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MINISTRY OF EDUCATION AND SCIENCE

MOSCOW STATE CIVIL UNIVERSITY

FIRE FIGHTING MEANS AND METHODS

COURSE WORK

WATER AS A FIRE FIGHTING MEDIUM

Completed by a student

3 courses, PB group

Alekseeva Tatyana Robertovna

Moscow 2013

Table of contents

• 5. Area of ​​application of water
• Bibliography

1. Fire extinguishing efficiency of water

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

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

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

slowing down chemical reactions in flames;

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

creating fire suppression conditions.

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

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

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

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

It is well known that the greatest efficiency When extinguishing fires, atomized, highly dispersed water is used. To obtain a highly dispersed jet of water, as a rule, high pressure is required, but even then the range of supply of sprayed water is limited to a short distance. The new principle of obtaining a highly dispersed flow of water is based on a new method of obtaining atomized water - by repeated sequential dispersion of a water jet.

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

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

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

2. Advantages and disadvantages of water

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

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

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

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

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

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

Water can dissolve some vapors, gases and absorb aerosols. This means that combustion products from fires in buildings can be deposited with water. For these purposes, sprayed and finely sprayed jets are used.

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

But at the same time, water has a number of disadvantages that narrow the scope of its use as a fire extinguishing agent. A large number of The water used in extinguishing can cause irreparable damage to material assets, sometimes no less than the fire itself. The main disadvantage of water as a fire extinguishing agent is that due to its high surface tension (72.8*-103 J/m2), it does not wet solid materials and especially fibrous substances well. Other disadvantages are: freezing of water at 0°C (reduces the transportability of water at low temperatures), electrical conductivity (makes it impossible to extinguish electrical installations with water), high density (when extinguishing light burning liquids, water does not limit the access of air to the combustion zone, but, spreading, promotes further spread of fire).

3. Intensity of water supply for extinguishing

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

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

I = Q o. s / 60tt 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 is the consumption of fire extinguishing agent during fire extinguishing or conducting an experiment, l, kg, m 3;

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

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

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

I = Qу / 60tт П,

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

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

I = 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 design unit of the fire parameter (m2, m3, m), the intensity of supply of fire extinguishing agents is divided into surface, volumetric and linear.

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

I z = 0.25 I tr,

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

Il = I s h t,

Where h t is the depth of extinguishing, m (assumed, when extinguishing with hand guns - 5 m, with 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, which is directly involved in stopping the combustion I pr. g, and the intensity of losses I sweat.

I = I pr. g + I sweat.

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

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

Tab.1

Extinguishing object	Intensity
1. Buildings and structures
Administrative buildings:
I - III degree fire resistance
IV degree of fire resistance
V degree of fire resistance
Basements
Attic spaces
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 spaces
Livestock buildings
I - III degree of fire resistance
IV degree of fire resistance
V degree of fire resistance
Cultural and entertainment institutions (theatres, cinemas, clubs, palaces of culture):
Auditorium
Utility rooms
Mills and elevators
Industrial buildings
I - II degree of fire resistance
III degree of fire resistance
IV - V degree of fire resistance
Paint shops
Basements
Combustible coatings large areas in industrial buildings:
When extinguishing from below inside a building
When extinguishing from outside from the coating side
When extinguishing from outside when a fire has developed
Buildings under construction
Trading enterprises and inventory warehouses
Refrigerators
Power plants and substations:
Cable tunnels and mezzanines (mist water supply)
Machine rooms and boiler rooms
Fuel galleries
Transformers, reactors, oil switches(supply of finely sprayed water)
2. Vehicles
Cars, trams, trolleybuses in open parking lots
Airplanes and helicopters:
Interior finishing (with mist water supply)
Structures containing 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, at humidity, %
Lumber in stacks within one group at humidity, %;
Round timber in stacks
Chips in piles with a moisture content of 30 - 50%
Rubber (natural or artificial), rubber and rubber products
Flax fire in dumps (supply of finely sprayed water)
Flax trusts (stacks, bales)
Plastics:
Thermoplastics
Thermosets
Polymer materials and products made from them
Textolite, carbolite, plastic waste, triacetate film
Peat on milling fields with a moisture content of 15 - 30% (with a specific water consumption of 110 - 140 l/m2 and extinguishing time of 20 minutes)
Milled peat in stacks (with a specific water consumption of 235 l/m and extinguishing time of 20 minutes)
Cotton and other fiber materials:
Open warehouses
Closed warehouses
Celluloid and products made from it
4. Flammable and combustible liquids (when extinguishing with finely sprayed water)
Petroleum products in containers:
With a flash point below 28°C
With a flash point of 28 - 60°C
With a flash point of more than 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 supplying water with a wetting agent, the supply intensity 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 production premises), volume according to SP 8.13130.2009, for external fire extinguishing and SP 10.13130.2009, for internal fire extinguishing.

4. Methods of supplying water for fire extinguishing

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

Automatic fire extinguishing systems provide:

24-hour temperature control and presence of smoke in the protected area;

activation of sound and light alerts

issuing an alarm signal to the fire department control panel

automatic closing of fire dampers and doors

automatic activation of smoke removal systems

turning off ventilation

shutdown of electrical equipment

automatic supply of fire extinguishing agent

submission notification.

The following are used as fire extinguishing agents: inert gas- freon, carbon dioxide, foam (low, medium, high expansion), fire extinguishing powders, aerosols and water.

fire extinguishing water fire extinguishing efficiency

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

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

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

A sprinkler is a valve that is activated by a heat-sensitive shut-off device. Typically, this is a glass flask containing 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 point, the glass shut-off device of the sprinkler is destroyed, due to destruction, the water/air supply valve opens, and the pressure in the pipeline drops. When the pressure drops, a sensor is triggered, which starts a pump that supplies water to the pipeline. This option provides required quantity water to the location of the fire.

Exists whole line sprinklers, which differ from each other by different operating temperatures.

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

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

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

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

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

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

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

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

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

Solid jets are used when extinguishing external and open or developed internal fires, when it is necessary to supply a large amount of water or if water needs to be infused impact force, as well as fires, when it is not possible to get close to the source, when neighboring and burning objects, structures, and apparatus are cooled from large distances. This method of extinguishing is the simplest and most common.

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

5. Area of ​​application of water

Water is used to extinguish fires of the following classes:

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

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

C - flammable gases.

Water should not be used to extinguish substances that release heat, flammable, toxic or corrosive gases upon contact with it. These substances include some metals and metallo organic compounds, metal carbides and hydrides, hot coal and iron. The interaction of water with burning alkali metals is especially dangerous. As a result of this interaction, explosions occur. If water gets on hot coal or iron, an explosive hydrogen-oxygen mixture may form.

Table 2 lists substances that cannot be extinguished with water.

Tab.2

Substance	Nature of interaction with water
Metals: sodium, potassium, magnesium, zinc, etc.	React with water to form hydrogen
Organoaluminum compounds	React explosively
Organolithium compounds
Lead azide, alkali metal carbides, metal hydrides, silanes	Decomposes to form flammable 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 o 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, electricity in a stream of water at a distance of 1.5 m from electrical equipment it is zero, and with the addition of 0.5% soda it increases to 50 mA. Therefore, when extinguishing fires with water, electrical equipment is de-energized. When using distilled water, it can even extinguish high-voltage installations.

6. Water applicability assessment method

If water gets on the surface of a burning substance, there may be pops, flashes, splashing of burning materials over a large area, additional fire, an increase in the volume of the flame, ejection of the burning product from technological equipment. They can be large scale or local in nature.

The lack of quantitative criteria for assessing the nature of the interaction of a burning substance with water makes it difficult to adopt optimal technical solutions using water in automatic fire extinguishing systems. To make an approximate assessment of the applicability of water products, two laboratory methods can be used. The first method consists of visual observation of the nature of the interaction of water with the test product burning in a small vessel. The second method involves measuring the volume of the releasing gas, as well as the degree of heating when the product interacts with water.

7. Ways to increase the fire extinguishing efficiency of water

To increase the scope of use of water as a fire extinguishing agent, special additives (antifreeze) are used that lower the freezing point: mineral salts (K 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 extinguishing.

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

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

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

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

One way to increase the effectiveness of fire extinguishing with water is to use finely sprayed water. The effectiveness of finely atomized water is due to the high specific surface area of ​​small particles, which increases the cooling effect due to the uniform penetrating effect of water directly on the combustion site and increasing heat removal. At the same time, the harmful effects of water on the environment are 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 parts - 2nd ed., revised. and additional - M.: Pozhnauka, 2004. - Part 1 - 713 p., - Part 2 - 747 p.

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

4. RTP Directory (Klyus, Matveikin)

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The very first means of fighting fire in history was water. She still remains the most effective means during fire fighting. Water fire extinguishing is considered one of the safest for people, which is important, which is why it is used to extinguish fires in cinema and concert halls, sports complexes, shopping centers, office buildings, in general, anywhere where a large crowd of people is constantly present.

Main advantages of water fire extinguishing

The most important advantage of water is its availability. Even if there is no internal water supply connected to the central main, alternative water reservoirs are always available. These include rivers, lakes, reservoirs and other reservoirs of both natural and artificial origin.

Water is a fairly effective means that can quickly extinguish paper, wood, coal, fabrics, rubber or flammable liquids that dissolve in water: low alcohol, acetone, organic acid and others. It is best to extinguish clothes with an aqueous solution.

The highest quality fire extinguishing occurs with the help of finely sprayed droplets, the diameter of which does not exceed 0.8 mm. At the same time, the irrigated surface increases significantly, water consumption decreases, and the cooling effect increases, which helps to save water. Water has cooling and wetting properties, and therefore it is used not only to extinguish a fire, but also to prevent the spread of a fire over large areas.

If extinguishing the flame with primary fire extinguishing means does not bring the desired result, then all material assets located in the room are doused with plenty of water, preventing them from igniting, if there is no real possibility of removing them from there.

Negative aspects of water fire extinguishing

Despite the many advantages, water fire extinguishing is not without its shortcomings. First of all, water is an excellent conductor electrical energy, therefore, to avoid short circuit, which can lead to increased fire, it is strictly prohibited to use water to extinguish electrical equipment operating on high voltage.

You should not use water as a fire extinguishing agent to extinguish the fire of substances that, upon contact with it, enter into a violent reaction. Aqueous solutions lose their effectiveness when interacting with burning hydrocarbons, as well as other substances that cannot mix with it, if their density does not reach unity.

Under certain circumstances, water not only does not eliminate the source of fire, but also helps the flame flare up with renewed vigor. This applies to fuels and lubricants, which do not mix with water, but rise to the surface and continue to burn there with ever-increasing power, occupying ever larger areas.

Enough arises dangerous situation when water enters oil-type baths engulfed in flames, as well as other containers containing burning high-boiling liquids or those that melt when heated solids. There are frequent cases of people receiving terrible burns to exposed parts of the body when extinguishing oil in a bathhouse with water.

It's also worth noting Negative influence aqueous solution for electrical appliances, electrical engineering, paper documentation, objects of history and art. It is not recommended to use water when extinguishing fires in libraries, museums, art galleries and exhibitions, archive rooms, and server rooms. This can cause irreparable damage, perhaps even more significant than fire damage.

Types of water fire extinguishing

Now there are the following types of water fire extinguishing:

1. sprinkler systems;
2. sprinkler installations;
3. deluge systems;
4. modular fine spray installations.

Sprinkler and deluge systems are a combination of the following elements:

1. pipelines (necessary for supplying water to the combustion site);
2. pumping stations(stabilize water pressure in pipelines);
3. sprinklers (promote irrigation of fire sites).

But modular-type fine-spray fire extinguishing systems are becoming increasingly popular. Modular installations are used where the protected object has existed for a long time and it is not possible to determine the exact amount of water for sprinkler and deluge systems, as well as to lay other expensive communication networks.

Sprinkler fire extinguishing

As a rule, these are the most basic and reliable systems, operating in automatic mode, which turn on independently when the temperature in the room rises to a critical level.

The sprinkler system includes pipes that constantly contain water under a certain pressure. The system ends with sprinklers (irrigators) that are triggered after the thermal lock breaks and spray liquid onto the source of fire. Moreover, the sprinklers do not work all at once, but only those located in a place with high temperature. The remaining sprinklers remain unused.

The main substance in a sprinkler system is water, which comes from a regular plumbing system. The water pressure must be at a certain level, which is maintained by shut-off valves. If there is a breakdown in the pipeline system or a complete shutdown, the water pressure in the system will be such that the device can initially operate.

The advantages of such a system are as follows:

1. automatic control;
2. no need for electricity;
3. no need for complex schemes feedback;
4. long service life;
5. being in constant working order.

The disadvantages include the following:

1. inertia;
2. direct dependence on water supply networks;
3. Do not extinguish electrical wiring;
4. It works only when the temperature in the room increases.

Deluge fire extinguishing

The main difference between deluges and sprinklers is the absence of a thermal lock in the former, and, as a result, differences in the method of operation. Such a system is not activated when reaching high temperature at the site, and upon receiving an alarm signal from the central console or from fire alarms. This helps reduce the system response time to a minimum, which greatly increases its efficiency.

Deluge systems can be installed on any objects. At the same time, water may be pumped into the pipelines, so the temperature in the rooms must be positive so that the water in them does not freeze and the pipes do not burst. Air can be pumped into the system, then there is no need for heated rooms.

Design of such systems

Before installing a water fire extinguishing system at a facility, it is necessary to develop an appropriate project, which must include the following data:

1. specific water supply sources;
2. water feeders;
3. pipelines;
4. sprinklers.

1. check the compatibility of materials used at the site with an aqueous solution;
2. define optimal view equipment;
3. determine the intensity of irrigation;
4. calculate the duration of the fire extinguishing process;
5. draw a diagram of the installation of sprinklers.

Only properly designed and professional installed system water fire extinguishing system will be able to fulfill its task - to quickly and effectively cope with a fire, preserving property and without causing harm to human health.

44. Fire extinguishing properties of water. Use of water when extinguishing fire

Water is one of the most accessible, cheapest and most widespread fire extinguishing agents, suitable for extinguishing both small and large fires. The fire extinguishing properties of water lie in the fact that it has a large heat capacity and is capable of removing a significant amount of heat from burning substances, reducing those

the temperature of the combustion source to such a level at which combustion becomes impossible. Water cannot be used:

· for extinguishing substances that react with it, for example, the metals potassium and sodium. Emitted hydrogen mixed with air forms an explosive mixture.

· when extinguishing live electrical installations, as well as when extinguishing calcium carbide due to the possibility of an explosion of the acetylene released.

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 this causes the liquid to spread and float to the surface of the water, which helps to increase the combustion zone.

If water is used in a sprayed state, in the form of finely dispersed particles, when the majority of drops of sprayed water have a size of less than 0.1 mm, then the surface of contact of water with burning substances increases, which contributes to a more intensive selection of heat from the combustion source by water and the formation of steam, promoting extinguishing. During indoor fires, a spray of water can be used to reduce temperature and smoke deposition. Water in a sprayed state can be used to extinguish burning oil products with a flash point above 120° C. AAAAAAAAAAAAAAAAAAAAAAAAAAA

Adding 0.2-2.0% (by weight) of foaming agents to water helps to reduce 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 extinguishing agents

The main indicators of fire hazard, which determine the critical conditions for the occurrence and development of the combustion process, are the self-ignition temperature and the concentration limits of ignition.

The auto-ignition temperature characterizes minimum temperature a substance or material in which there is a sharp increase in the rate of exothermic reactions, ending in the occurrence of flaming combustion.

The minimum concentration of flammable gases and vapors in the air at which they are capable of igniting and spreading a flame is called the lower concentration limit of ignition; the maximum concentration of flammable gases and vapors at which flame propagation is still possible is called the upper ignition concentration limit. The region of compositions and mixtures of flammable gases and vapors with air lying between the lower and upper flammability limits is called the ignition region.

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 flammability limits with increasing temperature can be assessed according to the following rule: for every 100° increase in temperature, the values ​​of the lower flammability limits decrease by 8-10%, and the upper flammability limits increase by 12-15%.

Concentration saturated vapors 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.

Dusts of many solid combustible substances suspended in the air also have the ability to form mixtures that ignite at high speed (explosive) with air. The minimum concentration of dust in the air at which it ignites is called the lower limit of dust ignition. Because the achievement is very high concentrations dust in a suspended state is practically unrealistic; the term “upper flammability limit” does not apply to dust.

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 ignite 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 of 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, formaldehyde, etc.), they are called flammable liquids (FL).

Ignition temperature is the temperature of a flammable substance at which it emits flammable vapors and gases at such a speed that, after ignition from the ignition source, stable combustion occurs. Temperature limits of ignition - temperatures at which saturated couples substances form concentrations in a given oxidizing environment equal to the lower and upper concentration limits of flammability of liquids, respectively.

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

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

flammable (combustible),

· slow-burning (hard-to-burn)

· non-flammable (non-combustible).

Combustibles include those substances and materials that, when ignited by an external source, continue to burn even after it is removed. Relatively flammable substances include those substances that are not capable of spreading a flame and burn only at the point of impact of the pulse; non-flammable are substances and materials that do not ignite even when exposed to sufficiently powerful impulses.

46. ​​Automatic fire extinguishing systems. Causes of industrial fires

Used in rooms with increased fire hazard.

1) splinker: the outlet of the sprinkler head is covered with plates, cat. when exposed to temperature, they melt and water from the system under pressure comes out of the head opening and irrigates the structures of the room or equipment in the area of ​​the sprinkler head. One head irrigates an area of ​​10-12 m.

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

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

It is impossible to extinguish fires with temperatures above 1800 - 2000 0 C with water, since this results in intense dissociation of water vapor into hydrogen and oxygen, which intensify the combustion process;

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

In all other cases, water is reliable, effective means for extinguishing fires and therefore it has found the widest application. Water has a number of advantages as a fire extinguishing agent: thermal resistance, which far exceeds the thermal resistance of other non-flammable liquids, high heat capacity and heat of evaporation, and relative chemical inertness. The negative properties of water include: a high freezing point and an anomaly in the change in density of water during cooling, which makes it difficult to use at low negative temperatures, relatively low viscosity and a high coefficient of surface tension, which impair the wetting ability of water and thereby reduce the coefficient of its use in the extinguishing process, as well as the electrical conductivity of water containing impurities.

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

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

When extinguishing flammable liquids and gases, a compact jet will have almost no effect on the flame. And, once on the surface of flammable liquids and gases, it will not cool it very effectively. Due to the high specific gravity of water compared to flammable hydrocarbons, it will quickly sink to the bottom. The cooling of the surface layers of a flammable liquid heated to boiling temperature will not be as intense as if sprayed or finely sprayed water were supplied. When extinguishing THM, compact jets of water supplied to the flame, just as in the first two cases, will not have an effect on the combustion zone, and once on the surface of the THM, they will not cool them very effectively and thus will contribute little to extinguishing.

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

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

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

2. Advantages and disadvantages of water

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

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

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

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

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

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

Water can dissolve some vapors, gases and absorb aerosols. This means that combustion products from fires in buildings can be deposited with water. For these purposes, sprayed and finely sprayed jets are used.

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

But at the same time, water has a number of disadvantages that narrow the scope of its use as a fire extinguishing agent. A large amount of water used in extinguishing can cause irreparable damage to material assets, sometimes no less than the fire itself. The main disadvantage of water as a fire extinguishing agent is that due to its high surface tension (72.8*-103 J/m2), it does not wet solid materials and especially fibrous substances well. Other disadvantages are: freezing of water at 0°C (reduces the transportability of water at low temperatures), electrical conductivity (makes it impossible to extinguish electrical installations with water), high density (when extinguishing light burning liquids, water does not limit the access of air to the combustion zone, but, spreading, promotes further spread of fire).

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