Ionization fire detectors: types and principle of operation. Using smoke detectors indoors How smoke detectors operate

Today's Russian market presents to consumers the widest selection of products in the field of production fire alarm, allowing to recognize a fire accurately, effectively and in the first seconds of its occurrence. There are several types of smoke detectors, which have their own advantages and disadvantages, depending on the principle of their operation.

Device characteristics

A smoke detector is an alarm system necessary to detect and report fire. necessary in all administrative buildings and social facilities, for timely warning of a fire and its rapid elimination. The article below discusses the main types of detectors, in particular smoke detectors.

IN fire protection system There are several types of detectors:

• smoke (smoke recognition) - divided into optical and ionization;
• thermal (reacting to a rapid increase in temperature): maximum, differential and maximum-differential.
• flame (open fire detection). Includes 4 flame detection range classes. Class 1 includes devices that react to fire from 25 meters or more. By 4th grade - from 8 meters.
• (triggered when gas is present);
• combined (including all types at once);

How separate species, there are manual call points, which are a fire alarm button or lever that is activated by manual control.

Fire smoke detectors are triggered when tiny smoke particles hit the optical-electronic camera of the sensor. The reaction speed of the device depends on their saturation. The principle of operation of smoke devices is based on the fact that the sent beam is scattered in the presence of smoke particles in the air. The device uses a special sensor to detect this change in radiation. The slightest “fogging” leads to activation of the alarm system.

Working principle of a smoke detector

These devices are used in households, in crowded places (schools, hospitals, shopping centers), in production.

The smoke detector is very popular due to its high sensitivity and rapid response to a fire. Its mechanism practically does not fail, and the number of false alarms is reduced to a minimum.

Types of smoke alarm devices

Depending on the method of fire detection, smoke detectors are divided into: optical and ionization.

Optical

Optical detectors operate by monitoring the physical composition of the air mass and trapping combustion products in it. These sensors include:

• Spot

Determine the source of fire in a small specific area. This type of sensor detects smoke by examining reflected infrared rays in a special optical camera. The smoke chamber consists of a device infrared radiation and a receiver for studying reflected air. Point smoke detectors come in a variety of shapes and models.

There are autonomous point smoke fire detectors and radio channel ones.

Equipped rechargeable batteries and sound sensors. They work independently, without operator supervision. They are easy to use and low in price. The principle of their operation is that smoke particles hit the optical camera. The device is hidden in a plastic case with different designs, combined with the interior of the room. Works both autonomously and from the network.

Radio channel point detectors operate on a specific radio wave, which, if a fire is detected, transmits a signal to the operator’s console. Battery operated. The distance between sensors is 4-5 meters.

• Linear

Monitor the premises for fire in the linear zone. They are used in industrial and large facilities (shopping centers, offices, public institutions). They are characterized by high sensitivity in detecting smoke. Linear smoke detectors are divided into two-component and single-component.

Two-component sensors consist of a receiver and a transmitter located on different sides of the room. As soon as smoke enters the controlled area, the fire alarm mechanism is activated.

Single-component devices are a single unit with a passive reflector that analyzes the state of the air.

They detect all types of smoke and are effective in operation.

• Aspiration

The most complex and expensive type of device of all types of smoke fire detectors. They are a powerful housing, inside of which there is a laser point detector and air intake tubes. They forcefully sample and analyze air from the room in a fast manner. They are used at important sites (archives, museums, ships) and, accordingly, are very expensive.

Ionization

An ionization fire smoke detector consists of two air intake chambers and produces radiation that is safe for human life and health. Fresh air passes through both chambers. If smoke appears in the room, its particles will linger in the 1st chamber, causing a decrease in the current strength in the 2nd. This is how the fire alarm goes off. There are 2 types of such alarms: radioisotope and electroinduction.

Most often, ionization sensors are used in large warehouses and in the manufacturing sector.

Radioisotope smoke detectors notify about a fire after the appearance and effect of smoke on the current. These sensors ionize the airspace with a special radioactive substance. When smoke enters one of the chambers of the device, it dissolves in charged current particles, as a result of which the voltage inside the chamber decreases and a signal is triggered.

PS automatic photoelectric radioisotope smoke detectors detect “black” smoke better than all other types of devices.

Electrical induction devices pass air from the controlled room into the charging chamber through a flue and analyze its composition. The particles of the intake air are exposed to a unipolar charge, and they acquire a space charge.

Electrical induction sensors examine the duration and amplitude of movement of air microparticles. If a deviation from the specified parameters occurs, the contact mechanism instantly closes and the fire signal is transmitted to the control point, where the operator monitors the operation of the system.

Electrical induction detectors are used at particularly important facilities, including the ISS.

Device

Fire notification can be targeted or non-targeted. This depends on how the particular detector is connected to the fire system.

They transmit a signal to the control panel, where the location of the fire is determined, since all devices are identified in the system under a certain number. Used in large buildings and industrial premises.

Non-addressable smoke detectors only emit an audible signal, and the location of a fire can only be determined by focusing on it.

The fire alarm system consists of plastic case, where the optical camera, light detector and refractive curtains are located. Air particles hitting the camera reflect radiation from the light source. The sensor circuit analyzes the composition and density of the luminescence through a light detector. When smoke is detected, an alarm is triggered. Refractive shutters protect the device from excess light and dust in the air.

Large accumulation of dust particles reduces the sensitivity of the detector and can lead to frequent failures. Therefore, it is important to regularly wipe the device from dust.

Optical smoke detectors can be equipped with LED and laser light emitters.

Ionization detectors consist of a chamber with two plates energized. The current comes from an ionization source: a coil or a radioactive isotope. If smoke enters the chamber, the voltage between the plates decreases and the fire alarm sensor is activated.

Where and what types are appropriate to use?

IN residential buildings, as a rule, optical point devices.

In large volumetric spaces, optical linear sensors with an addressable type of notification are used.

At particularly important facilities, optical aspiration fire alarm detectors are more often placed, capable of detecting the start of a fire in a matter of seconds.

Installation

When purchasing and installing smoke fire detectors, you need to pay attention to their main characteristics:

• warranty period;
• material;
• type of device;
• inertia and response speed;
• sensitivity;
• power consumption;
• operating range;
• coverage area.

The installation and number of fire detectors depends on the area of ​​the room, ceiling height, area of ​​the monitored sensor area, and the presence of hazardous areas.

At least 2 fire sensors are installed in one room. One device is used when: a) the area of ​​the room is small and corresponds to the covered area of ​​the sensor; b) if an addressable fire warning system is installed.

On average, any sensor covers an area of ​​55 sq.m. (with a ceiling height of 10-12 m) up to 85 sq.m. (ceiling height 3-3.5 m). If the ceilings are more than 12 meters, fire sensors are mounted in two levels - on the walls / on the ceiling. If point devices are installed at the top, then linear devices are installed on the walls.

Fire detectors are located under the ceilings and at a maximum distance from the walls of 450 cm. The distance between two smoke detectors should not exceed 900 cm.

If the ceilings are suspended, then smoke detectors are mounted between two ceilings and at least 1 meter from vent. If the room is of irregular shape or has non-standard engineering structures, the number of fire sensors should be increased.

Ionization fire detector – This is a high-tech automatic device for registering the source of a fire by the appearance in the gas-air environment of the protected room of volatile products of the combustion process - the smallest particles of soot and burning. This detection method is based on the property of ionized air to attract particles of the smoke stream, which gave rise to its name.

In terms of its effectiveness, this is one of the last stages of technical development, comparable in sensitivity, speed/inertia in detecting characteristic signs of the combustion process with the formation of smoke, only with gas, aspiration, flow sensors; exceeding the performance of optical-electronic devices intended for the same purposes.

Ionization fire detectors are capable of detecting a fire not only at the earliest stage by the appearance of volatile particles of the combustion reaction, but also react to any size of them; as well as color, depending on the physical and chemical parameters of the fire load in the protected premises, the so-called gray and black smoke; which is not available to most other automatic devices that detect the formation of a smoke flow.

Due to the complexity of production, technical control when creating such devices; The need for disposal/decontamination of expired ionization fire detectors only at specialized nuclear industry enterprises creates the prerequisites for the high cost of products.

Due to the presence in them, albeit within those permitted by government regulations, of a small amount of radioactive substances inside miniature radioisotope emitters, which are an integral design element in most product models; partly due to the established bias public opinion in our country they are not mass-produced.

However, their production continues abroad, and certified in in the prescribed manner products can be purchased at Russian market fire-technical products.

Smoke-ionization fire detector

According to the definition given in, this is an automatic device for detecting the source of fire, the method of operation of which is based on a change in the values ​​of the electric current passing through artificially ionized air when smoke particles appear in them, formed during the combustion of solid and liquid materials.

According to the controlled sign of fire, product design, technical device sensitive elements of sensors, a method for detecting smoke particles, there are two types of ionization fire detectors:

• Radioisotope.

This is a smoke fire detector that is triggered due to the impact of combustion products on the ionization current of the internal working chamber of the detector. The operating principle of a radioisotope detector is based on the ionization of the air in the chamber when it is irradiated with a radioactive substance. The operating principle of a radioisotope detector is based on the ionization of the air in the chamber when it is irradiated with a radioactive substance. When oppositely charged electrodes are introduced into such a chamber, an ionization current occurs. Charged particles “stick” to heavier smoke particles, reducing their mobility - the ionization current decreases. Its decrease to a certain value is perceived by the detector as an “alarm” signal.

Such a detector is effective in smoke of any nature. However, along with the advantages described above, radioisotope detectors have a significant drawback that should not be forgotten. We are talking about the use of a radioactive radiation source in the design of detectors. In this regard, problems arise in observing safety measures during operation, storage and transportation, as well as disposal of detectors after the end of their service life. Effective for detecting fires accompanied by the appearance of so-called “black” types of smoke, characterized by a high level of light absorption.

• Electroinduction.

Aerosol particles are sucked in from environment into a cylindrical tube (flue) using a small-sized electric pump and enter the charging chamber. Under the influence of a unipolar corona discharge, the particles acquire a volumetric electric charge and, moving further along the gas duct, enter the measuring chamber, where they induce an electrical signal on its measuring electrode, proportional to the volumetric charge of the particles and, consequently, their concentration. The signal from the measuring chamber enters the pre-amplifier and then into the signal processing and comparison unit. The sensor selects the signal by speed, amplitude and duration and provides information when specified thresholds are exceeded in the form of closing a contact relay.

1. High voltage modulator.
2. Voltage regulator.
3. Power unit.
4. Amplifier.
5. Information processing unit.
6. Charging chamber, electrode ring.
7. Charging chamber, electrode needle.
8. Capacitor.
9. Resistor.
10. Resistor.
11. Zener diode.
12. Induction electrode.
13. Light-emitting diode.
14. Aerosol consumption stimulator.
15. F – Output signal.

Structurally, the measuring line is a cylindrical gas duct, at the input of which there is a needle-cylinder charging chamber, and at the output there is a measuring electrode-ring and an air mixture flow stimulator.

The main parameter of an electrical induction fire detector, which allows the use of a floating threshold, is its sensitivity, which allows for a stable level of electrical signal proportional to the weight concentration of the aerosol over its entire possible range of change.

In , on the requirements for the design of APS, AUPT systems, it is recommended to select point smoke fire detectors in accordance with their sensitivity to various types smoke. According to this characteristic indicator, ionization fire detectors are unrivaled among similar devices, incl. effectively detects “black” smoke.

Operating principle of ionization fire detectors

The history of the invention of the smoke radioisotope detector is amazing. At the end of the 1930s. physicist Walter Jaeger was developing an ionization sensor to detect poison gas. He believed that the ions of air molecules formed under the influence of a radioactive element (Scheme A, B) would be bound by gas molecules and, due to this, would decrease electricity in the device circuit. However, small concentrations of the poisonous gas had no effect on the conductivity in the measuring ionization chamber of the sensor. Walter lit a cigarette out of frustration and soon noticed with surprise that the microammeter connected to the sensor recorded a drop in current. It turned out that smoke particles from a cigarette reproduced the effect that the poisonous gas could not provide (diagram B). This experiment by Walter Jaeger paved the way for the creation of the first smoke detector.

It is based on fixing and recording changes in the parameters of the electric current passing through ionized air molecules in the sensitive element of the sensor when they are exposed to small particles of volatile combustion reaction products.

When such particles enter the sensor chamber of an ionization smoke detector, due to the difference electrical potentials attach to ions, which reduces the speed of their movement and, as a result, the current strength; when their number decreases and is removed from the sensitive element of the device, the current strength begins to increase.

A decrease in the strength of the electric current passing through the ionized air to a threshold/critical value set by the product settings is perceived by the device as a sign of detecting a fire in the controlled area, the protected room; with the formation and transmission of an alarm message to control and control equipment APS installations or control unit of an automatic fire extinguishing system.

The operating principle of radioisotope smoke detectors is based on the ionization of the air in the control chamber of the sensitive element located inside the product body, with intense radiation from a low-power, narrowly directed source of radioactive radiation; In electric induction fire detectors, air ionization is carried out by a unipolar corona discharge of electric current.

Ionization detector design

The most widely used ionization radioisotope smoke detector compared to the electroinduction device consists of the following elements:

• Housings made of high-quality plastic, such as flame retardant polycarbonate, with air inlet and outlet openings, flue gases, protected both by a fine metal mesh from the penetration of insects, and by the shape of the body around them, their location on it to protect them from the effects of direct air currents.
• Mounting base with electronic printed circuit board, on which two ionization chambers are installed in series with the electrical circuit - control and measuring; a control unit with a microcontroller designed for data processing, signal transmission, and device addressing; input/output sliding clamp contacts/terminals for connection to the APS installation loop.
• Structurally, the control chamber is located inside the measuring chamber, being a closed volume protected from the penetration of smoke particles; while the measuring chamber is open, it is designed for free penetration and filtration of the gas-air environment to record changes occurring in it.

• A compact source of radioactive radiation, often containing a negligible amount of the isotope americium-241, deposited on metal foil, installed inside the control chamber. Its radiation penetrates through both chambers, forming positively and negatively charged particles in the air - air ions; in this case, the radioisotope radiation source carries a positive charge, and the external measuring chamber carries a negative charge. When power is supplied to the input contacts of the ionization fire detector, an electric field appears inside it.
• When accumulation occurs on the signal electrode installed at the boundary between the control and measuring smoke chambers, positive charge sufficient strength set by the microcontroller settings; It is generated through an analog-to-digital converter, which is part of an electronic integrated circuit, into an alarm signal transmitted to the device/unit of the alarm system installation.

The current strength in the ionized space inside such a fire detector remains stable only if normal conditions in the control zone are maintained.

At the slightest changes in the air, ionization fire detectors react sensitively, activating the entire complex of automatic fire protection, which makes it possible, if not to immediately eliminate the source of fire; then give the opportunity to localize it, give time until fire departments arrive, and minimize material damage.

general characteristics

Fire detector— a device for generating a fire signal. Using the term "sensor" is a misnomer because the sensor is part of the detector. Despite this, the term "sensor" is used in many industry regulations to mean "detector".

Legend

The symbol for fire detectors must consist of the following elements: IP Х1Х2Х3-Х4-Х5.
The abbreviation IP defines the name “fire detector”. Element X1 - indicates a controlled sign of fire; Instead of X1, one of the following digital designations is given:
1 - thermal;
2 - smoke;
3 - flame;
4 - gas;
5 - manual;
6...8 - reserve;
9 - when monitoring other signs of fire.
Element X2X3 denotes the operating principle of the PI; instead of Х2Х3 one of the following digital designations is given:
01 - using the dependence of the electrical resistance of the elements on temperature;
02 - using thermo-EMF;
03 - using linear expansion;
04 - using fusible or combustible inserts;
05 - using the dependence of magnetic induction on temperature;
06 - using the Hall effect;
07 - using volumetric expansion (liquid, gas);
08 - using ferroelectrics;
09 - using the dependence of the elastic modulus on temperature;
10 - using resonant-acoustic methods of temperature control;
11 - radioisotope;
12 - optical;
13 - electrical induction;
14 - using the “shape memory” effect;
15...28 - reserve;
29 - ultraviolet;
30 - infrared;
31 — thermobarometric;
32 - using materials that change optical conductivity depending on temperature;
33 — aeroionic;
34 - thermal noise;
35 - when using other principles of action.
Element X4 indicates the serial number of development of a detector of this type.
Element X5 indicates the class of the detector.

Classification based on restartability

Automatic fire detectors, depending on their capabilities restart after triggering they are divided into the following types:

• returnable detectors with the possibility of reactivation - detectors that, from the state fire alarm can return to the control state without replacing any nodes, if only the factors that led to their operation have disappeared. They are divided into types:
  • detectors with automatic reactivation - detectors that, after being triggered, independently switch to the monitoring state;
  • detectors with remote reactivation - detectors that, using a remote command, can be transferred to the monitoring state;
  • manually switched detectors - detectors that can be switched to the monitoring state using manual switching on the detector itself;
• detectors with replaceable elements - detectors that, after being triggered, can be transferred to the control state only by replacing some elements;
• detectors without the possibility of reactivation (without replaceable elements) - detectors that, after being triggered, can no longer be transferred to the monitoring state.

Classification by type of signal transmission

Automatic fire detectors are divided according to the type of signal transmission:

• dual-mode detectors with one output for transmitting a signal both about the absence and presence of signs of fire;
• multi-mode detectors with one output for transmitting a limited number (more than two) types of signals about a state of rest, fire alarm or other possible conditions;
• analogue detectors, which are designed to transmit a signal about the value of the fire sign controlled by them, or an analogue/digital signal, and which is not a direct fire alarm signal.

Application
Heat fire detector designed in the 19th century. Consists of two wires a and b, which are connected to each other by washers cc made of a material that does not conduct electricity. On the side of the device there is a tube d with a capsule e filled with mercury and closed from below with a wax plate. When the temperature rises, the wax melts, mercury is poured into the device and contact is established between the two wires, as a result of which a signal appears
Apply if initial stages A fire generates a significant amount of heat, for example in fuel and lubricant warehouses. Or in cases where the use of other detectors is impossible. Use in administrative and domestic premises is prohibited.
The highest temperature field is located at a distance of 10...23 cm from the ceiling. Therefore, it is in this area that it is desirable to place the heat-sensitive element of the detector. A heat detector located under the ceiling at a height of six meters above the fire will be triggered when the heat generated by the fire is 420 kW.

Spot
A detector that responds to fire factors in a compact area.

Multipoint
Heat multipoint detectors are automatic detectors, sensitive elements which are a collection of point sensors discretely located along the line. The step of their installation is determined by the requirements of regulatory documents and technical characteristics specified in the technical documentation for a specific product.

Linear (thermal cable)
There are several types of linear thermal fire detectors, structurally different from each other:

• semiconductor - a linear thermal fire detector, which uses a coating of wires with a substance having a negative temperature coefficient as a temperature sensor. This type of thermal cable only works in conjunction with an electronic control unit. When any section of the thermal cable is exposed to temperature, the resistance at the point of influence changes. Using the control unit, you can set different temperature response thresholds;
• mechanical - a sealed metal tube filled with gas is used as a temperature sensor for this detector, as well as a pressure sensor connected to an electronic control unit. When any part of the sensor tube is exposed to temperature, the internal gas pressure changes, the value of which is recorded by the electronic unit. This type of linear thermal fire detector is reusable. The length of the working part of the metal tube of the sensor is limited in length to 300 meters;
• electromechanical - a linear thermal fire detector, which uses a heat-sensitive material applied to two mechanically stressed wires (twisted pair) as a temperature sensor. Under the influence of temperature, the heat-sensitive layer softens, and the two conductors are short-circuited.

Smoke detectors are detectors that react to combustion products that can affect the absorption or scattering ability of radiation in the infrared, ultraviolet or visible ranges of the spectrum. Smoke detectors can be point, linear, aspirating and autonomous.

Application

The symptom that smoke detectors respond to is smoke. The most common type of detector. When protecting administrative and amenity premises with a fire alarm system, it is necessary to use only smoke detectors. The use of other types of detectors in administrative and utility premises is prohibited. The number of detectors protecting a room depends on the size of the room, the type of detector, the presence of systems (fire extinguishing, smoke removal, equipment blocking) controlled by the fire alarm system.
Up to 70% of fires arise from thermal microfoci that develop in conditions with insufficient access to oxygen. This development of the fire, accompanied by the release of combustion products and occurring over several hours, is typical for cellulose-containing materials. It is most effective to detect such fires by registering combustion products in small concentrations. Smoke or gas detectors can do this.

Optical

Smoke detectors using optical detection react differently to smoke different colors. Manufacturers currently provide limited information about smoke detector response in technical specifications. Detector response information includes only the nominal response (sensitivity) values ​​for gray smoke, not black smoke. Often a range of sensitivity is given instead of an exact value.

Spot

Triggered smoke detector (red LED lit continuously)

Smoke detectors must be closed during repairs in the room to prevent dust from entering.
A point detector responds to fire factors in a compact area. The operating principle of point optical detectors is based on the scattering of infrared radiation by gray smoke. They respond well to gray smoke released during smoldering in the early stages of a fire. Reacts poorly to black smoke, which absorbs infrared radiation.
For periodic maintenance of detectors, a detachable connection is required, a so-called “socket” with four contacts, to which the smoke detector is connected. To control the disconnection of the sensor from the loop, there are two negative contacts, which close when the detector is installed in a socket.

Smoke chamber and point smoke detector electronics
All IP 212-XX point smoke optical fire detectors according to the NPB 76-98 classification use the effect of diffuse scattering of LED radiation on smoke particles. The LED is positioned in such a way as to prevent direct contact of its radiation with the photodiode. When smoke particles appear, part of the radiation is reflected from them and hits the photodiode. To protect from external light, an optocoupler - an LED and a photodiode are placed in a smoke chamber made of black plastic.
Experimental studies have shown that the time to detect a test fire when smoke detectors are located at a distance of 0.3 m from the ceiling increases by 2..5 times. And when installing a detector at a distance of 1 m from the ceiling, it is possible to predict an increase in the time of fire detection by 10..15 times.
When the first Soviet optical smoke detectors were developed, there was no specialized element base, standard LEDs and photodiodes. In the IDF-1M photoelectric smoke detector, an SG24-1.2 type incandescent lamp and an FSK-G1 type photoresistor were used as an optocoupler. This determined the low specifications detector IDF-1M and poor protection from external influences: response inertia at an optical density of 15 - 20%/m was 30 s, supply voltage 27±0.5 V, current consumption more than 50 mA, weight 0.6 kg, background illumination up to 500 lux, speed air flow up to 6 m/s.
The combined smoke and heat detector DIP-1 used an LED and a photodiode, located in a vertical plane. It was no longer continuous radiation that was used, but pulsed radiation: duration 30 μs, frequency 300 Hz. To protect against interference, synchronous detection was used, i.e. the amplifier input was open only while the LED was emitting. This provided higher protection against interference than in the IDF-1M detector and significantly improved the characteristics of the detector: inertia decreased to 5 s at an optical density of 10%/m, i.e. 2 times smaller, the weight decreased by 2 times, the permissible background illumination increased 20 times, up to 10,000 lux, the permissible air flow speed increased to 10 m/s. In the "Fire" mode, the red LED indicator turned on. To transmit an alarm signal in the DIP-1 and IDF-1M detectors, a relay was used, which determined significant current consumption: more than 40 mA in standby mode and more than 80 mA in alarm, with a supply voltage of 24 ± 2.4 V and the need to use separate signal circuits and power circuits. The maximum time between failures of DIP-1 is 1.31·104 hours.

Linear detectors

Linear - a two-component detector consisting of a receiver block and an emitter block (or one receiver-emitter and reflector block) reacts to the appearance of smoke between the receiver and emitter blocks.

The design of linear smoke fire detectors is based on the principle of weakening the electromagnetic flux between a spatially separated radiation source and a photodetector under the influence of smoke particles. A device of this type consists of two blocks, one of which contains a source of optical radiation, and the other a photodetector. Both blocks are located on the same geometric axis in the line of sight.
A special feature of all linear smoke detectors is the self-test function with transmission of the “Fault” signal to the control panel. Because of this feature, simultaneously with other detectors, it is correct to use it only in alternating loops. Inclusion linear detectors into constant-sign loops leads to the blocking of the “Fire” signal by the “Fault” signal, which contradicts the airbag 75. Only one linear detector can be included in a constant-sign loop.
One of the first Soviet linear detectors was called DOP-1 and used an SG-24-1.2 incandescent lamp as a light source. A germanium photodiode was used as a photodetector. The detector consisted of a receiving and transmitting unit, which serves to emit and receive a light beam, and a light reflector, installed perpendicular to the directed light beam at the required distance. The nominal distance between the receiving and transmitting unit and the reflector is 2.5±0.1 m.
The Soviet-made photobeam device FEUP-M consisted of an emitter and a photodetector of an infrared beam.

Aspirating detectors

The aspiration detector uses forced air extraction from the protected volume with monitoring by ultra-sensitive laser smoke detectors and provides ultra-early detection critical situation. Aspirating smoke detectors allow you to protect objects in which it is impossible to directly place a fire detector.
The fire aspiration detector is applicable in archives, museums, warehouses, server and switching rooms of electronic communication centers, control centers, “clean” industrial areas, hospital premises with high-tech diagnostic equipment, television centers and radio broadcasting stations, computer rooms and other premises with expensive equipment. That is, for the most important premises where material assets are stored or where the funds invested in equipment are huge, or where the damage from stopping production or interruption of operation is great, or the lost profit from the loss of information is great. At such facilities, it is extremely important to reliably detect and eliminate the outbreak at the earliest stage of development, at the smoldering stage - long before the appearance of an open fire, or when overheating of individual components of an electronic device occurs. At the same time, taking into account that such zones are usually equipped with a temperature and humidity control system, and air filtration is performed in them, it is possible to significantly increase the sensitivity of the fire detector, while avoiding false alarms.
Disadvantage aspiration detectors is their high cost.

Autonomous detectors

Autonomous - a fire detector that responds to a certain level of concentration of aerosol combustion products (pyrolysis) of substances and materials and, possibly, other fire factors, in the housing of which an autonomous power source and all components necessary for detecting a fire and directly notifying about it are structurally combined. The autonomous detector is also a point detector.

Ionization detectors

The principle of operation of ionization detectors is based on recording changes in the ionization current that arise as a result of exposure to combustion products. Ionization detectors are divided into radioisotope and electrical induction.

Radioisotope detectors

A radioisotope detector is a smoke fire detector that is triggered due to the impact of combustion products on the ionization current of the internal working chamber of the detector. The operating principle of a radioisotope detector is based on the ionization of the air in the chamber when it is irradiated with a radioactive substance. When oppositely charged electrodes are introduced into such a chamber, an ionization current occurs. Charged particles “stick” to heavier smoke particles, reducing their mobility - the ionization current decreases. Its decrease to a certain value is perceived by the detector as an “alarm” signal. Such a detector is effective in smoke of any nature. However, along with the advantages described above, radioisotope detectors have a significant drawback that should not be forgotten. It's about on the use of a radioactive radiation source in the design of detectors. In this regard, problems arise in observing safety measures during operation, storage and transportation, as well as disposal of detectors after the end of their service life. Effective for detecting fires accompanied by the appearance of so-called “black” types of smoke, characterized by a high level of light absorption.
In Soviet radioisotope detectors (RID-1, KI), the source of ionization was the radioactive isotope of plutonium-239. Detectors are included in the first group of potential radiation hazards.

Radioisotope smoke detector RID-1
The main element of the RID-1 radioisotope detector is two ionization chambers connected in series. The connection point is connected to the control electrode of the thyratron. One of the chambers is open, the other is closed and acts as a compensating element. Ionization of the air in both chambers is created by an isotope of plutonium. Under the influence of applied voltage, an ionization current flows in the chambers. When smoke enters an open chamber, its conductivity decreases, the voltage in both chambers is redistributed, resulting in a voltage on the control electrode of the thyratron. When the ignition voltage is reached, the thyratron begins to conduct current. An increase in current consumption triggers an alarm. Radiation sources built into the detector do not pose a danger, since the radiation is completely absorbed by the ionization chambers. Danger can only arise if the integrity of the radiation source is compromised. The detector also uses a TH11G thyratron with a small amount of radioactive nickel; the radiation is absorbed by the volume of the thyratron and its walls. Danger may arise if the thyratron breaks.
The designated service life of the radioactive sources of the detectors was:
RID-1; KI-1; DI-1 - 6 years;
RID-6; RID-6m and similar - 10 years.
The radioisotope smoke fire detector type RID-6M has been mass-produced at the Signal plant (Obninsk, Kaluga region) for more than 15 years with a total production volume of up to 100 thousand units. in year. The RID-6M detector has a limited designated service life for alpha sources of the AIP-RID type - 10 years from the date of their release. There is a technology for installing new alpha sources of the AIP-RID type in fire detectors of previous years of production, which allows the continued operation of the detectors for another 10 years, instead of their forced dismantling and burial.
High sensitivity allows the use of radioisotope detectors as an integral component of aspiration detectors. When air from the protected premises is pumped through the detector, it can provide a signal when even an insignificant amount of smoke appears - from 0.1 mg/m³. In this case, the length of the air intake tubes is practically unlimited. For example, it almost always registers the fact of ignition of a match head at the entrance of an air intake tube 100 m long.

Electroinduction detectors

The operating principle of the detector: aerosol particles are sucked from the environment into a cylindrical tube (flue) using a small-sized electric pump and enter the charging chamber. Here, under the influence of a unipolar corona discharge, the particles acquire a volumetric electric charge and, moving further along the gas duct, enter the measuring chamber, where an electrical signal is generated on its measuring electrode, proportional to the volumetric charge of the particles and, consequently, their concentration. The signal from the measuring chamber enters the pre-amplifier and then into the signal processing and comparison unit. The sensor selects the signal by speed, amplitude and duration and provides information when specified thresholds are exceeded in the form of closing a contact relay.

Electrical induction detectors are used in the fire alarm systems of the Zarya and Pirs modules of the ISS.

Flame detectors

Flame detector - a detector that responds to electromagnetic radiation from a flame or smoldering hearth.
Flame detectors are used, as a rule, to protect areas where high detection efficiency is required, since fire detection by flame detectors occurs in the initial phase of a fire, when the temperature in the room is still far from the values ​​at which thermal fire detectors are triggered. Flame detectors provide the ability to protect areas with significant heat exchange and open areas where the use of heat and smoke detectors is not possible. Flame detectors are used to monitor the presence of overheated surfaces of units during accidents, for example, to detect a fire in the car interior, under the skin of the unit, to monitor the presence of solid fragments of overheated fuel on the conveyor.

Gas detectors

Gas detector - a detector that responds to gases released during smoldering or burning of materials. Gas detectors can react to carbon monoxide (carbon dioxide or carbon monoxide), hydrocarbon compounds.

Flow-through fire detectors

Flow fire detectors are used to detect fire factors as a result of analyzing the environment spreading through ventilation ducts exhaust ventilation. Detectors should be installed in accordance with the operating instructions for these detectors and the manufacturer’s recommendations, agreed upon with authorized organizations (those with permission for the type of activity).

Manual call points

Fire manual call point is a device designed to manually activate a fire alarm signal in fire alarm and fire extinguishing systems. Manual fire call points should be installed at a height of 1.5 m from the ground or floor level. The illumination at the installation site of the manual fire call point must be at least 50 Lux.
Manual fire call points must be installed on escape routes in places accessible for their activation in the event of a fire.
In structures for above-ground storage of flammable and combustible liquids, manual call points are installed on the embankment.
By 1900, 675 manual call points were installed in London with signal output to the fire service. By 1936 the number had increased to 1,732.
In 1925, in Leningrad there were manual call points in 565 points; in 1924, they transmitted about 13% of all fire reports in the city. At the beginning of the 20th century, there were manual call points included in ring loop recording device. When turned on, the detector produced an individual number of short circuits and open circuits and thus transmitted a signal to the Morse apparatus installed on the recording device. Manual call points designs of that time consisted of a clock mechanism with a pendulum escapement, consisting of two main gears and a signal wheel with three rubbing contacts. The mechanism is actuated by a coil spring, and the detector mechanism, when actuated, repeats the signal number four times. One spring winding is enough to send six signals. The contact parts of the mechanism are coated with silver to avoid oxidation. This type of alarm was proposed in 1924 by the Head of the Fire Telegraph Workshops A.F. Ryulman, whose devices were installed for experimental purposes in 7 points of the Central part of the city with a receiving station in the part named after. Comrade Lenin. The operation of the alarm system was opened on March 6, 1924. After ten months of trial operation, which showed that there was no case of non-reception of a signal and that the alarm operation showed complete trouble-free and accurate operation, the system was recommended for widespread use.

Application in hazardous areas

When protecting explosive objects with fire alarm systems, it is necessary to use detectors with explosion protection means. For point smoke detectors, the explosion protection type “intrinsically safe electrical circuit (i)” is used. For thermal, manual, gas and flame detectors, the explosion protection types “intrinsically safe electrical circuit (i)” or “flameproof enclosure (d)” are used. A combination of protections i and d is also possible in one detector.