MINISTRY OF EDUCATION AND SCIENCE

MOSCOW STATE CIVIL UNIVERSITY

FIRE FIGHTING MEANS AND METHODS

COURSE WORK

WATER AS A FIRE FIGHTING MEDIUM

Completed by a student

3 courses, PB group

Alekseeva Tatyana Robertovna

Moscow 2013

5. Area of ​​application of water

Bibliography

1. Fire extinguishing efficiency of water

Fire fighting is a set of actions and measures aimed at eliminating a fire. A fire can occur in 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 flammable substances and an oxidizer, but also the transfer of heat from the combustion zone to the combustible material. Therefore, fire extinguishing can be achieved in the following ways:

• isolating the combustion source from the air or reducing the oxygen concentration by diluting the air with non-flammable gases to a value at which combustion cannot occur;
• cooling the combustion source to temperatures below the ignition and flash temperatures;
• slowing down chemical reactions in flames;
• mechanical flame arrest by exposing the combustion source to a strong jet of gas or water;
• creating fire suppression conditions.

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

Most extinguishing agents are not universal, i.e. acceptable 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 maximum fire extinguishing effect at minimal cost. The choice of extinguishing agents must be made taking into account the class of fire. Water is the most widely used fire 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 physical and chemical properties of water and, first of all, the unusually high, in comparison with other liquids, energy intensity of evaporation and heating of water vapor. Thus, to evaporate one kilogram of water and heat the vapor 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 heating of its vapor is 10 times higher than the average for any other liquid. At the same time, the thermal conductivity of water and its vapor 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, high pressure is required, but even then the range of supply of sprayed water is limited to a short distance. New principle obtaining a highly dispersed flow of water is based on a new method of obtaining atomized water - by repeated sequential dispersion of a water jet.

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

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

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

2. Advantages and disadvantages of water

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 evaporation, mobility, chemical neutrality and lack of toxicity. Such properties of water provide effective cooling not only of burning objects, but also of objects located near the source of combustion, which helps prevent destruction, explosion and fire of the latter. Good mobility makes it easy to transport water and deliver it (in the form of continuous streams) to remote and hard-to-reach places.

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

Getting into the combustion zone, onto 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, 1700 liters of steam are formed during evaporation), due to which the reacting substances are diluted, which in itself helps to stop combustion, as well as displace air from the zone fire source.

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

Water has low thermal conductivity, which helps create reliable thermal insulation on the surface of the burning material. This property, in combination with the previous ones, allows it to be used not only for extinguishing, but also to protect materials from ignition.

The low viscosity and non-compressibility of water allow it to be supplied through hoses over considerable distances and under high pressure.

Water can dissolve some vapors, gases and absorb aerosols. This means that combustion products from fires in buildings can be deposited with water. For these purposes, sprayed and finely sprayed 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 scope of its use as a fire extinguishing agent. A large amount of water used in extinguishing can cause irreparable damage 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 does not wet solid materials and especially fibrous substances well. 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 limit the access of air to the combustion zone, but, spreading, promotes further spread of fire).

3. Intensity of water supply for extinguishing

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

In practical calculations, the amount of fire extinguishing agents required to stop a fire is determined by the intensity of their supply. The supply intensity is the amount of fire 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 fire extinguishing agents is determined experimentally and by calculations when analyzing extinguished fires:

Q O . s / 60tt P,

Where: - intensity of supply of fire extinguishing agents, l/ (m 2s), kg/ (m 2s), kg/ (m 3·cm 3/ (m 3·s), l/ (m ·s);o. с - consumption of fire extinguishing agent during fire extinguishing or conducting an experiment, l, kg, m 3;t - time spent extinguishing a fire or conducting an experiment, min;

P - the value of the calculated fire parameter: area, m 2; volume, m 3; perimeter or front, m.

The supply intensity can be determined through the actual specific consumption of the fire extinguishing agent;

Qу/60tт П,

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

For buildings and premises, the supply intensity is determined by the tactical consumption of fire extinguishing agents on existing fires:

Qf / P,

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

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

If in regulatory documents and reference literature there is no data on the intensity of the supply of fire extinguishing agents to protect objects (for example, during fires in buildings), it is established according to the tactical conditions of the situation and the implementation of combat operations to extinguish the fire, based on the operational-tactical characteristics of the object, or is taken reduced by 4 times compared to the required intensity of supply for fire extinguishing

h = 0.25I tr ,

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

l = I s h T ,

Where h T - extinguishing depth, m (assumed, when extinguishing with hand guns - 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 I pr. g , and loss intensity I sweat.

I pr. g +I sweat .

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

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

Extinguishing objectIntensity1. Buildings and structuresAdministrative buildings: I - III degree of fire resistance0.06IV degree of fire resistance0.10V degree of fire resistance0.15Basements0.10Attics0.10Hangars, garages, workshops, tram and trolleybus depots0.20Hospitals0.10Residential buildings and outbuildings: I -III degree of fire resistance0. 03IV degree of fire resistance0.10V degree of fire resistance0.15Basements0.15Attics0.15Livestock buildingsI - III degree of fire resistance0.10IV degree of fire resistance0.15V degree of fire resistance0.20Cultural and entertainment institutions (theatres, cinemas, clubs, palaces of culture): Stage0.20Auditory hall0.15Utilities premises 0.15 Mills and elevators 0.14 Industrial buildings I - II degree of fire resistance 0.35 III degree of fire resistance 0, 20 IV - V degree of fire resistance 0.25 Paint shops 0, 20 Basements 0.30 Combustible coatings of large areas in industrial buildings: When extinguishing from below inside the building 0.15 When extinguishing from outside from the side of the coating 0.08 When extinguishing from outside during a developed fire 0.15 Buildings under construction 0.10 Trade enterprises and warehouses of inventory items 0. 20 Refrigerators 0.10 Power plants and substations: Cable tunnels and mezzanines (supply water mist) 0, 20Machine rooms and boiler rooms0, 20Fuel supply galleries0,10Transformers, reactors, oil switches(supply of finely sprayed water) 0.102. Vehicles Cars, trams, trolleybuses in open parking lots 0.10 Airplanes and helicopters: Interior decoration(when supplying finely atomized water) 0.08 Structures with the presence of magnesium alloys 0.25 Hull 0.15 Vessels (dry cargo and passenger): Superstructures (internal and external fires) when supplying solid and finely atomized jets 0. 20 Holds 0. 203. Solid materials Loosened paper 0.30 Wood: Pulpwood, at humidity, %40 - 500, 20 Less than 400.50 Lumber in stacks within one group at humidity, %; 6 - 140.4520 - 300.30 Over 300, 20 Round timber in stacks 0.3 Chips in piles with a moisture content of 30 - 50% 0.10 Rubber (natural or artificial), rubber and rubber products 0.30 Flax in dumps (supply of finely sprayed water) 0, 20 Flax trusts (stacks, bales) 0.25 Plastics: Thermoplastics 0.14 Thermosets 0.10 Polymer materials and products made from them 0. 20 Textolite, carbolite, plastic waste, triacetate film 0.30 Peat on milling fields with a humidity of 15 - 30% (at specific consumption water 110 - 140 l/m2 and extinguishing time 20 min.) 0.10 Milled peat in stacks (with a specific water consumption of 235 l/m and extinguishing time 20 min) 0. 20 Cotton and other fibrous materials: Open warehouses 0. 20 Closed warehouses 0. 30 Celluloid and products made from it 0.404. Flammable and combustible liquids (when extinguishing with finely sprayed water) Acetone 0.40 Petroleum products in containers: With a flash point below 28 ° C 0.30 C flash point 28 - 60 ° C 0, 20 C flash point more than 60 ° C 0. 20 Flammable liquid spilled on the surface of the site, in trenches in technological trays 0, 20 Thermal insulation impregnated with petroleum products0, 20Alcohols (ethyl, methyl, propyl, butyl, etc.) in warehouses and distilleries0,40 Oil and condensate around the fountain well0, 20

Notes:

When supplying water with a wetting agent, the supply intensity according to the table is reduced by 2 times.

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

Water consumption for fire extinguishing is determined depending on the class of functional fire danger object, its fire resistance, fire hazard category (for production premises), volume according to SP 8.13130.2009, for external fire extinguishing and SP 10.13130.2009, for internal fire extinguishing.

4. Methods of supplying water for fire extinguishing

The most reliable systems for solving fire extinguishing problems are automatic fire extinguishing. These systems are activated by fire automatics based on sensor readings. In turn, this ensures prompt extinguishing of a fire without human intervention.

Automatic fire extinguishing systems provide:

activation of sound and light alerts

issuing an alarm signal to the fire department control panel

automatic closing of fire dampers and doors

automatic activation of smoke removal systems

turning off ventilation

shutdown of electrical equipment

automatic supply of fire extinguishing agent

submission notification.

The following are used as fire extinguishing agents: 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 systems, designed for local fire extinguishing, and deluge systems, for extinguishing fire over a large area. Sprinkler systems are programmed to operate when the temperature rises above a set point. When extinguishing a fire, a stream of sprayed water is applied in close proximity to the source of fire. The control units for these installations are of the “dry” type - for unheated objects, and the “wet” type - for rooms in which the temperature does not fall below 0 0WITH.

Sprinkler installations are effective for protecting premises where fire is expected to develop rapidly.

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

A sprinkler is a valve that is activated by a heat-sensitive shut-off device. Typically this is glass flask with a liquid that bursts at a given temperature. Sprinklers are installed on pipelines that contain water or air under high pressure.

As soon as the room temperature rises above the set temperature, the glass locking device the sprinkler is destroyed, due to destruction, the water/air supply valve opens, the pressure in the pipeline drops. When the pressure drops, a sensor is triggered, which starts a pump that supplies water to the pipeline. This option provides required quantity water to the location of the fire.

There are a number of sprinklers that differ from each other by different operating temperatures.

Pre-action sprinklers significantly reduce the likelihood of false alarms. The design of the device is such that both sprinklers included in the system must be opened to supply water.

Deluge systems, unlike sprinkler systems, are triggered by a command from a fire detector. This allows you to extinguish a fire at an early stage of development. The main difference between deluge systems is that water for extinguishing a fire is supplied to the pipeline directly when a fire occurs. These systems supply a significantly larger amount of water to the protected area at the time of fire. Typically, deluge systems are used to create water curtains and cool particularly 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 as in an automatic way- system fire alarm, and manually.

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

The smallest particles of water supplied under high pressure have high penetrating and smoke-precipitating properties. This system significantly enhances the fire extinguishing effect.

Water mist fire extinguishing systems are designed and created based on equipment low pressure. This allows for highly efficient fire protection With minimum consumption water and high reliability. Similar systems used to extinguish fires of various classes. The extinguishing agent is water, as well as water with additives, or a gas-water mixture.

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

The fire extinguishing effectiveness of water depends on the method of supplying it 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.

Solid jets are used when extinguishing external and open or developed internal fires, when it is necessary to supply a large amount of water or if the water needs to be given impact force, as well as fires when it is not possible to get close to the source, when cooling neighboring and burning objects from large distances, structures, devices. 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. Area of ​​application of water

Water is used to extinguish fires of the following classes:

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

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

C - flammable gases.

Water should not be used to extinguish substances that release heat, flammable, toxic or corrosive gases upon contact with it. Such substances include some metals and organometallic compounds, metal carbides and hydrides, hot coal and iron. The interaction of water with burning alkali metals is especially dangerous. As a result of this interaction, explosions occur. 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.

Substance Nature of interaction with water Metals: sodium, potassium, magnesium, zinc, etc. React with water to form hydrogen Aluminum organic compounds React with explosion Organolithium compounds Decompose to form flammable gases 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 accompanied by stormy heat release Bitumen, sodium peroxide, fats, oils Combustion intensifies, emissions of burning substances occur, splashing, boiling

Water installations are ineffective for extinguishing flammable and combustible liquids with a flash point less than 90 O WITH.

Water, which has significant electrical conductivity, in the presence of impurities (especially salts) increases electrical conductivity by 100-1000 times. When using water to extinguish live electrical equipment, electricity in a stream of water at a distance of 1.5 m from electrical equipment it 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, it can even extinguish high-voltage installations.

6. Water applicability assessment method

If water gets on the surface of a burning substance, pops, flashes, and splashing of burning materials on the surface may occur. large area, additional fire, increase in flame volume, release of burning product from process equipment. They can be large scale or local in nature.

The lack of quantitative criteria for assessing the nature of the interaction of a burning substance with water makes it difficult to adopt optimal technical solutions using water in automatic fire extinguishing systems. For approximate applicability assessment water resources Two laboratory methods can be used. The first method consists of visual observation of 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 releasing 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 scope of use of water as a fire extinguishing agent, special additives (antifreeze) are used that lower the freezing point: mineral salts (K 2CO 3, MgCl 2, CaCl 2), some alcohols (glycols). However, salts increase the corrosivity of water, so they are practically not used. The use of glycols significantly increases the cost of extinguishing.

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

To increase the fire extinguishing efficiency of water, additives are added to it to increase wetting ability, viscosity, etc.

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

To reduce the surface tension of water, it is recommended to use wetting agents - surfactants: wetting agent brand DB, emulsifier OP-4, auxiliary substances OP-7 and OP-10, which are the products of the 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 to produce air-mechanical foam. Adding wetting agents to water can significantly increase its fire extinguishing efficiency. When introducing a wetting agent, the water consumption for extinguishing is reduced by four times, and the extinguishing time is reduced by more than half.

One way to increase the effectiveness of fire extinguishing with water is to use finely sprayed water. The effectiveness of finely atomized water is due to the high specific surface area of ​​small particles, which increases the cooling effect due to the uniform penetrating effect of water directly on the combustion site and increasing heat removal. At the same time, it significantly reduces harmful effects water on the environment.

Bibliography

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

2.AND I. Korolchenko, D.A. Korolchenko. Fire and explosion hazard of substances and materials and means of extinguishing them. Directory: in 2 parts - 2nd ed., revised. and additional - M.: Pozhnauka, 2004. - Part 1 - 713 p., - Part 2 - 747 p.

.Terebnev V.V. Firefighting Supervisor's Handbook. Tactical capabilities of fire departments. - M.: Pozhnauka, 2004. - 248 p.

.RTP Directory (Klyus, Matveykin)

The main extinguishing agent in firefighting is water. It is almost universally available, cheap and at the same time very effective. When it is supplied to the combustion zone, water cools the most heated layer of the substance. At the same time, it partially evaporates and turns into steam, due to which the reacting substances are diluted, which in itself helps to stop the combustion, as well as displace air from the fire zone.

Water in the form of atomized and finely dispersed (finely dispersed) jets has increased efficiency when extinguishing a fire. Once in the combustion zone, it evaporates intensely, reducing the oxygen concentration and diluting the flammable vapors and gases involved in combustion. In addition, tiny drops of water moving at high speed penetrate well into porous materials.

Along with this, the water also has negative properties. The main disadvantage of water as a fire extinguishing agent is that, due to its high surface tension, it does not wet solid materials and especially fibrous substances well. To eliminate this drawback, surfactants (wetting agents, foaming agents) are added to water to obtain solutions whose surface tension is less than that of water.

Water reacts with some substances and materials (see table) releasing hydrogen, flammable gases, large amounts of heat, etc. Such substances cannot be extinguished with water.

Table. Substances and materials when extinguishing which it is dangerous to use water and other water-based fire extinguishing agents

Substance or material	Result of exposure to water
Lead azide	Unstable, explodes when humidity increases to 30%
Aluminum metal	When burned, it decomposes water into hydrogen and oxygen.
Bitumen	The supply of compact jets of water leads to emission and increased combustion
Alkali and alkaline earth metal hydrates
Silicon iron (ferrosilicon)	Hydrogen fluoride is released, which ignites spontaneously in air
Calcium phosphorous	Reacts with water to release hydrogen phosphide, which is self-igniting in air.
Calcium peroxide	Decomposes in water releasing oxygen
Aluminum carbide Barium carbide Calcium carbide Alkali metal carbides	Decomposes with water, releasing flammable gases, and explodes on contact with water
Nitric acid	Exothermic reaction
Sulfuric acid	Exothermic reaction
Hydrochloric acid	Exothermic reaction
Magnesium and its alloys	When burned, water breaks down into hydrogen and oxygen.
Sodium hydrogen Sodium metal	Reacts with water to release hydrogen
Sodium hydrosulfate	Gets very hot, may cause fire of flammable materials
Sodium peroxide Potassium peroxide	If water gets in, an explosive release and increased combustion are possible.
Sodium sulphide	It gets very hot (over 400 degrees C), can cause ignition of flammable substances, and if it comes into contact with the skin, it causes a burn, accompanied by difficult-to-heal ulcers
Quicklime	Reacts with water, releasing large amounts of heat
Nitroglycerine	Explodes when hit by a jet of water
Petrolatum	Providing compact jets may result in ejection and increased combustion.
Rubidium metal	Reacts with water to release hydrogen
Saltpeter l	Injecting jets of water into the nitrate melt leads to a strong explosive release and increased combustion
Sulfuric anhydride	Explosive release possible if water enters
Sesquil chloride	Interaction with water occurs with an explosion
Silans	Reacts with water to release hydrogenated silicon, which is self-igniting in air.
Termite Titanium and its alloys Titanium tetrachloride	Reacts with water releasing large amounts of heat
Triethylaluminum Chlorosulfinic acid	Reacts explosively with water
Zinc dust	Decomposes water into hydrogen and oxygen
Alkali metals (sodium, potassium, calcium, cesium, etc.)	Release hydrogen, which ignites from the heat of reactions

Along with this, water has properties that limit its scope of application. Thus, when extinguishing with 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.

Fires are extinguished with water using water fire extinguishing installations, fire trucks and water nozzles (manual and fire monitors). To supply water to these installations, they use industrial enterprises and in populated areas water pipes.

In case of fire, water is used for external and internal fire extinguishing. Water consumption for external fire extinguishing is taken in accordance with building codes and rules. Water consumption for fire extinguishing depends on the fire hazard category of the enterprise and the degree of fire resistance building structures building, volume of production premises.

One of the main conditions that external water supply systems must satisfy is to ensure constant pressure in the water supply network, maintained by constantly operating pumps, a water tower or a pneumatic installation. This pressure is often determined from the operating conditions of internal fire hydrants.

In order to ensure fire extinguishing at the initial stage of its occurrence, in most industrial and public buildings Internal fire hydrants are installed on the internal water supply network.

According to the method of creating water pressure, fire water pipelines are divided into high and low pressure water supply systems. Fire water pipes high pressure arranged in such a way that the pressure in the water supply is always sufficient to directly supply water from hydrants or stationary monitors to the site of the fire. From low-pressure water supply systems, mobile fire pumps or motor pumps take water through fire hydrants and supply it under the required pressure to the fire site.

The fire water supply system is used in various combinations: the choice of one or another system depends on the nature of the production, the territory it occupies, etc.

Water fire extinguishing installations include sprinkler and deluge installations. They are a branched, water-filled pipe system equipped with special heads. In the event of a fire, the system reacts (in different ways, depending on the type) and irrigates the structure of the room and equipment in response to the action of the heads.

Foam

Foams are used to extinguish solid and liquid substances that do not interact with water. The fire extinguishing properties of foam are determined by its expansion ratio - the ratio of the volume of foam to the volume of its liquid phase, durability, dispersibility and viscosity. In addition to its physical and chemical properties, these properties of the foam are influenced by the nature of the flammable substance, the conditions of the fire and the supply of foam.

Depending on the method and conditions of production, fire extinguishing foams are divided into chemical and air-mechanical. Chemical foam is formed by the interaction of solutions of acids and alkalis in the presence of a foaming agent and is a concentrated emulsion of carbon dioxide in aqueous solution mineral salts containing a foaming agent.

The use of chemical foam is being reduced due to the high cost and complexity of organizing fire extinguishing.

Foam-generating equipment includes air-foam barrels for producing low-expansion foam, foam generators and foam sprinklers for producing medium-expansion foam.

Gases

When extinguishing fires with inert gaseous diluents, carbon dioxide, nitrogen, smoke 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 caused by heat losses due to heating of the diluents and a decrease in the thermal effect of the reaction. Carbon dioxide (carbon dioxide) occupies a special place among fire extinguishing compounds, which is used to extinguish flammable liquid warehouses, battery stations,

drying ovens, stands for testing electric motors, etc.

It should be remembered, however, that carbon dioxide cannot be used to extinguish substances whose molecules include oxygen, alkali and alkaline earth metals, as well as smoldering materials. To extinguish these substances, nitrogen or argon is used, and the latter is used in cases where there is a danger of the formation of metal nitrides with explosive properties and shock sensitivity.

IN Lately developed new way supplying gases in a liquefied state into the protected volume, which has significant advantages over the method based on the supply of compressed gases.

With the new supply method, there is virtually no need to limit the size of objects allowed for protection, since the liquid occupies approximately 500 times less volume than an equal amount of gas and does not require much effort to supply it. In addition, when liquefied gas evaporates, a significant cooling effect is achieved and the limitation associated with the possible destruction of weakened openings is eliminated, since when liquefied gases are supplied, a soft filling mode is created without a dangerous increase in pressure.

Inhibitors

All fire extinguishing compounds described above have a passive effect on the flame. More promising are fire extinguishing agents that effectively inhibit chemical reactions in a flame, i.e. have an inhibitory effect on them. The most widely used fire extinguishing compounds are inhibitors based on saturated hydrocarbons, in which one or more hydrogen atoms are replaced by halogen atoms (fluorine, chlorine, bromine).

Halocarbons are poorly soluble in water, but mix well with many organic substances. The fire extinguishing properties of halogenated hydrocarbons increase with increasing sea mass of the halogen they contain.

Halocarbon compositions have physical properties convenient for fire extinguishing. Thus, high density values ​​of liquid and vapor make it possible to create a fire extinguishing jet and the penetration of droplets into the flame, as well as retention of fire extinguishing vapors near the combustion source. Low freezing temperatures allow these compounds to be used at sub-zero temperatures.

IN last years Powder compositions based on inorganic salts of alkali metals are used as fire extinguishing agents. They are characterized by high fire extinguishing efficiency and versatility, i.e. the ability to extinguish any materials, including those that cannot be extinguished by all other means.

Powder compositions are, in particular, the only means of extinguishing fires of alkali metals, organoaluminum and other organometallic compounds (they are manufactured by industry on the basis of sodium and potassium carbonates and bicarbonates, phosphorus-ammonium salts, lead-based powder for extinguishing metals, etc.) .

For effective fight with pockets of flame during a fire, special substances are needed that will localize and neutralize the fire, preventing it from spreading over large areas. These include special fire extinguishing agents, the main tasks of which are:

• exclude access of air to the source of fire;
• stop supplying flammable liquid and gaseous substances to the combustion area;
• reduce the activity of chemical reactions that support combustion;
• cool the combustion area to temperatures at which spontaneous combustion does not occur;
• dilute gaseous and liquid flammable media with non-flammable components.

In order to quickly and effectively extinguish a fire, it is important to select the correct fire extinguishing agent and ensure its rapid delivery to the source of the fire. The choice of compositions for fighting fire at a specific facility is determined based on their physical and chemical characteristics.

Application area

Fire extinguishing agents– these are special substances that are used to fill primary fire extinguishing systems, as well as for the use of various fire equipment, used to eliminate fires and open flames.

Primary fire extinguishing equipment includes individual means fire fighting in the form of hand-held and mobile fire extinguishers, autonomous systems extinguishing fires connected to the fire alarm system.

Depending on the object where the fire occurred and the class of fire, one or another type of substance can be used to effectively fight the fire. In order to correctly select fire extinguishing agents, the concept of their classification is an important aspect.

Classification of substances

To fight fire, means are used that can ensure a rapid cessation of combustion both on the surface and in volume due to the chemical and physical effect on the combustion object. All extinguishing agents can be divided into several categories.

• Cooling fire extinguishing agents. They provide a reduction temperature regime in combustion sources, which prevents spontaneous ignition of nearby materials and subsequent spread of fire. These include water and solid carbon dioxide.

• Insulating. These substances ensure that the supply of oxygen to hot surfaces is stopped, which prevents the continuation of combustion. These include various non-flammable dry powders, air-mechanical foam, and non-flammable solutions.

• Fire extinguishing agents are diluted. With their help, the oxygen concentration in combustion areas is reduced, and the fuel is also diluted with non-combustion additives. Such substances include inert gas and carbon dioxide, steam and sprayed water.

• Inhibitory. These substances reduce the activity of the chemical combustion reaction, as a result of which the flame begins to extinguish and goes out. Such substances include halogenated hydrocarbons.

Chemical and physical properties of fire extinguishing agents

To understand what substance should be used when extinguishing a fire, let's look at what types of fire extinguishing substances there are and their properties.

Water and aqueous saline solutions

Water is one of the most common substances for extinguishing fires of various classes. Wide practical use water is due to the fact that it is cheap, easily supplied to the fire site and can be stored for a long time.

High rates of extinguishing fire with water are determined by its high heat capacity, which at T=+20ºC is 1 kcal/l. When water evaporates from one liter of it, more than 1500 liters of supersaturated H2O steam can be formed, which subsequently displaces O2 from the combustion area. The vaporization process requires about 540 kcal of energy, which can significantly reduce the temperature of the combustion area.

Since water has a high surface tension, its penetrating properties are not always sufficient, especially when dusty materials are burning. In this case, it is used together with surfactants (0.50...4%).

Note!

To effectively extinguish forest/steppe fires, dissolve in water various salts. The most commonly used are ammonium sulfuric acid, calcium chloride, caustic salt, etc.

Restrictions:

Important to remember!

Water is not universal remedy fire extinguishing

You should avoid using it when extinguishing:

• electrified equipment that is under high voltage;
• alkali and alkaline earth metals, with which water reacts with the subsequent release of flammable hydrogen and a large amount of heat;
• substances that support combustion and without air access.

Fire extinguishing foam

These fire extinguishing agents and their classification involve the use of two types of foam - created by a chemical reaction or mechanically using air.

Chemical foam is obtained due to a chemical reaction between alkaline and acidic environment. The shell of individual bubbles of this type of foam includes a foaming material and an aqueous saline solution. The bubbles themselves are filled with CO 2, which appears as a result of the chemical reaction that occurs.

Air foam is obtained when mixing occurs air flow with special foaming agents. The bubble shell of this foam contains only a foaming agent.

Restrictions:

Foam cannot be used when extinguishing:

• electrified installations;
• alkaline earth and alkali metals.

Carbon dioxide

It is used in solid form, in the form of “carbon dioxide snow,” or in a gaseous/aerosol state.

The use of “carbon dioxide snow” can significantly lower the temperature at the source of the fire, and also reduces the concentration of oxygen supplied to the source of the flame. CO 2 in the solid state has a density of 1500 kg/m 3, and up to 500 liters of gas can be obtained from one liter of this substance.

These extinguishing agents in gaseous form are effectively used for bulk fire extinguishing. Gas fills the entire room, displacing oxygen from the combustion zone.

Aerosol mixtures of carbon dioxide will be useful when there is a high concentration of small combustible particles in the air, which can be precipitated using an aerosol.

Restrictions:

Important to remember!

CO 2 in any condition is dangerous for people. Therefore, access to the room where this material was used should be carried out using special protective equipment.

CO 2 cannot be used when extinguishing:

• ethyl alcohol;
• substances and materials that burn and smolder without access to oxygen.

Refrigerants for extinguishing

These substances are highly effective formulations containing halogenated hydrocarbons. Freon substances will be effective for quickly extinguishing fires different classes, including installations under operating voltage. Their effect is based on reducing the activity of chemical reactions that support combustion, as well as the possibility of interaction with oxygen air environment, which allows you to reduce its concentration.

Limitation:

Freons are toxic and dangerous to people. They cannot be used to extinguish:

• acidic substances;
• alkali and alkaline earth metals.

Detailed description of fire extinguishing agents

Conclusion

Thanks to a wide range of different extinguishing agents, you can effectively fight fires of various classes and varying complexity. To quickly neutralize a fire, it is important to choose the right extinguishing material. When choosing, you should take into account the restrictions on extinguishing certain substances, as well as the fact that some fire extinguishing material is toxic and may pose a danger to people and the environment.

Water is the most widely used and effective means of extinguishing fires.

Table 1: Comparison of the effectiveness of fire extinguishing agents (FAs)

Fire class	Combustible materials	Water	Foam	Powder		CO 2	Freon CF 3 Br	Other refrigerants
				PSB	PF
A	Solids that form coal (paper, wood, textiles, coal, etc.	4	4	1	3	1	2	1
IN	GZh and flammable liquids (gasoline, varnishes, solvents), melting materials (hydron, paraffin)	4	4	4	4	3	4	4
WITH	Gases (propane, methane, hydrogen, acetylene, etc.)	2	1	4	3	1	3	2
D	Metals (Al, Mg, etc.)	—	—	1	1	—	—	—
E	Electrical equipment (transformers, distribution boards and etc.)	2	—	2	2	3	4	3

As follows from Table 1, water and foam are the most effective means of extinguishing class A and B fires (class B mainly with fine or ultra-sprayed water).

The basis of the fire extinguishing effect of water is its cooling ability, which is due to its high heat capacity and heat of vaporization.

Having the highest heat absorption capacity, water is the most effective natural material for extinguishing fires. Drops of water entering the combustion center undergo two stages of heat absorption: when heated to 100°C and evaporation at a constant temperature of 100°C. In the first stage, 1 liter of water spends 335 kJ of energy, in the second phase - evaporation and transformation into water vapor - 2260 kJ.

When water enters a high-temperature zone or comes into contact with a burning substance, it partially evaporates and turns into steam. During evaporation, the volume of water increases almost 1670 times, due to which the air is displaced by water vapor from the fire source, and, as a result, the combustion zone is depleted of oxygen.

Water has high thermal stability. Its vapors can decompose into hydrogen and oxygen only at temperatures above 1700°C. In this regard, extinguishing with water most hard materials safe, since their combustion temperature does not exceed 1300 °C.

Water can dissolve some vapors, gases and absorb aerosols. Therefore, it can be used to precipitate combustion products during fires in buildings. For these purposes, finely atomized and ultra-atomized (water mist) jets are used.

Good mobility of water ensures ease of transportation through pipelines. Water is used not only to extinguish fires, but also to cool objects located near the source of fire. Thereby preventing their destruction, explosion and fire.

Mechanism for extinguishing fires with water:

• cooling the surface and reaction zone of burning substances;
• dilution (phlegmatization) of the environment in the combustion zone with steam generated during evaporation;
• isolation of the combustion zone from the air;
• deformation of the reaction layer and flame failure due to the mechanical impact of a water jet on the flame.

When extinguishing burning oil products in tanks with water, the drops supplied to the combustion source are essential. The optimal diameter of water droplets is 0.1mm when extinguishing gasoline; 0.3 mm - kerosene and alcohol; 0.5mm - transformer oil and petroleum products with a flash point above 60 °C.

High efficiency of extinguishing flammable substances that have a high combustion temperature and create a high flame pressure is achieved through the use of a mixture of small and large water droplets. In this case, small drops, evaporating in the flame combustion zone, reduce its temperature, and large drops, not having time to completely evaporate, reach the burning surface, cool it and, if their kinetic energy by the time they reach the burning surface is high enough, destroy the reaction layer.

Table 2: Areas of water application for different fire classes

Fire class	Subclass	Combustible substances and materials (objects)	Water sprayed by sprinklers	Finely sprayed water	Sprayed water with wetting agent
A	A1	Solid smoldering substances wetted with water (wood, etc.)	3	3	3
	A2	Solid smoldering substances that are not wetted by water (cotton, peat, etc.)	1	1	2
	A3	Solid non-smoldering substances (plastics, etc.)	2	3	3
	A4	Rubber products	2	2	3
	A5	Museums, archives, libraries, etc.	1	1	1
IN	IN 1*	Saturated and unsaturated hydrocarbons (heptane, etc.)	—	2	1
	AT 2*	Saturated and unsaturated hydrocarbons (gasoline, etc.)	—	2	1
	AT 3*	Water-soluble alcohols (C1-C3)	—	2	1
	AT 4*	Water-insoluble alcohols (C4 and higher)	—	2	1
	AT 5**	Acids - sparingly soluble in water	3	3	3
	AT 6**	Ethers and ethers (diethyl, etc.)	3	3	3
	AT 7**	Aldehydes and ketones (acetone, etc.)	3	3	3
WITH,	C1, C2, C3		—	—	—
E***	E1	EVC	1	1	1
	E2	Telephone nodes	2	2	2
	E3	Power plants	1	1	1
	E4	Transformer substations	2	2	2
	E5	Electronics	1	1	1

Note: “1” – suitable, but not recommended; “2” – fits satisfactorily; “3” – fits well; “4” – fits perfectly; “-” - not suitable, “*” - for flammable liquids and gas liquids with a flash point of up to 90 ° C; “**” - for flammable liquids and gases with a flash point of more than 90 °C; “***”—electrical equipment is live.

Water should not be used to extinguish the following materials:

• potassium, sodium, lithium, magnesium, titanium, zirconium, uranium, plutonium;
• organoaluminum compounds (reacts explosively);
• organolithium compounds, lead azide, carbides, alkali metals, hydrides of a number of metals, magnesium, zinc, calcium carbides, barium (decomposition with release of flammable gases);
• iron, phosphorus, coal;
• sodium hydrosulfite (spontaneous combustion occurs);
• sulfuric acid, thermites, titanium chloride (strong exothermic effect);
• bitumen, sodium peroxide, fats, oils, petrolatum (intensified combustion as a result of emission, splashing, boiling).

When extinguishing with water, oil products and many other organic liquids float to the surface, as a result of which the area of ​​the fire can increase significantly. For example: in case of fire of petroleum products located in the tank, it is not recommended to extinguish it with water. Oil products float above the water. Water, as a result of heating, turns into steam. Water vapor rises upward in portions, which causes burning oil products to splash out of the tank and makes it difficult for firefighters to access the fire.

Disadvantages of water include heat freezing. To lower the freezing point, special additives (antifreeze), some alcohols (glycols), and mineral salts (K 2 CO 3, MgCl 2, CaCl 2) are used. However, these salts increase the corrosivity of water, so they are practically not used. The use of glycols significantly increases the cost of the fire extinguishing agent.

Foaming agents, antifreeze and other additives also increase the corrosivity and electrical conductivity of water. As protection against corrosion, you can metal parts and pipelines apply special coatings, or add corrosion inhibitors to the water.

Expanding the scope of application of water for extinguishing electrical equipment under voltage is possible when using it in a fine and ultra-sprayed state.

The low wetting ability and low viscosity of water make it difficult to extinguish fibrous, dusty and especially smoldering materials. Materials with a large specific surface area, the pores of which contain the air necessary for combustion, are subject to smoldering. Such materials can burn with a greatly reduced oxygen content in environment. Penetration of fire extinguishing agents into the pores of smoldering materials is, as a rule, quite difficult.

When introducing a wetting agent (sulfonate), the water consumption for extinguishing is reduced by four times, and the extinguishing time is reduced by half.

In some cases, extinguishing with water becomes very effective if it is thickened with, for example, sodium carboxymethylcellulose or sodium alginate. Increasing the viscosity to 1-1.5 N*s/m2 allows you to reduce the extinguishing time by about 5 times. The best additives in this case are solutions of sodium alginate and sodium carboxymethylcellulose. For example, a 0.05% solution of sodium carboxymethylcellulose provides a significant reduction in water consumption for fire extinguishing. If, under certain extinguishing conditions with ordinary water, its consumption ranges from 40 to 400 l/m2, then when using “Viscous” water - from 5 to 85 l/m2. The average damage from fire (including as a result of exposure to water on materials) is reduced by 20%.

The most commonly used additives that increase the efficiency of water use are:

• water-soluble polymers to increase adhesion to burning objects (“Viscous water”);
• polyoxyethylene to increase the capacity of pipelines (“slippery water”);
• inorganic salts to increase the efficiency of extinguishing;
• antifreeze and salts to reduce the freezing point of water.

Currently, one of the most promising areas in the field of fire protection of objects for various purposes is the use of finely and ultra-sprayed water as a means of extinguishing fires. In this form, water is capable of absorbing aerosols, precipitating combustion products and extinguishing not only burning solids, but also many flammable liquids.

When water is supplied in a fine or ultra-sprayed state, the greatest fire extinguishing effect is achieved. The use of finely and ultra-sprayed water is especially important at facilities where it is required high efficiency extinguishing, there are restrictions on water supply and minimizing damage from water spills is relevant.

With the help of finely and ultra-sprayed water, the protection of many particularly socially and industrially significant objects can be ensured. These include: residential premises, hotel rooms, offices, educational institutions, dormitories, administrative buildings, banks, libraries, hospitals, computer centers, museums and exhibition galleries, sports complexes, industrial facilities, i.e. such objects where fire extinguishing must be carried out in the initial stage quickly enough and with low water consumption.

Additional benefits of using atomized water compared to a compact jet or spray stream:

• the ability to extinguish almost all substances and materials, with the exception of substances that react with water releasing thermal energy and flammable gases;
• high extinguishing efficiency due to the increased cooling effect and uniform irrigation of the fire with water;
• minimal water consumption - insignificant consumption allows you to avoid significant damage from the consequences of a spill and ensure the possibility of use subject to a water limit;
• Radiant Thermal Shielding - Use for Protection service personnel taking part in extinguishing the fire, personnel of fire departments, load-bearing and enclosing structures, as well as nearby material assets;
• dilution of flammable vapors and reduction of oxygen concentration in the combustion zone as a result of intensive formation of water vapor;
• reducing the temperature in rooms during a fire;
• uniform cooling of excessively hot metal surfaces load-bearing structures due to the high specific surface area of ​​the droplets, it eliminates their local deformation, loss of stability and destruction;
• effective absorption and removal of toxic gases and smoke (smoke deposition);
• low electrical conductivity of finely ultra-sprayed water makes it possible to use it as effective means fire extinguishing at electrical installations under voltage;
• environmental cleanliness and toxicological safety combined with protection of people from exposure hazardous factors fire - allows personnel to save valuables during work automatic installation fire extinguishing

Ultra-sprayed water in the combustion zone intensively evaporates. Protective layer water vapor can isolate the combustion zone, preventing the access of oxygen. When the oxygen concentration in the combustion area drops to 16-18%, the fire self-extinguishes.

Literature used: L.M.Meshman, V.A.Bylinkin, R.Yu.Gubin, E.Yu.Romanova. Automatic water and foam fire extinguishing systems. Design. Moscow city. — 2009