Fire extinguishing agents: chemical properties, types. Fire extinguishing agents (means): classification and requirements Water has a low thermal conductivity, which contributes to the creation of reliable thermal insulation on the surface of the burning material

Water is a universal fire extinguishing agent; moreover, it is quite acceptable and is available at any production site in unlimited quantities. So, to extinguish small fires, you can use the nearest water tap. To supply a large amount of water, enterprises create an internal fire water supply system.

The use of water is especially effective when extinguishing solid combustible materials - wood, paper, rubber, fabrics, which are the most often burning materials in a fire. It is also good to extinguish flammable liquids dissolving in it with water - acetone alcohols, organic acids.

The fire-extinguishing properties of water increase sharply if it enters the combustion zone in the form of spray jets, which reduces its consumption.

Water is successfully used to localize the fire, when the fire cannot be quickly extinguished. In this case, water is poured over all combustible substances, materials, structures and installations located in the immediate vicinity of the ignition source.

This is exactly what is done in rooms and on sites where cylinders with various compressed gases are installed. This technique is used successfully until cylinders or other objects are evacuated to a safe place.

Water is very effective in extinguishing fires, but its use in the conditions of radio electronics enterprises is less often limited. First of all, this is due to the fact that the electrical conductivity of water is quite high, therefore, it is impossible to extinguish a burning electrical equipment under voltage with it.

Also, water cannot be used if there are alkali metals in the fire zone - sodium, potassium.

It is especially dangerous if water gets into burning oil tanks and other containers with burning liquids or melting when heated by solid substances, since, depending on the amount of water and the temperature of the liquid, either its violent boiling occurs, or splashing and ejection of the burning liquid into the volume of the room. As a result, the intensity of combustion increases and the area of the fire expands. At the same time, the use of sprayed water jets makes it possible to successfully extinguish many flammable liquids, including various oils and kerosene.

4.3.2 Primary fire extinguishing means include:

· Boxes with sand;

· Felt felt 1x1 sq.m., asbestos cloth;

· Fire extinguishers;

Tap water

Asbestos cloth and felt blanket are used to extinguish substances and materials that stop burning without air access. These means completely cover the fire site. These funds are effective in case of a fire that occurs on a smooth surface (along the floor of the room) and the burning area is smaller than the size of a cloth or blanket.

Sand or collect small amounts of spilled flammable liquids, combustible liquids or solids that cannot be extinguished with water.

4.3.3 Fire extinguishers

The industry currently produces a variety of hand-held, mobile and stationary fire extinguishers.

In order to successfully fight a fire, it is necessary to clearly know the capabilities and areas of application of each fire extinguisher.

Carbon dioxide fire extinguishers ОУ - 2; OU - 3; OU - 5; OU - 8:

Hand-held fire extinguishers are steel cylinders with a bell.

To activate the fire extinguisher, you need to remove the fire extinguisher from the bracket, bring it to the fire, break the seal, pull out the pin, move the bell of the fire extinguisher to a horizontal position, pointing it at the fire, press the lever.

The stream of liquefied carbon dioxide leaving the cylinder through the socket is strongly cooled and turns into a gaseous state (snow).

The fire extinguishing effect is due to a decrease in the oxygen concentration in the combustion zone and the cooling of the burning one. All three devices are designed to extinguish the initial fires of various substances and materials, as well as electrical equipment under voltage up to 1000V.

This is because carbon dioxide does not contain water.

ОУ - cannot be extinguished:

Burning clothes on a person (may cause frostbite)

· Use to stop the combustion of alkali metals, as well as substances that continue to burn without access to oxygen from the environment (for example: a composition based on nitrate, nitrocellulose, pyroxylin).

Since carbon dioxide can escape from the cylinder, its charge should be monitored by weight and refilled periodically.

Hand-held powder fire extinguishers: OP - 4 (g); OP-5 (g); OP-8 (g); (gas generator type):

Powder fire extinguishers are designed to extinguish small fires of flammable liquids, electrical installations under voltage up to 1000V.

Hand-held fire extinguishers consist of a steel case inside which there is a charge (powder) and a working gas cylinder or a gas generator. Principle of operation: when the shut-off - starting device is triggered, the plug of the cylinder with the working gas (carbon dioxide, nitrogen) is pierced. Gas flows through the inlet pipe to the lower part of the fire extinguisher body and creates overpressure. The powder is forced through a siphon tube into a hose to the barrel. By pulling the trigger of the barrel, you can feed the powder in portions. Powder, falling on a burning substance, isolates it from oxygen and air.

Hand-held powder fire extinguishers: OP - 2 (z); OP-3 (s); OP-4 (s); OP - 8 (z) (injection type):

Hand-held fire extinguishers consist of a steel body inside which a charge (powder) is under pressure. Principle of operation: the working gas is pumped directly into the body of the fire extinguisher. When the locking - triggering device is triggered, the powder is displaced by the gas through the siphon tube into the hose to the barrel - nozzle or into the nozzle. The powder can be served in portions. When it gets on a burning substance, it isolates it from oxygen and air.

To activate: remove the fire extinguisher from the bracket, bring it to the fire, break the seal, pull out the pin, direct the hose with the nozzle to the fire, press the lever.

It should be taken into account that since the powders generally have the ability to slow down the rate of the combustion reaction and to some extent isolate the combustion center from the oxygen in the air, their cooling effect is small. This can lead to the fact that, if the thickness of the powder layer is insufficient, due to the small size of the charges of fire extinguishers, repeated flashes from objects that are incandescent during combustion are possible.

Air - foam fire extinguishers: ОВП - 5; ORP - 10:

Designed to extinguish small fires of solid and liquid combustible substances and smoldering materials at an ambient temperature of at least + 5 ° C. It consists of a steel case, inside which there is a charge - a solution of a foaming agent and a cylinder with a working gas. The principle of operation is based on the displacement of the foaming agent solution by the excess pressure of the working gas (air, nitrogen, carbon dioxide). When the shut-off device is triggered, the plug of the working gas cylinder is punctured. The foaming agent is forced out by gas pressure through the siphon tube into the nozzle. In the nozzle, the foaming agent is mixed with the suctioned air, resulting in foam. To activate: remove the fire extinguisher from the bracket, bring it to the fire, break the seal, pull out the pin, direct the foam generator to the fire, hit the start button or press the lever. Do not extinguish live electrical wiring and electrical appliances.

Air - emulsion fire extinguishers with fluorinated charge OVE - 5 (6) - AB - 03; OVE-2 (h); OVE-4 (h); OVE-8 (z) (fine-dispersed jet)
The newest, highly efficient, environmentally friendly and safe air-emulsion injection fire extinguisher (with a high-pressure gas cylinder) is designed to extinguish fires of solid combustible substances, flammable liquids and electrical equipment under voltage. In air-emulsion fire extinguishers, an aqueous solution of a fluorine-containing film-forming foaming agent is used as a charge, and any water spray is used as a nozzle. An emulsion is formed when droplets of a sprayed fire extinguisher charge hit a burning surface, on which a thin protective film is created, and the resulting foamed layer of an air emulsion protects this film from the effects of a flame. With OVE fire extinguishers, it is possible to extinguish electrical wiring and electrical appliances under voltage only with a fine-dispersed jet.

Aerosol generators (aerosol fire extinguishers) - SOT - 1; SOT - 5m; SOT - 5M:

Designed to extinguish fires in confined spaces when burning flammable and combustible liquids (oil products, solvents, alcohols), solid combustible materials of electrical equipment (including those under voltage).

In a volumetric aerosol fire extinguishing system, the extinguishing agent is an aerosol of salts and oxides of alkali and alkaline earth metals. And in a calm atmosphere, the aerosol cloud lasts up to 50 minutes. Aerosols formed when the SOT-1 generators are triggered; SOT - 5m; SOT - 5M is non-toxic, does not cause damage to property. The settled particles can be easily removed with a vacuum cleaner or washed off with water.

At all facilities, including in educational institutions, it is necessary to keep a register of primary fire extinguishing equipment .

Control over the condition of fire extinguishers is carried out in accordance with SP 9.13139.2009. “Fire fighting equipment. Fire extinguishers. Requirements for operation ".

Procedure in the event of a fire

In the event of a fire, the actions of employees should be primarily aimed at ensuring the safety of employees, their evacuation and rescue.

Every employee who detects a fire or its signs (smoke, smell or smoldering of various materials, temperature rise, etc.), must:

1. Immediately inform about this by phone 01 (at the same time, clearly state the address of the institution, the place of the fire, and also inform your position and surname).

2. Activate a fire warning system.

3. Proceed with the evacuation of people from the building to a safe place, according to the evacuation plan.

4. Notify the head of the institution or a substitute employee about the fire.

5. Arrange a meeting of fire departments, take measures to extinguish the fire with the fire extinguishing means available in the institution.

6. Arrange for checking children and workers evacuated from the building according to the available lists.

7. If necessary, call medical and other services to the place of fire.

8. Inform the chief of the arriving fire department about the presence of people in the building.

9. When evacuating and extinguishing a fire necessary:

· The evacuation of people should begin from the premises in which the fire broke out, and adjacent premises, which are threatened by the danger of the spread of fire and its signs of burning;

· The youngest children should be evacuated first;

· It is good to check all rooms to exclude the possibility of people hiding under tables, in closets and other places in the danger zone;

· Refrain from opening windows, doors, as well as breaking glass in order to avoid the spread of fire and smoke into adjacent rooms;

· When leaving rooms or buildings, you should close windows and doors behind you.

Good cooling property water due to its high heat capacity. When it hits a burning substance, the water partially evaporates and turns into steam. During evaporation, its volume increases 1700 times, due to which the oxygen in the air is displaced from the zone of the fire by water vapor. Water, having a high heat of vaporization, takes away a large amount of heat from burning materials and combustion products, which makes it an irreplaceable means of cooling. Water has a high thermal stability, its vapors only at a temperature over 1700 ° С can decompose into hydrogen and oxygen. In this regard, water extinguishing of most solid materials (wood, plastics, rubber, etc.) is safe, since the combustion temperature does not exceed them 1300 ° C... However, the interaction of water with alkali and alkaline-earth metals, which, when burning, create a temperature in the fire zone that exceeds the thermal resistance of water, can lead to serious consequences (eg, to explosions).

Water has a low thermal conductivity, which contributes to the creation of reliable thermal insulation on the surface of the burning material. This property, in combination with the previous ones, allows the use of water not only for extinguishing, but also for protecting materials from ignition. Low viscosity and incompressibility of water allows it to be fed over long distances and under high pressure. Water is capable of dissolving some gases and vapors, absorbing aerosols, and lowering the temperature in rooms. Water is also used for protection against thermal radiation (water curtain), for cooling heated surfaces of building structures of structures, installations, for deposition of combustion products on fires in buildings. For these purposes, sprayed and finely atomized jets are used, which leads to an increase in the fire extinguishing efficiency of water several times (see. Finely atomized water). Some GZh (liquid alcohols, aldehydes, organic acids, etc.) are soluble in water, therefore, mixing with it, they form non-flammable or less flammable solutions FIRE SAFETY. ENCYCLOPEDIA. ...

Substances and materials to which water and its solutions must not be supplied

Substance, material	The degree of danger
Lead azide	Explodes when humidity rises to 30% V.P. Ivannikov, P.P. Klyus Reference book of the head of extinguishing the fire. - M .: Stroyizdat, 1987.
Aluminum, magnesium, zinc, zinc dust	When burning, decompose water into oxygen and hydrogen
Bitumen	Delivery of compact jets of water leads to ejection and increased combustion
Hydrides of alkali and alkaline earth metals
Sodium hydrogen sulfite	Spontaneously ignites and explodes from the action of water
Explosive mercury	Explodes when hit by a compact water jet
Siliceous iron (ferrosilicon)	Phosphorous hydrogen is liberated, self-igniting in air
Potassium, calcium, sodium, rubidium, cesium metal	Reacts with water, producing hydrogen, may explode
Calcium and sodium (phosphorous)	React with water producing hydrogen phosphide, which ignites spontaneously in air
Potassium and sodium (peroxide)	In case of water ingress, an explosive release with increased combustion is possible.
Aluminum, barium and calcium carbides	Decomposes giving off flammable gases, possible explosion
Alkali metal carbides	Explode on contact with water
Magnesium and its alloys	When burning, decompose water into hydrogen and oxygen
Metaphos	Reacts with water with the formation of an explosive substance Terebnev V.V., Smirnov V.A., Semenov V.A., Firefighting (Handbook). 2nd edition. - Yekaterinburg: Kalan Publishing House, 2012 - 472s.
Sodium sulphide and hydrosulfuric acid	Heats up strongly (over 400 ° C), can cause a fire of flammable substances, as well as a burn if it comes into contact with the skin, accompanied by difficult-to-heal ulcers
Quicklime	Reacts with water, producing a lot of heat
Nitroglycerine	Explodes when hit by a jet of water
Saltpeter	The injection of a stream of water into the melt leads to a strong explosive release and increased combustion.
Sulfuric anhydride	Explosive release may occur if water enters
Sesquyl chloride	Reacts with water to form an explosion
Silanes	React with water to liberate hydrogenous silicon, which ignites spontaneously in air
Termite, titanium and its alloys, titanium tetrachloride, electron	Reacts with water, releasing a large amount of heat, decompose water into oxygen and hydrogen
Triethylaluminum and chlorosulfonic acid	Reacts with water to form an explosion
Aluminum phosphoride	Decomposes on water and self-ignites
Potassium cyanamide	When humidified, toxic hydrogen cyanide is released

Additives

Along with beneficial qualities, water also has negative properties. The main disadvantage of water as a fire extinguishing agent is its high surface tension.

In addition, excess water spilled when fighting a fire in a building can cause damage comparable to

The fire-extinguishing ability of water is determined by the cooling effect, the dilution of the combustible medium by the vapors formed during evaporation and the mechanical effect on the burning substance, i.e. blowing off the flame. The cooling effect of water is determined by significant values of its heat capacity and heat of vaporization. The diluting effect, leading to a decrease in the oxygen content in the ambient air, is due to the fact that the volume of steam is 1,700 times the volume of evaporated water. Along with this, water has properties that limit its scope. So, when extinguishing water, oil products and many other flammable liquids float and continue to burn on the surface, so water may be ineffective in extinguishing them. The fire extinguishing effect when extinguishing with water in such cases can be increased by supplying it in a sprayed state. Water containing various salts and supplied with a compact jet has significant electrical conductivity, and therefore cannot be used to extinguish fires at objects whose equipment is energized. Fire extinguishing with water is carried out with water fire extinguishing installations, fire trucks and water barrels (manual and fire monitors). To supply water to these installations, they use water pipes arranged at industrial enterprises and in settlements.

33. Advantages and disadvantages of air-mechanical foam as a fire extinguishing agent

Air-foam fire extinguishers are most suitable for extinguishing class A fires (especially with a low expansion foam barrel), as well as class B fires. The effectiveness of air-foam fire extinguishers significantly increases when fluorinated film-forming foaming agents are used as a charge. To obtain air-mechanical foam of medium expansion, a special device is used - a foam generator, which consists of a body with converging and expanding cones, a sprayer of a foam solution and a package of metal meshes. The air necessary for foaming is ejected by a sprayed jet of a foaming agent solution and is carried away by drops of it onto the mesh stack, where a foam stream is formed that emerges from the foam generator nozzle in the form of a jet. The disadvantage of air-foam fire extinguishers is the possibility of freezing of the working solution at negative temperatures, its rather high corrosive activity, the inapplicability of fire extinguishers for eliminating fires of equipment under voltage of electric current, and for extinguishing highly heated or molten substances, as well as substances that violently react with water ...

34. Advantages and disadvantages of non-combustible gases as a fire extinguishing agent

When extinguishing fires with inert gaseous diluents, carbon dioxide, nitrogen, flue or exhaust gases, steam, as well as argon and other gases are used. The fire-extinguishing effect of these compounds is to dilute the air and reduce the oxygen content in it to a concentration at which combustion stops. The fire-extinguishing effect when diluted with these gases is due to heat loss due to heating of the diluents and a decrease in the heat effect of the reaction. A special place among fire extinguishing compositions is occupied by carbon dioxide (carbon dioxide), which is used to extinguish flammable liquids warehouses, battery stations, drying ovens, stands for testing electric motors, etc.

It should be remembered, however, that carbon dioxide must not be used to extinguish substances containing oxygen, alkaline and alkaline earth metals, or smoldering materials. To extinguish these substances, nitrogen or argon is used, the latter being used in cases where there is a danger of the formation of metal nitrides with explosive properties and sensitivity to impact.

Water is one of the most widely used and most versatile fire fighting media. It is effective in extinguishing fires associated with the combustion of substances in all three states. Therefore, it is widely used to extinguish fires almost everywhere, except for those rare cases when it cannot be used. Water cannot be used to extinguish fires in the following cases:

do not extinguish flammable substances and materials with which water enters into intense chemical interaction with the release of heat or combustible components (for example, fires associated with the combustion of alkali and alkaline earth metals, metals such as lithium, sodium, calcium carbide and others, as well as acids and alkalis, with which water vigorously interacts);

fires cannot be extinguished with water, with temperatures above 1800 - 2000 0 С, since this leads to an intensive dissociation of water vapor into hydrogen and oxygen, which intensify the combustion process;

it is impossible to extinguish fires in which the use of water does not provide the required safety conditions for personnel. For example, high voltage electrical installations, etc.

In all other cases, water is a reliable, effective means for extinguishing fires and therefore it has found the most widespread use. Water has a number of advantages as a fire extinguishing agent: thermal stability, which is much higher than the thermal resistance of other non-combustible liquids, high heat capacity and heat of vaporization, and relative chemical inertness. The negative properties of water include: high freezing point and anomalous changes in the density of water during cooling, which makes it difficult to use at low negative temperatures, relatively low viscosity and high coefficient of surface tension, which worsen the wetting ability of water and thereby reduce the coefficient of its use in the extinguishing process, as well as the electrical conductivity of water containing impurities.

According to the mechanism of stopping combustion, water belongs to the category of cooling fire extinguishing agents. But the mechanism of stopping combustion itself depends on the combustion mode, on the type of fuel and its state of aggregation. When extinguishing fires associated with the combustion of flammable gases (always) and liquids (sometimes), the dominant mechanism for stopping combustion is the cooling of the combustion zone, which is implemented in the case of using the volumetric extinguishing method.

Water can be supplied to the combustion zone in the form of compact jets, spray jets and water mist. The last two cases most fully correspond to the concept of the volumetric supply of a liquid extinguishing agent to the combustion zone. The compact jet, passing through the combustion zone, will have almost no effect on it.

When extinguishing flammable and combustible liquids, the compact jet will have almost no effect on the flame. And, once on the surface of flammable and combustible liquids, it will not cool it very effectively. Due to the high specific gravity of water compared to combustible hydrocarbons, it will quickly sink to the bottom. The cooling of the surface layers of the combustible liquid heated to the boiling point will not be as intense as if sprayed or finely sprayed water was supplied. When extinguishing HMs, compact jets of water fed into the flame, as in the first two cases, will not affect the combustion zone, and once they hit the surface of HMs, they will not cool them very effectively and thus will not contribute much to extinguishing.

Powerful compact jets of water are supplied when extinguishing large developed fires of piles of wood, since with such an intense combustion, sprayed jets, and even more so finely sprayed water, will not reach not only the burning wood, but will not even get inside the flame torch. They will evaporate in the outer zones of the flame or be carried upward by intense gas streams, practically without affecting the combustion process.

In all other cases, sprayed jets and water mist are more effective both when extinguishing fires by volumetric method, and when extinguishing on the surface of combustible material. When the flame combustion stops, the compact jet is less effective because, flying through the combustion zone, it does not provide a cooling effect, since it has a small surface area of contact with the flame and a short interaction time. Whereas the sprayed jets have a much larger surface of contact with the flame and a lower flight speed, a longer interaction time. And even better are the conditions for heat removal from the flame torch near the finely sprayed water.

This means that the larger the contact surface of the liquid with the flame torch and the time of this contact, all other things being equal, the more intense the heat removal.Very small thermal and aerodynamic interaction with the flame torch for a compact jet, more for sprayed water, even more for finely sprayed water supplied to flame zone. The greatest extinguishing effect when water is supplied to the flame will be when its cooling effect is maximum. That is, when all the water supplied for extinguishing the fire evaporates due to the removal of heat from the flame, directly from the zone of the chemical combustion reactions. Therefore, with such a mechanism for stopping combustion, one should strive to ensure that the maximum possible amount of water evaporates in the volume of the flame torch, and not outside it. And when extinguishing with water by supplying it to the surface of combustible liquids or HM, a more uniform supply of sprayed water is effective because the maximum cooling effect will take place when all the water supplied to extinguish the fire is completely evaporated due to the removal of heat from the combustible material. Therefore, the water should be in contact with the surface (most heated) layers of flammable liquids, combustible liquids or THM until it evaporates completely.

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MINISTRY OF EDUCATION AND SCIENCE

MOSCOW STATE CONSTRUCTION UNIVERSITY

EXTINGUISHING MEANS AND METHODS

COURSE WORK

WATER AS A FIRE EXTINGUISHING MEDIA

Completed by a student

3 courses, group PB

Alekseeva Tatiana Robertovna

Moscow 2013

Table of contents

5. Scope of water
Bibliography

1. Fire extinguishing efficiency of water

Fire extinguishing is a set of actions and measures aimed at eliminating a fire that has arisen. A fire is possible with the simultaneous presence of three components: a combustible substance, an oxidizer and an ignition source. The development of a fire requires the presence of not only combustible substances and an oxidizing agent, but also the transfer of heat from the combustion zone to the combustible material. Therefore, fire extinguishing can be achieved in the following ways:

by isolating the source of combustion from air or reducing the oxygen concentration by diluting the air with non-combustible gases to a value at which combustion cannot occur;

cooling the seat of combustion to temperatures below the temperatures of ignition and flash;

slowing down the rate of chemical reactions in the flame;

mechanical stripping of the flame by exposing the combustion center to a strong jet of gas or water;

the creation of conditions for fire protection.

The results of the effects of all existing extinguishing agents on the combustion process depend on the physicochemical properties of burning materials, combustion conditions, supply intensity and other factors. For example, water can be used to cool and isolate (or dilute) the combustion center, with foam means - to isolate and cool, with inert diluents - to dilute the air, reducing the oxygen concentration, with freons - to inhibit combustion and prevent the spread of the flame with a powder cloud. For any extinguishing agent, only one extinguishing effect is dominant. Water has a predominantly cooling effect, foams - insulating, freons and powders - inhibiting.

Most extinguishing agents are not universal, i.e. suitable for extinguishing any fires. In some cases, extinguishing agents turn out to be incompatible with burning materials (for example, the interaction of water with burning alkali metals or organometallic compounds is accompanied by an explosion).

When choosing extinguishing agents, one should proceed from the possibility of obtaining the maximum extinguishing effect at the lowest cost. The choice of extinguishing media should be made taking into account the class of fire. Water is the most widely used extinguishing agent for extinguishing fires of substances in various states of aggregation.

The high fire extinguishing efficiency of water and the large scale of its use for extinguishing fires are due to a complex of special physicochemical properties of water and, first of all, the unusually high, in comparison with other liquids, the energy intensity of evaporation and heating of water vapor. So, for the evaporation of one kilogram of water and heating the vapors to a temperature of 1000 K, it is necessary to spend about 3100 kJ / kg, while a similar process with organic liquids requires no more than 300 kJ / kg, i.e. the energy intensity of the phase transformation of water and the heating of its vapors is 10 times higher than the average for any other liquid. Moreover, the thermal conductivity of water and its vapors is almost an order of magnitude higher than for other liquids.

It is well known that sprayed, highly dispersed water is most effective in extinguishing fires. To obtain a highly dispersed jet of water, as a rule, a high pressure is required, but at the same time, the range of the sprayed water supply is limited by a short distance. The new principle of obtaining a highly dispersed stream of water is based on a new method of obtaining atomized water - by multiple sequential dispersion of a water jet.

The main mechanism of action of water in extinguishing a fire in a fire is cooling. Depending on the degree of dispersion of water droplets and the type of fire, either predominantly the combustion zone, or the burning material, or both together can be cooled.

An equally important factor is the dilution of the combustible gas mixture with water vapor, which leads to its phlegmatization and the cessation of combustion.

In addition, sprayed water droplets absorb radiant heat, absorb a combustible component and lead to coagulation of smoke particles.

2. Advantages and disadvantages of water

The factors that determine the advantages of water as a fire extinguishing agent, in addition to its availability and low cost, are significant heat capacity, high latent heat of vaporization, mobility, chemical neutrality and lack of toxicity. Such properties of water provide effective cooling not only of burning objects, but also objects located near the source of combustion, which prevents destruction, explosion and ignition of the latter. Good mobility makes it easy to transport water and deliver it (in the form of continuous jets) to remote and hard-to-reach places.

The fire-extinguishing ability of water is determined by the cooling effect, the dilution of the combustible medium by the vapors formed during evaporation and the mechanical effect on the burning substance, i.e. blowing off the flame.

Getting into the combustion zone, on the burning substance, water takes away a large amount of heat from the burning materials and combustion products. At the same time, it partially evaporates and turns into steam, increasing in volume 1700 times (from 1 liter of water during evaporation, 1700 liters of steam are formed), due to which the reactants are diluted, which in itself contributes to the cessation of combustion, as well as the displacement of air from the zone the source of the fire.

Water has a high thermal stability. Its vapors only at temperatures above 1700 ° C can decompose into oxygen and hydrogen, thereby complicating the situation in the combustion zone. Most of the combustible materials burn at temperatures not exceeding 1300-1350 ° C and extinguishing them with water is not dangerous.

Water has a low thermal conductivity, which contributes to the creation of reliable thermal insulation on the surface of the burning material. This property, in combination with the previous ones, makes it possible to use it not only for extinguishing, but also for protecting materials from ignition.

Low viscosity and non-compressibility of water allow it to be fed through the sleeves over considerable distances and under high pressure.

Water is capable of dissolving some vapors, gases and absorbing aerosols. This means that water can precipitate combustion products on fires in buildings. For these purposes, sprayed and atomized jets are used.

Some flammable liquids (liquid alcohols, aldehydes, organic acids, etc.) are soluble in water, therefore, when mixed with water, they form non-flammable or less flammable solutions.

But at the same time, water has a number of disadvantages that narrow the area of its use as a fire extinguishing agent. A large amount of water used in extinguishing can cause irreparable damage to material assets, sometimes no less than the fire itself. The main disadvantage of water as a fire extinguishing agent is that, due to its high surface tension (72.8 * -103 J / m 2), it poorly wets solid materials and especially fibrous substances. Other disadvantages are: freezing of water at 0 ° C (reduces the transportability of water at low temperatures), electrical conductivity (makes it impossible to extinguish electrical installations with water), high density (when extinguishing light burning liquids, water does not restrict air access to the combustion zone, but, spreading, contributes to an even greater spread of fire).

3. Intensity of extinguishing water supply

Fire extinguishing agents are of paramount importance in stopping combustion. However, combustion can be eliminated only if a certain amount of extinguishing agent is supplied to stop it.

In practical calculations, the amount of extinguishing agents required to stop burning is determined by the intensity of their supply. The rate of supply is the amount of extinguishing agent supplied per unit of time per unit of the corresponding geometric parameter of the fire (area, volume, perimeter or front). The intensity of the supply of extinguishing agents is determined empirically and by calculations when analyzing extinguished fires:

I = Q about. s / 60tt P,

Where:

I is the intensity of the supply of fire extinguishing agents, l / (m 2 s), kg / (m 2 s), kg / (m 3 s), m 3 / (m 3 s), l / (m s) );

Qо. c is the consumption of the extinguishing agent during extinguishing a fire or conducting an experiment, l, kg, m 3;

Tt is the time spent on extinguishing a fire or conducting an experiment, min;

P is the value of the calculated parameter of the fire: area, m 2; volume, m3 ; perimeter or front, m

The flow rate can be determined through the actual specific consumption of the extinguishing agent;

I = Qу / 60tт П,

Where Qу is the actual specific consumption of the extinguishing agent during the time of stopping combustion, l, kg, m3.

For buildings and premises, the intensity of supply is determined by the tactical costs of fire extinguishing agents on fires that have taken place:

I = Qph / P,

Where Qf is the actual consumption of the extinguishing agent, l / s, kg / s, m3 / s (see, clause 2.4).

Depending on the calculated unit of the fire parameter (m 2, m 3, m), the intensity of the supply of fire extinguishing agents is divided into surface, volumetric and linear.

If there is no data in the regulatory documents and reference literature on the intensity of the supply of fire extinguishing agents to protect objects (for example, in case of fires in buildings), it is established according to the tactical conditions of the situation and the implementation of hostilities to extinguish the fire, based on the operational and tactical characteristics of the object, or take reduced by 4 times in comparison with the required intensity of supply for extinguishing a fire

I s = 0.25 I tr,

The linear intensity of the supply of extinguishing agents for extinguishing fires in the tables, as a rule, is not given. It depends on the situation at the fire and, if used in the calculation of fire extinguishing agents, it is found as a derived indicator of the intensity of the surface:

Il = I s h t,

Where h t is the extinguishing depth, m (accepted, when extinguishing with hand trunks - 5 m, fire monitors - 10 m).

The total intensity of the supply of fire extinguishing agents consists of two parts: the intensity of the fire extinguishing agent involved directly in stopping the combustion of I pr. G, and the intensity of losses I sweat.

I = I pr. G + I pot.

The average, practically feasible, values of the intensity of the supply of fire extinguishing agents, called optimal (required, calculated), established by experience and practice of extinguishing fires, are given below and in Table 1.

Intensity of water supply when extinguishing fires, l / (m 2 s)

Tab. 1

Extinguishing object	Intensity
1. Buildings and structures
Administrative buildings:
I - III degree of fire resistance
IV degree of fire resistance
V degree of fire resistance
Basements
Attic rooms
Hangars, garages, workshops, tram and trolleybus depots
Hospitals
Residential buildings and outbuildings:
I - III degree of fire resistance
IV degree of fire resistance
V degree of fire resistance
Basements
Attic rooms
Livestock buildings
I - III degree of fire resistance
IV degree of fire resistance
V degree of fire resistance
Cultural and entertainment institutions (theaters, cinemas, clubs, palaces of culture):

Auditorium
Utility rooms
Mills and elevators
Industrial buildings
I - II degree of fire resistance
III degree of fire resistance
IV - V degree of fire resistance
Paint shops
Basements
Combustible coverings of large areas in industrial buildings:
When extinguishing from below inside the building
When extinguishing from the outside from the side of the coating
When extinguishing outside in a developed fire
Buildings under construction
Trade enterprises and warehouses of inventory items
Refrigerators
Power plants and substations:
Cable tunnels and half-floors (water mist supply)
Machine rooms and boiler rooms
Fuel supply galleries
Transformers, reactors, oil switches (water mist supply)
2. Vehicles
Cars, trams, trolleybuses in open parking lots
Airplanes and helicopters:
Interior decoration (with water mist supply)
Constructions with the presence of magnesium alloys

Vessels (dry cargo and passenger):
Superstructures (internal and external fires) with the supply of solid and finely sprayed jets

3. Solid materials
Loose paper
Wood:
Balance, at humidity,%


Lumber in stacks within one group at humidity,%;



Round wood in stacks
Wood chips in heaps with a moisture content of 30 - 50%
Rubber (natural or artificial), rubber and industrial rubber goods
Flaxseed in dumps (water mist supply)
Lnotrests (stacks, bales)
Plastics:
Thermoplastics
Reaktoplasts
Polymer materials and products from them
Textolite, carbolite, plastic waste, triacetate film
Peat on milling fields with a moisture content of 15 - 30% (with a specific water consumption of 110 - 140 l / m2 and a quenching time of 20 minutes)
Milled peat in stacks (with a specific water consumption of 235 l / m and a quenching time of 20 minutes)
Cotton and other fibrous materials:
Open warehouses
Closed warehouses
Celluloid and articles thereof
4. Flammable and combustible liquids (when extinguishing with water mist)

Petroleum products in containers:
With a flash point below 28 ° C
With a flash point of 28 - 60 ° C
With a flash point over 60 ° C
Flammable liquid spilled on the surface of the site, in the trenches of the technological trays
Thermal insulation impregnated with petroleum products
Alcohols (ethyl, methyl, propyl, butyl, etc.) in warehouses and distilleries
Oil and condensate around the fountain well

Notes:

1. When water is supplied with a wetting agent, the flow rate according to the table is reduced by 2 times.

2. Cotton, other fibrous materials and peat should be extinguished only with the addition of a wetting agent.

Water consumption for fire extinguishing is determined depending on the functional fire hazard class of the facility, its fire resistance, fire hazard category (for industrial premises), volume in accordance with SP 8.13130.2009, for external fire extinguishing and SP 10.13130.2009, for internal fire extinguishing.

4. Methods of water supply for fire extinguishing

The most reliable systems for solving fire extinguishing tasks are automatic fire extinguishing systems. These systems are triggered by fire automatic devices according to the readings of the sensors. In turn, this ensures the prompt extinguishing of the fire site without human intervention.

Automatic fire extinguishing systems provide:

round-the-clock temperature control and the presence of smoke in the protected area;

activation of sound and light alerts

issuing an "alarm" signal to the fire brigade

automatic closing of fire retardant valves and doors

automatic switching on of smoke exhaust systems

shutdown ventilation

disconnection of electrical equipment

automatic supply of extinguishing agent

filing notification.

As a fire extinguishing agent, the following are used: inert gas - freon, carbon dioxide, foam (low, medium, high expansion), fire extinguishing powders, aerosols and water.

fire extinguishing water fire extinguishing efficiency

"Water" installations are divided into sprinkler installations, designed for local fire extinguishing, and deluge - for extinguishing fires over a large area. Sprinkler systems are programmed to operate when the temperature rises above a predetermined rate. When extinguishing a fire, a spray of water is sprayed in the immediate vicinity of the fire. Control units for these installations are of "dry" type - for unheated objects, and "wet" - for rooms where the temperature does not drop below 0 0 C.

Sprinkler installations are effective in protecting premises where fires are expected to develop rapidly.

Sprinklers of this type of installations are very diverse, this allows them to be used in rooms with different interiors.

The sprinkler is a valve that is triggered when exposed to a temperature-sensitive shut-off device. As a rule, it is a glass bulb with a liquid that bursts at a given temperature. Sprinklers are installed on pipelines containing high pressure water or air.

As soon as the room temperature rises above the set temperature, the glass shut-off device of the sprinkler collapses, due to the destruction, the water / air supply valve opens, the pressure in the pipeline drops. When the pressure drops, a sensor is triggered, which starts the pump supplying water to the pipeline. This option ensures the supply of the required amount of water to the fire site.

There are a number of sprinklers available with different response temperatures.

Pre-action sprinklers greatly reduce the likelihood of false alarms. The design of the device is such that to supply water, it is necessary to open both sprinklers that are part of the system.

Deluge systems, unlike sprinkler systems, are triggered by a fire detector. This allows you to extinguish a fire at an early stage of development. The main difference between deluge systems is that fire extinguishing water is supplied to the pipeline directly when a fire breaks out. At the moment of fire, these systems supply a significantly larger amount of water to the protected area. Typically, deluge systems are used to create water curtains and cool highly heat-sensitive and flammable objects.

To supply water to the deluge system, a so-called deluge control unit is used. The unit is activated electrically, pneumatically or hydraulically. The signal to start the deluge fire extinguishing system is given both automatically - by the fire alarm system, and manually.

One of the novelties on the fire extinguishing market is an installation with a water mist supply system.

The smallest particles of water, supplied under high pressure, have a high penetrating and smoke-settling ability. This system significantly enhances the fire extinguishing effect.

Water mist fire extinguishing systems are designed and created on the basis of low pressure equipment. This allows for highly effective fire protection with minimal water consumption and high reliability. Such systems are used to extinguish fires of different classes. The extinguishing agent is water, as well as water with additives, a gas-water mixture.

Water sprayed through a thin hole increases the area of effect, thus increasing the cooling effect, which then increases due to the evaporation of water mist. This fire extinguishing method provides excellent effect of deposition of smoke particles and reflection of heat radiation.

The fire extinguishing efficiency of water depends on the way it is supplied to the fire.

The greatest fire extinguishing effect is achieved when water is supplied in a sprayed state, since the area of simultaneous uniform cooling increases.

Continuous jets are used to extinguish external and open or developed internal fires, when it is necessary to supply a large amount of water or if it is necessary to impart an impact force to the water, as well as fires when it is not possible to come close to the hearth, when cooling neighboring and burning objects from large distances, structures, apparatuses. This method of extinguishing is the simplest and most common.

Continuous jets should not be used where there may be flour, coal and other dust that can form explosive concentrations.

5. Scope of water

Water is used to extinguish fires of classes:

A - wood, plastics, textiles, paper, coal;

B - flammable and combustible liquids, liquefied gases, oil products (extinguishing with water mist);

C - flammable gases.

Water must not be used to extinguish substances that emit heat, flammable, toxic or corrosive gases upon contact with it. These substances include certain metals and organometallic compounds, metal carbides and hydrides, hot coal and iron. The interaction of water with burning alkali metals is especially dangerous. Explosions are generated as a result of this interaction. If water gets on hot coal or iron, an explosive hydrogen-oxygen mixture may form.

Table 2 lists substances that cannot be extinguished with water.

Tab. 2

Substance	The nature of interaction with water
Metals: sodium, potassium, magnesium, zinc, etc.	React with water to form hydrogen
Organoaluminum compounds	React explosively
Organolithium compounds
Lead azide, alkali metal carbides, metal hydrides, silanes	Decompose to form flammable gases
Sodium hydrogen sulfate	Spontaneous combustion occurs
Sodium hydrogen sulfate	Interaction with water is accompanied by violent heat release
Bitumen, sodium peroxide, fats, oils	Combustion intensifies, emissions occur burning substances, splashing, effervescence

Water installations are ineffective for extinguishing flammable and combustible liquids with a flash point of less than 90 ° C.

Water with significant electrical conductivity, in the presence of impurities (especially salts), increases electrical conductivity by 100-1000 times. When using water to extinguish electrical equipment under voltage, the electric current in a stream of water at a distance of 1.5 m from the electrical equipment is zero, and with the addition of 0.5% soda, it increases to 50 mA. Therefore, when extinguishing fires with water, electrical equipment is de-energized. When using distilled water, even high-voltage installations can be extinguished with it.

6. Method for assessing the applicability of water

If water gets on the surface of a burning substance, pops, flashes, splashing of burning materials over a large area, additional ignition, an increase in the volume of the flame, and the release of a burning product from technological equipment are possible. They can be large-scale or localized.

The lack of quantitative criteria for assessing the nature of the interaction of a burning substance with water makes it difficult to make optimal technical solutions using water in automatic fire extinguishing installations. For a rough assessment of the applicability of aqueous products, you can use two laboratory methods. The first method is to visually observe the nature of the interaction of water with the test product burning in a small vessel. The second method involves measuring the volume of the evolving gas, as well as the degree of heating when the product interacts with water.

7. Ways to increase the fire extinguishing efficiency of water

To increase the area of application of water as a fire extinguishing agent, special additives (antifreezes) are used that lower the freezing point: mineral salts (K 2 CO 3, MgCl 2, CaCl 2), some alcohols (glycols). However, salts increase the corrosiveness of water, so they are practically not used. The use of glycols significantly increases the cost of extinguishing.

Depending on the source, the water contains various natural salts, which increase its corrosivity and electrical conductivity. Foaming agents, anti-freeze salts and other additives also enhance these properties. Corrosion of metal products in contact with water (bodies of fire extinguishers, pipelines, etc.) can be prevented either by applying special coatings to them, or by adding corrosion inhibitors to the water. As the latter, inorganic compounds are used (acid phosphates, carbonates, alkali metal silicates, oxidants such as sodium chromates, potassium or sodium nitrite, which form a protective layer on the surface), organic compounds (aliphatic amines and other substances capable of absorbing oxygen). The most effective of these is sodium chromate, but it is toxic. Coatings are commonly used to protect firefighting equipment against corrosion.

To increase the fire extinguishing efficiency of water, additives are introduced into it that increase the wetting ability, viscosity, etc.

The effect of extinguishing the flame of capillary-porous, hydrophobic materials such as peat, cotton and woven materials is achieved when surfactants - wetting agents are added to the water.

To reduce the surface tension of water, it is recommended to use wetting agents - surfactants: wetting agent of the DB brand, emulsifier OP-4, auxiliary substances OP-7 and OP-10, which are the products of addition of seven to ten molecules of ethylene oxide to mono - and dialkylphenols, the alkyl radical of which contains 8-10 carbon atoms. Some of these compounds are also used as foaming agents for producing air-mechanical foam. Adding wetting agents to water can significantly increase its fire extinguishing efficiency. With the introduction of a wetting agent, the water consumption for extinguishing decreases four times, and the extinguishing time - more than half.

One of the ways to increase the efficiency of water fire extinguishing is to use water mist. The efficiency of finely sprayed water is due to the high specific surface area of fine particles, which increases the cooling effect due to the penetrating uniform action of water directly on the combustion center and an increase in heat removal. At the same time, the harmful effect of water on the environment is significantly reduced.

Bibliography

1. Course of lectures "Means and methods of fire extinguishing"

2. A. Ya. Korolchenko, D.A. Korolchenko. Fire and explosion hazard of substances and materials and means of their extinguishing. Handbook: in 2 parts - 2nd ed., Revised. and add. - M .: Pozhnauka, 2004. - Part 1 - 713s., - Part 2 - 747s.

3. Terebnev V.V. Reference book of the head of extinguishing the fire. Tactical capabilities of fire departments. - M .: Pozhnauka, 2004 .-- 248p.

4. Directory of RTP (Klyus, Matveikin)

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