Automatic fire detection and extinguishing systems include:
- automatic fire alarm installations (AUPS), designed to detect a fire in its initial stage, report the location of its occurrence, and send an appropriate signal to the security post (duty post);
- automatic fire extinguishing systems (LUP), designed for automatic detection and extinguishing of fire in its initial stage with simultaneous giving of a fire alarm signal.
The current practice of designing LUP and AUPS is such that the AUPS simultaneously perform the functions of AUPS. AUP and AUPS systems protect buildings, premises in which flammable and combustible substances are stored or used, valuable equipment and raw materials, warehouses for petroleum products, varnishes, paints, book depositories, museums, premises with electronic computer equipment, etc.
Sensors that respond to fire factors (fire, smoke, gas, increased air temperature, increased rate of growth of any factor, etc.) in AUP and AUPS systems are fire detectors (FD), which are installed in the premises to be protected. In the event of a fire, they send a signal to the fire alarm control panel, control devices, and also to the control room. fire department(or to the post of duty personnel), where they inform about the situation that has arisen, indicating the room, zone where the PI was triggered.
When two or more PIs are triggered simultaneously (and they are usually placed in each room at least two), the control devices, depending on the program embedded in them: turn on the warning system and control the evacuation of people in case of fire, turn off the power supply technological equipment, turn on the smoke removal systems, close the doors of the room where the fire that has arisen is supposed to be extinguished with gas fire extinguishing agent, and at the same time delay the release of the fire extinguishing agent for the time during which people must leave the corresponding room; if necessary, turn off ventilation; in the event of a power failure, the system is switched to a backup power source, a command is given to release the fire extinguishing agent into the combustion zone, etc.
The choice of one or another type of PI depends on the predominant type of fire factors occurring (smoke, flame, etc.). For example, in accordance with "SP 5.13130.2009. Fire protection systems. Automatic fire alarm and fire extinguishing installations. Design standards and rules", approved by Order of the Ministry of Emergency Situations of Russia dated March 25, 2009 No. 175, industrial buildings containing wood, synthetic resins or fibers polymer materials, textile, rubber products, protect PI with smoke, heat, flame; premises with computer equipment, radio equipment, administrative and household and public buildings– smoke PIs, etc.
In Fig. Figure 34.1 shows one of the schemes for automatic fire detection and extinguishing. If a fire occurs in one of the premises, after two or more fire alarm sensors are triggered 2, the signal from them is sent to the control panel 1. This device sends a signal to the fire department (fire brigade post), turns on the warning lights 14 "Fire" located outside and inside the building, and the pump 6 water fire extinguishing or detonates squibs 8 launch of the gas fire extinguishing system. In addition, the automated workplace program can provide for simultaneous de-energization of process equipment through a disconnecting unit 10, turning on the warning lights 12 "Do not enter" signs installed outside the building and warning lights 13 "Go away" installed indoors.
In some cases, the program can also delay the release of gas until all doors are completely closed, when a high extinguishing concentration is required. In this case, the doors close automatically, and their position is controlled by sensors 4. If necessary, the fire warning and extinguishing system can be turned on manually by pressing one of the buttons 3. If a malfunction occurs in the automation system, a corresponding signal is sent to the fire brigade post. When the automatic mode is turned off, the sirens light up 11 "Automation disabled" located in the protected area.
All automatic fire extinguishing installations can be activated manually and automatically. In addition, they simultaneously perform the functions of an automatic fire alarm.
Automatic fire extinguishing installations are divided into design for: sprinkler, deluge, sprinkler-deluge, modular; according to the type of fire extinguishing agent used - water (including with finely sprayed water, droplets up to 100 microns), foam (including with high expansion foam), gas (using carbon dioxide, nitrogen, argon, various refrigerants, etc.) , powder (modular), aerosol, combined fire extinguishing.
In Fig. Figure 34.2 shows a diagram of a fire sprinkler installation as an example. It consists of a branched system of pipes 7 located under the ceiling and filled with water under pressure created by an automatic (auxiliary) water feeder 4. Sprinklers are screwed into the pipes every 3–4 m. 8, the outlet openings of which are closed with glass or metal fusible locks. If a fire occurs and the air temperature in the room reaches a certain value (for various sprinklers this is 57, 68, 72, 74 and up to 343 ° C (16 stages in total)), the locks are destroyed and water, spraying, enters the combustion zone. The nominal response temperature of sprinklers is usually approximately 1.5–1.14 times higher than the maximum permissible operating temperature in the room. Sprinkler automatic control systems with forced start are also used. In this case, control and alarm valve 5 is activated, the main water feeder is turned on 2 (pump) that draws water from a water source 1 (main tank or fire water supply) and a fire alarm is sounded.
Rice. 34.1.
СО1, СО2, СО3, СО1 – light alarm loops; 30 – sound warning loop; ShS1, ShS2, ShS3 – fire alarm sensor loops (PI); MANUAL – loop of manual start buttons; DS – door position control loop; AWS – automated workplace operator; 1 – fire alarm control panel; 2 – fire detectors (PI); 3 – manual fire extinguishing start buttons; 4 – door position sensors; 5 – water sprayers; 6 – water pump; 7 – fire extinguishing gas sprayers; 8 – gas start-up squibs; 9 – unit for disconnecting technological equipment from the network; 10 – sound fire alarm; 11, 12, 13, 14 – warning lights
When protecting unheated buildings where there is a danger of water freezing, sprinkler installations of a water-air system are used, filled with water only up to the control and alarm valves, after which there is compressed air in the pipelines with sprinklers. When the heads are opened, air first comes out, and then water begins to flow.
Rice. 34.2.
1 – water sources: 2 – main water feeder; 3 – auxiliary water feeder make-up pipeline; 4 – auxiliary water feeder; 5 – control and alarm valve; 6 – signaling device; 7 – distribution pipelines; 8 – sprinkler
Drenchers of deluge installations, unlike sprinklers, do not have fusible locks, and their outlets are constantly open, and the water supply network itself is closed by a group-action valve, which opens automatically from a signal from fire detectors.
Sprinkler systems irrigate only that part of the room in which the sprinklers are opened, and deluge systems irrigate the entire design part at once. These installations are used not only to extinguish fire, but also as water curtains to protect building structures, equipment, and raw materials from fire. The estimated irrigation area with one sprinkler or deluge type water sprinkler ranges from 6 to 36 m2, depending on their design and the diameter of the bore.
Sprinkler and deluge installations can also use a foam-forming solution as a fire extinguishing agent. Mixed sprinkler and deluge systems are also used.
Power supply to fire alarm systems and fire extinguishing installations must be carried out according to reliability category I (according to the PUE). That is, in the event of a power outage, the AUP and AUPS systems must be automatically transferred to backup power. The delay time is no more than the automatic switching time.
SP 5.13130.2009 defines the list of buildings and structures, individual equipment that are subject to protection by AUP and AUPS (Table 34.7). For example, buildings for public and administrative purposes, premises for placing personal computers are protected by AUPS regardless of their area, industrial premises with the presence of alkali metals when placed in ground floor with an area of 300 m2 or more - AUP, less than 300 m2 - AUPS, painting booths using flammable liquids and flammable liquids - AUP, regardless of the area.
The type of fire extinguishing and alarm installation or their combination, the extinguishing method, and the type of fire protection equipment are determined by the design organization specifically for each facility individually. This organization must have the appropriate license to design, install and maintain such systems. The register of such organizations is maintained by the Russian Ministry of Emergency Situations. After the fire automatics installations are put into operation, the head of the organization, by his order (instruction), appoints persons responsible for their operation (usually these are employees of the departments of the chief mechanic, chief power engineer, instrumentation and automation service).
Daily round-the-clock monitoring of the operation of the automatic fire control system and automatic fire control system is carried out by operational duty personnel (shift service, fire station), who must know the procedure for calling the fire department, the name and location of the premises protected by fire automatic fire control systems (aumatic fire control system, automatic fire control system), the procedure for maintaining operational documentation and determining the operability of the specified systems
The performance of automatic fire alarm systems is checked by exposing reusable detectors to exemplary (standardized) sources of heat, smoke and radiation (depending on the type of detector).
Table 34.7
List of buildings, structures, premises and equipment subject to protection by AUP and AUPS
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PREMISES |
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Object of protection |
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Standard indicator |
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Warehouse premises |
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300 m2 or more |
Less than 300 m2 |
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6. Categories A and B for explosion fire danger with the handling of flammable and combustible liquids, liquefied flammable gases, combustible dusts and fibers (except for those specified in clause 11 and premises located in buildings and structures for grain processing and storage) |
300 m2 or more |
Less than 300 m2 |
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Industrial premises |
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8.1. In the basement and basement |
Regardless of area |
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8.2. In overhead (except for those specified in clauses 11–18) |
300 m2 or more |
Less than 300 m2 |
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9.1. In the basement and basement: |
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9.1.1. Having no direct exits to the outside |
300 m2 or more |
Less than 300 m2 |
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9.1.2. If there are exits directly outside |
700 m2 or more |
Less than 700 m2 |
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9.2. Overground |
1000 m2 or more |
Less than 1000 m2 |
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11. Preparation areas: suspensions of aluminum powder, rubber adhesives; based on flammable liquids and gases: varnishes, paints, adhesives, mastics, impregnating compositions; rooms for painting, polymerization of synthetic rubber, compressor rooms with gas turbine engines, fire oil heaters. Rooms with generators driven by liquid fuel engines |
Regardless of area |
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20. Premises of railway transport: electrical machine rooms, equipment rooms, repair rooms, bogie and wheel rooms, dismantling and assembling of wagons, repair and assembly rooms, electric wagon rooms, wagon preparation rooms, diesel rooms, Maintenance rolling stock, container depots, production of switch products, hot processing tanks, thermal treatment chambers for oil bitumen cars, sleepers, impregnation, cylinders, impregnated wood sludge |
Regardless of area |
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Public premises |
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26. Premises for storing and issuing unique publications, reports, manuscripts and other documentation of special value (including archives of operating departments) |
Regardless of area |
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28. Exhibition halls |
1000 m2 or more |
Less than 1000 m2 |
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35. Accommodation premises: |
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35.1. Electronic computers operating in control systems for complex technological processes, the violation of which affects the safety of people |
Regardless of area |
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38. Premises for other administrative and public purposes, including built-in and attached |
Regardless of area |
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EQUIPMENT |
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Object of protection |
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Standard indicator |
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1. Painting booths using flammable liquids and gas liquids |
Regardless of type |
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2. Drying chambers |
Regardless of type |
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3. Cyclones (hoppers) for collecting flammable waste |
Regardless of type |
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4. Oil power transformers and reactors: |
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Regardless of power |
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200 MBA and above |
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6. Racks with a height of more than 5.5 m for storing flammable materials and non-combustible materials in flammable packaging |
Regardless of area |
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7. Oil tanks for hardening |
3 m3 or more |
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For installations with single-action detectors, testing is carried out by introducing an artificial damage (break) performed in the most remote distribution or branch box that has screw-in mounting terminals, or by disconnecting the most remote detector from the loop line.
The functionality of automatic fire extinguishing installations is checked by visual inspection control and measuring instruments and assessing the serviceability of individual components or checking the performance of the installation as a whole, which is carried out according to a specially developed program agreed with the State Fire Supervision Authority. Inspections are carried out at least once a quarter. Their results are documented in an appropriate act.
Effective fire extinguishing agents are inert gases (CO2 and N) and vapors. Mixing with flammable vapors and gases, they reduce the oxygen concentration and help stop the combustion of most flammable substances.
To solid (powder) fire extinguishing agents include chlorides of alkali and alkaline earth metals (fluxes), bicarbonate and carbon dioxide soda, solid carbon dioxide, sand, dry earth, etc. The effect of these substances is that their mass isolates the combustion zone from the combustible substance.
Fire extinguishing agents Intermittent powder (OP) fire extinguishers are designed to extinguish fires of gasoline, diesel fuel, varnishes, paints and other flammable liquids, as well as electrical installations under voltage up to 1000 V.
Carbon dioxide (CO) fire extinguishers are used to extinguish fires various substances and materials at ambient temperatures from -25 to +50°C, as well as live electrical equipment.
Air-foam fire extinguishers (AFP) are used to extinguish fires of liquid and solids and materials, with the exception of alkali and alkaline earth metals and their alloys, as well as for extinguishing fires of electrical equipment under voltage. Used at temperatures from +5 to +50°C.
Stationary means of extinguishing fires include sprinklers and deluge systems.
Sprinkler installations are branched pipes with water placed under the ceiling of the building at a temperature of at least 4°C. The sensors of these systems are sprinklers, the fusible lock of which opens when the temperature rises to 72°C, is activated 2-3 minutes after the temperature rises and sprays water.
Deluge installations are used in rooms with a high fire hazard.
All pipelines of these installations are constantly filled with water up to the deluge fittings located on the distribution pipelines. The installations are activated both automatically when fire detectors are triggered, and manually. They are used for simultaneous irrigation of the estimated area of individual parts of the building, creating water curtains in the openings of doors and windows, and irrigating elements of technological equipment.
In addition, to extinguish fires, mobile and stationary installations of water-foam, gas and powder compositions, which have different design and operation schemes, are used. Fire-fighting water supply systems of high and low pressure also play an important role. In buildings and workshops, water is supplied to the fire source through fire hydrants and fire hydrants connected to the water supply network. Each tap must have a fire hose 10, 15 or 20 m long and a fire nozzle. The pressure must ensure the supply of a compact jet to a height of at least 10 m. External hydrants are installed along roads and driveways at a distance of 100-150 m from each other, no closer than 5 m from the wall and no further than 2 m from the road.
Fire alarm and communications
Fire communications and alarms have great importance to implement measures to prevent fires, facilitate their timely detection and call fire departments to the place of fire, and also provide management and operational management of work in case of fire.
When using a fire alarm, notification of a fire occurs within a few seconds. The alarm system consists of a receiving station and detectors connected to it. Detectors are installed in prominent places in industrial premises, as well as outside them, so that a fire that occurs cannot interfere with the use of the detector. Depending on the connection method, electric fire alarms are divided into beam and loop. With a beam system, each detector independently communicates with the station using two wires - direct and return; the receiving station simultaneously receives signals from all detectors. The loop station provides a serial connection, and up to 50 detectors can be connected to one loop. A fire signal is given by pressing the detector button.
Automatic fire alarms require the presence of thermal sensors, which turn on detectors when the temperature rises to a certain limit. An automatic fire detector can be a metal plate made of alloys with different expansion coefficients. If the temperature rises, the plate bends and connects electrical contacts that activate sound and light signals.
Combustion sites can be detected by recording other parameters: radiation and flickering of flame, smoke, heat, ionization, pressure.
In rooms and small-capacity devices, it is advisable to use a pressure switch; for large volumes (more than 3 m3) - flame sensors, since the pressure switch in this case may respond late to combustion with subsequent explosion and fire.
The operating principle of an automatic smoke detector is based on the effect of combustion products on the ionization current in the ionization chamber when smoke enters it. A change in the ionization current activates an electronic relay, which turns on a sound and light alarm system.
Heat detectors are temperature-sensitive devices that respond to an increase in room temperature: the resistance of the semiconductor thermistor decreases, the current in the circuit increases, the voltage rises, as a result the thyratron is triggered. The detectors operate at preset temperatures (60, 80 and 100°C).
The light detector reacts to the radiation of an open flame. The action of the detector is based on the property of burning bodies to emit infrared and ultraviolet rays.
Combined detectors act as heat and smoke detectors.
The basis is a smoke detector with the connection of the electrical circuit elements required for its operation.
Evacuation from a fire zone Organization of evacuation from a fire zone
The process of evacuating people from a building is conventionally divided into three stages:
movement from the most remote place of permanent residence to an emergency exit;
movement from emergency exits from the premises to exits outside;
movement from the exits of the fire building and dispersion throughout the territory of the enterprise.
When designing buildings and structures, provisions are made for the safe evacuation of people in the event of a fire. Evacuation routes are passages, corridors, and stairs leading to an emergency exit that ensures the safe movement of people during the required evacuation time.
The following exits are considered evacuation exits:
from the premises of the first floor directly to the outside or through the lobby, corridor, staircase;
from the premises of any floor, except the first, into a corridor leading to a staircase, or to a staircase that has access directly outside or through a vestibule separated from adjacent corridors by partitions with doors;
from the room to an adjacent room on the same floor, provided with the exits indicated above.
All escape routes (passages, corridors, stairs, etc.) must have, if possible, even vertical enclosing structures without protrusions and be illuminated.
Fire alarms are used to provide timely notification of the time and place of a fire and take measures to eliminate it.
Fire alarm systems consist of fire detectors (sensors), communication lines, a receiving station, from where a fire signal can be transmitted to fire brigade premises, etc.
Electrical fire alarms, depending on the connection scheme of the detectors with the receiving station, are divided into beam and ring or loop.
With a beam scheme, separate wiring, called a beam, is supplied from the receiving station to each detector.
With a ring (daisy chain) scheme, all detectors are connected in series into one common wire, both ends of which are connected to the receiving station. At large facilities, several such wires or loops can be included in the receiving station, and up to 50 detectors can be included in one loop.
Fire detectors can be manual (buttons installed in corridors or staircases) and automatic, which convert non-electrical physical quantities (emission of thermal and light energy, movement of smoke particles, etc.) into electrical signals a certain shape, transmitted by wire to the receiving station.
Manual call point type PKIL-9 is activated by pressing a button. These detectors are located in prominent places (on staircases, in corridors) and are painted red. The person who notices the fire must break the protective glass and press the button. At the same time, the electrical circuit is closed and a sound signal is generated at the receiving station and the signal light lights up.
Detectors are divided into parametric ones, in which non-electrical quantities are converted into electrical ones, and generator ones, in which a change in a non-electrical quantity causes the appearance of its own electromotive force (EMF).
The most widespread time automatic detectors. Based on the principle of action on thermal, smoke, combined and light. Maximum action heat detectors ATIM-1 ATIM-3, depending on the setting, are triggered when the temperature rises to 60, 80 and 100 ° C. The detectors are triggered due to the formation of a bimetallic plate when heated. Each of these detectors can monitor an area of up to 15 m2. semiconductor thermal detectors PTIM-1, PTIM-2, the sensitive elements are thermal resistances, when heated, the current in the circuit changes. Detectors are triggered when the temperature rises to 40-60° C and protect an area of up to 30 m 2. Heat detectors DPS-038, DPS-1AG of differential action are triggered by a rapid increase in temperature (by 30 ° C in 7 s) and are used in explosive areas; the controlled area is 30 m2. Detectors of this type use thermocouples, in which thermo-EMF occurs when heated. DI-1 smoke detectors use an ionization chamber as a sensitive element. Under the influence of the radioactive isotope plutonium-239, an ionization current flows in the chamber. When smoke enters the chamber, the absorption of a-rays increases and the ionization current decreases. The combined detector KI-1 is a combination of smoke and heat detectors. A thermal resistance is additionally connected to the ionization chamber. Such detectors react both to the appearance of smoke and to an increase in temperature. The response temperature of such detectors is 60-80° C, the estimated service area is 50-100 m 2.
Detectors DI-1 and KI-1 are not installed in damp, heavily dusty rooms, as well as rooms containing vapors of acids, alkalis or the temperature of these rooms above +80 ° C, since these conditions can cause false alarms of the detectors.
Light detectors SI-1, AIP-2 react to the ultraviolet part of the flame spectrum. Their sensitive elements are photon counters. Detectors are installed in rooms with illumination of no more than 50 lux; the area they control is 50 m2.
Ticket 55
TO primary means include fire extinguishers, hydraulic pumps (piston pumps), buckets, barrels of water, boxes of sand, asbestos sheets, felt mats, felt mats, etc.
Fire extinguishers are chemical foam (OHP-10, OP-5, OKHPV-1O, etc.), air-foam (OVP-5, OVP-10), carbon dioxide (OU-2, OU-5, OU-8), carbon dioxide -bromoethyl (OUB-3, OUB-7), powder (OPS-6, OPS-10).
Chemical foam fire extinguishers of the type ОХП-10, ОХВП-10 (Fig. 3) consist of a steel cylinder containing an alkaline solution and a polyethylene glass with an acid solution. The fire extinguisher is activated by turning the handle up until it stops, which opens the glass with the acid solution. The fire extinguisher is turned upside down, the solutions are mixed and begin to interact. The chemical reaction is accompanied by the release of carbon dioxide, which creates overpressure. Under the influence of pressure, the resulting foam is injected into the combustion zone.
Chemical foam fire extinguishers of the OP-3 or OP-5 type are activated by the impact of the firing pin on a solid base. In this case, the glass flasks are broken, sulfuric acid is poured into the cylinder and enters chemical reaction with alkali. The resulting carbon dioxide as a result of the reaction causes intense foaming of the liquid and creates a pressure of about 9-12 atmospheres in the cylinder, due to which the liquid in the form of a jet of foam is ejected from the cylinder through the nozzle.
The duration of action of chemical foam fire extinguishers is about 60-65 s, and the jet range is up to 8 m.
Air-foam fire extinguishers (OVP-5, ORP-10) are charged at 5% aqueous solution foam concentrate PO-1. When the fire extinguisher is activated, the compressed carbon dioxide releases the foam solution through the foam nozzle, forming a stream of high-expansion foam.
The duration of action of air-foam fire extinguishers is up to 20 s, the range of the foam jet is about 4-4.5 m.
Carbon dioxide fire extinguishers OU-2 (Fig. 4) consist of a cylinder with carbon dioxide, a shut-off valve, a siphon tube, a flexible metal hose, a diffuser (snow-forming socket), a handle and a fuse. The shut-off valve has a safety device in the form of a membrane, which is activated when the pressure in the cylinder increases above the permissible limit. The gas in the cylinder is under a pressure of about 70 atmospheres (6-7 MPa) in a liquid state. Fire extinguishers are activated by turning the shut-off valve counterclockwise. When the valve is opened, carbon dioxide comes out in the form of snow. As the ambient temperature increases, the pressure in the cylinder can reach 180-210 atmospheres (180 - 210-105 Pa).
The operating time of carbon dioxide fire extinguishers is up to 60 s, range is up to 2 m.
Fig.3 Chemical foam fire extinguisher OHP-10
Fig.4. Carbon dioxide fire extinguisher OU-2
The carbon dioxide-bromoethyl fire extinguisher (OUB-7) consists of a cylinder filled with ethyl bromide, carbon dioxide, and compressed air to eject the extinguishing agent through a nozzle. The operating time of OUB-7 is about 35-40 s, the jet length is 5-6 m. OUB-7 is activated by pressing the starting handle. The fire extinguisher can be stopped by releasing the handle.
Powder fire extinguishers (OPS-6, OPS-10) consist of a body with a capacity of 6 or 10 l, a lid with a safety valve and a siphon tube, a gas cartridge with a capacity of 0.7 l, connected to the body with a pipe, flexible hose with extension and socket.
When the fire extinguisher is activated, the powder is pushed out of its body through a siphon tube by compressed gas, which presses on the mass of powder from above, passes through its thickness and, together with the powder, comes out.
The operating time of powder fire extinguishers is 30 s, the operating pressure is 8∙10 5 Pa, and the initial pressure in the gas cartridge is 15∙10 6 Pa.
All fire extinguishers are subject to periodic monitoring and recharging.
Stationary fire protection installations They are fixedly mounted devices, pipelines and equipment that are intended to supply fire extinguishing agents to the combustion zone.
Mobile installations in the form of pumps for supplying water and other fire extinguishing agents to the fire site are mounted on fire trucks. Fire engines include fire trucks, tank trucks, pump trucks, motor pumps, fire trains, motor ships, etc.
FIRST AID IN CASE OF ACCIDENTS
At communications enterprises, as a result of violation of safety rules or malfunction of equipment, accidents can result that lead to injury to the human body or disruption of its normal functioning.
Timely and qualified pre-hospital medical care for a victim can not only preserve his health, but also save his life itself. The absence of breathing and blood circulation for 4-6 minutes causes irreversible changes in the body, and the help of medical workers who arrived some time after the accident may be useless. Therefore, every communications technician must be able to quickly and correctly provide first aid help.
First aid consists of stopping the action of dangerous factors, temporarily stopping bleeding, applying aseptic (sterile) and splint dressings, fighting pain and carrying out revitalizing measures to restore cardiac breathing and, finally, delivering the victim to a medical facility.
FIRST AID FOR ELECTRIC SHOCK VICTIMS
First aid to a victim of electric current is divided into several stages:
freeing the victim from the effects of electric current;
determining the condition of the victim;
performing artificial respiration and chest compressions.
To free the victim from the effects of electric current, disconnect the electrical installation from the supply voltage using shutdown devices: buttons, switches, switches; if this cannot be done, then it is necessary to unscrew the plug fuses or cut the wires with sharp objects that have insulating handles. If the wire is lying on the victim, then you should use any non-conductive object (dry stick, board) to remove the wire from the victim and throw it to the side.
If a person comes under the influence of electric current while on a support, then to stop the current, a pre-grounded wire can be thrown onto the live wires, which will trigger the protection and cut off the voltage. In this case, it is necessary to take measures to prevent the victim from falling from the support.
In many cases, you can pull the victim by the clothes without touching the bare parts of his body with your hands, so as not to get exposed to electric current. If possible, you should first put on dielectric gloves and galoshes
Having freed the victim from the effects of electric current, his condition should be quickly assessed. If the victim is conscious, but has been under the influence of current for a long time, then he must be provided with complete rest and observation for 2-3 hours, since the disturbances caused electric shock, can occur without visible symptoms, but after some time pathological consequences can develop, including clinical death. In this regard, calling a doctor for all electric shock injuries is mandatory. If the victim is unconscious, but breathing and cardiac activity are preserved (the pulse is palpable), then he should be placed comfortably and evenly on his back, loosen tight clothing, create a flow fresh air. Then the victim should be given ammonia to sniff from time to time, sprinkled with water and constantly rub and warm the body. If vomiting occurs, the victim's head should be turned to one side to the left.
If the victim has no signs of life (no pulse can be felt, no heartbeat, convulsive irregular breathing), then resuscitation (resuscitation) should be started immediately. First of all, it is necessary to normalize breathing as the main source of oxygen supply to all organs and blood circulation, which delivers oxygen to all tissues of the human body. Restore the victim's breathing using artificial respiration. Artificial respiration can be performed different ways: manual (methods of Sylvester, Schaefer, etc.); “mouth to mouth” or “mouth to nose”; hardware-manual.
Manual artificial respiration methods are ineffective because they do not provide sufficient air supply to the victim’s lungs. In recent years, methods of artificial respiration “mouth to mouth” and mouth to nose have become widespread.” These methods involve forcibly filling the victim's lungs with air from the lungs of the person providing assistance by insufflation. As you know, the air around us contains about 21% oxygen, and the air exhaled from the lungs contains 16%.
This amount of oxygen is sufficient to maintain some degree of gas exchange in the lungs. With one tire, 1-1.5 liters of air enter the victim’s lungs, which is significantly more than with manual methods. Insufflation should be carried out at the frequency of your own breathing, but not less than 10-12 times per minute. If the victim takes an independent breath, then the insufflation should be timed to coincide with the time of the victim’s own inhalation. You should not stop artificial respiration at the first spontaneous breath; it must be continued for some time, since irregular and weak spontaneous breaths cannot ensure sufficient gas exchange in the lungs.
Hardware-manual methods of artificial respiration are implemented using bellows devices that provide sufficient gas exchange in the victim’s lungs. The most convenient to use are portable devices RPD 1 and RPA-2.
To restore cardiac activity, indirect or closed heart massage is performed. The one who provides assistance stands on the left side of the victim and places the heel of his palm on the lower third of the sternum, and places the hand of the other hand on top of the first. Using body weight, he presses on the sternum with such force that it moves towards the spine by 3-6 cm. 60-70 pressures should be applied per minute. Signs of recovery of the heart are the appearance of its own pulse, pinkening of the skin, constriction of the pupils.
Often indirect cardiac massage is combined with artificial respiration. If two people provide assistance, then one performs cardiac massage, and the other performs artificial respiration. After every three to four pressures, one blowing follows.
If one person is involved in providing assistance, then the cyclicity of artificial respiration and chest compressions changes: 3-4 injections, then 15 compressions, 2 injections, 15 compressions, etc.
FIRST AID FOR WOUNDS. STOP BLEEDING
A wound is a consequence of mechanical damage to tissues and the human body. Various microbes can be introduced into the wound, so you should definitely consult a doctor to treat the wound and administer anti-tetanus serum. You should not wash the wound with water, remove soil, cover the wound with powders or other medicinal agents, or remove blood clots from the wound; Only the medical worker. It is necessary to open the individual package, apply sterile material to the wound and then bandage it. To stop capillary or venous bleeding, lift the limb upward and apply a pressure bandage to the wound. To stop arterial bleeding, sharply bend the limb at the joint, press the artery with a finger, and apply a tourniquet or twist. A rubber cord is used as a tourniquet, and belts, towels, scarves, etc. are used as a twist. A tourniquet or twist is applied above the wound at a distance of 5-7 cm from its edge. A note should be placed under the tourniquet or twist indicating the time of application. In the summer, apply a tourniquet for 2 hours, in cold weather - for 1 hour. Then loosen the tourniquet for 2-3 minutes so that blood can flow to the injured limb, otherwise tissue necrosis may occur. If bleeding resumes after loosening the tourniquet, the tourniquet is tightened again.
FIRST AID FOR FRACTURES, BRUISES AND STRAINS
For fractures and dislocations, first aid consists of ensuring complete immobility and immobilization of the damaged part of the body. Immobilization is necessary to reduce pain and prevent further injury to the soft tissues of the body from bone fragments.
Signs of fractures are pain, an unnatural shape of the damaged part of the body, and mobility of the bone in the area of the fracture. To ensure immobility, special splints or improvised means are used - ski poles, boards, umbrellas, etc. Splints must be chosen of such length as to immobilize two joints - above and below the fracture. If the fracture is open, you should first bandage the wound with an aseptic bandage and then apply a splint.
For skull fractures, the victim is laid on his back, his head is turned to one side, and cold is applied to the head (ice, snow or cold water in plastic bags).
In case of spinal fractures, a wide board or shield is carefully placed under the victim, or the victim is turned on his stomach face down. When turning over, care must be taken not to bend the spine, otherwise the spinal cord may be injured.
In case of a fracture or dislocation of the collarbone, you should place a ball of cotton wool or soft fabric. Bandage the arm, bent at a right angle, to the body or tie it with a scarf to the neck. Apply cold to the damaged area.
For fractures and dislocations of the arm bones, splints should be applied and the arm should be suspended at a right angle from a braid or jacket field. Apply cold to the damaged area. Trying to fix a dislocation on your own can lead to more severe injury; Only a doctor or paramedic can professionally correct a dislocation.
For rib fractures, the chest should be tightly bandaged during exhalation.
For any kind of bruises and sprains, the damaged area should be tightly bandaged and a cold object should be applied to it.
FIRST AID FOR BURNS AND FROSTBITE
A burn is tissue damage that occurs under the influence of low temperature, chemicals, electric current, sunlight and x-rays. There are four degrees of burns: 1st - redness of the skin, 2nd formation of blisters, 3rd necrosis of the entire thickness of the skin and 4th - charring of tissues. The severity of the damage depends on the degree and area of the burn. If more than 20% of the body surface is damaged, the burn causes changes in the central nervous and cardiovascular systems. The victim may go into shock. When providing first aid, apply a sterile bandage, ice pack or cold water to the damaged area and send the victim to the hospital.
You should not open the blisters, tear off the stuck clothing, sealing wax, rosin, as this can lead to infection and prolonged wound healing. You should also not lubricate the burn wound with ointments, oils, or powders. If the eyes are burned by a voltaic arc, they should be washed with a 2-3% solution boric acid and send the victim to the hospital.
In case of chemical burns (acids or alkalis), the damaged area must be washed for 10-15 minutes with water (preferably running water), and then with a neutralizing solution - for burns with acids, 5% potassium permanganate or 10% drinking solution - soda (one teaspoon per glass of water), for burns with alkalis with a 5% solution of acetic or boric acid. To wash the eyes, use weaker, 2-3% solutions.
Frostbite is damage to body tissues as a result of exposure to low temperatures. Most often, the lower extremities are affected by frostbite. First aid for frostbite involves warming the entire body and rubbing the frostbitten parts with a soft, dry cloth (gloves, scarf, etc.). Snow should not be used for rubbing, since the ice particles it contains can damage the skin, which promotes infection and prolongs the healing process. After the damaged area turns red, it is necessary to apply a bandage with some kind of fat (oil, lard, etc.) and keep the damaged limb in an elevated position. The victim must be sent to a medical facility.
FIRST AID FOR FAINTING, HEAT AND SUN STROKE, POISONING. CARRYING AND TRANSPORTING THE VICTIMS
Fainting is a sudden, short-term loss of consciousness. Fainting is preceded by a faint state (nausea, dizziness, darkening of the eyes). In case of fainting, the victim should be laid on his back with his head slightly bowed, loosen tight clothing, create an influx of fresh air, give him a sniff of ammonia, and apply a heating pad to his legs. the victim will wake up, you can give him hot coffee. 100
Heatstroke is a sharp sudden disorder of the central nervous system. nervous system, arising as a result of re-singing of the whole organism. Heat stroke occurs when exposed to high temperatures for a long time environment, staying in premises with high humidity and insufficient air movement. In this case, the heat transfer mechanism is disrupted, which leads to serious disorders in the body. Close to heatstroke is sunstroke, which occurs as a result of overheating of the head by direct sunlight.
With thermal and sunstroke the victim must be quickly transferred to a cool, shaded place, placed on his back with his head slightly elevated, ensure rest, create an influx of fresh air and put ice or cold lotions on his head.
When carrying and transporting a victim, you should be very careful not to cause him pain, additional injury, and thereby not cause a worsening of his condition. It is best to carry it on a stretcher (special or made from improvised material). When laying on a stretcher, you should lift the victim and place the stretcher under him, rather than carrying the victim to the stretcher. For fractures of the spine or lower jaw, the victim is placed on his stomach if the stretcher is soft.
On level ground the victim is carried feet first, and when climbing uphill or up stairs - head first. Porters should walk out of step, with their knees slightly bent, so that the stretcher sways as little as possible. When carried over long distances, straps are tied to the handles of the stretcher and thrown over the shoulder. When transporting by transport (by car, cart), maximum comfort should be created and shaking should be avoided; It is better to lay the victim directly on a stretcher, spreading something soft (hay, grass, etc.).
TB requirements for telephone station equipment
Currently, coordinate stations AMTS-3, ARM-2 and quasi-electronic station “Metakonta YUS”, transmission systems K-60P, K-1920P, K-1920U etc. are used to organize long-distance telephone communication. workshops have significantly reduced the noise level and thereby improved the working conditions of communication workers. All work at telephone and telegraph stations is carried out in accordance with the Safety Rules for the equipment and maintenance of telephone and telegraph stations. Of all the MTS workshops, the linear equipment and ale workshops pose the greatest danger from the point of view of electric shock.
When working in a linear hardware shop (LAS), you should be especially careful, since some racks are powered from the network alternating current voltage 220 V, and others are supplied with remote power supply voltage (DP), which can reach large values. For example, for the K-1920P system the DC voltage is 2 kV.
The LAC is powered using a two-beam circuit from two independent sources. Voltage direct current supplied to the equipment through non-insulated buses located at a height. Touching the tires is only possible when working on a stepladder. To eliminate such touching, the Metakont YUS system uses a cable instead of tires.
To check the passage of signals towards the line and switching shops in the LAC for K-1920P equipment, test racks IS-1UV and IS-2UV are installed. For ease of maintenance, the IS-2UV rack is equipped with a table, and measuring instruments and control handles are placed on a vertical panel in the optimal working area.
In LAC, racks are installed in rows, between which there is a passage of sufficient width for safe and convenient maintenance of the equipment. Red arrows are placed on cabinets and racks, the equipment of which is supplied with DC voltage, warning personnel about the danger of electric shock. To prevent touching live parts that are energized by the DP, in some systems, for example, K-60P, blocking of the DP circuits is used.
To protect the LAC equipment from possible overloads, the racks are equipped with automatic or fusible fuses. When fuses blow or other malfunctions occur, optical and audio alarms are triggered; signal lamps are located on cabinets, on an ordinary banner and on a station-wide display. For example, when the linear amplifiers of the K-1920U system exit three lamps, the “US” lamp on the protection and alarm board (CCD), the “Tract” signal on the ordinary banner, the red common rack lamp light up, and the bell rings. To prevent electric shock in front of introductory, introductory and test racks, DP racks, auxiliary end racks (SVT), racks automatic regulators voltage (SARN), dielectric mats must be placed, and the rack housings must be grounded.
When carrying out preventive and repair work On the current-carrying parts of the LAC equipment, the voltage is removed from them, i.e., work is carried out with complete removal of voltage. If it is impossible to remove the voltage on equipment up to 500 V, then, as an exception, it is allowed to carry out work without removing the voltage, but with the obligatory use of dielectric gloves, dielectric mats and tools with insulating handles. This is especially true for electrical measurements and identifying locations of circuit damage. air lines exposed to the dangerous influence of power lines and electrified railways. When connecting measuring instruments to live cable conductors, it is necessary to wear dielectric gloves in the presence of a second person. It is prohibited to take measurements during a thunderstorm.
The cable cores are soldered onto the boxes. The pins of the cable boxes, through which the DC voltage is supplied, are enclosed in insulating tubes, and the box sockets are closed with protective covers. A red arrow is applied to the cover. The lines on the boxes are switched using double-pair plugs with a plastic body or special arms with an insulating coating on the part that is handled by hand. When rearranging arms or plugs, it is necessary to pay attention to the condition of the insulation.
When working on a line or equipment that involves touching live parts that are energized by the DP, it must be turned off. The head of the amplification point is responsible for the timely switching off and switching on of the DP. All orders, as well as the time of switching off and switching on the DP are recorded in the work log. The DC voltage is turned off by switches on which posters are posted: “Do not turn on! People are working." The number of posters on one switch must correspond to the number of crews working on the line. To prevent erroneous switching on of the DC, additional visible ones are made in the circuit by removing fuses or rearranging the high-voltage arms. Removing high-voltage arms is only permitted while wearing dielectric gloves while standing on a dielectric mat.
After removing the DC voltage, the cable is discharged to the ground using a spark gap - a metal rod connected to a grounding device and mounted on an insulating rod.
Turning on the DP voltage and removing the warning poster is allowed only after receiving messages from all crews working on the line about the possibility of turning on the voltage.
In automatic and semi-automatic communication shops, as well as in switch shops, the equipment is placed on racks, the design of which excludes the possibility of touching live parts. The racks are equipped with fuses and alarm devices.
Preventative work is carried out, as a rule, with complete stress relief and only in exceptional cases without stress relief using protective equipment. It is forbidden to check the absence of voltage by hand; it is necessary to use voltage meters or indicators. When replacing indicator lights or fuses on switches and cabinets, do not touch free hand grounded metal structures, otherwise electric shock may occur.
When performing work on switching and testing equipment using cord pairs, it is necessary to grasp only the insulated part of the plug and ensure that the cord is not damaged. When inspecting or repairing equipment, if the illumination of the workplace is insufficient, you can use a portable lamp. It must be designed for a voltage no higher than 42 V, since workshops are classified as high-risk areas. To connect lamps to the cabinet, a special socket is installed at the end of each row.
Telephone operators use microtelephone devices (headsets) when working. To reduce the impact of acoustic discharges on telephone operators (for example, when hit by a lightning line), acoustic discharge limiters (fritters) are switched on parallel to the telephone headset. To reduce pressure on the head, phones are equipped with soft headphones.
Quick detection and signaling of a fire, timely calling fire departments and notifying people in the area about a fire possible danger, allows you to quickly localize fires, carry out evacuation and take the necessary measures to extinguish the fire. Therefore, enterprises must be provided with communication means and fire alarm and warning systems.
To report a fire at any time of the day, you can use special and general purpose, radio communication, centralized installations fire alarm. Fire warning systems must ensure, in accordance with developed evacuation plans, the transmission of warning signals simultaneously throughout the entire house (structure), and, if necessary, sequentially or selectively to its individual parts (section floors). The number of detectors (speakers), their placement and power must ensure the necessary audibility in all places where people are. Internal radio broadcast networks can be used to transmit warning texts and control evacuation. The room from which the fire alarm system is controlled should be located on the lower floors of buildings, at the entrance to staircases, in places with 24-hour duty personnel.
The fastest and most reliable means of detecting signs of fire and signaling a fire is considered to be an automatic fire alarm installation (AUPS), which must operate around the clock. Depending on the connection diagram, a distinction is made between beam (radial) and ring AUPS (Fig. 4.37). The operating principle of the AUPS is as follows: when at least one of the detectors is triggered, a “Fire” signal is sent to the control panel.
Rice. 4.37. Schemes of radial (a) and ring (b) connections in AUPS: 1 - detectors; 2 - receiving and control device; 3 - power supply from the mains; 4 - emergency power supply; 5 - power switching system; 6 - connecting wires
Addressable fire detectors are activated only in the network radial type; in this case, the location of the fire is determined by the number of the plume (beam) that issued the “Fire” signal. Addressable fire detectors include both radial and ring type networks; The fire address is determined by the installation location of the detector that issued the “Fire” signal by its address number.
At fire and explosion hazardous facilities, in addition to fire alarms, AUPS can issue commands to the control circuits of automatic fire extinguishing, smoke removal, fire warning, ventilation, process and electrical equipment of the facility.
Based on the method of transmitting messages (notifications) about a fire, fire alarm systems are divided into autonomous and centralized. In stand-alone AUPS installations, the “Fire” alarm signal from the detector is sent to a control panel, which is installed in a room with 24-hour duty personnel. The next person calls the fire department reception post and transmits information. In centralized fire alarm systems, fire warnings from control panels are transmitted through a communication channel (for example, a pager communication channel or a radio channel) to a centralized fire monitoring console.
Manual call point
One of the main elements of AUPS is fire detectors - devices that generate a fire signal. There are manual and automatic fire detectors. A manual fire call point (Fig. 4.38, a) is turned on by the person who detects the fire by pressing the start button. They can be used to signal a fire from the premises of the enterprise. Inside the building, manual call points are installed as additional technical means automatic AUPS.
Rice. 4.38. Fire detectors: a - manual IR-P; b - thermal IP-105; c - smoke IPD-1; g - flame detector IP
Automatic fire detectors
They are triggered without human intervention, from exposure to factors accompanying a fire: increased temperature, appearance of smoke or flame.
Thermal fire detectors
According to the operating principle, they are divided into: maximum (IT-B, IT2-B, IP-105, SPTM-70), which are triggered when Pirogovo reaches the air temperature at the place of their installation; differential (Hb 871-20), which respond to the rate of increase of the temperature gradient; maximum differential (IT1-MGB, V-601), which are triggered by one or another prevailing temperature change.
The principles of operation and design of thermal fire detectors can be different: using low-melting materials that are destroyed as a result of exposure to elevated temperatures; using thermoelectromotive force; using dependency electrical resistance elements from temperature; using temperature deformations of materials; using the dependence of magnetic induction on temperature, etc.
The fire detector IP-105 (see Fig. 4.38, b) is a magnetic contact device with a contact output. It works on the principle of changing magnetic induction under the influence of high temperature. As the air temperature rises, the magnetic field decreases, and when a threshold temperature value is reached, the contact, which is located in a sealed chamber, opens. In this case, a “Fire” signal is sent to the control panel.
Smoke detectors
Smoke is detected using photoelectric (optical) or radioisotope methods. The operating principle of the IPD-1 optical fire smoke detector (see Fig. 4.38, c) is based on the registration of scattered light (Tindol effect). An emitter and receiver operating in infrared light, located in an optical chamber in such a way that rays from the emitter cannot reach the receiver directly. In the event of a fire, smoke enters the optical chamber of the detector. Light from the emitter is scattered by smoke particles (Fig. 4.39) and enters the receiver. As a result, a “Fire” signal is generated and sent to the control panel. In radioisotope smoke detectors, the sensitive element is an ionization chamber with a source of α-radiation (Fig. 4.40). The smoke that is generated during a fire reduces the degree of ionization in the chamber and is registered by the detector.
Rice. 4.39. Diffusion luminous flux particles smoke: 1 - source 2 - smoky environment; 3 - smoke particles
Rice. 4.40. Light ionization chamber (emitter) of a radioisotope smoke detector: 1 - anode; 2 - cathode
Fire flame detectors
(IP, IP-P, IP-PB) allow you to quickly identify the source of an open flame. The detector's sensitive photocell detects flame radiation in the ultraviolet or infrared parts of the spectrum. Combined detectors IPK-1, IPK-2, IPK-3 simultaneously monitor two factors that accompany a fire: smoke and temperature.
Fire detectors are characterized by: response threshold - the lowest value of the parameter to which they respond; inertia - the time from the beginning of the factor action is controlled until the moment of operation; protected area - the floor area controlled by one detector. In table 4.13 shows the comparative characteristics of detectors of various types.
Table 4.13.
Some burglar alarm detectors (sensors) (for example, ultrasonic, optical-electric) have high sensitivity and are capable of very quickly (more like fire detectors) detecting the first signs of fire. Therefore, they can combine security and fire functions. However, such detectors can only be additional elements AUPS, which enhance fire safety protected object. After all, the security alarm operates after hours, and the fire alarm operates around the clock.
When choosing the type and design of an automatic fire detector, it is necessary to take into account the purpose of the protected premises, the fire characteristics of the materials it contains, the primary signs of fire and operating conditions in accordance with DBN V.2.5-13-98.
For the right choice automatic fire detectors, it is necessary to take into account the characteristics of the intended purpose of the protected premises, the degree of their fire hazard, the specifics of the technological process, the fire characteristics of the materials in the room, the primary signs of a fire and the nature of its possible development. It is also necessary to take into account the presence of automatic fire extinguishing systems and other features of the facility.
The type and design of fire detectors must be selected taking into account the environmental conditions in the protected premises and the class of the explosive or fire hazardous area.
The number and location of fire detectors depends on the size, shape, operating conditions and purpose of the room, the design of the floor (covering) and ceiling height, the presence and type of ventilation, the load of the room with materials and equipment, as well as the type and type of fire detectors and in each specific case determined by the design organization that received a license for this type of activity in the prescribed manner.
Fire detectors are installed, as a rule, under the covering (ceiling). In some cases, their location on walls, beams, columns, as well as suspension on cables is allowed, provided they are at a distance of no more than 0.3 m from the level of the coating (floor) and no more than 0.6 m from the ventilation openings.
In rooms with equal ceilings, point fire detectors are usually located evenly over the ceiling area, taking into account the size of the room, as well as the technical parameters of the detectors. It is recommended to install point fire detectors according to triangular or square placement patterns (Fig. 4.41).
Rice. 4.41.
a - distance between detectors, b - distance from wall to detector
In some cases, detectors are placed in areas of probable fire, on the paths of convective air flows, and also near fire-hazardous equipment.
The distance between detectors is taken taking into account the area controlled by one detector. The latter significantly depends on the height of the protected room. Therefore, the greater the height of the protected room, the smaller area, controlled by a detector. The distance from the detector to the wall, as a rule, is taken to be two times less than the distance between the detectors.
As the practice of operating fire detectors has shown, thermal fire detectors should be used in small and medium height and relatively small volume. When the height of the room is 7-9 m, the use of heat detectors is impractical due to the ineffectiveness of registering the source of the fire.
The threshold temperature for operation of maximum and maximum differential heat detectors must be no less than 20 ° C and no more than 70 ° C higher than the maximum permissible temperature in the room.
Differential heat detectors effective in areas where, under normal operating conditions, there is no sudden increase in ambient temperature. Such detectors should not be installed near heat sources that could cause false alarms.
Smoke detectors are installed in rooms where a fire is likely to be accompanied by significant smoke emissions. When placing them, it is necessary to take into account the paths and speeds of air flows from ventilation systems.
Flame detectors are installed in rooms where there is a risk of fire with an open flame. Various industrial exposures (operating welding machines or other sources of ultraviolet or infrared radiation) must be avoided. Flame detectors must be protected from direct sun rays and direct influence of sources artificial lighting. When locating flame detectors, it is necessary to take into account their technical characteristics: viewing angle, area protected by the detector, maximum fire detection range (distance from the detector to the most “visible” point).
It should be noted that when selecting and placing automatic fire detectors, it is necessary to be guided by the requirements and recommendations of DBN V.2.5-13-98.
Fire communications and alarms are designed for timely notification of a fire (notification communication), management of fire departments (dispatcher communications) and management of fire extinguishing. For these purposes, telephone and radio communications (manual fire call points), electric fire alarms (EFS), automatic fire alarms (AFS), live communications, beeps, calls, etc. are used.
Rice. 1. Manual call point diagram
Manual fire call points are installed at national economic facilities and in residential premises, in corridors, passages, and staircases. The alarm is generated by pressing a button. Manual call points PKIL (fire push-button beam detector) are connected to the receiving station. When you press the K button, one of the circuits opens, which leads to the activation and reception of an alarm signal. A current is supplied from the receiving station, which turns on the telephone, and the person who raised the alarm receives confirmation that the signal has been received. A microtelephone handset can be connected to the Mt terminals for conversations with the duty officer.
In industrial buildings with an area of more than 500 m2, classified according to fire hazard categories A, B and C, warehouses and retail premises, exhibition halls, museums, theatrical and entertainment venues and some others, it is recommended to install electric fire alarm systems (EFS). EPS can be automatic or manual. In turn, automatic fire alarm systems, depending on the physical factor to which they respond, are divided into thermal (i.e., responsive to increased temperature), smoke, light and combined. In addition, automatic fire detectors are divided into maximum, maximum differential and differential. Maximum action sensors are triggered when the controlled parameter reaches a specified value. Differential sensors react to changes in the speed of a given parameter, and maximum 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 a coverage area - the floor area 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. The sensitive element can be a low-melting alloy, as in DTL detectors (low-melting thermal sensor); thermocouples, as in DPS detectors (fire alarm sensor) or semiconductor thermistors in POST detectors. Smoke detectors have two main methods of detecting smoke - photoelectric and radioisotope. A photoelectric smoke detector (PSD) detects smoke by detecting light reflected from smoke particles with a photocell. A semiconductor smoke detector (SSD) operates on the same principle.
A radioisotope smoke detector (RSD) 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 (CDs) that respond to heat and smoke. Light fire detectors register the radiation of a flame against the background of extraneous light sources. The 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 increasingly being used. They have very high sensitivity and can combine security and fire functions. These devices respond to changes in the characteristics of the ultrasonic field filling the protected room under the influence of air movement that occurs during a fire. The table shows the main characteristics of various types of detectors.
Table 1. Characteristics of various detectors
The main elements of any automatic fire alarm system are: detectors-sensors located in protected premises; a receiving station designed to receive signals from sensors and generate alarms; power devices that provide electrical current to the system; linear structures - systems of wires connecting detectors to the receiving station.
Rice. 2. Connection of fire detectors with 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 connection is used in enterprises where people are present around the clock. The installation branches can include both push-button and automatic detectors. The sequential system is installed at large facilities.