Fire detectors. Fire communication and signaling at the enterprise Communication means and automatic fire extinguishing installations

Not everyone pays attention to small appliances that are hidden on the ceilings of the premises. This is natural, because, seeing something everywhere and everywhere, the brain simply ceases to perceive this something as an unusual phenomenon. And besides, we must also take into account the fact that any such devices are made with the expectation of maximum mimicry with the surface on which they are fixed. Such a complex explanation was required by an ordinary fire alarm, the importance of which should not be underestimated.

Fire detector design

Even if you paid attention to various sensors, this still does not mean anything. The fact is that such traps are just a control system, so to speak, external sense organs that serve the entire system.

They can react to a wide variety of stimuli, and therefore, if we discuss the types of fire alarms, it is impossible not to touch on such a topic.

The detector, which is the very one that is proudly called an alarm, consists of many parts, where the sensors are only the outer part of the structure. So, for example, in addition to traps that respond to various fire factors (smoke, temperature, open fire, etc.), it can also be a whole signal recognition system, with other components, as well as an automatic extinguishing mechanism, etc.

Views and connections

The classification of such devices is quite wide. This is mainly due to the fact that they are used everywhere. It is reasonable that different types are used for each class of premises.

However, it is quite difficult to list the main types of fire communication and alarm systems, simply because these mechanisms are classified very differently. The device is quite complex, and there are also a lot of technical solutions, and therefore we will go through the main types.

Transmitted signal type

Actually, the system for transmitting a signal from an alarm to other elements is a mandatory part of the design, regardless of type. Indeed, if the sensor detects a fire, but the signal does not arrive, there is no point in such a device at all. But the mechanism of action can be of four main types:

• Single-mode, which only signals a fire as such. That is, the sensors turn on only if the necessary conditions occur. But these types of fire alarms are no longer used.
• The most common are dual-mode. The point here is that when the traps do not detect a dangerous situation, they transmit a signal that everything is in order. This means that the system is functioning normally. If the signal does not pass, then the sensor is broken and must be replaced.
• Multi-mode models are "sharpened" specifically for large buildings. After all, the inspector will not walk along kilometer-long corridors just to check why the trap is not transmitting. Such a system is the main view in the school. The security requirements there are high, and they can only be ensured in this way.
• Analog - the most advanced. They react not to a critical, but to any change in the monitored indicators.

signal transmission

This characteristic can also distinguish the types of fire alarms from each other. The transfer can be:

• wired, using cables;
• wireless, where they use a radio signal, or even just a Wi-Fi network.

• Thresholding models only start transmitting when temperature, smoke, or some other characteristic exceeds the threshold;
• Differential detectors emphasize every change in parameters. So you will be notified whenever the value goes up or down;
• Combined systems work by identifying breaking changes, but keeping track of all the others at the same time.

Number of sensors - localization rules

Salt lies in the fact that for rooms of different sizes, the types of fire alarms will be different.

According to this parameter, all fire detectors will be classified as follows:

• Point models are a single sensor that most often mounts directly to the detector for space saving and ease of use. Just such functionality you can see in almost every apartment.
• Multi-point models are many sensors that hide in one specific place. That is, if point devices respond to any one specific parameter, then these devices can track their whole galaxy at once.
• Linear, in turn, are interesting in that they track a number of devices. That is, an arbitrary line is drawn from the detector, along which, for example, emitters and photocells are placed. The latter allows you to monitor the level of smoke in the room. Such systems, as in the above example, are called paired, but they can also be single.

Type of sensors

The classification of traps is just the factor by which the signaling working area is determined. Despite the importance of the previous points, the choice is most often made on the basis of the quality of the sensors. There is no escape from this.

For example, the type and type of fire alarm in a school can be very different. But what kind of traps will be installed is determined by the law on fire safety of institutions.

Heat traps

This is the oldest type, since they were used one hundred and fifty to two hundred years ago. Today, their design is a conventional thermocouple, which, in turn, starts to work, that is, conduct current, only at a certain air temperature. These types of fire alarms, photos of which are available in the article presented to the readers, can be seen in any building of the last century.

The problem here is pretty obvious - the temperature of the air only rises when the fire is lit.

That is, there is a problem with the speed of response. The last century was the heyday of such sensors, they were installed everywhere. At the same time, they are gradually being replaced by other species.

smoke eliminators

If we talk about such specific things as views, it would be blasphemy not to mention smoke detectors. After all, it is they who today occupy a leading position in this special market in every sense.

Smoke is one of the main signs of a fire. Interestingly, he appears first in most cases. It is often even possible to observe smoke for quite a long time until a flame appears - for example, when wiring is smoldering. So, the advantages over the previous type are obvious. The fire is monitored even at the embryonic stage, and therefore it allows you to take preventive measures.

Everything works on the transparency of the air, but smoke can be determined according to different principles. Linear models use a directional beam of different ranges in their work - a reflective or photocell is also required for operation, which will respond to the beam hit.

When there is no reaction, it means that the transparency is broken, the sensor will work.

If the first type uses the optical and ultraviolet wavelengths, then the second, point, work is based on infrared radiation.

Such waves simply should not return to the trap under normal conditions. If the signal is reflected back, this means the presence of foreign substances in the air.

Point sensors cost less than linear ones, but the latter are, accordingly, more reliable. So you still have to choose.

Flame sensors

This view is common for industrial premises, workshops, etc. That is, you can only work with a flame, since the air is dusty, and the temperature is a priori increased.

They can be infrared or ultraviolet - these are the two main types.

Thus, the device reacts to the heat generated, but immediately, and not when it heats the air, as it works with thermal traps. You can also use electromagnetic sensors - they will respond precisely to this component of the flame, thus avoiding false alarms.

Signaling

A fire can also be tracked through the usual ultrasonic security system of the apartment.

The bottom line here is on what principle the device works. In this case, this is the movement of air masses.

The alarm will respond not only to the intruder, who moves the air while moving, but also to an open flame. The latter will certainly raise a whole layer of heated air up, which will cause the device to operate.

However, relying on such a system is not worth it, since it is not designed to track fires.

For a full-fledged broadcast of announcements, the communication system includes in its activities the complex use of telecommunication hardware and auxiliary means.

Hardware

The automatic control system refers to the engineering base for automation and informatization of garrison control, its most important component is a system that provides. It, in its action, covers the main divisions of the garrison.

The fundamental basis of its functioning is based on mobile and fixed communication nodes, which in turn are based on modern hardware, due to which their full control is performed.

The main communication tools include the following hardware:

1. technical communication devices (various radio stations, telecontrol equipment, radio transmitters, sound recording devices, telegraph station, radio repeaters, and other units whose main purpose is to receive (transmit) and convert various types of information);
2. uninterruptible power generators, precision instruments, rectifiers and chargers;
3. line wire facilities (cables for underground and underwater purposes, light field communication cables that provide mobility, cables for long-distance communication, cables for distribution purposes, as well as auxiliary facilities, the main function of which is laying and building reliable communication lines);
4. means of communication signal type (lighting and sound).

Using an alarm in an alert

In order to quickly detect and immediately notify the fire department about the current critical situation caused by uncontrolled fire, as well as the place of its direct action, alarm means are used.

Today, preference is given to electric fire alarms (EPS). Given the device of the installed sensor, which notifies of a dangerous situation, the automatic type fire alarm system is divided into:

• devices, the activation of which occurs at the time of the appearance of smoke;
• devices that turn on with strong temperature fluctuations;
• devices that operate in the event of a fire;
• combined devices.

In addition, other types of signaling are used: beam systems and loop-type systems.

Beam systems - are used in institutions located at a relatively short distance. Basically, the length of lines at such enterprises is insignificant.

If they are triggered, a special item will display information only about a certain number of a particular beam, without identifying a direct detector installed on the territory of the organization.

The loop-type warning system differs from the beam version of the devices in that the installation of the detectors takes place in one structured line (loop). Typically, such a design can include about fifty detectors.

The operation of this device is based on this principle - the signal is transmitted from the detector to the receiving station with a certain code. The installation of detectors in the loop takes place under different numbers, differing in their personal code. By fixing the received code, the receiving station determines the location and number of a specific detector.

As for the enterprises that are engaged in food products, their territories install detectors of differential and maximum action of the thermal type, as well as those that react to smoke and the combined type of detectors (smoke + heat).

Device type selection

Everyone knows the fact that a fire can go unnoticed for a long time. It can only manifest itself as a sluggish smoldering or have a hidden heat source, which, in turn, will flare up for a long time, since it will not have enough air.

The course of this stage can last quite a long time, about several hours. In this regard, an apparatus that notifies people of a fire only with an increase in temperature or the appearance of an open flame will be able to report a fire only when it is in full swing.

Based on this, the following conclusion can be drawn that the most effective detector will be a device that reacts to smoke and gaseous combustion products.

It is worth paying attention to the fact that detectors that react to smoke work faster than their counterparts, which signal a rise in the temperature level.

As devices notifying about the occurrence of smoke, ionization sensors are used. The ionizing substance in the chamber is plutonium, which produces alpha radiation. The operation of the sensor is based on changes in the electrical conductivity of gas accumulations that appear as a result of irradiation of a radioactive substance.

When ignition occurs, accompanied by smoke or its absence, even with the slightest release of heat, the properties of the atmosphere around us begin to change significantly, since ionization and a change in the composition of the gas occur. As a result of the described phenomenon, an ultra-sensitive detector of the DI type was produced.

This device is designed for long-term use and continuous operation at temperatures from -29 °C to +59 °C. The coverage of such a detector is 100 sq.m. Installation of such devices in buildings, the atmosphere of which is saturated with alkalis and acids, is irrational.

The most common representative of automated heat detectors is the PTIM-type heat detector (maximum action semiconductor heat detector). In the case of an increase in the temperature level in the room, the sensor responsible for the thermal resistance sharply reduces its effect, which in turn leads to an increase in the voltage on the control electrode.

As soon as this voltage exceeds the permissible level, the ignition voltage will begin its action, that is, the detector will be activated. The area of ​​its impact is 10 m 2 .

According to the principle of the sensitive element used, automated detectors are divided into:

• semiconductor;
• bimetallic;
• on thermocouples.

Detectors operating according to the thermal principle of operation are divided into the following types:

• maximum differential;
• differential;
• maximum.

ATIM are detectors of the maximum type. They begin to operate when the temperature in the building reaches a peak. These devices can be adjusted and configured to operate from +60 to +80 °C, regardless of the rate of temperature increase. The frequency of operation of the device is up to 2 minutes. Coverage area is 15 sq.m.

The differential type of detectors shows its activity during the period of temperature increase, which increases at a certain rate. So, for example, the TEDS device reacts within seven seconds to sharp fluctuations in the increase in temperature (30 degrees). The control area is 30 sq.m.

Detectors of maximum differential action are activated when the temperature level rises in a certain room. The DMD detector responds after no more than 50 seconds. Covered control area - 25 sq.m.

In addition, thermal type detectors have one very significant drawback - the time from the start of activation and giving an alarm signal can be several minutes.

To date, models of the combined type are actively used, which react to heat and smoke.

The main component of the combined action detector is an electrometric thyratron, the principle of its operation is based on the interaction of two sensors: a heat controller and a device that reacts to smoke.

For timely detection with immediate notification to the central department of fire departments about the fire and the place of its occurrence, signaling and communication means are used.

The most reliable fire alarm system is the electrical alarm system (EPS). Depending on the sensors that notify of a fire, automatic fire alarm systems are divided into: thermal, responding to an increase in temperature in the room; smoke, reacting to the appearance of smoke; light, reacting to the appearance of a flame or infrared rays; combined.

The main elements of any electrical fire alarm system (Fig.) are: detectors-sensors located in the protected premises; a receiving station designed to receive fire signals from detectors and automatic alarms; power devices that provide power to the system with electric current from the mains and batteries; linear structures, which are a system of wires connecting the detectors to the receiving station.

Rice. Scheme of the device of electrical fire alarm systems: a - beam (radial); b - loop (ring); 1 - detectors-sensors; 2 - receiving station; 3 - battery backup power supply; 4 - power supply from the network (with current conversion); 5 - system for switching from one power supply to another; 6 - linear structures (wiring)

According to the method of connecting the detectors to the receiving station, beam (radial) and loop (ring) EPS systems are distinguished.

Beam systems (see Fig. a) are more common in enterprises located in a relatively small area, where the length of the lines is insignificant or where a telephone cable can be used. Up to three or four detectors can be included in each beam. When they are triggered, the receiving station will only know the number of this beam without fixing the detector.

The EPS loop system differs from the beam system in that the detectors are connected in series to a single-wire line (loop). Up to 50 detectors are usually included in one loop. The operation of the loop system is based on the principle of transmitting a certain code from the detector to the receiving station. The loop includes detectors with different numbers, which differ from each other by the code. The receiving station determines the number and location of this detector by the code.

At food enterprises, they use: heat detectors of maximum and differential action; smoke detectors, as well as combined smoke and heat detectors.

It is known that often for a long time a fire is preceded only by smoldering or a latent source of heat, which flares up slowly due to lack of air. The duration of this initial phase of the fire can be several hours. Therefore, a system whose operation depends on a rise in temperature or on the presence of an open flame can signal a fire only after the latter has reached the highest phase of development. Therefore, a detector that is sensitive to smoke or combustion gases is far superior to other systems.

The response time of a smoke detector is much shorter than the pulse time of heat detectors.

Ionization sensors are used as smoke detectors. The source of ionization in the chamber is plutonium-239, which emits α-rays. The principle of operation of an ionization sensor is based on a change in the electrical conductivity of gases that occurs under the influence of irradiation of a radioactive substance.

When ignited with or without smoke, even with very small amounts of heat released, the physical state of the surrounding atmosphere changes greatly due to ionization and changes in its gas composition. Based on this phenomenon, a highly sensitive smoke detector of the DI type was created.

It is designed for repeated action and continuous operation at temperatures from -30 to +60 °C. The coverage area of ​​one detector is about 100 m 2 . It is not advisable to install this type of detectors in rooms where the air is constantly filled with acid and alkali vapors.

Automatic heat detectors include PTIM-type heat detectors (maximum action semiconductor heat detector).

With an increase in the ambient temperature, the semiconductor thermal resistance (sensor) decreases sharply and the voltage at the control electrode increases. As soon as this voltage exceeds the ignition voltage, the thyratron will "light up", i.e. the detector will work. Controlled area 10 m 2 .

Depending on the sensitive element used, automatic detectors can be: bimetallic; on thermocouples; semiconductor.

Heat detectors according to the principle of operation are divided into maximum, differential and maximum differential.

The detectors of the maximum type ATIM are triggered when the temperature in the room rises to the limit to which they are adjusted. These detectors can be adjusted to a response temperature of +60 or +80°C, regardless of the rate of its rise. Operation inertia - up to 2 min; controlled area - up to 15 m 2 .

Differential action detectors are triggered at a certain rate of temperature rise. The TEDS detector is triggered by an abrupt increase in temperature by 30 °C for no more than 7 s. Controlled area - about 30 m 2 .

Maximum differential detectors are triggered by an increase in ambient temperature. The DMD detector has an inertia of no more than 50 s; controlled area - about 25 m 2 .

Thermal detectors have various designs. The basic principles of the device of heat detectors are shown in fig.

Rice. Thermal automatic detectors: a - fusible closing; b - fusible opening; c - self-healing; 1 - bimetallic plate; 2,3- contacts; 4 - insulating base; 5 - adjusting screw

Thermal detectors have a significant drawback - inertia (the time from the onset of fire to the alarm can be several minutes).

In practice, installations with combined detectors that respond to smoke and heat have found wide application.

The executive element of the combined detector is an electrometric thyratron, the potential of which is determined by the state of two sensors: the smoke sensor of the ionization chamber and the heat sensor of the thermal resistance.

The heat sensor, together with a constant resistance, forms a circuit connected to the control electrothyratron through the resistance of the ionization chamber.

The combined detector gives a signal at an ambient temperature of 70 °C. If smoke appears in the zone of its action, the signal will be given after 10 s; area controlled by the detector is 150 m 2 .

Light detectors react to the appearance of a flame. The sensitive element is a photon counter, which detects the ultraviolet part of the flame spectrum.

According to safety requirements, signaling equipment must have working and protective grounding.

The economic assessment of a fire alarm installation is a specific indicator that reflects the cost of protecting 1 m 2 of floor area. This indicator is defined as the quotient of the total investment divided by the total area protected by the detectors.

Rating: 2.25

Rated: 4 people

Fire communication and signaling are intended for timely reporting of a fire (notification communication), management of fire departments (dispatching communication) and management of fire extinguishing. For these purposes, telephone and radio communications (manual fire detectors), electric fire alarms (EPS), automatic fire alarms (APS), live communications, beeps, calls, etc. are used.

Rice. 1. Diagram of a manual call point
Manual fire detectors are installed at public facilities and in residential premises, in corridors, aisles, and in stairwells. An alarm signal is given by pressing a button. PKIL manual call points (beam fire button detector) are connected to the receiving station. Pressing the K button opens one of the circuits, which leads to the operation and reception of an alarm signal. A current is supplied from the receiving station, which turns on the phone, and the person who raised the alarm receives confirmation that the signal has been received. A handset can be connected to the Mt terminals for negotiations with the attendant.
In industrial buildings with an area of ​​​​more than 500 m2, classified by fire hazard to categories A, B and C, warehouse and retail premises, exhibition halls, museums, theater and entertainment venues and some others, it is recommended to install electrical fire alarm systems (EPS). EPS are automatic and manual action. In turn, automatic fire alarm systems, depending on the physical factor to which they respond, are divided into thermal (i.e., responsive to temperature increase), smoke, light and combined. In addition, automatic fire detectors are divided into maximum, maximum differential and differential. Sensors of maximum action are triggered when the controlled parameter reaches a predetermined value. Differential sensors respond to a change in the speed of a given parameter, and the most differential sensors react to both.
Fire detectors of all types are characterized by a response threshold - the minimum value to which they respond, inertia - the time from the start of the controlled parameter to the moment it is triggered, and the coverage area - the floor area that is controlled by one sensor.

The principle of operation of thermal fire detectors is to change the physical and mechanical properties of the sensitive elements of these devices under the influence of temperature. A fusible alloy can serve as a sensitive element, as in DTL detectors (thermal fusible sensor); thermocouples, as in DPS detectors (fire alarm sensor) or semiconductor thermistors in POST detectors. Smoke detectors have two main smoke detection methods - photoelectric and radioisotope. A photoelectric smoke detector (IDF) detects smoke by registering light reflected from smoke particles with a photocell. The semiconductor smoke detector (DIP) works on the same principle.
A radioisotope smoke detector (RID) has an ionization chamber with sources of α-particles as a sensitive element. An increase in smoke content reduces the degree of ionization in the chamber, which is recorded.
There are combined detectors (KI) that react to heat and smoke. Light fire detectors register flame radiation against the background of extraneous light sources. Light detector type SI-1 detects a fire by ultraviolet radiation of the flame. The sensitive elements of these detectors are various photodetectors - semiconductor photoresistors, gas-filled photocells with an external photoelectric effect.
Ultrasonic detectors are being used more and more. They have a very high sensitivity and can combine security and fire functions. These devices respond to changes in the characteristics of the ultrasonic field that fills the protected room under the action of the movement of the air that occurs during a fire. The table shows the main characteristics of detectors of various types.

Table 1. Characteristics of various detectors
The main elements of any automatic fire alarm system are: detectors located in the protected premises; a receiving station designed to receive signals from sensors and generate alarms; power devices that provide power to the system with electric current; linear structures - systems of wires connecting detectors with a receiving station.

Rice. 2. Connecting fire detectors to the receiving station:
1 - receiving station; 2 - fire detectors; 3 - power supply
Fire detectors are connected to the receiving station in two ways - in parallel or in series. Parallel switching is used in enterprises with round-the-clock stay of people. Push-button and automatic detectors can be included in the installation branch. A sequential system is installed in large facilities.