Medium multiplicity VMP supply using the GPS-600 generator

Air-mechanical foam (AMF) is a class of foams used in fire extinguishing, obtained by mechanically introducing air bubbles into a foam solution. Currently, air-mechanical foam is practically the only type of foam used (by type of formation). Chemical foams are generally considered harmful to the environment and human health.

Foam is a dispersed system consisting of cells - air (gas) bubbles, separated by films of water containing a stabilizer (foaming agent).

Air-mechanical foams are produced by mixing aqueous solutions of foaming agents with air.

Foam, like any dispersed system, can be obtained in two ways:

• condensation, i.e. the combination of very small (microscopic) gas bubbles into larger ones;
• dispersion, i.e. crushing large air bubbles and inclusions into smaller ones, and therefore more stable.

The dispersion method is based on obtaining foam as a result of crushing and distributing air or gas in a solution with a foaming agent. Usually small portions of gas are introduced into the solution and crushed there to the size of small bubbles. The easiest way to achieve this is by blowing gas through a tube lowered into a liquid, or by spraying liquid onto a metal mesh through which gas is forced. In this way, monodisperse foams can be obtained, i.e. foams consisting of bubbles of the same size.

The most powerful and effective dispersive foam systems are designed for fire extinguishing. They are so reliable and productive that they are widely used in a wide variety of sectors of the national economy. There are mainly three groups of devices used.

The first group includes air-foam barrels that operate on the principle of a turbulent jet: a foaming agent solution under pressure is ejected from the nozzle, capturing air from the environment, crushed and mixed in a turbulent flow. The foam resulting from vigorous mixing of the solution and air is ejected through a pipe called a foam nozzle. Such foam is characterized by low expansion and heterogeneity of structure, so it is unstable.

In air-foam barrels

In air-foam barrels

The second group of devices uses nozzles that form spray jets, which are now most widely used (we are talking about modern barrels with a depletor. For example, barrels KURS-8, RSKU-50A, SHTORM RSP-80V-16 and others like that). The sprayed foam solution, after leaving the nozzle at high speed, foams upon contact with air. Such devices also create low expansion foam and, even at low pressures, eject a stream of foam over long distances, which makes it easier to extinguish large fires.

In nozzles forming atomized jets

In foam generators of the third group, foaming occurs on meshes. The foaming agent solution is ejected under pressure from the nozzle, falls in the form of drops onto the mesh cells and wets them. The air flow supplied by a fan or ejector blows foam bubbles on the mesh cells. These bubbles break away from the mesh and form foam with small, uniform pores of enormous expansion (1000 or more). Such foam generators produce up to 15 thousand liters of foam in 1 s, and the jet flight range reaches 8-12 mgorban Yu.I. Fire robots and gun equipment in fire automatics and fire protection. - M.: Pozhnauka, 2013. - 352 pp..

On foam generator grates

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Production - air-mechanical foam - Great Encyclopedia of Oil and Gas, article, page 1

Receiving - air-mechanical foam

Page 1

Obtaining stable and homogeneous air-mechanical foam is the most critical stage in creating high-quality foam plastics.  

To obtain air-mechanical foam, the following foaming agents are used.  

To obtain air-mechanical foam, air-foam barrels, foam generators and foam sprinklers are used. Air-foam nozzles and foam generators are used in mobile installations to extinguish external and internal fires. Internal fire hydrants are often equipped with air-foam nozzles.  

To obtain air-mechanical foam of this expansion ratio, other devices and installations can also be used.  

To obtain air-mechanical foam, special equipment and aqueous solutions of software are required.  

To obtain air-mechanical foam, a foaming agent is introduced into the water.  

To obtain air-mechanical foam, a foaming agent PO-1 is used, consisting of kerosene contact, wood glue and ethyl alcohol.  

To obtain air-mechanical foam, air-foam barrels, foam generators and foam sprinklers are used.  

To obtain stable air-mechanical foams, the concentration of the considered foaming agents must exceed the critical concentration for the formation of micelles (0ОШ-О.  

To obtain stable air-mechanical foams, the concentration of the foaming agents considered must exceed the critical concentration for the formation of micelles (0 01 - 0 001 M) and lie outside the region of the sharpest decrease in surface tension.  

To obtain high-expansion air-mechanical foam and supply it to burning tanks with petroleum products, high-expansion foam generators of the GVP-600 and GVP-2000 types, modernized foam lifters of the Trofimov system, PO-1 foam concentrates or other foam concentrates recommended by the VNIIPO Ministry of Internal Affairs of the USSR are used.  

Pages:      1    2    3    4

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Air-mechanical foam

Air-mechanical foam is formed as a result of intensive mechanical mixing of an aqueous solution of a foaming agent with air.

To obtain foam, foam concentrates PO-1 and PO-6 are used.

Foaming agent PO-l is a neutralized kerosene contact containing at least 45% sulfonic acids. To obtain the required expansion and durability of the foam, 4.5% glue and 10% alcohol or ethylene glycol are added to it.

Foaming agent PO-6 is a product of alkaline hydrolysis of industrial animal blood. To make the foam stable, 1% ferrous sulfate is added to it. To prevent the foam concentrate from rotting when long-term storage, 4% sodium fluoride is added to it.

Foam concentrates must meet the requirements of GOST 6948-54 and GOST 9603-61.

Air-mechanical foam consists of bubbles, the shell of which is formed from a foaming agent solution. The bubbles contain (depending on the foaming agent) air up to 90%, water 9.5% and foaming agent up to 0.5%. Specific gravity foam from 0.11 to 0.17.

Air-mechanical foam is obtained using special devices (mixers and air-foam barrels). The durability of foam based on foaming agent PO-1 is 30 minutes, and that based on foaming agent PO-6 is at least 60 minutes.

VNIIPO has developed a foam concentrate formulation PO-8 to produce air-mechanical foam of increased resistance, which is used when extinguishing petroleum products and polar liquids (alcohol, acetone, etc.).

Air-mechanical foam is divided into normal and high expansion foam according to the output expansion rate.

Foam of normal expansion is considered when from 1 liter of foaming agent PO-1 and 25 liters of water produces from 200 to 300 liters of foam, from 1 liter of foaming agent PO-6 and 25 liters of water - from 125 to 175 liters.

Foam from foaming agent PO-6 is more stable than foaming agent PO-1. To obtain normal expansion foam, aqueous solutions of foaming agents PO-1 (3-4% by volume) and PO-6 (4-6% by volume) are used.

Foaming agent PO-1 is considered suitable if the foam output ratio is at least 10 and its durability is at least 30 minutes, and foaming agent PO-6 is considered suitable if the foam output ratio is at least 5 and its durability is at least 60 minutes.

Normal expansion foam adheres well to vertical surfaces, so it can be used to protect materials and structures from burning when exposed to radiant heat.

It is advisable to use air-mechanical foam of normal expansion for extinguishing petroleum products with a flash point of 45 ° C and above, located in containers, and petroleum products with a flash point of 45 ° C and below (with the exception of aviation gasoline), spilled in a thin layer on a hard surface or on the surface of water .

It can also be used for extinguishing petroleum products with a flash point of 45 ° C and below (except for gasoline) in containers. But at the same time, we must remember that to extinguish oil products with a flash point of 28 ° C and below in an area of ​​no more than 100 m2, you can use air-mechanical foam of normal expansion based on the foaming agent PO-1, and on an area of ​​​​no more than 400-500 m2 - on based on foam concentrate PO-6. The distance from the upper edge of the side of the container to the liquid surface should be no more than 2 m. This condition should also be observed when extinguishing oil products with a flash point of 28 to 45 ° C.

Foaming agents are ineffective when extinguishing fires of polar liquids (alcohol, ether, acetone).

To extinguish petroleum products (gasoline, kerosene, crude oil, fuel oil), along with the PO-1 foaming agent, the NB wetting agent is used.

VNIIPO has developed a method for extinguishing oil products in containers by supplying air-mechanical foam through a layer of fuel. In this case, the fire can be extinguished at any level of fuel in the containers.

High expansion foam based on foam concentrates PO-1 or PO-6 is produced by a special generator operating on the principle of enhanced air suction. It can be used to localize fires of solid substances and flaming combustion in premises. Foam provides high fire-extinguishing efficiency when extinguishing petroleum products.

When it extinguishes a flaming fire in the premises, smoke and combustion products are displaced, combustion sources are localized, and favorable conditions are created for the complete cessation of combustion.

As rooms are filled with high-expansion foam, the temperature in them quickly decreases as a result of the displacement of hot gases, combustion cessation and partial cooling of structures. The temperature in a burning room, as practice shows, immediately after introducing foam into it can drop from 1000 ° C or more to 65-50 ° C.

After filling the room with foam, the temperature in it may rise again, since the heated floor structures do not have time to cool due to the short-term effect of the foam.

High expansion foam can only extinguish a fire due to the presence of a large amount of air in it and the limited time of its supply. The smoldering areas of solid substances remain unextinguished.

Under the influence of the heat released during smoldering, the foam quickly collapses.

Complete elimination of smoldering sites depends on the intensity and time of foam supply and on how quickly it penetrates to the burning sites.

In practice, high expansion foam is not thermally conductive. Fluctuations in ambient temperature from -30 to +30° C do not have a significant effect on the quality of the foam. At low temperatures (below -15° C), the durability of the foam decreases somewhat, although a stable crust forms on its surface. High temperature accelerates the destruction of foam.

Foam does not have a harmful effect on most materials and equipment, and does not create additional load on structures due to its insignificant volumetric weight.

The foaming solution is a good wetting agent and therefore freely penetrates into materials, including fibrous ones.

When using air-mechanical foam, the work of firefighters when extinguishing a fire is greatly facilitated. Therefore, it is widely used in extinguishing fires; it is the main fire extinguishing agent.

When extinguishing oil products, it is necessary to use the calculated amount of both chemical and air-mechanical foam. Instructions for their calculation are set out in Appendix 4 of the Rules fire safety on river transport of the Ministry of River Fleet of the RSFSR."

Carbon dioxide (technical name for carbon dioxide) CO2 is a colorless gas with a barely noticeable odor, does not burn and does not support combustion, and does not conduct current. The fire extinguishing concentration of carbon dioxide vapor in the air should be 22.4% (by volume). At 0°C and a pressure of 36 kgf/cm2 it easily liquefies, passing from a gaseous state to a liquid one.

The heat of evaporation of liquid carbon dioxide is 47.7 cal/kg. With the rapid evaporation of liquid carbon dioxide, solid (snow-like) carbon dioxide is formed. The specific gravity of such carbon dioxide at a temperature of -79° C is 1.53.

Carbon dioxide or carbon dioxide snow directed into the fire zone reduces the oxygen concentration in it to such a level that combustion is impossible, and also cools the burning substance and the environment, as a result of which combustion stops.

Carbon dioxide is used to extinguish fires in enclosed spaces (in conditions of limited air exchange) and in a relatively small area directly in the air. It is used to extinguish fires in live electrical installations.

When extinguishing fires in enclosed spaces, 0.495 kg/m3 of carbon dioxide is consumed, and in the most fire-hazardous rooms - 0.594/kg/m3.

Flame combustion in the cargo hold of a ship when carbon dioxide is used stops in cases where the percentage of oxygen in it decreases to 14%. The smoldering continues. To stop it, the oxygen content in the hold must be brought to 5%. Carbon dioxide must be fed into the hold until smoldering stops completely, and it can last from several hours to one or two days.

Carbon dioxide as an independent fire extinguishing agent is rarely used in stationary fire-fighting installations on river transport. It is replaced by more effective means- halohydrocarbons: ethyl bromide, methylene bromide, tetrafluorodibromoethane, which are included in the composition of such fire extinguishing mixtures as “3.5”, SRC and one-component freon-114B2.

trudova-ohrana.ru

Supply of air-mechanical foam. (with foam concentrate taken from an external container).

Perform operations to install the fire fighting equipment at the work site and start the fire pump. Next do the following:

Remove the plug from the fitting and attach the hose in its place;

Lower the second end of the hose into a container with foaming agent;

Open the foam mixer tap;

Place the dispenser in the required working position;

Apply air-mechanical foam.

Note:

When working from an external container, the dispenser must be tightly closed, especially when drawing water from a reservoir. If the dispenser does not shut off, the pump will suck in one foam agent instead of water.

Fire hand nozzles are designed to form and direct continuous and sprayed water jets when extinguishing fires.

Trunks depending on design features and main parameters are classified into:

Normal pressure barrels;

Trunks high pressure.

Normal pressure barrels provide the supply of water and fire extinguishing solutions at a pressure in front of the barrel from 0.4 to 0.6 MPa (4 to 6 kgf/cm2), imported ones from 0.7 MPa (7 kgf/cm2).

High-pressure barrels provide the supply of water and fire extinguishing solutions at a pressure in front of the barrel from 2 to 3 MPa (from 20 to 30 kgf/cm2).

Depending on the presence (absence) of a blocking device, trunks are divided into:

Non-overlapping;

Overlapping.

Normal pressure barrels, depending on the nominal bore of the connecting head, are divided according to standard sizes into barrels:

With nominal diameter DN 50;

With nominal diameter DN 70.

Depending on their functionality, trunks are divided into trunks:

Forming only a continuous stream;

Sprayers that produce only a spray jet;

Universal, forming both a continuous and sprayed stream;

With a protective curtain, additionally forming a water curtain to protect the shooter from thermal radiation;

Combined, forming water and foam jets.

Specifications:

Tests must be carried out under normal climatic conditions.

Periodic tests must be carried out at least once a year and after repairs. Each barrel must be marked in a visible place containing the following information:

a) inventory number;

b) date of the test performed;

c) fire department number;

The marking must be maintained throughout the life of the barrel. The inventory number is applied to the metal body of the fire hand barrel by punching or engraving. It is allowed to apply the test date and fire department number with paint.

It is prohibited to apply the inventory number to the metal body of the fire hand gun using erasable, fading means (marker, felt-tip pen). The thermally insulating barrel cover must be made of low-density polyethylene according to GOST or other materials with the same thermal conductivity. The length of the fireman's hand gun strap must be at least 50 cm.

Fireman's hand barrel

RS-50 RS-70 Dual – force

SRK-50 RSP-70 RSK3-70

Barrels are tested in the following order:

a) external inspection;

During inspection they check appearance, fastening of assembly units and parts, the presence of a thermally insulating coating of the body, designations and markings, as well as completeness for compliance with GOST requirements. The appearance of traces of corrosion, nicks, dents, cracks and other mechanical damage and defects on barrel parts is not allowed. Sharp corners and edges on parts should be dulled. The fastening of individual parts and assembly units must prevent spontaneous loosening and unscrewing. The barrel body must have a thermal insulating coating. The check is carried out visually.

b) checking the strength and tightness of the barrel body, the tightness of the shut-off device;

The strength and tightness of the bodies of the specified equipment must be ensured under hydraulic pressure, the trunks must withstand hydraulic pressure of 0.9-1.0 MPa (9-10 kgf/cm2) and, at the same time, the appearance of traces of water (in the form of drops) on the outer surfaces of its parts and leaks at joints. Holding time under pressure is at least 2 minutes.

c) checking the control force of the overlap device;

Checking the force on the control handle of the shut-off device when water is supplied to the barrel under operating pressure. The valve handle moves freely to all positions, regulates and shuts off the water supply. When the barrel is turned off, the water supply is completely shut off.

d) checking the closure of the connecting heads;

Checking the closure of the heads of the trunks is carried out manually, and it must be ensured that they enter along the spiral protrusion by an amount equal to 1.0-1.5 times the width of the fang.

e) checking the parameters of a continuous jet;

The quality of the continuous stream is checked visually. Formation of a continuous stream at the exit from the nozzle (without grooves, stratification and signs of spraying). When checking the range of a continuous stream, the barrel is fixed at an angle of inclination to the horizon of 30 degrees at a height of 1 m from the cut of the outlet to the test site.

The distance (maximum, at the outermost drops) of the jet is measured from the projection of the barrel nozzle onto the test site. When determining the range of the jet, the tester must stand opposite the exit of the jet and place a mark at the place where the extreme drops fall. Measurement accuracy +0.2 m.

f) checking the parameters of the spray jet;

The quality of the spray jet is checked visually.

The test results are entered into the PTV test log and documented in a report (not necessary for fire trunks), which must contain:

a) test date;

b) inventory number designation of the barrel subjected to testing;

c) test procedure;

d) list regulatory documents, on the basis of which the tests were carried out;

e) test results.

Check during operation.

You need to make sure that:

There are no obvious damages, all parts are in place, not broken, secured

properly, stickers are not damaged, etc.;

The filter mesh at the barrel inlet is not clogged with debris;

The threaded inlet fits tightly to the barrel, ensuring a tight connection;

The valve handle moves freely to all positions, regulates and shuts off the water supply.

When the barrel is turned off (the valve handle is moved forward all the way), the water supply is completely shut off;

The barrel flow rate corresponds to the indicators obtained on the basis of pump pressure and barrel recoil;

The bumper easily rotates and adjusts the shape of the jet at any flow position;

Turning the bumper into the flushing mode and leaving it does not affect the flow; the pressure is restored after a drop;

The pressure adjustment button rotates freely and switches the barrel pressure.

poznayka.org

VMP

Topic Purpose: types and design of equipment for producing air-mechanical foam

Type of lesson: class-group

Allotted time: 1 class hour.

Detailed lesson plan.

Foaming agents general purpose

General purpose foaming agents are manufactured from cheap and readily available raw materials. Used to produce foam and wetting solutions.

Designed to extinguish fires of oil products, wood, fabric, paper, peat, cotton, rubber, plastics, etc. They are used to produce low, medium and high expansion foam.

These include:

Purpose Converters

Foaming agents for special purposes are used to produce foam when extinguishing fires of petroleum products and various classes of flammable liquids in the most fire-hazardous objects, as well as for use with sea water, at low temperatures and other special conditions. Some of them are made from scarce, expensive raw materials.

These include:

Physico-chemical and fire extinguishing properties of foams.

Fire extinguishing foams are divided into chemical and air-mechanical.

Chemical foam (multiplicity up to 6) is obtained as a result of a chemical reaction between the acidic and alkaline parts:

Fe2(S04)3+6NaHC03-)-3Na2S04+2Fe(OH)3+6C02

h3S04+2NaHC03->Na2S04+2C02+2h30

Air-mechanical foam is obtained by mechanical movement of three components: water, foaming agent and air.

According to GOST 12.1.114-82, VMP is divided into three types:

VMF low multiplicity K<20 (для расчетов К=10) ВМП

average multiplicity 20^K^200 (for calculations K=100)

High multiplicity HFMP K>200 (for calculations K=1000)

Physico-chemical and fire-extinguishing properties of foams and their scope.

Fire extinguishing foams are a collection of bubbles

consisting of

liquid shell filled with air or gases, i.e. foam is

concentrated emulsion of gas and liquid.

Chemical foam consists of 80% CO2 (carbon dioxide), 19.7% aqueous solution and 0.3% foaming agents.

VMP consists of 83-99.6% air and 0.4-17% aqueous solution of PO.

The main properties of foams, regardless of the method of their production, are the following:

1. Foam ratio is the ratio of the volume of foam to the volume of foaming liquid. The multiplicity depends on the type, quality and concentration of PO in water, on the design of the foam device, on the pressure in front of the sprayer and on the temperature of the sucked air.

2. Foam durability is the ability to resist destruction over a certain period of time. Foam durability is the time during which the foam is destroyed by 50% of its original volume. Resistance depends on: the type of software, the properties and temperature of the substances with which it interacts, the method of supply, and the height of the foam layer. t=3.8-18min (SAMPO - several hours)

3. High heat capacity - foam, when destroyed, cools burning substances (building structures, flammable liquids and gas liquids) due to the aqueous solution of the foaming agent present in its structure.

4. Low density 4-170 kg/m3. The density depends on the expansion ratio of the foam. The foam floats on the surface of liquids, does not create excessive load on the coating, and eliminates loss of stability of the vessel when extinguishing fires.

5. Low thermal conductivity - it is close to the thermal conductivity of stationary gases. This allows the foam to be used as a heat-insulating screen against the action of radiant energy.

6. Insulating ability - when extinguishing with foam, the foam layer prevents the penetration of vapors into the combustion zone and heat from the combustion zone to the surface of the substance.

7. Viscosity - the ability of foam to spread.

8. Dispersity - degree of grinding i.e. bubble sizes. With increasing foam dispersion, its lifetime, viscosity and vapor-gas impermeability increase.

Method of producing foams and purpose for fire extinguishing:

Low expansion foam – SVE trunks; SVPE; ORT-50 with a nozzle – extinguishing cotton and related substances, also used for extinguishing rubber-shaped products and paralon.

Medium expansion foam – GPS-600; GPS-800; GPS - 2000 - extinguishing flammable liquids.

High expansion foam is obtained ONLY with the help of a fire exhaust fan. Extinguishing volumetric fires (basements). You can breathe in this foam.

Schemes of combat deployment with VMP supply

studfiles.net

3.3. Instruments and apparatus for producing air-mechanical foam

Air-mechanical foam is designed to extinguish fires of liquid (fire class B) and solid (fire class A) flammable substances. Foam is a cellular-film dispersed system consisting of a mass of gas or air bubbles separated by thin films of liquid.

Air-mechanical foam is obtained by mechanically mixing the foaming solution with air. The main fire extinguishing property of foam is its ability to prevent the entry of flammable vapors and gases into the combustion zone, as a result of which the combustion stops. The cooling effect of fire extinguishing foams also plays a significant role, which is largely inherent in low expansion foams containing a large amount of liquid.

An important characteristic of fire extinguishing foam is its expansion ratio - the ratio of the volume of foam to the volume of the foaming agent solution contained in the foam. There are foams of low (up to 10), medium (from 10 to 200) and high (over 200) expansion. Foam barrels are classified depending on the expansion ratio of the resulting foam (Fig. 3.23).

FOAM FIRE TRUNKS

To obtain low expansion foam

To obtain medium expansion foam

Combined to produce low and medium expansion foam

Rice. 3.23. Classification of foam fire nozzles

A foam barrel is a device installed at the end of a pressure line to form jets of air-mechanical foam of various expansion rates from an aqueous solution of a foaming agent.

To obtain low expansion foam, manual air-foam barrels SVP and SVPE are used. They have the same device, differing only in size, as well as an ejector device designed to suck the foaming agent from the container.

The SVPE barrel (Fig. 3.24) consists of a body 8, on one side of which a pin connection head 7 is screwed to connect the barrel to a hose pressure line of the appropriate diameter, and on the other side, a pipe 5 made of aluminum alloy and intended for the formation of air-mechanical foam is attached to the screws and directing it to the fire. There are three chambers in the barrel body: receiving6, vacuum3 and outlet4. On the vacuum chamber there is a nipple 2 with a diameter of 16 mm for connecting a hose 1 having a length of 1.5 m, through which the foam agent is sucked in. At a working water pressure of 0.6 MPa, a vacuum is created in the chamber of the barrel body of at least 600 mm Hg. Art. (0.08 MPa).

Rice. 3.24. Air-foam barrel with ejecting device type SVPE:

1 – hose; 2 – nipple; 3 – vacuum chamber; 4 – exit chamber; 5 – guide pipe; 6 – receiving chamber; 7 – connecting head; 8 – body

The principle of foam formation in the SVP barrel (Fig. 3.25) is as follows. The foaming solution, passing through hole 2 in the barrel body 1, creates a vacuum in the cone chamber, due to which air is sucked through eight holes evenly spaced in the guide pipe 4 of the barrel. The air entering the pipe is intensively mixed with the foam-forming solution and forms a stream of air-mechanical foam at the exit from the barrel.

Rice. 3.25. Air-foam SVP barrel:

The principle of foam formation in the SVPE barrel differs from SVP in that it is not the foam-forming solution that enters the receiving chamber, but water, which, passing through the central hole, creates a vacuum in the vacuum chamber. A foam agent is sucked into the vacuum chamber through a nipple through a hose from a backpack barrel or other container. Technical characteristics of fire trunks for producing low expansion foam are presented in table. 3.10.

Table 3.10

To obtain air-mechanical foam of medium expansion from an aqueous solution of a foaming agent and supply it to the fire, medium expansion foam generators are used.

Depending on the foam productivity, the following standard sizes of generators are available: GPS-200; GPS-600; GPS-2000. Their technical characteristics are presented in table. 3.11.

Table 3.11

Foam generators GPS-200 and GPS-600 are identical in design and differ only geometric dimensions nozzle and housing. The generator is a portable type water-jet ejector apparatus and consists of the following main parts (Fig. 3.26): generator housing 1 with a guide device, a mesh package 2, a centrifugal sprayer 3, a nozzle 4 and a collector 5. The atomizer body, in which the atomizer3 and coupling head GM-70 are mounted, is attached to the generator manifold using three stands. Mesh package 2 is a ring covered along the end planes with a metal mesh (mesh size 0.8 mm). The vortex-type atomizer3 has six windows located at an angle of 12°, which causes swirling of the flow of working fluid and ensures a sprayed jet at the outlet. Nozzle 4 is designed to form a foam stream after a package of meshes into a compact stream and increase the flight range of the foam. Air-mechanical foam is obtained by mixing three components in a generator in a certain proportion: water, foaming agent and air. A flow of foaming agent solution is fed under pressure into the sprayer. As a result of ejection, when a sprayed jet enters the collector, air is sucked in and mixed with the solution. A mixture of drops of foaming solution and air falls on the mesh package. On grids, deformed drops form a system of stretched films, which, enclosed in limited volumes, form first elementary (individual bubbles) and then mass foam. The energy of the newly arriving droplets and air forces the mass of foam out of the foam generator.

As a foam fire nozzle of a combined type, we will consider the combined fire extinguishing installations (UKTP) “Blizzard”, which can be manual, stationary and mobile. They are designed to produce air-mechanical foam of low and medium expansion. Technical characteristics of UKTP of various designs are presented in table. 3.12. In addition, a range diagram and an irrigation map have been developed for these trunks (Fig. 3.27), which makes it possible to more clearly assess their tactical capabilities when extinguishing fires.

Table 3.12

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Foam hand fire nozzles. Types of foam fire nozzles

Today I would like to consider and delve into the system of fire-technical weapons, namely, foam hand-held fire nozzles, which are used directly during fire extinguishing to supply foam of different expansion rates. Foam is a great tool for improving our firefighting capabilities. This is an extremely effective method of extinguishing several types (classes) of fires simultaneously in a short time. The use of foam fire nozzles makes it possible to use the same volume of water more efficiently compared, for example, with conventional water nozzles. Thus, the use of foam fire nozzles in fire extinguishing greatly facilitates the work of the firefighters themselves and speeds up the fire extinguishing process itself.

Basics of fire foam formation and delivery

Before we directly examine foam fire nozzles, let’s recall how air-mechanical foam is formed.

Air-mechanical foam is produced by mixing a concentrated solution of a foaming agent with water in order to create a solution of a foaming agent of the required concentration. After the solution is formed, it must be filled with air to obtain foam. Since foam is essentially air bubbles of different sizes.

There are several common methods of enriching a foam solution with air, the most used in fire protection are the following:

• filling with air directly at the outlet of the foam fire nozzle nozzle;
• filling due to a special pneumatic system of the car, mixing of foam concentrate, water and air occurs in the system;
• and the third method is to use the ejection method (special ejection nozzles) of the barrel, nozzle.

Let's look at what types of foam fire nozzles can be used by fire departments today.

Types of foam fire nozzles

And so, above we defined the trunks by the type of mixing of the foaming agent solution with air. Among the three listed methods, I would like to note, and if I can say highlight, ejection types of foam barrels.

Ejection barrels have a number of advantages that set them apart from the rest, namely:

• simplicity of design;
• lack of additional devices for air supply;
• the ability to obtain foam of different expansion ratios.

In such foam barrels, air is supplied due to the Venturi effect. When the foaming agent solution passes through the center of the barrel nozzle, a low level of pressure is created, allowing air to enter the nozzle and produce foam at the exit.

Today, the main manual foam nozzles are air-foam ejection nozzles (SVP, SVPE-4, SVPE-8), medium expansion foam generators (GPS-200, GPS-600, GPS-2000).

Manual foam barrels SVP(E)

Manual foam nozzles SVP(E) are designed for the formation of low expansion fire extinguishing foam and further direction it to the source of the fire. They are a hollow metal (aluminum) pipe, about 50 cm long, with a 66 mm connecting head.

Air is sucked in through four holes in the barrel body. The holes themselves and the SVP(E) barrel body are made in such a way that when the solution passes through the barrel body, a vacuum (vacuum) is formed in it and required amount air was sucked into the barrel.

Fundamentally, the other models of SVP(E) foam barrels do not differ from each other; only the overall productivity in terms of foam volume varies from 2-8 m3/min and water flow from 4 to 16 l/s.

Tactical and technical characteristics of foam hand barrels SVP(E)

Also today, manufacturing plants produce special nozzles for hand-held water nozzles, which visually and structurally resemble SVP(E) barrels and can supply foam.

Medium expansion foam generators

The very name of the barrel GPS-600 (200, 2000) speaks about the type of this barrel, and more specifically, the multiplicity of fire-technical foam obtained at the output. Medium expansion foam, which, unlike low expansion foam, is much better for fire extinguishing.

The principle of operation of the GPS is identical to that stated above, the peculiarity is the presence of a special metal mesh at the exit from the barrel. When a foaming agent solution enriched with air hits the mesh, bubbles are blown out, which form fire-fighting foam of medium expansion.

Tactical and technical characteristics of GPS

Considering the tactical and technical characteristics of the foam barrels presented above, it can be stated that in terms of their parameters (working pressure in front of it and the flow rate of the aqueous foam solution) they are almost identical, and therefore they can be used from the same types of stationary and portable foam mixers.

In fact, we have examined the most common hand-held foam nozzles, which are used today by units of the Ministry of Emergency Situations in the CIS. But I wanted to touch a little on foreign analogs of foam barrels.

Foreign analogues of foam hand barrels

In principle, of course, foreign analogues of barrels are no different and the process of foam formation is identical, the only difference is in some useful design features.

Among the many options for barrels, I would like to dwell on this portable system for supplying foam from the Scotty company, although this system is not an original development and has many analogues, but as an example it is just the thing.

The essence of this system is that any line (line with water supply) with a water portable fire nozzle can be turned into a line for supplying low expansion foam in a very short time. All this is possible through the use of a portable 20 liter backpack with a foaming agent, a pipeline with a quick-release connector for connecting to an ejection nozzle on the water barrel.

Here are the basic devices that can be used to supply low and medium expansion foam to extinguish a fire.

And finally, I would like to note some disadvantages of using foam barrels and the foam concentrate itself:

• the biggest drawback is the price of the foam concentrate, which starts from $10 per 1 liter and higher, depending on its characteristics and type;
• the need for mandatory flushing of the vehicle's pump-hose system from foam concentrate;
• special rules for storing foam concentrate;
• harmful to the environment, for example, in some European countries (Germany, France) the use of foam for educational purposes is prohibited.

Air-mechanical foam is designed to extinguish fires of liquid (fire class B) and solid (fire class A) flammable substances. Foam is a cellular-film dispersed system consisting of a mass of gas or air bubbles separated by thin films of liquid.

Air-mechanical foam is obtained by mechanically mixing the foaming solution with air. The main fire extinguishing property of foam is its ability to prevent the entry of flammable vapors and gases into the combustion zone, as a result of which the combustion stops. The cooling effect of fire extinguishing foams also plays a significant role, which is largely inherent in low expansion foams containing a large amount of liquid.

An important characteristic of fire extinguishing foam is its multiplicity– the ratio of the volume of foam to the volume of the foaming agent solution contained in the foam. There are foams of low (up to 10), medium (from 10 to 200) and high (over 200) expansion. . Foam barrels are classified depending on the expansion ratio of the resulting foam (Fig. 3.23).

FOAM FIRE TRUNKS

To obtain low expansion foam