Fire localization means. Theoretical provisions

The main types of equipment designed to protect various objects from fires include alarm and fire extinguishing equipment.

Fire alarm

Fire alarms must quickly and accurately report a fire and indicate its location. Most reliable system fire alarm is electrical fire alarm. The most advanced types of such alarms additionally provide automatic activation of the fire extinguishing means provided at the facility. Schematic diagram The electrical alarm system is shown in Fig. 1. It includes fire detectors installed in protected premises and connected to the signal line; receiving and control station, power supply, sound and light alarms, as well as automatic installations fire extinguishing and smoke removal.

The reliability of the electrical alarm system is ensured by the fact that all its elements and the connections between them are constantly energized. This ensures monitoring of plant malfunctions.

Rice. 1 Schematic diagram of the electrical fire alarm system: 1- sensors-detectors; 2- receiving station; 3- backup power supply; 4- mains power supply; 5- switching system; 6- wiring; 7- actuating mechanism fire extinguishing systems.

The most important element Alarm systems are fire detectors that convert physical parameters characterizing a fire into electrical signals. Based on the method of actuation, detectors are divided into manual and automatic. Manual call points produce an electrical signal into the communication line a certain shape at the moment the button is pressed.

Automatic fire detectors are activated when parameters are changed environment at the time of the fire. Depending on the factor that triggers the sensor, detectors are divided into thermal, smoke, light and combined. The most widespread heat detectors, sensitive elements, which can be bimetallic, thermocouple, semiconductor.

Smoke fire detectors, reacting to smoke, have a photocell or ionization chambers as a sensitive element, as well as a differential photo relay. Smoke detectors come in two types: point detectors, which signal the appearance of smoke at the location where they are installed, and linear-volume detectors, which operate on the principle of shading the light beam between the receiver and the emitter.

Light fire detectors based on fixing various components spectrum of an open flame. The sensitive elements of such sensors react to the ultraviolet or infrared region of the optical radiation spectrum.

The inertia of the primary sensors is important characteristic. Has the greatest inertia thermal sensors, the smallest - light.

A set of measures aimed at eliminating the causes of a fire and creating conditions under which continuation of combustion will be impossible is called fire extinguishing.

To eliminate the combustion process, it is necessary to stop the supply of either fuel or oxidizer to the combustion zone, or to reduce the supply of heat flow to the reaction zone. This is achieved:

1. Strong cooling of the combustion site or burning material with the help of substances (for example, water) with high heat capacity.

2. Isolation of the combustion source from atmospheric air or by reducing the oxygen concentration in the air by supplying inert components to the combustion zone.

3. Using special chemicals, inhibiting the rate of oxidation reaction.

4. Mechanical flame suppression using a strong jet of gas and water.

5. By creating fire barrier conditions under which the flame spreads through narrow channels, the cross-section of which is smaller than the extinguishing diameter.

To achieve the above effects, the following are currently used as extinguishing agents:

1. Water that is supplied to the fire source in a continuous or sprayed stream.

2. Various types of foams (chemical or air-mechanical), which are air or carbon dioxide bubbles surrounded by a thin film of water.

The main types of equipment designed to protect various objects from fires include alarm and fire extinguishing equipment.

Fire alarm must quickly and accurately report a fire, indicating its location. The most reliable fire alarm system is the electric fire alarm. The most advanced types of such alarms additionally provide automatic activation of the fire extinguishing means provided at the facility. A schematic diagram of the electrical alarm system is shown in Fig. 18.1. It includes fire detectors installed in protected premises and connected to the signal line; reception and control station, power supply, sound and light alarms, as well as automatic fire extinguishing and smoke removal installations.

Rice. 18.1. Schematic diagram of the electrical fire alarm system:

1 - detector sensors; 2- receiving station; 3-backup power supply;

4-block – mains power supply; 5- switching system; 6 - wiring;

7-actuator mechanism of the fire extinguishing system

The reliability of the electrical alarm system is ensured by the fact that all its elements and the connections between them are constantly energized. This ensures constant monitoring of the serviceability of the installation.

The most important element of the alarm system is fire detectors, which convert physical parameters characterizing a fire into electrical signals. Based on the method of actuation, detectors are divided into manual and automatic. Manual call points produce an electrical signal of a certain shape into the communication line at the moment the button is pressed.

Automatic fire detectors are activated when environmental parameters change at the time of a fire. Depending on the factor that triggers the sensor, detectors are divided into thermal, smoke, light and combined. The most widespread are heat detectors, the sensitive elements of which can be bimetallic, thermocouple, or semiconductor.

Smoke fire detectors that react to smoke have a photocell or ionization chambers as a sensitive element, as well as a differential photo relay. Smoke detectors come in two types: point detectors, which signal the appearance of smoke at the location where they are installed, and linear-volume detectors, which operate on the principle of shading the light beam between the receiver and the emitter.

Light fire detectors are based on fixing various | components of the open flame spectrum. The sensitive elements of such sensors react to the ultraviolet or infrared region of the optical radiation spectrum.

The inertia of the primary sensors is an important characteristic. Thermal sensors have the greatest inertia, light sensors the least.

A set of measures aimed at eliminating the causes of a fire and creating conditions under which continuation of combustion will be impossible is called fire extinguishing.

To eliminate the combustion process, it is necessary to stop the supply of either fuel or oxidizer to the combustion zone, or to reduce the supply of heat flow to the reaction zone. This is achieved:

Strong cooling of the combustion site or burning material with the help of substances (for example, water) with high heat capacity;

By isolating the combustion source from atmospheric air or reducing the oxygen concentration in the air by supplying inert components to the combustion zone;

The use of special chemicals that inhibit the rate of oxidation reaction;

Mechanical flame suppression with a strong jet of gas or water;

By creating fire suppression conditions under which the flame spreads through narrow channels, the cross-section of which is smaller than the extinguishing diameter.

To achieve the above effects, the following are currently used as extinguishing agents:

Water that is supplied to the fire source in a continuous or sprayed stream;

Various types of foams (chemical or air-mechanical), which are air or carbon dioxide bubbles surrounded by a thin film of water;

Inert gas diluents, which can be used: carbon dioxide, nitrogen, argon, water vapor, flue gases, etc.;

Homogeneous inhibitors - low-boiling halogenated hydrocarbons;

Heterogeneous inhibitors - fire extinguishing powders;

Combined formulations.

Water is the most widely used extinguishing agent.

Providing enterprises and regions with the necessary volume of water for fire fighting is usually done from the general (city) water supply network or from fire reservoirs and containers. Requirements for fire water supply systems are set out in SNiP 2.04.02-84 “Water supply. External networks and structures" and in SNiP 2.04.01-85 "Internal water supply and sewerage of buildings."

Fire-fighting water supply systems are usually divided into low- and medium-pressure water supply systems. Free pressure during fire extinguishing in water supply network low pressure at the design flow rate must be at least 10 m from the ground surface level, and the water pressure required for fire extinguishing is created by mobile pumps installed on hydrants. In a high-pressure network, a height of a compact jet of at least 10 m must be ensured at the full design flow rate of water and the location of the barrel at the level of the highest point of the tall building. High pressure systems are more expensive due to the need to use increased strength pipelines, as well as additional water tanks at the appropriate height or pumping water station devices. Therefore, high-pressure systems provide for industrial enterprises, more than 2 km away from fire stations, as well as in populated areas with a population of up to 500 thousand people.

R and p.1 8.2. Integrated water supply scheme:

1 - water source; 2-water intake; 3-station first lift; 4-water treatment facilities and a second lift station; 5-water tower; 6 main lines; 7 - water consumers; 8 - distribution pipelines; 9-entry into buildings

A schematic diagram of the united water supply system is shown in Fig. 18.2. Water from a natural source enters the water intake and is then supplied by pumps from the first lift station to the structure for treatment, then through water pipelines to the fire control structure ( water tower) and further along the main water supply lines to the entrances to the buildings. The construction of water pressure structures is associated with uneven water consumption by hour of the day. As a rule, the fire-fighting water supply network is made ring-shaped, providing two water supply lines and thereby high reliability of water supply.

The regulated water consumption for fire extinguishing consists of the costs for external and internal fire extinguishing. When rationing water consumption for external fire extinguishing, it is based on the possible number of simultaneous fires in locality, arising in I for three adjacent hours, depending on the number of residents and the number of storeys of buildings (SNiP 2.04.02-84). Consumption rates and water pressure in internal water supply systems in public, residential and auxiliary buildings are regulated by SNiP 2.04.01-85, depending on their number of floors, length of corridors, volume, purpose.

For indoor fire extinguishing, automatic fire extinguishing devices are used. The most widely used installations are those that distribution devices use sprinkler (Fig. 8.6) or deluge heads.

sprinkler head is a device that automatically opens the water outlet when the temperature inside the room increases due to a fire. Sprinkler systems turn on automatically when the indoor temperature rises to a predetermined limit. The sensor is the sprinkler head itself, equipped with a low-fusible lock that melts when the temperature rises and opens a hole in the water pipeline above the fire. A sprinkler installation consists of a network of water supply and irrigation pipes installed under the ceiling. Sprinkler heads are screwed into the irrigation pipes at a certain distance from each other. One sprinkler is installed on an area of 6-9 m2 of room, depending on fire danger production. If in the protected premises the air temperature can drop below + 4 °C, then such objects are protected by air sprinkler systems, which differ from water ones in that such systems are filled with water only up to the control and alarm device, distribution pipelines located above this device in unheated room, are filled with air pumped by a special compressor.

Deluge installations in design they are similar to sprinklers and differ from the latter in that the sprinklers on the distribution pipelines do not have a fusible lock and the holes are constantly open. Deluge systems are designed to form water curtains, to protect the building from fire in the event of a fire in an adjacent building, to form water curtains in the room to prevent the spread of fire and for fire protection in conditions of increased fire danger. The deluge system is turned on manually or automatically by the first signal from an automatic fire detector using a control and starting unit located on the main pipeline.

Air-mechanical foams can also be used in sprinkler and deluge systems. The main fire-extinguishing property of foam is to isolate the combustion zone by forming a vapor-proof layer of a certain structure and resistance on the surface of the burning liquid. The composition of air-mechanical foam is as follows: 90% air, 9.6% liquid (water) and 0.4% foaming agent. Characteristics of foam that determine it

fire extinguishing properties are durability and multiplicity. Resistance is the ability of foam to be maintained at high temperatures over time; air-mechanical foam has a durability of 30-45 minutes, the expansion ratio is the ratio of the volume of foam to the volume of the liquid from which it is obtained, reaching 8-12.

| Foam is produced in stationary, mobile, portable devices and hand-held fire extinguishers. Foam of the following composition is widely used as a fire extinguishing agent I: 80% carbon dioxide, 19.7% liquid (water) and 0.3% foaming agent. The multiplicity of chemical foam is usually 5, durability is about 1 hour.

Fire safety

Assessment of fire hazardous areas.

Under fire usually understand an uncontrolled combustion process, accompanied by the destruction of material assets and creating a danger to human life. Fire can take various shapes, but they all ultimately come down to chemical reaction between flammable substances and air oxygen (or other types of oxidizing media), which occurs in the presence of a combustion initiator or under conditions of self-ignition.

The formation of a flame is associated with the gaseous state of substances, therefore the combustion of liquid and solids involves their transition to the gaseous phase. In the case of liquid combustion, the process usually consists of simple boiling with evaporation at the surface. During the combustion of almost all solid materials, the formation of substances that can evaporate from the surface of the material and enter the flame area occurs through chemical decomposition (pyrolysis). Most fires are associated with the combustion of solid materials, although the initial stage of the fire may be associated with the combustion of liquid and gaseous flammable substances, widely used in modern industrial production.

During combustion, it is customary to subdivide two modes: a mode in which the combustible substance forms a homogeneous mixture with oxygen or air before combustion begins (kinetic flame), and a mode in which the fuel and oxidizer are initially separated, and combustion occurs in the area of their mixing (diffusion combustion) . With rare exceptions, during extensive fires, a diffusion combustion mode occurs, in which the combustion rate is largely determined by the rate of entry of the resulting volatile combustible substances into the combustion zone. In the case of combustion of solid materials, the rate of entry of volatile substances is directly related to the intensity of heat exchange in the contact zone of the flame and the solid combustible substance. The mass burnout rate [g/m 2 × s)] depends on the heat flow perceived by the solid fuel and its physical and chemical properties. IN general view this dependence can be represented as:

Where Qpr-heat flow from the combustion zone to solid fuel, kW/m2;

Qyx-heat loss of solid fuel into the environment, kW/m2;

r-heat required for the formation of volatile substances, kJ/g; for liquids it is the specific heat of vaporization/

The heat flow coming from the combustion zone to the solid fuel depends significantly on the energy released during the combustion process and on the conditions of heat exchange between the combustion zone and the surface of the solid fuel. Under these conditions, the mode and rate of combustion can largely depend on the physical state of the combustible substance, its distribution in space and the characteristics of the environment.

Fire and explosion safety substances are characterized by many parameters: ignition, flash, spontaneous combustion temperatures, lower (LKPV) and upper (UKPV) concentration limits of ignition; the speed of flame propagation, linear and mass (in grams per second) rates of combustion and burnout of substances.

Under ignition refers to ignition (the occurrence of combustion under the influence of an ignition source), accompanied by the appearance of a flame. Ignition temperature - minimum temperature substances that cause combustion (uncontrolled combustion outside a special fireplace).

Flash point is the minimum temperature of a combustible substance at which gases and vapors are formed above its surface that can flare up (flare up - quickly burn without the formation of compressed gases) in the air from an ignition source (a burning or hot body, as well as electrical discharge, having a supply of energy and temperature sufficient to cause combustion of the substance). The spontaneous combustion temperature is the highest low temperature, at which there is a sharp increase in the rate of the exothermic reaction (in the absence of an ignition source), ending in flaming combustion. Concentration flammability limits are the minimum (lower limit) and maximum (upper limit) concentrations that characterize the areas of ignition.

The flash point, self-ignition and ignition temperature of flammable liquids is determined experimentally or by calculation in accordance with GOST 12.1.044-89. Bottom and top concentration limits ignition of gases, vapors and combustible dusts can also be determined experimentally or by calculation in accordance with GOST 12.1.041-83*, GOST 12.1.044-89 or the manual for “Calculation of the main indicators of fire and explosion hazard of substances and materials”.

The fire and explosion hazard of production is determined by fire hazard parameters and the amount of materials and substances used in technological processes, design features and operating modes of equipment, the presence of possible ignition sources and conditions for the rapid spread of fire in the event of a fire.

According to NPB 105-95, all objects are in accordance with their nature technological process According to explosion and fire hazards, they are divided into five categories:

A – explosion and fire;

B – fire and explosion hazard;

B1-B4 – fire hazardous;

The above standards do not apply to premises and buildings for the production and storage of explosives, means of initiating explosives, buildings and structures designed in accordance with special norms and rules approved in the prescribed manner.

Categories of premises and buildings determined in accordance with tabular data regulatory documents, used to establish regulatory requirements to ensure explosion and fire safety of the specified buildings and structures in relation to planning and development, number of storeys, areas, location of premises, constructive solutions, engineering equipment etc.

A building belongs to category A if its total area of category A premises exceeds 5 % all premises, or 200 m\ If premises are equipped with automatic fire extinguishing installations, it is allowed not to classify buildings and structures in which the share of category A premises is less than 25% (but not more than 1000 m2) as category A;

Category B includes buildings and structures if they do not belong to category A and the total area of premises of categories A and B exceeds 5% of the total area of all premises, or 200 m 2; it is allowed not to classify a building as category B if the total area of premises of categories A and B in the building does not exceed 25% of the total area of all premises located in it (but not more than 1000 m2) and these premises are equipped with automatic fire extinguishing installations;

A building belongs to category B if it does not belong to category A or B and the total area of premises of categories A, B and C exceeds 5% (10% if the building does not have premises of categories A and B) of the total area of all premises. In the case of equipping premises of categories A, B and C with automatic fire extinguishing installations, it is allowed not to classify the building as category B if the total area of category A, B and C premises does not exceed 25% (but not more than 3500 m2) of the total area of all premises located in it ;

If the building does not belong to categories A, B and C and the total area of premises A, B, C and D exceeds 5% of the total area of all premises, then the building belongs to category D; it is allowed not to classify a building as category D if the total area of premises of categories A, B, C and D in the building does not exceed 25% of the total area of all premises located in it (but not more than 5000 m2), and premises of categories A, B, C and G are equipped with automatic fire extinguishing installations;

Under fire resistance understand the ability of building structures to resist high temperatures in fire conditions and still perform their normal operational functions.

The time (in hours) from the start of testing a structure for fire resistance until the moment at which it loses its ability to maintain load-bearing or enclosing functions is called fire resistance limits.

A loss bearing capacity is determined by the collapse of the structure or the occurrence of extreme deformations and is indicated by the indices R. The loss of enclosing functions is determined by the loss of integrity or thermal insulation ability. The loss of integrity is caused by the penetration of combustion products beyond the insulating barrier and is designated by the index E. The loss of thermal insulation capacity is determined by an increase in temperature on the unheated surface of the structure by an average of more than 140 °C or at any point on this surface by more than 180 °C and is designated by the index J.

The main provisions of methods for testing structures for fire resistance are set out in GOST 30247.0-94 “Building structures. Test methods for fire resistance. General requirements" and GOST 30247.0-94 "Building structures. Test methods for fire resistance. Load-bearing and enclosing structures."

The degree of fire resistance of a building is determined by the fire resistance of its structures (SNiP 21 - 01 - 97).

SNiP 21-01-97 regulates the classification of buildings according to the degree of fire resistance, structural and functional fire hazard. These standards came into force on January 1, 1998.

The class of structural fire hazard of a building is determined by the degree of participation of building structures in the development of a fire and the formation of its hazardous factors.

According to fire danger building construction are divided into classes: KO, K1, IC2, KZ (GOST 30-403-95 “Building structures. Method for determining fire hazard”).

According to the functional fire hazard, buildings and premises are divided into classes depending on the method of their use and the extent to which the safety of people in them, in the event of a fire, is at risk, taking into account their age, physical condition, sleep or wakefulness, type the main functional contingent and its quantity.

Class F1 includes buildings and premises associated with permanent or temporary residence of people, which includes

F1.1-- children's preschool institutions, homes for the elderly and disabled, hospitals, dormitories of boarding schools and children's institutions;

F 1.2-hotels, hostels, dormitories of sanatoriums and holiday homes, campsites and motels, boarding houses;

F1.3 - multi-apartment residential buildings;

F1.4 - individual, including blocked houses.

Class F2 includes entertainment, cultural and educational institutions, which includes:

F2L theatres, cinemas, concert halls, clubs, circuses, sports facilities and other institutions with seats for spectators in indoors;

F2.2 - museums, exhibitions, dance halls, public libraries and other similar indoor institutions;

F2.3 is the same as F2.1, but located in the open air.

The Federal Law class includes public service enterprises:

F3.1 - trade and catering enterprises;

F3.2-stations;

Federal Law.Z - clinics and outpatient clinics;

F3.4 - premises for visitors to consumer and public service enterprises;

F3.5 - physical education, health and sports training institutions without stands for spectators.

Class F4 includes educational establishments» scientific and design organizations:

F4.1- secondary schools, secondary specialized educational institutions, vocational schools, extracurricular educational institutions;

F4.2 - higher educational institutions, institutions of advanced training;

F4.3-government institutions, design and engineering organizations, information and publishing organizations, research organizations, banks, offices.

The fifth class includes production and warehouse premises:

F5.1 - production and laboratory premises;

F5.2 - warehouse buildings and premises, parking lots without Maintenance, book depositories and archives;

F5.3 - agricultural buildings. Production and warehouses, as well as laboratories and workshops in buildings of classes F1, F2, FZ, F4 belong to class F5.

According to GOST 30244-94 “Construction materials. Methods of testing for combustibility" building materials, depending on the value of flammability parameters, are divided into combustible (G) and non-combustible (NG).

Determination of flammability building materials carried out experimentally.

For finishing materials In addition to the flammability characteristic, the concept of the value of the critical surface heat flux density (CSHD), at which stable flame combustion of the material occurs (GOST 30402-96), is introduced. Depending on the value of the KPPTP, all materials are divided into three flammability groups:

B1 - KShGShch is equal to or more than 35 kW per m 2;

B2 - more than 20, but less than 35 kW per m 2;

B3 - less than 2 kW per m 2.

According to the scale and intensity, fires can be divided into:

An isolated fire that occurs in a separate building (structure) or in a small isolated group of buildings;

A continuous fire, characterized by simultaneous intense burning of the predominant number of buildings and structures in a certain building area (more than 50%);

Firestorm, a special form of spreading continuous fire, formed under conditions of an upward flow of heated combustion products and rapid entry towards the center of the firestorm significant amount fresh air(wind speed 50 km/h);

A massive fire that occurs when there is a combination of separate and continuous fires in an area.

The spread of fires and their transformation into continuous fires under other conditions equal conditions determined by the building density of the site. The influence of the density of buildings and structures on the probability of fire spread can be judged from the indicative data given below:

Distance between buildings, m. 0 5 10 15 20 30 40 50 70 90 Probability of spread across

heat, %. ... ...... ... 100 87 66 47 27 23 9 3 2 0

The rapid spread of fire is possible with the following combinations of the degree of fire resistance of buildings and structures with building density: for buildings of fire resistance degrees I and II, the building density should be no more than 30%; for buildings of III degree -20%; for buildings of IV and V degrees - no more than 10%.

The influence of three factors (building density, degree of fire resistance of the building and wind speed) on the speed of fire spread can be traced in the following figures:

1) at a wind speed of up to 5 m/s in buildings of fire resistance levels I and II, the fire spread speed is approximately 120 m/h; in buildings of IV degree of fire resistance - approximately 300 m/h, and in the case of a combustible roof up to 900 m/h; 2) at a wind speed of up to 15 m/s in buildings of I and II degrees of fire resistance, the fire spread speed reaches 360 m/s.

Means for localizing and extinguishing fires.