Posted 08/01/2010

Fire protection

Every city has a fire department. Any large enterprise has its own service fire safety. However, even in the most cultural countries, people and valuables are lost in fires.

Combustion

There are four necessary conditions fire occurrence:

Flammable substance;

Oxidizing agent (most often air oxygen);

Ignition source;

Path of fire spread.

Combustion is not always accompanied by flame. Organic substances containing more than 60% carbon, and inorganic substances that release oxides of aluminum, magnesium, potassium, sodium, etc., burn with a bright flame.

Incomplete combustion of substances produces smoke, which may contain toxic compounds: carbon monoxide, vapors of acids, alcohols, aldehydes, etc.

For example, when celluloid burns, hydrocyanic acid is formed. Substances are divided into non-flammable, slow-burning and flammable. Refractory flames are capable of burning under the influence of an ignition source, but go out after the source is removed. The fire hazard of flammable substances increases as they are crushed.

Flammable solids

Mineral Construction Materials on an organic binder (starch, bitumen, etc.), which makes up less than 6% of the mass, are non-flammable. If the organic binder makes up from 7 to 15% of the mass, the materials are low-flammable.

Flammable substances are those that ignite, for example, from a spark or a hot electrical wire. Some substances are capable of spontaneous combustion. It occurs after self-heating of a large mass of porous substance from its oxidation by air under conditions of weak heat removal. For example, wet grain and oily rags ignite spontaneously.

Flammable liquids

Vapors of all flammable liquids are heavier than air and therefore accumulate in the lower part of the premises, in ditches, etc. Diesel fuel (solar oil), lubricating oil, fuel oil have a high ignition temperature and therefore, not being very heated, cannot ignite from a spark or matches.

Flash point is the temperature at which vapors formed above the surface of a substance are capable of flaring up from an ignition source, but the rate of their formation is insufficient for stable combustion. The lower the flash point of liquid vapor, the greater its explosion hazard.

Flammable gases

In order for a gas mixed with air to ignite, its concentration must be within certain limits:

According to this table, acetylene is the most explosive and flammable gas. It is followed by hydrogen.

Hydrogen and methane are lighter than air and accumulate in the upper parts of rooms. Acetylene is heavier than air and accumulates at the bottom.

Absolutely pure flammable gases are rarely used in technology. Usually they are mixed with odorous substances to detect
leaks.

Combustible dusts.

Dust from a flammable substance is much more dangerous than the same substance in a dense mass. Airgel (lying dust) can be capable of spontaneous combustion, aerosol (dust in the air) is explosive. Dust is more explosive the more smaller size its particles.

The concentration of dust that is usually explosive is such that visibility is reduced to 3 - 4 meters.

Dust can accumulate in air ducts, low areas, basements and attics. A local dust outbreak can cause a large volume of settled dust to swirl and cause a powerful explosion. To reduce the risk of a dust explosion, it is moistened, a mineral additive is added, and inert gas is supplied to the dusty containers of technical devices.

Preventing fire in an enterprise.

Care must be taken to ensure that all four necessary conditions for a fire do not occur simultaneously (see section Combustion).

In enterprises, the greatest danger arises when starting or stopping devices that use or generate flammable materials.
liquids, vapors, dust, as well as in case of breakdown of such devices, accompanied by the release of hazardous substances into the room. The risk of an accident is especially high during testing. Apparatus or pipeline with dangerous substance may rupture due to excessive internal pressure. It may result from deposits solids, faulty taps or automatic systems adjustments.

The apparatus or pipeline may also be damaged by a vehicle or a heavy falling object.

The source of ignition may be:

Malfunctions of electric heating devices;

Sparking electrical outlets, switches;

Overheating of bearings in engines;

Static electricity discharges;

Sparks when using steel tools./p>

Possible ways of fire spread:

Ventilation ducts;

Elevator shafts;

Cable tunnels;

Combustible flooring, flammable wall covering.

Fire extinguishing, emergency evacuation, warning, and communication equipment should be maintained in order. Fire exits and fire escapes must be clear, in working order, accessible, illuminated, and provided with signs.

Preventing fire in the home.

To have fewer flammable items in your home, do not have a large library and try to use metal furniture. If possible, do without carpets, “paths”, linoleum, curtains and curtains (all this burns well, and curtains contribute to the spread of fire from the lower floors up through the windows). Instead of curtains, it is better to use aluminum blinds. Synthetic materials emit very toxic smoke when burned, so preference should be given to things made of metals and minerals. (Of course, it is almost impossible to fully implement these tips, so you need to be aware of the existing danger and carefully follow the protective measures that are available.)

Wall decoration with leather, fabric, and plastic poses a significant threat. As for paper wallpaper, tightly glued in one layer, then their fire hazard is negligible.

If you have a lot of books and papers, you don’t need to at least keep them concentrated (all in one room, on one shelf). It is better to have fewer of them in rooms where a TV, iron, boiler, etc. are used. Get into the habit of removing the boiler from the table immediately after use. Place a stand with a hot iron or soldering iron, a mug with a boiler on, an electric stove, etc. metal pallet and away from flammable objects - so that even if these devices overheat, a fire cannot start. You must make sure that you cannot accidentally touch the switched-on device or snag the electrical wire going to it.

You should also not do the following:

Plug several into one outlet household appliances high power;

Leave on heating devices unattended in the next room: you can easily forget about them, and if they are in the same room with you, they will at least remind you of themselves with the smell of burning;

Use homemade fuses in the electrical network or exclude fuses;

Heat varnishes and paints on a gas stove;

Store gasoline and other flammable liquids in large quantities in your home or on the balcony; wash clothes indoors in gasoline or another solvent;

Block possible escape routes: put bars on the windows that cannot be opened from the inside, litter the fire escape on the balcony, etc.

Your own TV or refrigerator may catch fire. Keep these devices away from anything that burns easily. Do not place books or newspapers on or near them. The refrigerator is dangerous because it remains on when you are not at home. Place it on a tile or metal sheet to make it difficult for the fire to spread. When leaving for a long time, turn off the refrigerator altogether. There should be enough space around the TV for air movement, so you should not place the TV in a niche. The fire of the TV is caused by dust that accumulates inside it. You should clean the inside of the TV once a year and clean the room more often. To be able to quickly disconnect a device that has caught fire from the electrical network, you must have easy access to an electrical outlet.

Cases of significant damage have been reported residential buildings due to fire or explosion of materials stored in apartments, basements and attic spaces. For example, there was a case where a building was destroyed because several bags of calcium carbide (used in welding work to produce flammable ethylene gas), these bags were filled with water, the basement was filled with a mixture of ethylene and air, and the mixture exploded. Therefore, be interested in the condition of the non-residential premises your home and what is stored in them. Categorically object to their use as warehouses, even if they assure you that only non-combustible items are intended to be placed there. Also take an interest in the activities and mental state of your neighbors. You need to stay away from everyone who is too unhappy, too enterprising, too unbalanced, too low, or put them away from you. These people are capable of starting a fire or explosion in their home (either through negligence or intentionally), which could damage your apartment. Smokers are especially dangerous. They tend to throw their unextinguished cigarette butts anywhere, and also, for example, they can fall asleep on the bed with a cigarette in their hand, after which the blanket or pillow will begin to smolder and everyone sleeping in the same apartment, if not burned, will suffocate from the smoke.

If the house uses gas stoves, it is imperative to ensure that the entrance is locked from outsiders - to prevent them from deliberately damaging the gas pipeline for terrorist or hooligan purposes. When designing large buildings, they include a smoke protection system. The self-closing door devices included in this system must not be removed or maintained in a faulty state.

Make sure that the buildings in which you live, work or frequently visit comply with fire safety rules:

Fire escapes were not cluttered;

Emergency exits were not blocked;

Fire equipment was available and in good working order;

No flammable materials accumulated;

The children didn't have fun with the fire;

If possible, object to installation suspended ceilings, finishing walls with leather or plastic and other decorative efforts leading to an increase in the amount of combustible materials in the premises.

Preparing to extinguish a fire in a home.

Store 20 liters of water in a canister or plastic bottles. Water is also useful for other purposes, of which a lot will be revealed when the water supply system fails. To reduce bacteria growth in water, add potassium permanganate to it. Buy a car fire extinguisher. Keep a filter gas mask ready. It increases the chances of successful evacuation, although it protects only from smoke and from toxic substances released during combustion, but not from carbon monoxide (if you do not use a special nozzle - a “hopcalite cartridge”) and not from a lack of oxygen in the room./p>

You should have a long hose ready that can be quickly and firmly attached to the water tap.

Preparing for evacuation.

When entering a building where you will spend some time, pay attention to where other exits are located, including emergency exits. If possible, do not leave outerwear and things in the wardrobe, but keep them with you. In a crowded room (such as a movie theater), take a seat close to the exit.

Wear shoes from genuine leather, completely covering the foot.

It is better to always have more clothes with you (not necessarily on yourself). Wear gloves - if not on your hands, then in your pockets. Do not wear shorts or short-sleeved shirts (preferably roll up long sleeves). Of the materials used in the manufacture of clothing, dense woolen fabrics and natural leather best resist fire.

If your workplace is located away from the exits from the building, it is possible that in the event of a fire you will have to make your way through areas engulfed in flames or smoke, so you should have a gas mask, additional clothing, and water to wet clothes and exposed parts of the body at the ready. Water may be needed, among other things, to extinguish a small fire. If you have to get out of a burning part of the building through a smoky corridor, you may find that it is better to do this on all fours, since the smoke usually collects from above.

At home and at work, keep a thick rope ready at the window for lowering to the lower floor or to the ground. You should wear gloves when rappelling (otherwise you will skin your palms), so it's best to keep a spare pair of gloves with the rope. Instead of rope, you can use a belt. It is more convenient in that it compactly rolls up into a roll, which quickly unfolds if necessary, if you throw it out of the window, securing one end. An alternative to gloves is a retarder: a device that may take the form of a strong plate with several holes through which the rope or tape is passed in a zigzag pattern. The retarder is attached to the chest with an auxiliary belt passing under the arms. The holes in the moderator must be made in excess: the number required is selected experimentally. In the absence of gloves and a retarder, the method used by rock climbers is recommended: the descending person sits, as it were, on a loop of rope or tape,
passing under the thigh of his right or left leg and then thrown behind his back near his neck.

It is also advisable to have a medium-sized ax at the ready - in case you have to break into a door or fight off those who want to take away your means of self-rescue.

Fire flow

In buildings with a “corridor” layout, fire spreads along the passages at a speed of up to 5 meters per minute. Often, already 20 minutes after the start of the fire, the fire penetrates from the floor on which it arose to the next floors - through windows, ventilation ducts, etc. And it only takes a few minutes for the smoke to spread throughout the fire after the start of the fire. staircases on all floors above the fire site. The upper floors, as a rule, are the most smoky. As the fire begins to be extinguished, the smoke emission may increase.

When the fire temperature is high, the strength of the floors decreases and they may collapse. Sometimes collapse occurs even after the end of the fire, since their strength is not restored after the temperature drops. Among other things, the ceilings may not be able to withstand the weight of the water that has accumulated on them and was poured onto the fire.

Fires on the upper floors are most dangerous: water pumps do not have enough power, fire escapes are not long enough.

Evacuation

In case of fire, the following factors are dangerous:

Open fire and sparks;

Thermal radiation;

High air temperature, especially if the air is humid;

Toxic combustion products in the air;

Reduced oxygen concentration in the air;

Collapsed parts of structures;

Flying pieces of exploding equipment.

The cause of death in fires is most often not fire and heat, but poisoning by toxic substances released into the air (for example, hydrocyanic acid or nitrogen oxides). A few breaths of toxic smoke are enough to make you lose consciousness. Especially a lot of toxic substances are formed when plastics burn.

Carbon dioxide (CO2) at 3 percent concentration is life-threatening if inhaled within 30 minutes. When the oxygen concentration in the air is below 10%, a person loses consciousness, so it is necessary to try to evacuate through a heavily smoky place only if other methods of rescue are not available.

Before starting individual evacuation, it is necessary, if possible, to wet clothes with water. The lack of a gas mask is partially compensated for by placing a damp cloth over the nose and mouth. You need to take some water with you: you may need it to help someone or make some small section of the path passable.

You should also take with you some object (briefcase, tray, etc.) with which you could shield your head from thermal radiation, and possibly from falling burning objects. A thick layer of clothing protects from short-term exposure to thermal radiation. When moving through a burning building, you must close all doors behind you to prevent air from entering the burning area and preventing the spread of smoke.

When evacuating in case of fire, you must not use elevators (except for special fire elevators). After switching on in a multi-story building internal system fire alerts, all ordinary (non-fire) elevators switch to the “Fire danger” mode: the cabins are lowered to the first floor and blocked there.

This is done to prevent cabins with passengers from getting stuck. In multi-section residential buildings there are transitions from section to section through balconies. From the fifth floor and above, the balconies are connected by fire escapes.

It must be borne in mind that during fires in multi-story buildings, flows of fire and smoke in corridors and on staircases can dramatically change their paths of movement due to the destruction of walls and ceilings. This means that a corridor remote from the place of combustion and lightly smoky can fill with flames and hot combustion products in a few seconds and become impassable.

If a fire occurs in a multi-storey residential building that does not have flammable elements in its structure, and the escape routes are heavily smoked, it is better not to try to go through the smoke, but to lock yourself in your apartment, caulk the doors and windows with damp material, and seal the cracks in them with adhesive tape, plug the exits ventilation ducts, stock up on water and wait for the firefighters to do their job.

Firefighting

80% of fires occur when people are nearby. Fire service cause in 20..25% of fire cases. In other cases, they put out the fire themselves. About half of the fires are dealt with before firefighters arrive.

The following fire extinguishing techniques are used:

Reduced access of air to the combustion site;

Reduced oxygen content in the air;

Cooling of the combustion zone;

Introducing combustion inhibitors (chemical reaction retarders);

Separation of the burning substance from that which has not yet been touched by the combustion process;

Creating a barrier to the spread of combustion.

The following substances are used for extinguishing:

Water-based foams;

Gases: carbon dioxide, argon, nitrogen;

Powders based on inorganic salts of alkali metals: carbonates and bicarbonates of sodium, potassium, etc.

Electrical installations under current are extinguished with powders and inert gases. Water and foam cannot be used in this case, because water conducts electricity. Alkali metals (sodium, calcium, etc.) are extinguished with powders. Water and foams cannot be used because water reacts with metals, which releases hydrogen. Flammable liquids (gasoline, alcohol, varnish, etc.) are extinguished with foams, powders, and non-flammable gases. Water should not be used because the burning liquid is lighter than water and will pool above it.

In case of fire electrical appliance First of all, disconnect the power supply. Small objects that catch fire can be extinguished by throwing a thick cloth over them, preferably a damp one. In some situations, you can use sand or soil to extinguish. Sand is stored in advance near the place where it may be needed.

If there is a fire indoors, do not rush to open doors and windows, as the consequences may not be what you expected. On the one hand, it is desirable to get rid of smoke along evacuation routes, but, on the other hand, the flow of fresh air to the combustion site intensifies the fire. If you cannot put out a fire in a room, it may be better to simply leave it, closing the doors and windows tightly.

A fire in an enclosed space, having depleted the available supply of oxygen, sharply reduces its intensity, but if a passage for fresh air is opened (a door is broken open, a window is broken), then the burning will intensify, and its intensification may have the character of an explosive flash with the emission of flame towards the opened passage . Therefore, if it is assumed that something is burning behind the door (the door is hot, smoke is coming from the cracks), you should not open it without being prepared for a possible explosion.

Protection from technical disasters

It is better not to settle near dangerous objects (fire hazardous, explosive, radioactive, chemically hazardous, etc.) or even stay near them unless there is a great need. If it is necessary to work at such facilities or in their immediate vicinity, you must do following:

1. Study the nature of the possible danger;

2. Understand the signs and signals that will indicate the occurrence of an emergency;

3. Explore the surrounding area for opportunities for self-evacuation;

4. Inquire about the implemented and envisaged protective measures. As far as possible, ensure that these measures are not provided for appearances, but are effective;

5. Prepare two individual emergency kits (with protective equipment, medications, etc.): one for constant carrying with you, the other, more extensive, for storage at the workplace;

6. Prepare means of insulating the room in which you may have to wait out the release of harmful substances;

7. Make sure that those around you are also prepared for a possible accident, otherwise they will be a burden when it happens.

Authorities and enterprise administrations tend to downplay the scale of accidents and delay giving the signal to evacuate. Therefore, we must rely more on our own organs of perception, our own sources of information, our own detector devices. In the event of an accident that causes harmful substances to appear in the environment, the choice must be made between prompt evacuation and isolation of the room in which you are located. During evacuation vital importance has the direction of the wind: the greater the angle between the direction of the wind and the direction of exit from the zone of action of harmful factors, the sooner success will be achieved. Therefore, when you are on or near a dangerous object, you must always pay attention.
obsession with approximately which direction the wind is blowing on the current day (of course, it can change direction during the day).

As a rule, the greatest contamination of the environment occurs in the first minutes or hours after an accident, and subsequently the source of contamination is eliminated or dries up, and the wind partially carries it away harmful substances. Therefore, sheltering for several hours in an isolated room turns out to be effective. Insulation consists of sealing ventilation holes, as well as door and window cracks. The best material For this purpose - adhesive tape. A person needs at least one cubic meter air per hour, but if exhaled air is mixed with inhaled air, the volume of air must be several times greater.

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16. Fire safety

According to the standard definition fire is an uncontrolled combustion outside a special fireplace, developing in time and space, dangerous to people and causing material damage.

16.1 Basic concepts, terms and definitions

Fire safety– the state of protection of individuals, property, society and the state from fires.

Fire safety can be ensured by measures fire prevention and active fire protection.

Fire prevention– a set of measures necessary to prevent a fire or reduce its consequences.

Active fire protection – measures to ensure successful fight with fires or explosive situations.

Combustion – chemical reaction, accompanied by the release of a large amount of heat and usually glow.

Combustion requires the presence of a combustible substance, oxygen (an oxidizing agent; the oxidizing agent can be not only oxygen, but also chlorine, fluorine, bromine, etc.) and a source of thermal energy for ignition. The source of ignition can be flames, electric sparks, hot solids and etc.

There are several physical forms of combustion: flash, ignition, spontaneous combustion and spontaneous combustion.

Flash– fast combustion combustible mixture, not accompanied by the formation of compressed gases. At the same time, to continue combustion, the amount of heat that is generated during the short-term flash process is not enough.

Flammable substance(material, mixture) – a substance capable of burning independently after removal of the ignition source.

Fire– the occurrence of combustion under the influence of an ignition source.

Ignition– ignition accompanied by the appearance of flame.

Spontaneous combustion– the phenomenon of a sharp increase in the rate of exothermic reactions, leading to the combustion of a substance in the absence of an ignition source.

Self-ignition– spontaneous combustion accompanied by the appearance of a flame.

Smoldering– flameless combustion of a solid substance.

Explosion– an extremely rapid chemical (explosive) transformation, accompanied by the release of energy and the formation of compressed gases capable of producing mechanical work.

Flammability– the ability of a substance (material, mixture) to burn independently. Based on flammability, substances and materials are divided into flammable, slow-burning and non-flammable.

Flammable substance– a substance (material, mixture) capable of burning independently after removal of the ignition source.

Low-flammable substance– a substance (material) capable of burning under the influence of an ignition source, but not capable of spontaneous combustion after its removal.

Non-flammable substance– a substance (material) not capable of combustion.

Most liquids used in industry are flammable. They burn in air, and under certain conditions the combustion process is accompanied by boiling or emission of burning liquid. Liquid vapors with air can form explosive mixtures.

To ensure fire safety of the technological process associated with the circulation of liquids, it is necessary to know their indicators fire danger: flash point and ignition temperature.

Flash point– the lowest (under special test conditions) temperature of a combustible substance at which vapors and gases are formed above its surface that can flare up in the air from the ignition source, but the rate of their formation is still insufficient for subsequent combustion.

Flash point- the temperature of a flammable substance at which it emits flammable vapors and gases at such a speed that, after ignition from an ignition source, stable combustion occurs.

Auto-ignition temperature– the lowest temperature of a substance (material, mixture), at which a sharp increase in the rate of exothermic reactions occurs, ending in the occurrence of flaming combustion.

When substances burn, decomposition products, vapors, and gases are released, which are often poisonous, asphyxiating, or have other effects. harmful effects per person. The fire hazard characteristics of these substances are the smoke generation coefficient and the toxicity of combustion products.

Smoke generation coefficient D– a value characterizing the optical density of smoke formed during the combustion of a substance with a given saturation in the volume of the room.

Based on their smoke-forming ability, substances are divided into three groups:

With low smoke-forming ability (D<50).
With moderate smoke generating capacity (50<Д<500).
With high smoke-forming ability (D>500).

Determines smoke-forming ability by registering the weakening of illumination when a light beam passes through a smoke-filled space.

Based on toxicity, combustion products are divided into 4 groups.

Extremely dangerous - with a toxicity index of up to 13 g/m3.
Highly hazardous - with a toxicity index of up to 40 g/m3.
Moderately hazardous - with a toxicity index of up to 120 g/m3.
Slightly hazardous - with a toxicity index of more than 120 g/m3.

16.2. Main causes of fires

An analysis of the causes of fires shows that the main and most common prerequisites for the occurrence of fires in enterprises are:

violation of the technological regime;
careless handling of open fire;
overheating of bearings;
sparks of mechanical origin;
static electricity discharges;
unextinguished cigarette butts and matches;
improper warehousing and storage of materials;
violation of operating modes of ventilation and heating devices;
sabotage.

In electrical installations, the cause of a fire can be:

wire overload;
high transition resistances;
electric arc or spark;
short circuit.

The cause of a short circuit may be:

damage to wire insulation;
contact with non-insulated wires by conductive objects (wrench, screwdriver);
exposure of wires to chemically active substances (battery);
incorrect installation of the unit.

16.3. Fire classification

In accordance with fire safety rules in the Russian Federation PPB-01-93, fires are divided into 5 classes.

Class A – fires of solid substances, mainly of organic origin, the combustion of which is accompanied by smoldering (wood, textiles, paper, coal) and not accompanied by smoldering (plastic).

Class B – fires of flammable liquids or melting solids, insoluble in water (gasoline, ether, petroleum products), soluble in water (alcohol, methanol, glycerin).

Class C – gas fires.

Class D – fires of metals and their alloys.

Class E – fires associated with the burning of electrical installations.

Classification is necessary for the selection of fire extinguishing installations and primary fire extinguishing agents. The fire class of each fire extinguisher is indicated in the passport.

16.4. Classification of production facilities by fire hazard

16.5. Fire prevention

Fire prevention is based on eliminating the conditions necessary for combustion and the principles of ensuring safety.

Security can be achieved:

1) Fire prevention measures

2) Alarm about fires.

16.5.1. Fire Prevention Measures

organizational (proper operation of machines and in-plant transport, proper maintenance of buildings and territories, fire safety training for workers, organization of voluntary fire protection, issuance of orders on fire safety issues);
technical (compliance with fire safety rules, design standards, installation of electrical wires and equipment, heating, ventilation, lighting, correct placement of equipment);
security restrictions (prohibition of smoking in undesignated places, welding and other hot work in fire hazardous areas, etc.);
operational - timely preventive inspections, repairs and tests of process equipment.

In accordance with the rules PPB-01-93, to prevent fires, it is important to locate production in buildings of a certain fire resistance. Fire resistance is the resistance of buildings to fire.

Based on fire resistance, buildings are divided into 5 levels. The degree of fire resistance is characterized by the flammability of the substance and the fire resistance limit. The fire resistance limit of a building is the time, expressed in hours, after which the structure loses its load-bearing or enclosing capacity. Loss of load-bearing capacity means the collapse of a building structure in a fire. Loss of barrier ability means heating the structure to a temperature, an increase in which can cause spontaneous combustion of substances located in an adjacent room, or the formation of cracks in the structure through which combustion products can penetrate into adjacent rooms.

In accordance with the degree of fire resistance and the category of fire hazard of the production, the number of storeys of the building and fire breaks are determined.

Reducing the fire hazard of structures is of great importance.

Many rooms have wooden partitions, cabinets, shelving, etc. Increasing the flammability resistance of wooden structures is achieved by plastering them or lining them with fireproof or fire-resistant materials, deep or surface impregnation with fire-retardant compounds, and coating with fire-retardant paint or coating. Similar measures must be applied to other combustible structural materials.

The process of thermal decomposition of wood occurs in two phases:

the first phase of decomposition is observed when wood is heated to 250° (to the ignition temperature) and occurs with heat absorption;
the second phase - the combustion process itself occurs with the release of heat. The second phase consists of two periods of combustion of gas formed during the thermal decomposition of wood (flame phase of combustion) and combustion of the resulting charcoal (smoldering phase).

The flammability of wood is significantly reduced when it is impregnated with fire retardants. Heating wood leads to the decomposition of fire retardants with the formation of strong acids (phosphoric and sulfuric) and the release of non-flammable gases that prevent the burning and smoldering of the protected wood.

The most common fire retardants include ammonium phosphate, dibasic and monosubstituted, ammonium sulfate, borax and boric acid. Borax and boric acid are taken in a 1:1 mixture.

Thermal insulating materials include asbestos cement sheets, gypsum fiber, asbestos vermiculite, perlite boards, asbestos cardboard, and various plasters. Protection with these materials is used only in enclosed spaces.

Paints and coatings consist of a binder, filler and pigment. The resulting film in fire-retardant paints serves both fire-retardant and decorative purposes (due to the pigment).

Liquid glass, cement, gypsum, lime, clay, synthetic resins, etc. are used as binders for fire-retardant paints and coatings. Fillers are chalk, talc, asbestos, vermiculite, etc. Pigments include methopane, zinc white, mummy, ocher, chromium oxide, etc.

The main methods of fire-retardant impregnation of wooden structures and products can be superficial and deep. In some cases, fire retardant compounds are applied to the surface, in others they are impregnated into the material in bathtubs or in deep impregnation units under pressure.

The effectiveness of a fire retardant is measured by the time it takes for a sample or structural element to ignite from a heat source. The cessation of combustion and smoldering after removal of the heat source determines the quality of the fire retardant composition.

The flammability characteristics of building materials and structures have been established:

ignition time;
burning rate;
time of cessation of combustion and smoldering after removal of the ignition source.

The burning rate is determined by the ratio of the percentage of weight loss of the sample under fire exposure to the test time. The study of flammability is carried out by testing standard samples of the material under specified heat sources, the position of these sources relative to the sample and the test time.

16.5.2. Fire alarm

To fight fires, timely reporting of fires is important. Electrical and automatic alarm systems are used to report a fire.

Successfully fighting a fire depends on quickly and accurately reporting the fire and its location to the local fire brigade. For this purpose, electric (EPS), automatic (APS), and sound fire alarm systems can be used, which include a horn, siren, etc. Telephone and radio communications are used as a means of fire alarm.

The main elements of electrical and automatic fire alarms are detectors installed at objects, receiving stations that register the outbreak of a fire, and linear structures connecting detectors to receiving stations. Reception stations located in special fire department premises must be manned 24 hours a day.

Basic requirements for fire alarms:

must be located in places accessible for inspection;
sensors must be highly sensitive.

Sensors are used thermal, smoke, ultrasonic and combined.

Sensors can be: maximum – they are triggered when the controlled parameters reach a given value; differential – react to changes in the speed of a given parameter; maximally differential – they react to both.

The principle of operation of thermal sensors is to change the physical and mechanical properties of sensitive elements under the influence of temperature (low-melting alloy). An alloy is used to connect two plates. When heated, the alloy melts, the plates open the electrical circuit, and a signal is sent to the remote control.

Smoke detectors have two main methods of detecting smoke: photoelectric (PDE) and radioisotope (RID). The IDF detector detects smoke by detecting light reflected from smoke particles with a photocell. The RID has an ionization chamber with a source of a-particles as a sensitive element. An increase in smoke content reduces the rate of ionization in the chamber, which is recorded.

A combined detector (CD) responds to both rising temperatures and smoke.

A light fire detector (SI) detects the radiation of a flame against the background of extraneous light sources.

The ultrasonic sensor has high sensitivity and can combine security and alarm functions. These sensors respond to changes in the characteristics of the ultrasonic field filling the protected room.

Currently, enterprises use beam and ring electric fire alarms.

Beam fire alarm system TOL-10/50 is used in enterprises with round-the-clock presence of people and provides reception of signals, telephone conversation with the detector, and launching of stationary fire extinguishing installations.

The ring fire alarm system TKOZ-50M is designed for 50 manual detectors. The station provides signal reception, recording by a recording device and automatic transmission of the signal to the fire department.

In premises where people are not present 24/7, automatic fire detectors are installed. The triggering factor for these detectors is smoke, heat, light, or both factors combined.

Reliable fire communications and alarms play an important role in the timely detection of fires and calling fire departments to the scene of a fire. By purpose, fire communications are divided into:

notification communication;
dispatch communication;
fire communication.

16.6. Fire extinguishing agents

16.6.1. Fire extinguishing agents

The impact of fire extinguishing agents on the source of a fire can be different: they cool the burning substance, isolate it from the air, and remove the concentration of oxygen and flammable substances. In other words, fire extinguishing agents act on the factors that cause the combustion process.

Principles of combustion termination.

Isolating the combustion source from air or reducing the oxygen concentration with non-flammable gases to a value at which combustion cannot occur:

cooling the combustion site below certain temperatures;
intense inhibition of the rate of chemical reaction in the flame;
mechanical flame arrest by the action of a jet of gas or water;
creation of fire-barrier conditions.

To extinguish fires, water, aqueous solutions of chemical compounds, foam, inert gases and gas compositions, powders and various combinations of these agents are used.

Water- the main means of extinguishing fires. It is used in the combustion of solid, liquid and gaseous substances and materials. The exception is some alkali metals and other compounds that decompose water. Water for extinguishing is used in the form of solid (compact) jets, in a sprayed and finely sprayed (fog-like) state, and also in the form of steam.

The ability to extinguish a fire with water is based on its cooling effect, dilution of the flammable medium, water vapor formed during evaporation and mechanical effect on the burning substance (flame failure).

Foams are an effective and convenient fire extinguishing agent and are widely used to eliminate the combustion of various substances, especially flammable and combustible liquids.

Foam is a cellular-film system consisting of a mass of gas or air bubbles (cells) separated by thin films of liquid.

Fire extinguishing foams are divided into two groups according to the method of formation: chemical and air-mechanical.

Chemical foam is produced in large quantities in foam generators by contacting foam powders with water, consisting of an alkaline part (bicarbonate of soda), an acid part (aluminum sulfate) and a foaming agent (substances of protein origin, synthetic, various surfactants, etc.).

In chemical foam fire extinguishers, foam is formed by the reaction of aqueous solutions of sodium bicarbonate containing licorice extract, sulfuric acid and an iron tanning agent.

Chemical foam is approximately 80% carbon dioxide, 19.7% water and 3% foaming agent.

Air-mechanical foam is formed in generators as a result of mechanical mixing of air, water and foaming agent and comes in low, medium and high expansion. Depending on the type of foam concentrate and the foam expansion ratio, it is used to extinguish flammable liquids and combustible liquids.

Air-mechanical foam is economical, non-electrically conductive, harmless to people, can be easily and quickly produced during a fire, and, unlike chemical foam, does not cause metal corrosion and does not damage equipment and materials on which it comes in contact.

The main fire extinguishing property of foam is its ability to isolate the burning substance and materials from the surrounding air, reduce the concentration of oxygen in the combustion zone, as well as its cooling effect.

Gas fire extinguishing agents. These means include: water vapor, carbon dioxide ( carbon dioxide), inert gases (nitrogen, argon), as well as fire extinguishing compounds based on halogenated hydrocarbons, which are gases or highly volatile liquids (ethyl bromide, chlorobromomethane).

Carbon dioxide in snow-like and gaseous states is used in various fire extinguishers and stationary installations to extinguish fires in enclosed spaces and small open fires.

Inert gases are used to fill volumes in which, when the oxygen concentration is reduced to 5% or lower, hot work can be performed (cutting, welding metals, etc.).

Powdered substances are dry compositions based on sodium carbonate and bicarbonate. Powders are used to extinguish metals and various solid and liquid flammable substances and materials.

Powder compositions are non-toxic, do not have a harmful effect on materials and can be used in combination with sprayed water and foam extinguishing agents. A negative property of powders is that they do not cool burning substances, and they can re-ignite from heated structures.

16.6.2. Stationary installations and fire extinguishing devices

Stationary fire extinguishing installations consist of permanently installed apparatus and devices connected by a pipeline system for supplying fire extinguishing agents to the protected objects.

Automatic fire extinguishing installations are classified depending on the use of extinguishing agents:

water - using solid, atomized, finely atomized water jets;
water chemical - using water with various additives (wetting agents, thickeners, etc.);
foam - using air-mechanical foam;
gas - using carbon dioxide, halogenated hydrocarbons, inert gases;
powder - using fire extinguishing powders;
combined - using several extinguishing agents.

One of the promising areas that ensures the fire safety of objects is the installation of fire-fighting automatics - sprinkler and deluge installations (the terms are taken from the English words: to sprinkle - to splash and to drench - to wet). These installations are used by many commercial warehouses.

Sprinkler systems are designed for quick automatic extinguishing and localization of a fire when water can be used as a fire extinguishing agent. Simultaneously with the supply of sprayed water to the fire, the system automatically gives a fire signal.

In sprinkler installations, air-mechanical foam can also be used as a fire extinguishing agent.

Sprinkler installations, adapted for extinguishing with air-mechanical foam, are equipped instead of SP-2 sprinkler heads with special foam heads (OP foam sprinkler), allowing one head to protect a floor area of 20 - 25 m2. To form air-mechanical foam in installations, a 3–5% solution of foaming agent PO-1 is used.

Depending on the temperature in the protected premises, sprinkler systems are divided into water, air and air-water.

Water sprinkler systems are installed in rooms where the temperature is constantly maintained above 4 °C. The pipelines of this system are always filled with water. When the air temperature rises or is exposed to flame, the fusible locks of the sprinkler heads are unsoldered, water comes out of the holes, irrigating the protection zone.

Air sprinkler systems are installed in unheated buildings. The pipelines of this system are filled with compressed air. In this case, there is compressed air before the control and alarm valve, and water after the control and alarm valve. When the sprinkler head of the air system is opened, after the air has escaped, water enters the network and extinguishes the fire.

Air-water systems are a combination of air and water sprinkler systems. The sprinkler installation is activated automatically by melting the fusible lock of the sprinkler head.

Deluge installations are designed for automatic and remote fire extinguishing with water. There are automatic and manual deluge installations. In automatic deluge installations, water is supplied to the network using a group-action valve. Under normal conditions, the automatic inducement valve is held in the closed position by a cable system with fusible locks. In the event of a fire, the lock melts, the cable breaks, the valve opens under water pressure and water flows into the deluge. In a manual deluge plant, water is supplied after the valve is opened. Unlike splicler systems, in deluge installations, water sprayers (deluges) are constantly open.

Fire extinguishers are designed to extinguish fires in their initial stages. Based on the type of fire extinguishing agent used, they are divided into foam, gas and powder.

Foam fire extinguishers are designed to extinguish small fires of solid materials and substances and flammable liquids. They are not used to extinguish fires in electrical installations that are under voltage, because chemical foam is electrically conductive.

Chemical foam fire extinguishers OHP-10, OP-M.

Air-foam fire extinguishers OVP-5, OVP-10.

Carbon dioxide fire extinguishers OU-2, OU-5, OU-8 are used to extinguish various substances and materials (with the exception of alkali metals), live electrical installations, Vehicle etc.

Carbon dioxide-bromoethyl fire extinguishers OUB-3A and OUB-7A are designed to extinguish small fires of various flammable substances, smoldering materials, and live electrical installations.

Powder fire extinguishers OP-1, OP2B, OP-10 are designed to extinguish small fires of flammable liquids, gases, live electrical installations, metals and their alloys.

Automatic aerosol fire extinguisher SOT-1 - designed to extinguish fires of solid and liquid flammable substances (alcohols, gasoline), smoldering and solid materials, electrical equipment in closed spaces.

The operating principle is based on the strong inhibitory effect of a fire extinguishing aerosol composition made from ultrafine products on the combustion reactions of substances in air oxygen.

The aerosol has no harmful effects on humans and is easily removed. Disposable fire extinguisher.

The UAP-A fire extinguisher automatically detects and extinguishes fire in small confined spaces. The fire extinguisher is installed on the ceiling in the center of the room. If a fire occurs, the fusible element is destroyed, the fire extinguisher container is opened and a substance (freon or powder) is released into the room, creating an environment that does not support combustion.

16.7. Responsibility for violation of fire safety rules

Responsibility for violation of fire safety requirements lies with:

property owners;

persons authorized to own, use or dispose of property (managers of enterprises;

persons duly appointed responsible for ensuring fire safety).

All substances are divided into flammable, low-flammable and non-flammable.

Substances that can burn independently after the ignition source is removed are called flammable.

Substances that do not burn in air are called non-flammable.

Occupying an intermediate position flame retardant substances that ignite when exposed to an ignition source, but stop burning when it is removed.

All flammable substances are divided into the following main groups:

1. Combustible gases (GG)– substances capable of forming flammable and explosive mixtures with air at temperatures not exceeding 50 °C. GG includes individual substances: ammonia, acetylene, butadiene, butane, hydrogen, methane, carbon monoxide, propane, hydrogen sulfide, formaldehyde, as well as vapors of flammable liquids and gas liquids.

Flammable gases are explosive at any ambient temperature.

There are:

Light gas: which at a temperature of 20 °C and a pressure of 100 kPa has a density of less than< 0,8 по отношению к плотности воздуха (т.е. относительную плотность).

Heavy gas:> 1.2. if the relative density is in between, then both possibilities should be considered.

Liquefied gas: which, at a temperature below 20 °C or a pressure above 100 kPa, or under the combined action of both these conditions, turns into a liquid.

2. Flammable liquids (flammable liquids)– substances capable of burning independently after removal of the ignition source and having a flash point not higher than 61 ° C (in a closed crucible). These liquids include individual substances: acetone, benzene, hexane, heptane, xylene, methyl alcohol, carbon disulfide, styrene, acetic acid, chlorobenzene, ethyl alcohol, as well as mixtures and technical products: gasoline, diesel fuel, kerosene, solvents.

Explosive flammable liquids are those whose flash point does not exceed 61 °C, and the vapor pressure at a temperature of 20 °C is less than 100 kPa (about 1 atm.).

3. Flammable liquids (FL)– substances capable of burning independently after removal of the ignition source and having a flash point above 61 ° C (in a closed crucible) or 66 ° C (in an open crucible). GZ includes the following individual substances: aniline, hexyl alcohol, glycerin, ethylene glycol, as well as mixtures and technical products, for example, oils: transformer oil, vaseline, castor oil.

GLs with a flash point > 61 °C are classified as fire hazardous, but those heated under production conditions to a flash point or higher are classified as explosive.

4. Combustible dusts (GP)– solid substances in a finely dispersed state. HP in the air (aerosol) is capable of forming explosive mixtures with it. Dust (aerogel) settled on walls, ceilings, and equipment surfaces is a fire hazard.

According to the degree of explosion and fire hazard, GPs are divided into four classes.

1 class– the most explosive are aerosols that have a lower concentration limit of flammability (explosiveness) (LCEL) of up to 15 g/m 3 (sulfur, naphthalene, rosin, mill dust, peat, ebonite).

2nd grade– explosive – aerosols having an LEL value from 15 to 65 g/m 3 (aluminum powder, flour dust, hay dust, shale dust).

3rd grade– the most fire hazardous are aerogels with an LFL value of more than 65 g/m 3 and a self-ignition temperature of up to 250 ° C (tobacco, elevator dust).

4th grade– fire hazardous – aerogels with an LEL value of more than 65 g/m 3 and a self-ignition temperature of more than 250 °C ( sawdust, zinc dust).

Page 3

Solid flammable substances in the form of air suspensions are prepared for combustion at any temperature. Their preparedness is determined by the concentration in the air.

Solid flammable substances undergo various changes when heated, the nature of which depends on their chemical composition and molecular structure. The combustion of the first group of solids proceeds in the same way as the combustion of liquids. The combustion of the second group proceeds differently.

Inorganic solid combustible substances - metals, metalloids and their compounds, when heated, almost all melt and form a layer of vapor above the surface.

Vapor-gas, liquid, dust-like and solid flammable substances are in technological processes in the form of raw materials, processed materials, finished products, as well as structural elements buildings, structures, installations and equipment made of flammable materials.

When heated, some solid flammable substances melt, evaporate (sulfur, stearin, rubber) and burn in a vapor state.

Some solid flammable substances melt and evaporate when heated (sulfur, bitumen, stearin, rubber) and burn in a vapor state. Others, such as coal, wood, paper, fabrics, when heated, decompose into gaseous products and a solid substance - coal. Coke, charcoal and anthracite do not melt or decompose when heated, but burn in solid form. When heated, liquid flammable substances evaporate and their vapors are involved in the process of combustion or explosion.

When heated, some solid flammable substances melt, evaporate (sulfur, stearin, rubber) and burn in a vapor state. Coke, charcoal and anthracite do not melt or decompose when heated and burn in solid form. Liquid flammable substances evaporate when heated, and their vapors are involved in the process of combustion or explosion.

Some solid flammable substances melt and evaporate when heated (sulfur, stearin, rubber) and burn in a vapor state.

When heated, some solid flammable substances melt, evaporate and burn in a vapor state (sulfur, rubber, etc. Other flammable substances (coke, charcoal) do not melt when heated and burn in a solid state.

Of the solid combustible substances, fibrous and finely crushed materials are most susceptible to ignition from sparks: cotton, felt, fabric, hay, chaff, wool, etc. All of them have low thermal conductivity and a large surface, which helps preserve the thermal energy of the spark in a small volume of combustible substance and quickly I'll heat it up.

Dusts of solid combustible substances, as well as fibers of some combustible materials, when mixed with air, form dust-air mixtures in suspension, which can be explosive or fire hazardous.

For solid flammable substances, the flash point is the temperature at which they emit so many vapors or gases that when mixed with air, when briefly exposed to a flame, they ignite, but do not burn further.

Of the solid combustible substances, fibrous and finely crushed materials are most susceptible to ignition from sparks: cotton, felt, fabric, hay, chaff, wool and others. All of them have low thermal conductivity and a large heat absorption surface, which contributes to the conservation of the thermal energy of the spark in a small volume of combustible substance and rapid heating. Since a small volume of solid combustible substances is heated by a spark, the resulting gaseous decomposition products are not enough to form a combustible mixture. Because of this, ignition of fibrous substances by sparks is not accompanied by the formation of a flame, but occurs in the form of smoldering carbon residue. Only heated bodies of significant size can cause ignition of solids with the formation of a flame.

Based on their composition, solid flammable substances are divided into individual and complex. The composition of complex combustible substances is expressed by their content of carbon C, hydrogen H, oxygen O, nitrogen N, sulfur S, ash A and moisture W. It can separately characterize organic, combustible, dry and working weight flammable substance. Each of these characteristics is determined by the components included within it.

FIRE TACTICS

LECTURE NOTES

Topic: Fire and its development

Arkhangelsk, 2015

Literature:

1. Federal Law of December 21, 1994 N 69-FZ “On Fire Safety”.

2. Federal Law of July 22, 2008 N 123 Federal Law “Technical Regulations on Fire Safety Requirements”.

3. Terebnev V.V., Podgrushny A.V. Fire tactics - M.: - 2007

I'M WITH. Pozik. RTP Directory. Moscow. 2000

5. Ya.S. Pozik. Fire tactics. Moscow. Stroyizdat. 1999

6. M.G.Shuvalov. Basics of firefighting. Moscow. Stroyizdat. 1997

Study questions:

1 questionGeneral concept about the combustion process. Conditions necessary for combustion (combustible substance, oxidizer, ignition source) and its cessation. Combustion products. Complete and incomplete combustion. Brief information on the nature of combustion of solid combustible materials, flammable and combustible liquids, gases, flammable mixtures of vapors, gases and dusts with air

2. Question

General concept of the combustion process. Conditions necessary for combustion (combustible substance, oxidizer, ignition source) and its cessation. Combustion products. Complete and incomplete combustion. Brief information about the nature of combustion of solid combustible materials, flammable and combustible liquids, gases, flammable mixtures of vapors, gases and dusts with air.

Combustion is any oxidation reaction in which heat is released and the glow of burning substances or their decomposition products is observed.

For combustion to occur, certain conditions are necessary, namely the combination in one place at one time of three main components:

flammable substance, in the form of combustible materials (wood, paper, synthetic materials, liquid fuel etc.);

· an oxidizing agent, which most often is air oxygen when burning substances; in addition to oxygen, oxidizing agents can be chemical compounds containing oxygen in their composition (saltpeter, perchlorites, nitric acid, nitrogen oxides) and individual chemical elements: chlorine, fluorine, bromine;

· an ignition source that constantly and in sufficient quantities enters the combustion zone (spark, flame).

ignition source

O 2 flammable substance

The absence of one of the listed elements makes it impossible for a fire to occur or leads to the cessation of combustion and the elimination of the fire.

Most fires involve the combustion of solid materials, although the initial stage of a fire may involve the combustion of liquid and gaseous flammable substances used in modern industrial production.

Ignition and combustion of most flammable substances occurs in the gas or vapor phase. The formation of vapors and gases from solid and liquid flammable substances occurs as a result of heating. In this case, liquids boil with evaporation, and materials volatilize, decompose, or pyrolyze from the surface of solids.

Solid flammable substances behave differently when heated:

· some (sulfur, phosphorus, paraffin) melt;

· others (wood, peat, coal, fibrous materials) decompose with the formation of vapors, gases and solid coal residues;

· still others (coke, charcoal, some metals) do not melt or decompose when heated. The vapors and gases released from them mix with air and oxidize when heated.

The glow of the flame occurs because light is emitted by hot carbon particles that do not have time to burn.

A mixture of a flammable substance with an oxidizer is called a combustible mixture. Depending on the state of aggregation of the combustible mixture, combustion can be:

Homogeneous (gas-gas);

Heterogeneous (solid-gas, liquid-gas).

At homogeneous combustion the fuel and oxidizer are mixed, and when heterogeneous they have an interface.

Depending on the ratio of oxidizer and combustible substance in the flammable mixture, two types of combustion are distinguished:

· complete combustion - combustion of lean mixtures, when the oxidizer is much larger than the combustible substance and the resulting products are not capable of further oxidation - carbon dioxide, water, nitrogen oxides and sulfur.

· incomplete combustion - combustion of rich mixtures, when the oxidizer is significantly less than the combustible substance, incomplete oxidation of the decomposition products of substances occurs. Products of incomplete combustion – carbon monoxide, alcohols, ketones, acids.

A sign of incomplete combustion is smoke, which is a mixture of vapor, solid and gaseous particles. In most cases, fires involve incomplete combustion of substances and strong smoke emission.

Combustion can occur in several ways:

· flash - rapid combustion of a combustible mixture, not accompanied by the formation of compressed gases. It does not always lead to fire, since the heat generated is not enough;

· fire – the occurrence of combustion under the influence of an external ignition source;

· ignition – ignition using a flame;

Spontaneous combustion - the occurrence of combustion under the influence of internal source ignition (thermal exothermic reactions).

· spontaneous combustion – spontaneous combustion with the appearance of a flame.

Characteristics of flammable substances

Substances that can burn independently after removing the source of ignition are called combustible, in contrast to substances that do not burn in air and are called non-flammable. An intermediate position is occupied by difficultly combustible substances that ignite when exposed to an ignition source, but stop burning after the latter is removed.

All flammable substances are divided into the following main groups.

1. Combustible gases (GG)- substances capable of forming flammable and explosive mixtures with air at temperatures not exceeding 50° C. Combustible gases include individual substances: ammonia, acetylene, butadiene, butane, butyl acetate, hydrogen, vinyl chloride, isobutane, isobutylene, methane, carbon monoxide, propane , propylene, hydrogen sulfide, formaldehyde, as well as vapors of flammable and combustible liquids.

2. Flammable liquids (flammable liquids)- substances capable of burning independently after removal of the ignition source and having a flash point not higher than 61° C (in a closed crucible) or 66° (in an open crucible). These liquids include individual substances: acetone, benzene, hexane, heptane, dimethylforamide, difluorodichloromethane, isopentane, isopropylbenzene, xylene, methyl alcohol, carbon disulfide, styrene, acetic acid, chlorobenzene, cyclohexane, ethyl acetate, ethylbenzene, ethyl alcohol, as well as mixtures and technical products gasoline, diesel fuel, kerosene, white alcohol, solvents.

3. Flammable liquids (FL)- substances capable of burning independently after removal of the ignition source and having a flash point above 61° (in a closed crucible) or 66° C (in an open crucible). Flammable liquids include the following individual substances: aniline, hexadecane, hexyl alcohol, glycerin, ethylene glycol, as well as mixtures and technical products, for example, oils: transformer oil, vaseline, castor oil.

4. Combustible dusts (GP)- solids in a finely dispersed state. Combustible dust in the air (aerosol) can form explosive mixtures with it. Dust (aerogel) settled on walls, ceilings, and equipment surfaces is a fire hazard.

Combustible dusts are divided into four classes according to the degree of explosion and fire hazard.

Class 1 - the most explosive - aerosols with a lower concentration limit of ignition (explosiveness) (LCEL) of up to 15 g/m 3 (sulfur, naphthalene, rosin, mill dust, peat, ebonite).

Class 2 - explosive - aerosols with an LEL value from 15 to 65 g/m 3 (aluminum powder, lignin, flour dust, hay dust, shale dust).

3rd class - the most fire hazardous - aerogels with an LFL value greater than 65 g/m 3 and a self-ignition temperature of up to 250 ° C (tobacco, elevator dust).

4th class - fire hazardous - aerogels with an LFL value greater than 65 g/m 3 and a self-ignition temperature greater than 250 ° C (sawdust, zinc dust).

Below are some characteristics of flammable substances necessary for predicting emergency situations.

Indicators of explosion and fire hazard of flammable gases and vapors of flammable and combustible liquids

Table 1.

substance	symbols	flash point	concentration limits explosiveness (ignition)
		tspr, ° C	lower (NKPV)	upper (VKPV)
			% by volume	g/m 3 at 20° C	by volume	g/m 3 at 20 °C
ETHERS AND ETHERS
Amyl acetate	LVZH		1.08	90.0	10.0	540.0
Butyl acetate	LVZH		1.43	83.0	15.0	721.0
Diethyl alcohol Ethylene oxide	LVZH VV	-4 3 -	1.9 3.66	38.6 54.8	51.0 80.0	1576.0 1462.0
ethyl acetate	LVZH	-3	2.98	80.4	11.4	407.0
ALCOHOLS
Amyl	LVZH		1.48	43.5	-	-
Methyl	LVZH		6.7	46.5	38.5	512.0
Ethyl	LVZH		3.61	50.0	19.0	363.0
LIMIT HYDROCARBONS
Butane	GG	-	1.8	37.4	8.5	204.8
Hexane	LVZH	-23	1.24	39.1	6.0	250.0
Methane	GG	-	5.28	16.66	15.4	102.6
Pentane	LVZH	-44	1.47	32.8	8.0	238.5
Propane	GG	-	2.31	36.6	9.5	173.8
Ethane	GG	-	3.07	31.2	14.95	186.8
UNSATURATE HYDROCARBONS
Acetylene	BB	-	2.5	16.5	82.0	885.6
Butylene	GG	-	1.7	39.5	9.0	209.0
Propylene	GG	-	2.3	34.8	11.1	169.0
Ethylene	BB	-	3.11	35.0	35.0	406.0
AROMATIC HYDROCARBONS
Benzene	LVZH	-12	1.43	42.0	9.5	308.0
Xylene	LVZH		1.0	44.0	7.6	334.0
Naphthalene	GP4	-	0.44	23.5	-	-
Toluene	LVZH		1.25	38.2	7.0	268.0
COMPOUNDS CONTAINING NITROGEN AND SULFUR
Ammonia	GG	-	17.0	112.0	27.0	189.0
Aniline	GJ		1.32	61.0	-	-
Hydrogen sulfide	GG	-	4.0	61.0	44.5	628.0
Carbon disulfide	LVZH	-43	1.33	31.5	50.0	157.0
PETROLEUM PRODUCTS AND OTHER SUBSTANCES
Gasoline (boiling point 105 ° C) Gasoline (same 64...94 ° C) Hydrogen	LVZH LVZH GG	-36 -36 -	2.4 1.9 4.09	137.0 - 3.4	4.9 5.1 880.0	281.0 - 66.4
Kerosene	LVZH	>40	0.64	-	7.0	-
Petroleum gas	GG	-	3.2	-	13.6	-
Carbon monoxide	GG	-	12.5	145.0	80.0	928.0
Turpentine	LVZH		0.73	41.3	-	-
Coke gas	GG	-	5.6	-	30.4	-
Blast gas	GG	-	46.0	-	68.0	-

Flash point- the lowest temperature of a liquid at which a steam-air mixture is formed near its surface, capable of flaring up from a source and burning, without causing a stable combustion of the liquid.

Upper and lower explosive concentration limits(ignition) - respectively, the maximum and minimum concentration of flammable gases, vapors of flammable or combustible liquids, dust or fibers in the air, above and below which an explosion will not occur even if there is a source of initiation of the explosion.

The aerosol is capable of exploding when solid particle sizes are less than 76 microns.

Upper explosive limits dusts are very large and are practically difficult to reach indoors, so they are not of interest. For example, the VCPV of sugar dust is 13.5 kg/m 3 .

BB- explosive substance - a substance capable of explosion or detonation without the participation of oxygen in the air.

Auto-ignition temperature- the lowest temperature of a combustible substance at which a sharp increase in the rate of exothermic reactions occurs, ending in the occurrence of flaming combustion.

General concept of fire. a brief description of phenomena occurring during a fire. Hazardous Fire Factors and their secondary manifestations. Classification of fires. Gas exchange in a fire. Conditions conducive to the development of fire, the main ways of fire spread.

Fire – uncontrolled combustion causing material damage, harm to the life and health of citizens, and the interests of society and the state. (No. 69-FZ “On Fire Safety” dated December 21, 1994).

By fire uncontrolled combustion is considered outside a special focus causing material damage (RTP directory, P.P. Klyus, V.P. Ivannikov).

Fire is complex physical-chemical process, which, in addition to combustion, includes general phenomena characteristic of any fire, regardless of its size and location of origin (mass and heat transfer, gas exchange, smoke formation). These phenomena are interconnected and develop in time and space. Only eliminating the fire can lead to their cessation.

General phenomena can lead to the emergence of particular phenomena, i.e. those that may or may not occur in fires. These include: explosions, deformation and collapse of technological devices and installations, building structures, boiling or release of petroleum products from tanks, etc.

A fire is also accompanied by social phenomena that cause not only material but also moral damage to society. These include death, thermal injuries, poisoning by toxic combustion products, and panic. This is a special group of phenomena that causes significant psychological overload and stress in people.

Signs of a fire:

– combustion process;

– gas exchange;

– heat exchange.

They change in time, space and are characterized by fire parameters.

To the main factors characterizing possible development combustion process in a fire, include: fire load, mass burnout rate, linear speed flame propagation over the surface of burning materials, intensity of heat release, flame temperature, etc.

Under fire load understand the mass of all flammable and slow-burning materials located indoors or in open space, related to the floor area of the room or the area occupied by these materials in open space (kg/m2).

Burnout rate– loss of mass of material (substance) per unit of time or combustion (kg/m 2 s).

Linear speed of combustion propagation– physical quantity characterized by the translational movement of the flame front in in this direction per unit of time (m/s).

Under the temperature of a fire in fences understand the average volumetric temperature of the gas environment in the room.

Under the temperature of fire in open spaces– flame temperature.

During a fire, gaseous, liquid and solid substances are released. They are called combustion products, i.e. substances formed as a result of combustion. They are distributed in gas environment and create smoke.

Smoke– a dispersed system of combustion products and air, consisting of gases, vapors and hot particles. The volume of smoke released, its density and toxicity depend on the properties of the burning material and on the conditions of the combustion process.

Smoke formation in a fire - the amount of smoke, m 3 /s, emitted from the entire area of the fire.

Smoke concentration– the amount of combustion products contained per unit volume of the room (g/m3, g/l, or in volume fractions).

Fire area(S P)– the area of projection of surface combustion of solid and liquid substances and materials onto the surface of the earth or floor of the room.

Fire area has its own borders: perimeter and front.

Fire perimeter (P P) is the length of the outer boundary of the fire area.

Fire front (F P) – part of the fire perimeter in the direction of which combustion spreads.

Fire area shapes

Depending on the location of the fire, the type of combustible materials, space-planning solutions of the facility, characteristics of structures, meteorological conditions and other factors, the fire area has a circular, angular and rectangular shape (Fig. 2 - 5).

Circular fire area shape (Fig. 2) occurs when a fire occurs in depth large plot with a fire load and in relatively calm weather, it spreads in all directions with approximately the same linear speed (timber warehouses, grain tracts, combustible coatings of large areas, industrial, as well as warehouses large area, etc.).

Corner shape (Fig. 3, 4 ) characteristic of a fire that occurs at the border of a large area with a fire load and spreads inside the corner under any meteorological conditions. This form of fire area can occur on the same objects as the circular one. Maximum angle The area of the fire depends on geometric figure area with fire load and the place where combustion occurs. Most often, this form is found in areas with an angle of 90° and 180°.

Rectangular the shape of the fire area (Fig. 5) occurs when a fire occurs on the border or in the depths of a long section with a flammable load and spreads in one or several directions: downwind - with a larger one, against the wind - with a smaller one, and in relatively calm weather with approximately the same linear speed (long buildings of small width of any purpose and configuration, rows of residential buildings with outbuildings in rural settlements, etc.).

Fires in buildings with small rooms take on a rectangular shape from the start of combustion. Ultimately, as combustion spreads, the fire can take the shape of a given geometric section (Fig. 6)

The shape of the area of a developing fire is the main one for determining the design scheme, the directions of concentration of forces and extinguishing means, as well as the required quantity of them under the appropriate parameters for carrying out combat operations. To determine the design scheme, the real shape of the fire area is reduced to the figures of the correct geometric shape(Fig. 7 a, b, in a circle with radius R(with a circular shape), a sector of a circle with a radius R and angle α (with angular shape), rectangle with side width a and length b(with a rectangular shape).

Fig.7. Calculation schemes for fire area shapes

A) circle; b) rectangle; c) sector

Circular shape of the fire area

Fire area – S P = pR 2 S P = 0.785 D 2

Fire perimeter – P P = 2pR

Fire front – Ф П = 2pR

Angular shape fire

Fire area – S P = 0.5 aR 2

Fire perimeter – P П = R(2+a)

Fire front – Ф П = aR

Linear velocity of propagation – V L = R/t

Rectangular fire shape