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

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

Fire class	combustible materials	Water	Foam	Powder		CO 2	Freon CF 3 Br	Other freons
Fire class	combustible materials	Water	Foam	PSB	PF	CO 2	Freon CF 3 Br	Other freons
BUT	Coal-forming solids (paper, wood, textiles, coal, etc.)	4	4	1	3	1	2	1
AT	GZh and flammable liquids (gasoline, varnishes, solvents), consumable materials (hydron, paraffin)	4	4	4	4	3	4	4
FROM	Gases (propane, methane, hydrogen, acetylene, etc.)	2	1	4	3	1	3	2
D	Metals (Al, Mg, etc.)	—	—	1	1	—	—	—
E	Electrical equipment (transformers, switchboards, etc.)	2	—	2	2	3	4	3

As shown in Table 1, water and foam are the most effective extinguishing agents for class A and B fires (class B mostly water mist or ultra mist).

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

With the highest heat-absorbing capacity, water is the most effective natural material for extinguishing fires. Drops of water, falling into the combustion chamber, pass through two stages of heat absorption: when heated to 100°C and evaporated at a constant temperature of 100°C. For the first stage, 1 liter of water spends 335 kJ of energy, for the second phase - evaporation and transformation into water vapor - 2260 kJ.

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

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

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

Good mobility of water makes it easy to transport it through pipelines. Water is used not only to extinguish fires, but also to cool objects located near the source of combustion. Thereby preventing their destruction, explosion and fire.

Mechanism of extinguishing fires with water:

cooling of the surface and the 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 on the flame of the water jet.

When extinguishing burning oil products in tanks with water, drops supplied to the combustion center 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 combustible substances that have a high combustion temperature and create a large flame pressure is achieved through the use of a mixture of small and large water droplets. In this case, small drops, evaporating in the zone of flame combustion, 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 temperature established in the combustion process. reaction layer.

Table 2: Scope of application of water for different fire classes

Fire class	Subclass	Combustible substances and materials (objects)	Water sprayed by sprinklers	Finely sprayed water	Sprayed water with wetting agent
BUT	A1	Solid smoldering substances wetted by water (wood, etc.)	3	3	3
	A2	Solid smoldering substances 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
AT	IN 1*	Limit and unsaturated hydrocarbons (heptane, etc.)	—	2	1
	IN 2*	Limit and unsaturated hydrocarbons (gasoline, etc.)	—	2	1
	AT 3*	Water-soluble alcohols (С1-С3)	—	2	1
	AT 4*	Alcohols, water insoluble (C4 and above)	—	2	1
	AT 5**	Acids are sparingly water soluble	3	3	3
	AT 6**	Ethers simple and complex (diethyl, etc.)	3	3	3
	AT 7**	Aldehydes and ketones (acetone, etc.)	3	3	3
FROM,	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 combustible liquids with a flash point up to 90 ° C; "**" - for flammable liquids and combustible liquids with a flash point of more than 90 ° C; "***" - electrical equipment under voltage.

Water must not be used to extinguish the following materials:

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

Petroleum products and many other organic liquids, when extinguished with water, float to its surface, as a result of which the fire area can increase significantly. For example: in case of ignition of oil products located in the tank, it is not recommended to extinguish with water. Oil products float above the water. Water, as a result of heating, turns into steam. Water vapor rises in portions, which causes splashing of burning oil products from the tank and makes it difficult for firefighters to access the fire.

The disadvantages of water include a high freezing point. To lower the freezing point, special additives (antifreezes), some alcohols (glycols), 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, antifreezes and other additives also increase the corrosivity and electrical conductivity of water. As a protection against corrosion, special coatings can be applied to metal parts and pipelines, or corrosion inhibitors can be added to the water.

Expansion of the scope of water for extinguishing electrical equipment under voltage is possible when using it in a fine and ultra-spray 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 are subject to smoldering, the pores of which contain the air necessary for combustion. Such materials can burn at a greatly reduced oxygen content in the environment. The penetration of fire extinguishing agents into the pores of smoldering materials, as a rule, is rather difficult.

With the introduction of a wetting agent (sulfonate), the water consumption for quenching is reduced by a factor of four, and the quenching time is reduced by a factor of two.

In some cases, extinguishing with water becomes very effective if it is thickened with, for example, the sodium salt of carboxymethyl cellulose or sodium alginate. Increasing the viscosity to 1-1.5 N * s / m 2 allows you to reduce the extinguishing time by about 5 times. The best additives in this case are solutions of sodium alginate and sodium carboxymethyl cellulose. For example, a 0.05% solution of sodium carboxymethyl cellulose provides a significant reduction in water consumption for fire fighting. If, under certain conditions of extinguishing with ordinary water, its consumption is from 40 to 400 l / m 2, then when using "Viscous" water - from 5 to 85 l / m 2. The average damage from a fire (including the impact of water on materials) is reduced by 20%.

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

water-soluble polymers to increase adhesion to a burning object ("Viscous water");
polyoxyethylene to increase the throughput of pipelines ("slippery water");
inorganic salts to increase the efficiency of extinguishing;
antifreezes and salts to reduce the freezing point of water.

At present, one of the most promising areas in the field of fire protection of objects for various purposes is the use of fine and ultra-sprayed water as a means of extinguishing fires. In this form, water is able to absorb aerosols, precipitate combustion products and extinguish not only burning solids, but also many combustible liquids.

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

With the help of fine and ultra-sprayed water, many especially socially and industrially significant objects can be protected. 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 facilities where fire extinguishing must be carried out at the initial stage quickly enough and with low water consumption.

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

the possibility of extinguishing almost all substances and materials, with the exception of substances that react with water with the release of thermal energy and combustible gases;
high extinguishing efficiency due to increased cooling effect and uniform water spraying of the fire;
minimal water consumption - a small consumption allows you to avoid significant damage from the consequences of the strait and ensure the possibility of using it under the condition of a water limit;
shielding of radiant thermal radiation - use for the protection of service personnel involved in extinguishing a fire, personnel of fire departments, load-bearing and enclosing structures, as well as nearby material assets;
dilution of combustible vapors and a decrease in the concentration of oxygen in the combustion zone as a result of the intensive formation of water vapor;
lowering the temperature in the premises in case of fire in them;
Uniform cooling of excessively heated metal surfaces of load-bearing structures due to the high specific surface area of droplets - eliminates their local deformation, loss of stability and destruction;
effective absorption and removal of toxic gases and smoke (smoke precipitation);
low electrical conductivity of finely ultra-dispersed water - makes it possible to use it as an effective fire extinguishing agent at electrical installations under voltage;
environmental friendliness and toxicological safety, combined with the protection of people from the effects of fire hazards, allows personnel to save value during the operation of an automatic fire extinguishing installation.

Ultrasprayed water in the combustion zone evaporates intensively. A protective layer of water vapor can isolate the combustion zone, preventing access to oxygen. When the oxygen concentration in the combustion chamber drops to 16-18%, the fire will self-extinguish.

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

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MINISTRY OF EDUCATION AND SCIENCE

MOSCOW STATE CONSTRUCTION UNIVERSITY

MEANS AND METHODS OF FIRE EXTINGUISHING

COURSE WORK

WATER AS A FIRE EXTINGUISHING MEANS

Completed by a student

3 courses, PB group

Alekseeva Tatyana Robertovna

Moscow 2013

Table of contents

5. Scope of water
Bibliography

1. Fire extinguishing efficiency of water

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

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

cooling the combustion source to temperatures below the ignition and flash temperatures;

slowing down the rate of chemical reactions in the flame;

mechanical breakdown of the flame by exposing the combustion source to a strong jet of gas or water;

creating conditions for fire protection.

The results of the effects of all existing extinguishing agents on the combustion process depend on the physicochemical properties of the burning materials, combustion conditions, supply intensity and other factors. For example, water can be used to cool and isolate (or dilute) the combustion site, with foam agents - to isolate and cool, with inert diluents - to dilute the air, reducing the oxygen concentration, with freons - to inhibit combustion and prevent the spread of 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. suitable for extinguishing any fires. In some cases, extinguishing agents are incompatible with burning materials (for example, the interaction of water with burning alkali metals or organometallic compounds is accompanied by an explosion).

When choosing extinguishing agents, one should proceed from the possibility of obtaining the maximum fire extinguishing effect at minimum cost. The choice of extinguishing agents should 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, the energy intensity of evaporation and heating of water vapor. Thus, the evaporation of one kilogram of water and heating of the vapor to a temperature of 1000 K requires about 3100 kJ/kg, while a similar process with organic liquids requires no more than 300 kJ/kg, i.e. the energy intensity of the phase transformation of water and the heating of its vapors is 10 times higher than the average for any other liquid. At the same time, the thermal conductivity of water and its vapors is almost an order of magnitude higher than for other liquids.

It is well known that sprayed, highly dispersed water has the greatest efficiency in extinguishing fires. To obtain a highly dispersed water jet, as a rule, high pressure is required, but even so, the range of atomized water supply is limited by a small distance. The new principle of obtaining a highly dispersed water flow is based on a new method for obtaining atomized water - by repeated successive dispersion of a water jet.

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

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

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

2. Advantages and disadvantages of water

Factors that determine the merits of water as a fire extinguishing agent, in addition to 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 for burning objects, but also for objects located near the source of combustion, which makes it possible to prevent destruction, explosion and ignition of the latter. Good mobility ensures the ease of transporting water and its delivery (in the form of continuous jets) to remote and hard-to-reach places.

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

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 by 1700 times (from 1 liter of water during evaporation, 1700 liters of steam are formed), due to which the reactants are diluted, which in itself contributes to the cessation of combustion, as well as the displacement of air from the zone seat of fire.

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

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

The low viscosity and incompressibility of water make it possible to supply it through hoses over long distances and under high pressure.

Water is able to dissolve some vapors, gases and absorb aerosols. This means that water can precipitate combustion products on fires in buildings. For these purposes, sprayed and finely sprayed jets are used.

Some combustible liquids (liquid alcohols, aldehydes, organic acids, etc.) are soluble in water, therefore, when mixed with water, they form non-flammable or less combustible 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 to property, sometimes no less than the fire itself. The main disadvantage of water, as a fire extinguishing agent, is that due to the high surface tension (72.8 * -103 J / m 2), it poorly wets solid materials and especially fibrous substances. Other disadvantages are: freezing of water at 0°C (reduces the transportability of water at low temperatures), electrical conductivity (makes it impossible to extinguish electrical installations with water), high density (when extinguishing light burning liquids, water does not restrict air access to the combustion zone, but, spreading, contributes to the spread of fire).

3. The intensity of the water supply for extinguishing

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

In practical calculations, the amount of fire extinguishing agents required to stop burning is determined by the intensity of their supply. The intensity of the supply 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 empirically and by calculations in the analysis of extinguished fires:

I = Q o. s / 60t P,

Where:

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

Qo. c - consumption of fire extinguishing agent during extinguishing a fire or conducting an experiment, l, kg, m 3;

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

P - the value of the design parameter of the fire: area, m 2; volume, m3 ; perimeter or front, m.

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

I \u003d Q / 60t P,

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

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

I \u003d Qf / P,

Where Qf is the actual consumption of the 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 the supply of fire extinguishing agents is divided into surface, volumetric and linear.

If the normative documents and reference literature do not contain data on the intensity of the supply of fire extinguishing agents to protect objects (for example, in case of fires in buildings), it is set according to the tactical conditions of the situation and the implementation of combat operations to extinguish the fire, based on the operational and tactical characteristics of the object, or take reduced by 4 times compared with the required intensity of supply for extinguishing a fire

I s \u003d 0.25 I tr,

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

Il \u003d I s h t,

Where h t is the depth of extinguishing, m (accepted, 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 the cessation of combustion I pr. g, and the intensity of losses I sweat.

I \u003d I pr. g + I sweat.

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

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

Tab.1

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

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

Vessels (dry cargo and passenger):
Superstructures (internal and external fires) when supplying solid and fine spray jets

3. Hard materials
paper loosened
Wood:
Balance, with humidity, %


Lumber in stacks within the same group at humidity,%;



Round wood in stacks
Chips in piles with a moisture content of 30 - 50%
Rubber (natural or artificial), rubber and rubber products
Flax camp in dumps (supply of mist water)
Flax straws (stacks, bales)
Plastics:
Thermoplastics
Thermoplastics
Polymeric materials and products from them
Textolite, carbolite, plastic waste, triacetate film
Peat on milling fields with a moisture content of 15 - 30% (at a specific water consumption of 110 - 140 l / m2 and an extinguishing time of 20 minutes)
Milling peat in stacks (at a specific water consumption of 235 l/m and extinguishing time of 20 min)
Cotton and other fibrous materials:
open warehouses
Closed warehouses
Celluloid and products made from it
4. Flammable and combustible liquids (when extinguishing with water mist)

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

Notes:

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

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

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

4. Ways of supplying fire extinguishing water

The most reliable in solving fire extinguishing problems are automatic fire extinguishing systems. These systems are activated by fire automatics according to the readings of sensors. In turn, this ensures prompt extinguishing of the source of fire without human intervention.

Automatic fire extinguishing systems provide:

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

sound and light alerts

issuing an "alarm" signal to the fire department

automatic closing of fire dampers and doors

automatic activation of smoke exhaust systems

shutdown of ventilation

shutdown of electrical equipment

automatic supply of fire extinguishing agent

submission notification.

The following are used as a fire extinguishing agent: 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, designed for local extinguishing of fires, and deluge - for extinguishing a fire over a large area. Sprinkler installations are programmed to operate when the temperature rises above a predetermined rate. When extinguishing a fire, a jet of sprayed water is supplied in the immediate vicinity of the source of ignition. The control units of these installations are of the "dry" type - for unheated objects, and the "wet" type - for rooms where the temperature does not fall below 0 0 C.

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

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

The sprinkler is a valve that operates when exposed to a temperature-sensitive locking device. As a rule, this is a glass flask with a liquid that bursts at a given temperature. Sprinklers are installed on pipelines containing water or air under high pressure.

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

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

Pre-action sprinklers significantly reduce the chance of false triggering. The design of the device is such that both sprinklers that are part of the system must be opened to supply water.

Drencher systems, unlike sprinklers, are triggered by a fire detector command. This allows you to eliminate the fire at an early stage of development. The main difference between deluge systems is that fire extinguishing water is supplied to the pipeline immediately when a fire occurs. These systems at the time of a fire supply a significantly larger amount of water to the protected area. As a rule, deluge systems are used to create water curtains and cool especially sensitive to heat and flammable objects.

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

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

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

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

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

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

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

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

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

5. Scope of water

Water is used to extinguish fires of classes:

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

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

C - combustible gases.

Water must not be used to extinguish substances that, on contact with it, release heat, flammable, toxic or corrosive gases. 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. When water gets on hot coal or iron, an explosive hydrogen-oxygen mixture may form.

Table 2 lists substances that cannot be extinguished with water.

Tab.2

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

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

Water, 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, the electric current in the water jet at a distance of 1.5 m from the electrical equipment is zero, and with the addition of 0.5% soda, it increases to 50 mA. Therefore, when extinguishing fires with water, electrical equipment is de-energized. When using distilled water, even high-voltage installations can be extinguished with it.

6. Method for evaluating the applicability of water

When water gets on the surface of a burning substance, pops, flashes, splashing of burning materials over a large area, additional ignition, an increase in the volume of the flame, and the release of a burning product from process equipment are possible. They may 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 make optimal technical solutions using water in automatic fire extinguishing installations. For a tentative assessment of the applicability of water products, two laboratory methods can be used. The first method consists in 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 outgassing gas, as well as the degree of heating during the interaction of the product with water.

7. Ways to improve the fire extinguishing efficiency of water

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

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

To increase the fire-extinguishing efficiency of water, additives are introduced into it that 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: DB brand wetting agent, OP-4 emulsifier, 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 blowing agents for the production of air-mechanical foam. The addition of wetting agents to water can significantly increase its fire extinguishing efficiency. With the introduction of a wetting agent, the water consumption for quenching is reduced by four times, and the quenching time is more than halved.

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

Bibliography

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

2. A.Ya. Korolchenko, D.A. Korolchenko. Fire and explosion hazard of substances and materials and means of extinguishing them. Directory: in 2 hours - 2nd ed., Revised. and additional - M.: Pozhnauka, 2004. - Part 1 - 713s., - Part 2 - 747s.

3. Terebnev V.V. Handbook of the head of fire fighting. Tactical capabilities of fire departments. - M.: Pozhnauka, 2004. - 248 p.

4. Handbook of RTP (Klyus, Matveikin)

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44. Fire extinguishing properties of water. The use of water in fire fighting

Water is one of the most readily available, cheap and widely available extinguishing agents, suitable for both small and large fires. The fire-extinguishing properties of water lie in the fact that it has a high heat capacity, is able to take a significant amount of heat from burning substances, reducing those

the temperature of the combustion source to such an extent that combustion becomes impossible. Water must not be used:

For extinguishing substances that react with it, for example, potassium and sodium metals. The released hydrogen in a mixture with air forms an explosive mixture.

when extinguishing electrical installations under voltage, as well as when extinguishing calcium carbide due to the possibility of an explosion of acetylene released during this.

For fire extinguishing, water is used in the form of compact jets, in a sprayed state, in a finely dispersed state, and also in the form of air-mechanical foam. It is impossible to use compact jets when extinguishing burning flammable liquids, since in this case the liquid that floats to the surface of the water spreads, which contributes to an increase in the combustion zone.

If water is used in atomized state, in the form of fine particles, when most of the drops of atomized water are less than 0.1 mm in size, then the surface of contact between water and burning substances increases, which contributes to a more intensive removal of heat from the combustion source and the formation of steam, quenching aid. Atomized jet of water during fires in the premises can be used to reduce temperature and smoke deposition. Water spray can be used to extinguish burning oil products with a flash point above 120 ° C. AAAAAAAAAAAAAAAAAAAAAAAAAAA

Addition of 0.2-2.0% (by mass) of foaming agents to water helps to lower the surface tension, as a result of which its fire-extinguishing properties are improved, water consumption is reduced by 2-2.5 times, and the extinguishing time is reduced.

45. Fire hazardous properties of materials and substances. Primary fire fighting equipment

The main indicators of fire danger, which determine the critical conditions for the onset and development of the combustion process, are the autoignition temperature and the concentration limits of ignition.

The autoignition temperature characterizes the minimum temperature of a substance or material at which a sharp increase in the rate of exothermic reactions occurs, ending in the occurrence of flame combustion.

The minimum concentration of combustible gases and vapors in the air at which they are able to ignite and spread a flame is called the lower concentration limit of ignition; The maximum concentration of combustible gases and vapors at which flame propagation is still possible is called the upper concentration limit of ignition. The region of compositions and mixtures of combustible gases and vapors with air lying between the lower and upper limits of ignition is called the region of ignition.

Flammable concentration limits are not constant and depend on a number of factors. The greatest influence on the ignition limits is exerted by the power of the ignition source, the admixture of inert gases and vapors, the temperature and pressure of the combustible mixture.

The change in flammable limits with increasing temperature can be estimated by the following rule: for every 100 ° increase in temperature, the lower flammable limits decrease by 8-10%, and the upper flammable limits increase by 12-15%.

The concentration of saturated vapors of liquids is in a certain relationship with its temperature.

Using this property, it is possible to express the concentration limits of ignition of saturated vapors in terms of the temperature of the liquid at which they are formed.

The ability to form high-speed flammable (explosive) mixtures with air is also possessed by airborne dusts of many solid combustible substances. The minimum concentration of dust in the air at which it ignites is called the lower flammable limit of dust. Since achieving very high concentrations of dust in suspension is practically impossible, the term "upper flammable limit" does not apply to dusts.

Fire hazard indicators that characterize the critical conditions for the formation of evaporation or decomposition of condensed substances and materials sufficient for combustion of gaseous combustible products include flash and ignition temperatures, as well as ignition temperature limits.

The flash point is the lowest (under special test conditions) temperature of a combustible substance at which vapors and gases are formed above the surface that can flare up in the air from an ignition source, but the rate of their formation is still insufficient for subsequent combustion. Using this characteristic, all flammable liquids can be divided into two classes according to fire hazard:

1) liquids with a flash point up to 61 ° C (gasoline, ethyl alcohol, acetone, sulfuric ether, nitro enamels, etc.), they are called flammable liquids (flammable liquids);

2) liquids with a flash point above 61 ° C (oil, fuel oil, formalin, etc.), they are called flammable liquids (LL).

Ignition temperature - the temperature of a combustible substance at which it releases flammable vapors and gases at such a rate that, after igniting them from an ignition source, stable combustion occurs. Temperature limits of ignition - temperatures at which saturated vapors of a substance form concentrations in a given oxidizing environment equal to the lower and upper concentration limits of ignition of liquids, respectively.

The fire hazard of substances is characterized by linear (expressed in cm / s) and mass (g / s) burning (flame propagation) and burnout rates (g / m2-s or cm / s), as well as the limiting oxygen content at which combustion is still possible. For conventional combustible substances (hydrocarbons and their derivatives), this limiting oxygen content is 12-14%, for substances with a high upper flammability limit (hydrogen, carbon disulfide, ethylene oxide, etc.), the limiting oxygen content is 5% or lower.

In addition to the listed parameters, it is important to know the degree of flammability (combustibility) of substances to assess the fire hazard. Depending on this characteristic, substances and materials are divided into:

combustible (combustible)

slow-burning (flammable)

Non-combustible (non-combustible).

Combustibles include such substances and materials that, when ignited by an external source, continue to burn even after its removal. Slow-burning substances include those that are not capable of spreading a flame and burn only at the point of impact of the pulse; non-combustible are substances and materials that do not ignite even when exposed to sufficiently powerful pulses.

46. Automatic fire extinguishing installations. Causes of fires at work

Used in rooms with increased fire hazard.

1) sprinkler: the outlet of the sprinkler head is closed with plates, cat. when exposed to temperature, they melt and water from the system under pressure exits the head hole and irrigates the structure of the room or equipment in the area of \u200b\u200bthe sprinkler head. One head irrigates an area of 10-12 m.

MINISTRY OF EDUCATION AND SCIENCE

MOSCOW STATE CONSTRUCTION UNIVERSITY

MEANS AND METHODS OF FIRE EXTINGUISHING

COURSE WORK

WATER AS A FIRE EXTINGUISHING MEANS

Completed by a student

3 courses, PB group

Alekseeva Tatyana Robertovna

Moscow 2013

5. Scope of water

Bibliography

1. Fire extinguishing efficiency of water

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

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

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

2. Advantages and disadvantages of water

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

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

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

The low viscosity and incompressibility of water make it possible to supply it through hoses over long distances and under high pressure.

Water is able to dissolve some vapors, gases and absorb aerosols. This means that water can precipitate combustion products on fires in buildings. For these purposes, sprayed and finely sprayed jets are used.

Some combustible liquids (liquid alcohols, aldehydes, organic acids, etc.) are soluble in water, therefore, when mixed with water, they form non-flammable or less combustible 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 to property, sometimes no less than the fire itself. The main disadvantage of water, as a fire extinguishing agent, is that due to the high surface tension (72.8 * -103 J / m 2) it poorly wets solid materials and especially fibrous substances. Other disadvantages are: freezing of water at 0°C (reduces the transportability of water at low temperatures), electrical conductivity (makes it impossible to extinguish electrical installations with water), high density (when extinguishing light burning liquids, water does not restrict air access to the combustion zone, but, spreading, contributes to the spread of fire).

3. The intensity of the water supply for extinguishing

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

Q about . s / 60t P,

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

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

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

Qu / 60t P,

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

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

Qf / P,

Where Qf is the actual consumption of the 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 the supply of fire extinguishing agents is divided into surface, volumetric and linear.

h = 0.25 I tr ,

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

l = I s h t ,

Where h t - extinguishing depth, m (accepted, 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 the cessation of combustion I ave. g , and loss intensity I sweat.

I ave. g + I sweat .

The average, practically expedient, values of the intensity of the supply of fire extinguishing agents, called optimal (required, calculated), established empirically and in the 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 resistance 0.06 IV degree of fire resistance 0.10 V degree of fire resistance 0.15 Basement premises 0.10 Attic premises 0.10 Hangars, garages, workshops, tram and trolleybus depots 0.20 Hospitals 0.10 Residential buildings and auxiliary buildings: I - III degree of fire resistance 0.10 03IV degree of fire resistance 0.10V degree of fire resistance 0.15 Basement premises 0.15 Attic premises 0.15 Livestock buildings I - III degree of fire resistance 0.10 IV degree of fire resistance 0.15 V degree of fire resistance 0.20 premises0.15Mills and elevators0.14Industrial buildingsI - II degree of fire resistance0.35III degree of fire resistance0, 20IV - V degree of fire resistance0.25Paint shops0.20Basements0.30Combustible coatings of large areas in industrial buildings: When extinguishing from below inside the building0.15When extinguishing outside from the coating side0, 08When extinguishing and outside in case of 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 mezzanine (water mist supply) 0. 20 Engine rooms and boiler rooms 0. 20 Fuel supply galleries 0.10 Transformers, reactors, oil switches (supply of atomized water) 0.102. Vehicles Cars, trams, trolleybuses in open parking lots0.10 Aircraft and helicopters: Interior finishes (when water mist is supplied) 0.08 Structures with magnesium alloys 0.25 Hull 0.15 Vessels (dry cargo and passenger): and fine spray jets 0, 20 Holds 0, 203. Hard materials Loose paper 0.30 Wood: Balanced, at humidity, % 40 - 500, 20 Less than 400.50 Timber in piles within one group at humidity, %; 6 - 140.4520 - 300.30More than 300.20Roundwood in piles0.3Chips in heaps with a moisture content of 30 - 50% 0.10Rubber (natural or artificial), rubber and rubber products0.30 Flax in dumps (sprayed water supply) 0, 20 Flax straws (stacks, bales) 0.25 Plastics: Thermoplastics 0.14 Thermoplastics 0.10 Polymeric materials and products made of them 0.20 Textolite, carbolite, waste plastics, triacetate film 0.30 Peat on milling fields with a moisture content of 15 - 30% (at a specific water consumption of 110 - 140 l / m2 and extinguishing time 20 min.) 0.10 Milling peat in piles (at a specific water consumption of 235 l / m and extinguishing time 20 minutes) 0.20 Cotton and other fibrous materials: Open warehouses 0.20 Closed warehouses 0.30 Celluloid and products from it 0.404 . Flammable and combustible liquids (when extinguishing with water mist) Acetone0.40 Petroleum products in containers: With a flash point below 28 ° C0.30 With a flash point of 28 - 60 ° C0, 20 With a flash point of more than 60 ° C0, 20 Combustible liquid spilled on the site surface, in trenches of technological trays0, 20 Thermal insulation impregnated with oil products0, 20Alcohols (ethyl, methyl, propyl, butyl, etc.) in warehouses and distilleries0.40 Oil and condensate around a fountain well0,20

Notes:

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

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

4. Ways of supplying fire extinguishing water

The most reliable in solving fire extinguishing problems are automatic fire extinguishing systems. These systems are activated by fire automatics according to the readings of sensors. In turn, this ensures prompt extinguishing of the source of fire without human intervention.

Automatic fire extinguishing systems provide:

sound and light alerts

issuing an "alarm" signal to the fire department

automatic closing of fire dampers and doors

automatic activation of smoke exhaust systems

shutdown of ventilation

shutdown of electrical equipment

automatic supply of fire extinguishing agent

submission notification.

The following are used as a fire extinguishing agent: 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, designed for local extinguishing of fires, and deluge - for extinguishing a fire over a large area. Sprinkler installations are programmed to operate when the temperature rises above a predetermined rate. When extinguishing a fire, a jet of sprayed water is supplied in the immediate vicinity of the source of ignition. The control units of these installations are of the "dry" type - for unheated objects, and "wet" - for rooms where the temperature does not fall below 0 0FROM.