "advanced" models of autonomous devices are also being produced, by connecting which with a telephone (copper) wire you can get an alarm system (but without a control panel). The operation of one sensor in it causes the operation of the others. These are, for example, such detectors as "EI 100C" (EI Ltd, Ireland, $ 17), "DIP-43M" ("IVS Signalspetsavtomatika", price - 576 rubles), etc. You are guaranteed to hear the signal of such a system, in no matter what room they are in. This is a plus. The downside is that it is difficult to figure out by ear exactly where the fire occurred. After all, everyone is “buzzing” at once!
Fire alarm systems
Typically, fire alarm systems consist of detectors of the types listed above, as well as a mandatory control panel (device) - PKP, which receives their signals. Such systems are usually called traditional by specialists. Currently, there are three main types of such systems: non-address, address, address-analogue.
Non-address systems consist of threshold (smoke, heat, flame) and manual call points connected to the control panel by a wire (it is also called a line or loop). Sensors do not have their own e-mail address, which would be reported to the console. As a result, when one of them is triggered, neither its number nor the room where it is located is marked on the remote control. Only the number of the loop (line) on which the triggered sensor is installed is fixed. As a result, the owners, in order to understand the situation, must quickly inspect all the premises guarded by this line. To facilitate the determination of the place of ignition, they try to lay one line in each room. But this way (increasing the number of lines) is not always suitable, since it greatly complicates the wiring diagram and increases the cost of installation work. That is why the use of conventional systems is considered appropriate only for small objects (less than 20 rooms).
In protozoa address systems the so-called addressable module is built into the threshold detectors, which in the "FIRE" mode broadcasts its code through the loop to the control panel. This code determines the specific place of signal formation, which increases the speed of response to it. This is, one might say, the cheapest way to transform an unaddressed system into an addressable one (for example, the "S2000-AP1" module from NVP "BOLID", price $ 10). Another advantage of such a system is that it is possible to carry out not one line to each room, but to create extended lines, saving wires and labor of installers. However, a detector equipped with an addressable module cannot control its status and send a "FAULT" signal to the control panel, and if the addressable module fails, the control panel will no longer receive signals from the sensor. Polling address systems use a different type of control panel, and the detector's communication with them becomes two-way. The control panel not only receives signals from the detectors, but also automatically tests the presence of communication with them and their operability (performed every few seconds). As a result, the reliability of the ATP is significantly increased, and you can always be sure that the sensors are in good working order and will work on time. Yes, and using polling and address systems is easier - both for owners and installers. For example, temporary removal of one of the sensors (repair, preventive maintenance) does not cause failure of the entire loop - the control panel simply notes during the next poll that the sensor is missing. In addition, polling systems make it possible to form not only a linear, but also a branched structure of loops (with a number of sensors of the order of 100), which in some cases makes it possible to simplify and, therefore, reduce the cost of installation work. To work in such systems, detectors can already be offered not only with an accurate three-position setting of the sensitivity level, but also with automatic compensation for the dustiness of the smoke chamber (for example, sensors of the Leonardo series from System SENSOR, which the manufacturer calls "intelligent").
Change No. 4 of 20.11. 2000 to SNiP 2.08.01-89* "RESIDENTIAL BUILDINGS"
3.21. The premises of apartments and dormitories (except for bathrooms, bathrooms, showers, laundry rooms, saunas) should be equipped with autonomous optical-electronic smoke detectors that meet the requirements of NPB 66-97, with protection category IP 40 (according to GOST 14254-96). The detectors are installed on the ceiling. It is allowed to install on the walls and partitions of rooms not less than 0.3 m from the ceiling and at a distance of the upper edge of the detector's sensitive element from the ceiling of at least 0.1 m.
SNiP 31-02-2001 "SINGLE APARTMENT HOUSES"
6.13. Houses with a height of three floors or more must be equipped with autonomous optical-electronic smoke detectors that meet the requirements of NPB - 66 - 97, or other detectors with similar characteristics. At least one fire detector must be installed on each floor of the house. Smoke detectors should not be installed in the kitchen, as well as in bathrooms, showers, toilets, etc. rooms.
"General provisions for the technical requirements for the design of residential buildings with a height of more than 75 m"
(developed by the State Unitary Enterprise NIATs Moskom-Architecture, approved by the Moscow government). We will not quote this document, but we will only say that in buildings with a height of 75 to 100 m, addressable fire alarm systems must be installed without fail, and in buildings with a height of 100 to 150 m - addressable analog, that is, systems that make it possible management of evacuated residents, for example, with the help of light and sound annunciators installed on stairwells. Above the entrances to the apartments, automatic fire extinguishing should be arranged. The apartments must have primary fire extinguishing equipment and fire hydrants in the bathrooms, bathrooms, corridors. In addition to the fire alarm system, video surveillance is mandatory in the houses (on stairwells, to control the progress of the evacuation).
Address-analogue system. In it, the detector is not only periodically interrogated by the control panel, but also in response reports the value of the parameter controlled by it: temperature, smoke concentration, optical density of the medium, etc. That is, the control panel is here the center for collecting telemetric information. By the nature of the change in controlled parameters reported by different detectors installed in the same room, it is the control panel, and not the detector (as in the case of addressable and non-addressed systems) that generates a fire signal, which increases the reliability of fire detection. The analog addressable system also has several more advantages compared to the polling address: The number of loops can be reduced to one - ring (it is sometimes called a loop), to which up to 99 automatic detectors + 99 manual call points, addressable sirens and control modules are connected ventilation, smoke removal, etc. The failure of the sensor or a broken wire will not disrupt the operation of the system - it will continue to interrogate the sensors both on one side of the break and on the other, informing those who operate it which sensor has failed or between which sensors an open has occurred. “Thresholds” for triggering sensors can be set for each room and even changed depending on the time of day, day of the week, etc. For example, during the daytime, to eliminate false alarms from cigarette smoke, the sensitivity of certain smoke detectors can be automatically the clock is again set to the maximum (such an algorithm is implemented, for example, in an alarm system with sensors of the 200 series from SYSTEM SENSOR).
Control panels (panels) - PKP
It is the control panels that control the detection lines (loop lines) with the sensors installed in them, provide indication of detected malfunctions and fire, and command the sound and light alarm lines (if there are any in the system). The control panel is powered by 220 V AC mains, but uses an internal voltage of 12 or 24 V. In the event of mains power failure, it is supplied with back-up batteries (1 or 2 12 V batteries).
To make it clear how the system works, let's look at what happens when, for example, a smoke detector is triggered. In its normal state, it consumes a current of no more than 100 μA. But, having caught the smoke, it goes into an alarm state - turns on the LEDs, thereby increasing the current consumption to 30 mA (this value depends on the design of the remote control). The control panel, having detected an increased current consumption, turns on the LED fire indicators and activates the audible alarm. The fire detector remains fixed in the "alarm" state, even if it no longer senses smoke, which guarantees the detection of a smoke zone in case smoke enters the detector only intermittently. An "alarm" signal can only be "reset" from the control panel by removing power from the detection line by pressing a special button. In unaddressed systems, the loop has its own "reset" button.
For each of the systems (non-addressed, addressable, addressable-analogue) their own control panels are used, which differ in the set of functions performed. If in conventional systems, devices simply mark the line on which the operation occurred (as in "Signal-20 and - 20P" from the NVP "BOLID", the price is 2350-2720 rubles; "Granite-24" from the "Siberian Arsenal", the price - 2800 rubles; "PPK-2" from "IVS SIGNALSPETSAVTOMATIKA", etc.), then in the address schemes they provide automatic checking of the health of lines and sensors ("Rainbow-2A" from "Argus-Spektr", price - from 6340 rubles. ), and in analog addressable systems they even detect a line fault (Raduga-3 from Argus-Spektr, price - from 15,900 rubles, as well as devices from Esser (Essertronic 8000C) and Apollo).
The control panel for each of the listed systems can be conditionally divided into devices of small, medium and large "information capacity". It depends on the number of connected loops, sensors and functions performed. And for each specific object (house, apartment), the most suitable devices are selected. What is there to advise? Perhaps it is always better to prefer a device from a major manufacturer (foreign or domestic) that has been on the market for a long time. Which device to choose from the assortment of a particular manufacturer should be determined by the company that installs your alarm system. But here, let me give you a few tips.
First, it is better to choose, as it is now customary to say, an "intuitive" PKP. That is, so that everything that is displayed on its panel, you understand even in a half-asleep state. And so that they can quickly and easily perform any necessary actions with the device, because there will be no time to read the instructions for managing it during a fire.
Secondly, it is always better to prefer PKP, so to speak, with a small margin. For example, with the ability to connect another loop without changing previously laid lines.
Thirdly, in the event of a fire, a “smart” device should automatically perform a number of necessary actions for you, which the owner, in the heat of fighting a fire, may well forget about. For example, turn off the supply and exhaust ventilation in order to prevent the spread of fire through this system, turn off the power to the main electrical consumers, etc.
Annunciators
Behind this concept are hidden all actuating devices that will start working on the command of the control panel after a fire is detected. In the simplest case, these are sound, light or light-sound annunciators (in other words, "sirens", "howlers", "flashers" and "blinkers"). Placed inside the dwelling, even not very powerful annunciators will warn you in time of an impending disaster. More powerful devices located on the walls, roof or in the attic of a country house will bring the signal of a fire to the public. It’s just necessary that there is someone who will perceive (see, hear) the fire signal given by the system and quickly respond to it - go to find out what happened, and in case of a real fire, put it out or call the fire brigade. And, therefore, this notification option is suitable only for your own home in a cottage village with centralized security. Yes, and even then with a big stretch - it is also not easy for the guards to immediately figure out which building the siren is howling in. Neither for an apartment building, nor for a summer cottage or a garden partnership in which there is no centralized security, this method of notification is completely unsuitable.
In apartment buildings and telephonized cottage settlements, you can output the signal from home control panels to the security console, and let it take appropriate action. It is only necessary to jointly equip its post with an appropriate remote control.
And how to organize the sending of a fire message from the fire alarm system installed in the house if there is no telephone connection? And for this case, there are a number of devices. For settlements in which there is security, special radio communication systems are produced. All houses in this case are equipped with a device that can transmit a pre-recorded voice message, and the guard post is equipped with a receiving device for the corresponding number of houses. (In a similar way, the issue of sending messages about incidents when calling private security is solved, if the country house is guarded by it. The difference is only in the power of the transmitting device.)
If there is no own security in an apartment building or village, but they are in the GSM cellular coverage area, you can use devices that will send an SMS message about the incident. These devices are called dialers. They are capable of both connecting to any security and fire alarm system, and being used as an independent control panel (determined by the design). When an alarm is triggered, the device sends an SMS signal to any (there may be three or more) cell phone numbers specified by the owner (you, relatives, friends, neighbors, etc.).
Perhaps the most common device of this type at present is GSM-UO-4C (company "Bolid", price - about $ 130). The cost of installing a turnkey system based on it costs about $ 400. A significant drawback of the system is that it can operate only in a heated room (working temperature - from +1 to +45 C). Similar in principle of operation, but more modern devices are offered by such companies as Pyronix (devices of the Matrix series, price - from $ 30 to $ 120, Formula of Security (models of the ForSec-GSM series - from $ 450), etc.
Cost of fire alarm systems (ATS)
The cheapest non-address fire alarm systems are based on domestically produced equipment (we have already outlined the range of manufacturers). So, a point smoke sensor costs from 160 to 400 rubles, a linear smoke sensor - from 2980 to 7180 rubles, a thermal passive one - from 11 to 60 rubles, a differential one - from 150 to 350 rubles, an optical open flame - from 1350 to 5600 rub. etc. In general, domestic sensors do their job well, but, as a rule, they are somewhat inferior to imported counterparts in terms of reliability and aesthetics.
Fire alarm systems of an average price level are usually created on the basis of sensors and control devices of such well-known foreign companies as ADEMCO, System Sensor, Napco, Texecom, PYRONIX. So, a point smoke detector in this price category will cost $15-30, a linear smoke detector - $100-500, a differential one - $10-20, etc.
Address systems are expensive SPS. Most often they are built on specialized control panels and sensors from ESSER, ESMI, Honeywell, Securiton, etc. In this category, a point smoke detector costs from $30 to $100, a linear smoke detector - from $500 to $1000, a differential one - from $30 to $30. 60, optical open flame - $200 to $500.
Despite the fact that addressless detectors are the cheapest, the installation of a complex SPS based on them can be quite expensive. Addressable detectors are at least 50% more expensive than non-addressed ones, but installation of SPS based on them can be cheaper. So, according to a number of companies we interviewed, for a building with an area of more than 500 m 2, the address system is already cheaper than the non-address one. And the larger the area, the greater the gain in money. True, not all experts who participated in our survey agreed with this statement. Some rightly noted that it is not so much the area that matters, but the number of protected premises and their location - factors that determine the configuration and branching of the system being created. (And they immediately proposed several non-address schemes for a large house of 20 rooms using easy-to-manage control panels, which are no more expensive than address ones.) Apparently, there is some truth in both statements - for each specific object, you need to select your own system , optimally suited both in terms of technical parameters and price. And in order to get several alternative options and choose the best one, you should contact not one company, but several at once.
But everyone agreed that address systems are cheaper to maintain. Cheaper already because they themselves find a malfunction - it remains only to fix it.
The equipment for addressable analog systems has the highest cost. If, for example, an addressable threshold detector from SYSTEM SENSOR will cost an average of $ 15, then a detector for an analog addressable system from APOLLO will already cost $ 50, and from ESSER - $ 90. The high cost of detectors, and therefore The systems assembled on their basis are still holding back their use in city apartments and private houses.
Having installed a fire alarm system, you should be prepared for the fact that the costs will not be limited to this. It will be necessary to regularly (at least once every six months, and better - once a quarter) pay for the call of a specialist to carry out maintenance work (the list of necessary actions and their frequency are indicated in the passports of the control panel and detectors). For small SPS, the cost of such work is approximately 1000 rubles, for complex ones, of course, it is more expensive, but, fortunately, not directly proportional to the cost of the system. It is better not to undertake them yourself - you can lose the guarantee (it is usually given for a year, after which a contract for post-warranty service is concluded).
And the last thing to say at the end of this part of the review. In the field of electronic protection of an individual house, a fire alarm is usually an integral part of the security and fire system and is controlled by one control panel. The devices operating in such security systems are already called differently - PPKOP, that is, receiving and control security and fire. But we do not discuss such systems today - unfortunately, the volume of the review is small.
The editors would like to thank NPO PULSE, the FORMULA SECURITY group of companies, the INTEGRATED SAFETY alliance, and System Sensor Fair Detectors for their assistance in preparing the material.
UDC 614.842.4
MODERN SYSTEMS FOR EARLY FIRE DETECTION
M. V. Savin, V. L. Zdor
All-Russian Research Institute of Fire Defense EMERCOM of Russia
A brief description of the various types of fire detectors, their advantages and disadvantages is given. The device and advantages of aspiration fire detectors are considered in detail.
One of the most important elements of a fire alarm system are the fire-broadcasters. They are subdivided depending on the type of physical fire factor to which they react, and, accordingly, are classified into heat, smoke, gas, flame detectors, combined. In addition, depending on the configuration of the measuring zone, there are point, multipoint and linear fire detectors. The point fire detector reacts to the fire factor controlled near its compact sensing element. A multi-point fire detector characterizes a discrete arrangement of point sensitive elements in a measuring line. A linear fire detector is a detector whose geometric shape of the control zone has an extended section, that is, environmental control is carried out along a certain line. Each type of fire detector has its own advantages and disadvantages. The combination of these properties determines the scope of their application. But still, all these detectors have one common drawback - this is the so-called "passive" scanning of the protected area. After all, they actually wait until the factors accompanying the fire (smoke, elevated temperature) themselves find themselves in the detection field of the detector. In particular, a smoke detector will only give an alarm when smoke enters the detector chamber, which largely depends on the presence of air currents in the protected room.
At present, aspiration fire detectors have begun to be actively introduced in our market. They represent the detector itself, consisting of a sensitive element and a signal processing circuit, which can be located both inside and outside the protected premises, and a system of intake pipelines through which air samples are transported from outside.
protected room to the sensitive element of the aspiration fire detector.
Aspirating fire detectors have several major advantages over traditional smoke detection systems. First of all, ensuring the delivery of air samples to the sensitive element, regardless of the presence of forced and natural air flows in the protected room.
Aspirating fire detectors provide so-called cumulative detection. As smoke spreads and disperses throughout a room, its concentration decreases and it becomes increasingly difficult to detect it by traditional means. Cumulative detection refers to the ability to draw air from many points within a protected area into a single detector. Aspiration fire detectors continuously take small amounts of air samples throughout the protected area and transfer them to the sensing element of the aspiration fire detector.
One of the service functions of modern aspiration fire detectors is the ability to continuously monitor the general background of air dust content, predicting and adjusting their work in accordance with the realities of the protected object. This is another of the possible applications of this product - monitoring the purity of the air in the room. In addition, most of the detectors constantly analyze possible malfunctions in their work (contamination in the pipes, clogging of the smoke intake openings, etc.).
In essence, aspiration fire detectors are intelligent fire microstations. They, like conventional fire alarm systems, include fixed and peripheral equipment. As peripheral equipment, there are both a system of intake pipelines with smoke-suction capillary tubes, and various
FIRE AND EXPLOSION SAFETY 6"2003
modules (Fig. 1) designed to perform such functions as providing a visual indication of the status of an aspiration detector in individual zones, setting, testing and servicing, as well as programming an individual detector and the entire network as a whole.
As a sensitive element of aspiration fire detectors, both conventional fire detectors (smoke or gas) (Fig. 2) and intelligent smoke detection systems using the method of scanning laser technology (Fig. 3) can be used.
Let us analyze the principle of operation of aspiration fire detectors using the example of the VESDA series detectors from Vision Fire & Security. Air from the protected room is continuously sucked into the detector using a high-performance fan (aspirator) through the system of intake pipes (Fig. 4). A sample of this air is passed through filters. Dust and contamination are first removed before the sample enters the optical smoke detection chamber. Then, at the second stage of purification (if any), an additional supply of a portion of pure
air to prevent contamination of optical surfaces and ensure calibration stability and long life of the aspirating detector. After the filter, the air sample enters the measuring chamber, where the presence of smoke is detected. The signal is then processed and displayed using a bar graph, alarm threshold indicators or a graphic display (depending on the detector version). Further, aspiration detectors through a relay or interface can transmit this information to the devices of the fire control panel, fire control, to the centralized monitoring console or other external devices.
Emerging fires usually go through four stages: smoldering, visible smoke, flame and fire. On fig. 5 shows how the development of sunbathing proceeds in time. Note that the length of the first stage, smoldering, allows more time to detect a potential fire and therefore control its spread before it causes significant damage and destruction. Traditional smoke detectors often detect smoke when a fire has already started, resulting in
t-th stage: 2nd stage:
Smoldering Fire Visible
1 Traditional
3rd Stage Flame
4th stage! Fire I
VESDA Fire 2 (Extinguishing system activated)
significant material damage. A number of aspiration fire detectors, due to their features, make it possible to detect a fire at the smoldering stage and recognize the process of its spread.
The scope of aspiration fire detectors is quite wide:
In warehouses;
In generalist department stores that hold a variety of inventories ranging from raw materials and bulk merchandise to retail commodities and finished goods;
In electronic data processing sites, such as Internet data centers, network management and similar systems, which present a significant fire hazard due to their high power requirements and density of electronic circuits;
In areas with cleanrooms, such as semiconductor manufacturing plants, research and development organizations, pharmaceutical manufacturing facilities, which pose a significant fire hazard due to the constant supply of flammable materials;
In the energy industry, which uses various types of fuel to generate electricity.
Aspiration fire detectors with an air filtration system have a low probability of
the ability to generate false alarms, which makes it possible to reduce significant material damage that could occur during false start-up of fire extinguishing systems, shutdown of the technological process, etc.
At the same time, aspirating fire detectors can be used in buildings and premises with increased requirements for aesthetics - these are modern offices, visual, rehearsal, lecture, reading and conference rooms, meeting rooms, backstage, foyers, halls, corridors, dressing rooms, as well as historical buildings, cathedrals, museums, exhibitions, art galleries, book depositories, archives.
Aspiration fire detectors can be used:
In extreme conditions: at low temperatures, mechanical overloads and harsh operating conditions, since the intake pipeline system and the direct sensor element of the detector can be installed in different rooms;
They can work both independently as individual means, and as part of automatic systems for collecting and processing information about the situation and transmitting signals to external devices in various ways (via wires, radio channels, etc.);
As an effective means of generating a start signal for starting fire extinguishing systems due to the presence of several levels of alarms and an adjustable sensitivity range. At the same time, for the implementation of the algorithm for starting fire extinguishing means, it is assumed that there are two separate detection points that are necessary for the system to operate, that is, the presence of two separate aspiration fire detectors. Therefore, smoke detectors
aspiration type are a serious addition to the complex of measures to ensure the safety of premises along with traditional fire detectors, in no way diminishing the significance and capabilities of the latter.
FIRE FLASH SAFETY 6"2003
Manufacturing company "Vision Fire & Security" "Securiton-Hekatron" "ESSER"
Characteristic Name of aspiration fire detector
VESDA Laser VESDA Laser PLUS SCANNER VESDA Laser COMPACT RAS ASD 515-1 RAS ASD XL ARS 70 LRS-S 700
Power, V 18...30 18.30 18.30 20.28 18.38 24.30 18.30
Operating temperature, °С -20...+60 -20...+60 -20...+60 0...+60 0...+52 0...+50 -10.+60
Sensitivity, % 0.005.20 0.005.20 0.005.20 Determined by fire detector 0.005.1 Determined by fire detector 0.005.20
Smoke detection technology Laser Laser Laser Optical smoke detector Laser Optical smoke detector Laser
Maximum pipe length in a beam, m 200 200 50 60 60 80 200
Pipe diameter, mm 25 25 25 25/40 25/40 25 25
Hole diameter, mm 2.6 2.6 2.6 3.4 3.4 2.6 2.6
Maximum protected area, m2 2000 2000 500 800 800 1200 1600
Number of filters, pcs. 2 2 2 No No 1 2
Number of fire danger levels, pcs. 4 4 2 1 4 1 4
Dimensions, mm 350 x 225 x 125 350 x 225 x 125 225 x 225 x 85 285 x 360 x 126 317 x 225 x 105 285 x 360 x 126 225 x 225 x 95
Weight, kg 4.0 4.0 1.9 2.7 3.4 2.7 3.5
Networking VESDANet (99 devices) VESDANet (99 devices) VESDANet (99 devices) No LaserNet (127 devices) No VESDANet (99 devices)
Auto compensation mode AutoLearnm programmable AutoLearnmm programmable AutoLearnmm programmable No Yes No Programmable
The aspiration fire detectors of the following leading Western companies are currently certified on the Russian market:
"Vision Fire & Security" (Australia) - fire smoke aspiration detectors of the VESDA Laser PLUS series (Fig. 6), VESDA Laser SCANNER (Fig. 7), VESDA Laser COMPACT (Fig. 8);
"Schrack Seconet AG" (Austria) - smoke and aspiration fire detectors RAS ASD
515-1 (FG030140), manufactured by Securiton-Hekatron, Germany (Fig. 9);
"Fittich AG" (Switzerland) - RAS ASD 515-1 smoke aspiration fire detectors, manufactured by "Securiton-Hekatron", Germany;
"MINIMAX GmbH" (Germany) - aspiration fire detectors AMX 4002.
The table shows the comparative characteristics of some types of aspiration fire detectors.
The cost of damage from a fire, even in a single room, can reach impressive amounts. For example, when there is equipment in the premises, the price of which significantly exceeds the cost of a fire protection device. Traditional fire extinguishing methods are unsuitable in this case, since their use threatens no less damage than the fire itself.
That is why there is a growing need for early fire detection systems that can detect signs of a fire in its infancy and take prompt measures to prevent it. Early fire detection equipment performs its functions due to ultra-sensitive sensors. These are temperature sensors, smoke sensors, as well as chemical, spectral (flame-responsive) and optical sensors. All of them are part of a single system aimed at early detection and super-efficient fire localization.
The most important role here is played by the property of early fire detection devices for continuous monitoring of the chemical composition of the air. When burning plastic, plexiglass, polymeric materials, the composition of the air changes dramatically, which should be recorded by the electronics. For such purposes, semiconductor gas-sensitive sensors are widely used, the material of which is capable of changing the electrical resistance from chemical exposure.
Systems using semiconductors are improving all the time, the market for semiconductors is constantly growing, as evidenced by the performance of financial markets. Modern semiconductor sensors are able to capture the minimum concentrations of substances released during combustion. First of all, these are hydrogen, carbon monoxide and dioxide, aromatic hydrocarbons.
When the first signs of a fire are detected, the work of fire extinguishing systems is just beginning. The detection equipment operates accurately and quickly, replacing several people and excluding the human factor when extinguishing a fire. These devices are ideally connected to all building systems that can speed up or slow down the spread of a fire. The early detection system, if necessary, will completely turn off the ventilation of the room, in the required quantity - power supply elements, turn on the alarm, and ensure timely evacuation of people. And most importantly - launch a fire extinguishing complex.
In the earliest stages, extinguishing a fire is much easier than in later stages and may take only a few minutes. Fire extinguishing at the initial stages can be carried out using methods that exclude the physical destruction of objects located in the room. Such a method is, for example, extinguishing by replacing oxygen with a non-combustible gas. In this case, the liquefied gas, when it becomes volatile, lowers the temperature in the room or in a particular area, and also suppresses the combustion reaction.
Fire doors are an integral part of any fire safety system. This is a structural element that prevents the spread of fire to neighboring rooms for a certain time.
Early fire detection devices are indispensable in the first place to ensure the safety of people. Their necessity has been proved by numerous and bitter experience. Fire is one of the most unpredictable natural disasters, as evidenced by the entire history of human civilization. In our time, this factor has not become less relevant. On the contrary, today even a local fire can cause catastrophic losses associated with the failure of expensive equipment and machinery. That is why it is profitable to invest in such an early detection system.
In the Russian Federation, about 700 fires occur every day, in which more than 50 people die. Therefore, the preservation of human life remains one of the most important tasks of all security systems. Recently, the topic of early fire detection has been increasingly discussed.
Developers of modern fire fighting equipment compete in increasing the sensitivity of fire detectors to the main signs of a fire: heat, optical radiation from the flame and smoke concentration. A lot of work is being done in this direction, but all fire detectors are triggered when at least a small fire has already started. And few people discuss the topic of detecting possible signs of a fire. However, devices that can register not a fire, but only the threat or probability of a fire, have already been developed. These are gas fire detectors.
Comparative analysis
It is known that a fire can occur both from a sudden emergency (explosion, short circuit), and with the gradual accumulation of dangerous factors: the accumulation of combustible gases, vapors, overheating of a substance above the flash point, smoldering insulation of electrical cable wires from overload, rotting and heating of grain and etc.
On fig. Figure 1 is a graph of a typical gas fire detector response to a fire starting with a burning cigarette dropped on a mattress. The graph shows that the gas detector reacts to carbon monoxide after 60 minutes. after a burning cigarette hits the mattress, in the same case, the photoelectric smoke detector reacts after 190 minutes, the ionization smoke detector - after 210 minutes, which significantly increases the time for making a decision to evacuate people and eliminate the fire.
If you fix a set of parameters that can lead to the start of a fire, then you can (without waiting for the appearance of a flame, smoke) change the situation and avoid a fire (accident). If a signal from a gas fire detector is received early, the maintenance personnel will have time to take measures to mitigate or eliminate the threat factor. For example, it can be ventilation of the room from combustible vapors and gases, in case of insulation overheating, turning off the cable power and switching to the use of a backup line, in case of a short circuit on the electronic board of computers and controlled machines, extinguishing a local fire and removing the faulty unit. Thus, it is the person who makes the final decision: call the fire brigade or eliminate the accident on their own.
Types of gas detectors
All gas fire detectors differ in the type of sensor:
- metal oxide,
- thermochemical,
- semiconductor.
Metal oxide sensors
Metal oxide sensors are manufactured on the basis of thick-film microelectronic technology. Polycrystalline alumina is used as a substrate, on which a heater and a metal oxide gas sensitive layer are deposited on both sides (Fig. 2). The sensing element is placed in a housing protected by a gas-permeable sheath that meets all fire and explosion safety requirements.
Metal oxide sensors are designed to determine the concentration of combustible gases (methane, propane, butane, hydrogen, etc.) in the air in the concentration range from thousandths to units of percent and toxic gases (CO, arsine, phosphine, hydrogen sulfide, etc.) at the level of maximum permissible concentrations, as well as for the simultaneous and selective determination of the concentrations of oxygen and hydrogen in inert gases, for example, in rocket technology. In addition, they have a record low electric power required for heating (less than 150 mW) for their class, and can be used in gas leak detectors and fire alarm systems, both stationary and portable.
Thermochemical gas detectors
Among the methods used to determine the concentration of combustible gases or vapors of combustible liquids in the atmospheric air, the thermochemical method is used. Its essence lies in measuring the thermal effect (additional increase in temperature) from the oxidation reaction of combustible gases and vapors on the catalytically active sensor element and further converting the received signal. The alarm sensor, using this thermal effect, generates an electrical signal proportional to the concentration of combustible gases and vapors with different proportionality factors for different substances.
During the combustion of various gases and vapors, the thermochemical sensor generates signals of different magnitudes. Equal levels (in % LEL) of various gases and vapors in air mixtures correspond to unequal sensor output signals.
The thermochemical sensor is not selective. Its signal characterizes the level of explosiveness, determined by the total content of combustible gases and vapors in the air mixture.
In the case of control of a set of components, in which the content of individual, previously known combustible components ranges from zero to a certain concentration, it can lead to a control error. This error also exists under normal conditions. This factor must be taken into account to set the limits of the range of signal concentrations and the tolerance for their change - the limit of the permissible basic absolute error of operation. The measurement limits of the signaling device are the smallest and highest values of the concentration of the determined component, within which the signaling device measures with an error not exceeding the specified one.
Description of the measuring circuit
The measuring circuit of the thermochemical converter is a bridge circuit (see Fig. 2). Sensitive B1 and compensating B2 elements located in the sensor are included in the bridge circuit. The second branch of the bridge - resistors R3-R5 are located in the signaling unit of the corresponding channel. The bridge is balanced by resistor R5.
During catalytic combustion of an air mixture of combustible gases and vapors on the sensitive element B1, heat is released, the temperature rises and, consequently, the resistance of the sensitive element increases. There is no combustion on the compensating element B2. The resistance of the compensating element changes with its aging, changes in the supply current, temperature, speed of the controlled mixture, etc. The same factors act on the sensitive element, which significantly reduces the imbalance of the bridge caused by them (zero drift) and the control error.
With stable bridge power, stable temperature, and controlled mixture speed, bridge unbalance results with a significant degree of accuracy from changes in the resistance of the sensing element.
In each channel, the power supply of the sensor bridge provides a constant optimum temperature of the elements by regulating the current. As a temperature sensor, as a rule, the very same sensitive element B1 is used. The bridge unbalance signal is taken from the bridge diagonal ab.
Semiconductor gas sensors
The principle of operation of semiconductor gas sensors is based on a change in the electrical conductivity of a semiconductor gas-sensitive layer during chemical adsorption of gases on its surface. This principle allows them to be effectively used in fire alarm devices as alternative devices to traditional optical, thermal and smoke signaling devices (detectors), including those containing radioactive plutonium. And the high sensitivity (for hydrogen from 0.00001% by volume), selectivity, speed and low cost of semiconductor gas sensors should be considered as their main advantage over other types of fire detectors. The physical and chemical principles of signal detection used in them are combined with modern microelectronic technologies, which leads to low cost of products in mass production and high technical characteristics.
Semiconductor gas sensitive sensors are high-tech elements with low power consumption (from 20 to 200 mW), high sensitivity and increased speed up to fractions of a second. Metal oxide and thermochemical sensors are too expensive for this use. The introduction into production of gas fire detectors based on semiconductor chemical sensors manufactured using group technology makes it possible to significantly reduce the cost of gas detectors, which is important for mass use.
Regulatory requirements
Regulatory documents for gas fire detectors have not yet been fully developed. The existing departmental requirements of RD BT 39-0147171-003-88 apply to oil and gas industry facilities. NPB 88-01 on the placement of gas fire detectors says that they should be installed indoors on the ceiling, walls and other building structures of buildings and structures in accordance with the operating instructions and recommendations of specialized organizations.
However, in any case, in order to accurately calculate the number of gas detectors and correctly install them at the facility, you first need to know:
- parameter by which safety is controlled (type of gas that is released and indicates a hazard, eg CO, CH4, H2, etc.);
- the volume of the room;
- purpose of the premises;
- availability of ventilation systems, air overpressure, etc.
Summary
Gas fire detectors are next-generation devices, and therefore they still require new research studies from domestic and foreign companies involved in fire systems to develop a theory of gas emission and distribution of gases in rooms of different purposes and operation, as well as to conduct practical experiments to development of recommendations for the rational placement of such detectors.
This system is designed to detect the initial stage of a fire, transmit a notice about the place and time of its occurrence, and, if necessary, turn on automatic fire extinguishing and smoke removal systems.
An effective fire warning system is the use of alarm systems.
The fire alarm system must:
Quickly identify the location of the fire;
Reliably transmit a fire signal to the receiving and control device;
Convert the fire signal into a form convenient for perception by the personnel of the protected facility;
Remain immune to the influence of external factors other than fire factors;
Quickly identify and report malfunctions that prevent the normal functioning of the system.
Industrial buildings of categories A, B and C, as well as objects of national importance, are equipped with fire-fighting automation.
The fire alarm system consists of fire detectors and converters that convert the fire initiation factors (heat, light, smoke) into an electrical signal; a control station that transmits a signal and turns on light and sound alarms; as well as automatic fire extinguishing and smoke removal installations.
Detecting fires at an early stage makes it easier to extinguish them, which largely depends on the sensitivity of the sensors.
Announcers, or sensors, can be of various types:
- thermal fire detector- an automatic detector that responds to a certain temperature value and (or) its rate of increase;
- smoke fire detector- an automatic fire detector that reacts to aerosol combustion products;
- radioisotope fire detector - a smoke fire detector that is triggered due to the influence of combustion products on the ionized flow of the detector's working chamber;
- optical fire detector- a smoke fire detector that is triggered due to the influence of combustion products on the absorption or propagation of the detector's electromagnetic radiation;
- flame fire detector- reacts to the electromagnetic radiation of the flame;
- combined fire detector- responds to two (or more) fire factors.
Heat detectors are divided into maximum, which are triggered when the temperature of the air or the protected object rises to the value to which they are adjusted, and differential, which are triggered at a certain rate of temperature increase. Differential thermal detectors can usually also operate in maximum mode.
Maximum thermal detectors are characterized by good stability, do not give false alarms and have a relatively low cost. However, they are insensitive and even when placed at a short distance from the places of possible fires, they work with a significant delay. Differential type heat detectors are more sensitive, but their cost is high. All heat detectors must be placed directly in the working areas, so they are subject to frequent mechanical damage.
Rice. 4.4.6. Schematic diagram of the detector PTIM-1: 1 - sensor; 2 - variable resistance; 3 - thyratron; 4 - additional resistance.
Optical detectors are divided into two groups : IR - direct vision indicators, which should "see" the fire, and photovoltaic flue. The sensing elements of direct vision indicators are of no practical importance, since they, like heat detectors, must be located in close proximity to potential sources of fire.
Photoelectric smoke detectors are triggered when the luminous flux in the illuminated photocell is weakened as a result of air smoke. Detectors of this type can be installed at a distance of several tens of meters from a possible source of fire. Dust particles suspended in the air can lead to false alarms. In addition, the sensitivity of the device decreases markedly as the finest dust settles, so the detectors must be regularly inspected and cleaned.
Ionization smoke detectors for reliable operation, it is necessary to thoroughly inspect and check at least once every two weeks, remove dust deposits in a timely manner and adjust the sensitivity. Gas detectors are triggered by the presence of gas or an increase in its concentration.
Smoke detectors designed to detect products of combustion in the air. The device has an ionization chamber. And when smoke from a fire enters it, the ionization current decreases, and the detector turns on. The response time of a smoke detector when smoke enters it does not exceed 5 seconds. Light detectors are arranged according to the principle of operation of ultraviolet radiation from a flame.
The choice of the type of automatic fire alarm detector and the installation location depends on the specifics of the technological process, the type of combustible materials, the methods of their storage, the area of the room, etc.
Heat detectors can be used to control premises at the rate of one detector per 10-25 m2 of floor. A smoke detector with an ionization chamber is capable (depending on the installation location) of serving an area of 30 - 100m 2 . Light detectors can control an area of about 400 - 600m 2 . Automatic detectors are mainly installed on the stream or suspended at a height of 6 - 10 m from the floor level. The development of the algorithm and functions of the fire alarm system is carried out taking into account the fire hazard of the facility and architectural and planning features. At present, the following fire alarm installations are used: TOL-10/100, APST-1, STPU-1, SDPU-1, SKPU-1, etc.
Rice. 4.5.7. Scheme of the automatic smoke detector ADI-1: 1.3 - resistance; 2 - electric lamp; 4 - ionization chamber; 5 - scheme for connecting to the electrical network
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