Extinguishing a fire with water: rules, advantages and disadvantages. Fire extinguishing agents: chemical properties, types The effect of extinguishing the flames of capillary-porous, hydrophobic materials such as peat, cotton and woven materials is achieved by adding fire
Water is the most widely used and effective means extinguishing fires.
Table 1: Comparison of the effectiveness of fire extinguishing agents (FAs)
| Fire class | Combustible materials | Water | Foam | Powder | CO 2 | Freon CF 3 Br | Other refrigerants | |
| PSB | PF | |||||||
| A | Solids that form coal (paper, wood, textiles, coal, etc. | 4 | 4 | 1 | 3 | 1 | 2 | 1 |
| IN | GZh and flammable liquids (gasoline, varnishes, solvents), melting materials (hydron, paraffin) | 4 | 4 | 4 | 4 | 3 | 4 | 4 |
| WITH | Gases (propane, methane, hydrogen, acetylene, etc.) | 2 | 1 | 4 | 3 | 1 | 3 | 2 |
| D | Metals (Al, Mg, etc.) | — | — | 1 | 1 | — | — | — |
| E | Electrical equipment (transformers, distribution boards, etc.) | 2 | — | 2 | 2 | 3 | 4 | 3 |
As follows from Table 1, water and foam are the most effective means of extinguishing class A and B fires (class B mainly with fine or ultra-sprayed water).
The basis of the fire extinguishing effect of water is its cooling ability, which is due to its high heat capacity and heat of vaporization.
With the highest heat absorption capacity, water is the most efficient natural material for extinguishing fires. Drops of water entering the combustion center undergo two stages of heat absorption: when heated to 100°C and evaporation at a constant temperature of 100°C. In the first stage, 1 liter of water spends 335 kJ of energy, in the second phase - evaporation and transformation into water vapor - 2260 kJ.
When water enters a high-temperature zone or comes into contact with a burning substance, it partially evaporates and turns into steam. During evaporation, the volume of water increases almost 1670 times, due to which the air is displaced by water vapor from the fire source, and, as a result, the combustion zone is depleted of oxygen.
Water has a high thermal resistance. Its vapors can decompose into hydrogen and oxygen only at temperatures above 1700°C. In this regard, extinguishing most solid materials with water is safe, since their combustion temperature does not exceed 1300 °C.
Water can dissolve some vapors, gases and absorb aerosols. Therefore, it can be used to precipitate combustion products during fires in buildings. For these purposes, finely atomized and ultra-atomized (water mist) jets are used.
Good mobility of water ensures ease of transportation through pipelines. Water is used not only to extinguish fires, but also to cool objects located near the source of fire. Thereby preventing their destruction, explosion and fire.
Mechanism for extinguishing fires with water:
- cooling the surface and reaction zone of burning substances;
- dilution (phlegmatization) of the environment in the combustion zone with steam generated during evaporation;
- isolation of the combustion zone from the air;
- deformation of the reaction layer and flame failure due to the mechanical impact of a water jet on the flame.
When extinguishing burning oil products in tanks with water, the drops supplied to the combustion source are essential. Optimal diameter water drops are 0.1mm when extinguishing gasoline; 0.3 mm - kerosene and alcohol; 0.5mm - transformer oil and petroleum products with a flash point above 60 °C.
High efficiency of extinguishing flammable substances that have a high combustion temperature and create a high flame pressure is achieved through the use of a mixture of small and large water droplets. In this case, small drops, evaporating in the flame combustion zone, reduce its temperature, and large drops, not having time to completely evaporate, reach the burning surface, cool it and, if their kinetic energy by the time they reach the burning surface is high enough, destroy the reaction layer.
Table 2: Areas of application of water for various classes fire
| Fire class | Subclass | Combustible substances and materials (objects) | Water sprayed by sprinklers | Finely sprayed water | Sprayed water with wetting agent |
| A | A1 | Solid smoldering substances wetted with water (wood, etc.) | 3 | 3 | 3 |
| A2 | Solid smoldering substances that are not wetted by water (cotton, peat, etc.) | 1 | 1 | 2 | |
| A3 | Solid non-smoldering substances (plastics, etc.) | 2 | 3 | 3 | |
| A4 | Rubber products | 2 | 2 | 3 | |
| A5 | Museums, archives, libraries, etc. | 1 | 1 | 1 | |
| IN | IN 1* | Saturated and unsaturated hydrocarbons (heptane, etc.) | — | 2 | 1 |
| AT 2* | Saturated and unsaturated hydrocarbons (gasoline, etc.) | — | 2 | 1 | |
| AT 3* | Water-soluble alcohols (C1-C3) | — | 2 | 1 | |
| AT 4* | Water-insoluble alcohols (C4 and higher) | — | 2 | 1 | |
| AT 5** | Acids - sparingly soluble in water | 3 | 3 | 3 | |
| AT 6** | Ethers and ethers (diethyl, etc.) | 3 | 3 | 3 | |
| AT 7** | Aldehydes and ketones (acetone, etc.) | 3 | 3 | 3 | |
| WITH, | C1, C2, C3 | — | — | — | |
| E*** | E1 | EVC | 1 | 1 | 1 |
| E2 | Telephone nodes | 2 | 2 | 2 | |
| E3 | Power plants | 1 | 1 | 1 | |
| E4 | Transformer substations | 2 | 2 | 2 | |
| E5 | Electronics | 1 | 1 | 1 |
Note: “1” – suitable, but not recommended; “2” – fits satisfactorily; “3” – fits well; “4” – fits perfectly; “-” - not suitable, “*” - for flammable liquids and gas liquids with a flash point of up to 90 ° C; “**” - for flammable liquids and gases with a flash point of more than 90 °C; “***”—electrical equipment is live.
Water should not be used to extinguish the following materials:
- potassium, sodium, lithium, magnesium, titanium, zirconium, uranium, plutonium;
- organoaluminum compounds (reacts explosively);
- organolithium compounds, lead azide, carbides, alkali metals, hydrides of a number of metals, magnesium, zinc, calcium carbides, barium (decomposition with release of flammable gases);
- iron, phosphorus, coal;
- sodium hydrosulfite (spontaneous combustion occurs);
- sulfuric acid, thermites, titanium chloride (strong exothermic effect);
- bitumen, sodium peroxide, fats, oils, petrolatum (intensified combustion as a result of emission, splashing, boiling).
When extinguishing with water, oil products and many other organic liquids float to the surface, as a result of which the area of the fire can increase significantly. For example: in case of fire of petroleum products located in the tank, it is not recommended to extinguish it with water. Oil products float above the water. Water, as a result of heating, turns into steam. Water vapor rises upward in portions, which causes burning oil products to splash out of the tank and makes it difficult for firefighters to access the fire.
The disadvantages of water include its high freezing point. To lower the freezing point, special additives (antifreeze), some alcohols (glycols), and mineral salts (K 2 CO 3, MgCl 2, CaCl 2) are used. However, these salts increase the corrosivity of water, so they are practically not used. The use of glycols significantly increases the cost of the fire extinguishing agent.
Foaming agents, antifreeze and other additives also increase the corrosivity and electrical conductivity of water. As protection against corrosion, you can metal parts and pipelines apply special coatings, or add corrosion inhibitors to the water.
Expanding the scope of use of water for extinguishing electrical equipment under voltage is possible when using it in a fine and ultra-sprayed state.
The low wetting ability and low viscosity of water make it difficult to extinguish fibrous, dusty and especially smoldering materials. Materials with a large specific surface area, the pores of which contain the air necessary for combustion, are subject to smoldering. Such materials can burn with a greatly reduced oxygen content in environment. Penetration of fire extinguishing agents into the pores of smoldering materials is, as a rule, quite difficult.
When introducing a wetting agent (sulfonate), the water consumption for extinguishing is reduced by four times, and the extinguishing time is reduced by half.
In some cases, water extinguishing becomes very effective if it is thickened with, for example, sodium carboxymethylcellulose or sodium alginate. Increasing the viscosity to 1-1.5 N*s/m2 allows you to reduce the extinguishing time by about 5 times. The best additives in this case are solutions of sodium alginate and sodium carboxymethylcellulose. For example, a 0.05% solution of sodium carboxymethylcellulose provides a significant reduction in water consumption for fire extinguishing. If, under certain extinguishing conditions with ordinary water, its consumption ranges from 40 to 400 l/m2, then when using “Viscous” water - from 5 to 85 l/m2. The average damage from fire (including as a result of exposure to water on materials) is reduced by 20%.
The most commonly used additives that increase the efficiency of water use are:
- water-soluble polymers to increase adhesion to burning objects (“Viscous water”);
- polyoxyethylene to enhance bandwidth pipelines (“slippery water”);
- inorganic salts to increase the efficiency of extinguishing;
- antifreeze and salts to reduce the freezing point of water.
Currently, one of the most promising areas in the field of fire protection of objects for various purposes is the use of finely and ultra-sprayed water as a means of extinguishing fires. In this form, water is capable of absorbing aerosols, precipitating combustion products and extinguishing not only burning solids, but also many flammable liquids.
When water is supplied in a fine or ultra-sprayed state, the greatest fire extinguishing effect is achieved. The use of finely and ultra-sprayed water is especially important at facilities where it is required high efficiency extinguishing, there are restrictions on water supply and minimizing damage from water spills is relevant.
With the help of finely and ultra-sprayed water, the protection of many particularly socially and industrially significant objects can be ensured. These include: residential premises, hotel rooms, offices, educational institutions, dormitories, administrative buildings, banks, libraries, hospitals, computer centers, museums and exhibition galleries, sports complexes industrial facilities, i.e. such objects where fire extinguishing must be carried out in the initial stage quickly enough and with low water consumption.
Additional benefits of using atomized water compared to a compact jet or spray stream:
- the ability to extinguish almost all substances and materials, with the exception of substances that react with water releasing thermal energy and flammable gases;
- high extinguishing efficiency due to the increased cooling effect and uniform irrigation of the fire with water;
- minimal water consumption - insignificant consumption allows you to avoid significant damage from the consequences of a spill and ensure the possibility of use subject to a water limit;
- shielding of radiant thermal radiation - used to protect service personnel taking part in fire extinguishing, personnel of fire departments, load-bearing and enclosing structures, as well as nearby material assets;
- dilution of flammable vapors and reduction of oxygen concentration in the combustion zone as a result of intensive formation of water vapor;
- reducing the temperature in rooms during a fire;
- uniform cooling of overheated metal surfaces load-bearing structures due to the high specific surface area of the droplets, it eliminates their local deformation, loss of stability and destruction;
- effective absorption and removal of toxic gases and smoke (smoke deposition);
- low electrical conductivity of finely ultra-sprayed water - makes it possible to use it as an effective fire extinguishing agent in electrical installations under voltage;
- environmental cleanliness and toxicological safety combined with the protection of people from exposure to hazardous fire factors - allows personnel to save valuables during work automatic installation fire extinguishing
Ultra-sprayed water in the combustion zone intensively evaporates. A protective layer of water vapor can isolate the combustion zone, preventing the access of oxygen. When the oxygen concentration in the combustion area drops to 16-18%, the fire self-extinguishes.
Literature used: L.M.Meshman, V.A.Bylinkin, R.Yu.Gubin, E.Yu.Romanova. Automatic water and foam fire extinguishing systems. Design. Moscow city. — 2009
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 a reliable, effective means for extinguishing fires and therefore it has found the most widespread use. Water has a number of advantages as a fire extinguishing agent: thermal 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. Cooling heated to boiling point surface layers flammable liquid 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, 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.
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 a reliable, effective means for extinguishing fires and therefore it has found the most widespread use. Water has a number of advantages as a fire extinguishing agent: thermal 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, 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.
Send your good work in the knowledge base is simple. Use the form below
Students, graduate students, young scientists who use the knowledge base in their studies and work will be very grateful to you.
Posted on http://www.allbest.ru/
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 the rate of chemical reactions in the flame;
mechanical flame arrest by exposing the combustion source to a strong jet of gas or water;
creating fire suppression conditions.
The results of the effects of all existing extinguishing agents on the combustion process depend on the physical and chemical properties of burning materials, combustion conditions, supply intensity and other factors. For example, water can be used to cool and isolate (or dilute) the source of combustion, foam agents can be used to isolate and cool, inert diluents can dilute the air, reducing the oxygen concentration, and freons can inhibit combustion and prevent the spread of flame by a powder cloud. For any extinguishing agent, only one fire extinguishing effect is dominant. Water has a predominantly cooling effect, foams have an insulating effect, freons and powders have an inhibitory effect.
Most extinguishing agents are not universal, i.e. acceptable for extinguishing any fires. In some cases, extinguishing agents turn out to be incompatible with burning materials (for example, the interaction of water with burning alkali metals or organometallic compounds is accompanied by an explosion).
When choosing extinguishing agents, one should proceed from the possibility of obtaining the maximum fire extinguishing effect when minimum costs. The choice of extinguishing agents must be made taking into account the class of fire. Water is the most widely used fire extinguishing agent for extinguishing fires of substances in various states of aggregation.
The high fire extinguishing efficiency of water and the large scale of its use for extinguishing fires are due to a complex of special physical and chemical properties of water and, first of all, the unusually high, in comparison with other liquids, energy intensity of evaporation and heating of water vapor. Thus, to evaporate one kilogram of water and heat the vapor to a temperature of 1000 K, it is necessary to spend about 3100 kJ/kg, while a similar process with organic liquids requires no more than 300 kJ/kg, i.e. The energy intensity of the phase transformation of water and heating of its vapor is 10 times higher than the average for any other liquid. At the same time, the thermal conductivity of water and its vapor is almost an order of magnitude higher than for other liquids.
It is well known that sprayed, highly dispersed water is most effective in extinguishing fires. To obtain a highly dispersed jet of water, as a rule, high pressure is required, but even then the range of supply of sprayed water is limited to a short distance. 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 the dilution of the flammable gas mixture with water vapor, which leads to its phlegmatization and cessation of combustion.
In addition, sprayed water droplets absorb radiant heat, absorb the flammable component and lead to coagulation of smoke particles.
2. Advantages and disadvantages of water
Factors that determine the advantages of water as a fire extinguishing agent, in addition to its availability and low cost, are significant heat capacity, high latent heat of evaporation, mobility, chemical neutrality and lack of toxicity. Such properties of water provide effective cooling not only of burning objects, but also of objects located near the source of combustion, which helps prevent destruction, explosion and fire of the latter. Good mobility makes it easy to transport water and deliver it (in the form of continuous streams) to remote and hard-to-reach places.
The fire extinguishing ability of water is determined by the cooling effect, dilution of the flammable medium by vapors formed during evaporation and the mechanical effect on the burning substance, i.e. flame failure.
Getting into the combustion zone, onto the burning substance, water takes away a large amount of heat from the burning materials and combustion products. At the same time, it partially evaporates and turns into steam, increasing in volume 1700 times (from 1 liter of water, 1700 liters of steam are formed during evaporation), due to which the reacting substances are diluted, which in itself helps to stop combustion, as well as displace air from the zone fire source.
Water has high thermal stability. Its vapors can only decompose into oxygen and hydrogen at temperatures above 1700°C, thereby complicating the situation in the combustion zone. Most flammable materials burn at a temperature not exceeding 1300-1350°C and extinguishing them with water is not dangerous.
Water has low thermal conductivity, which helps create reliable thermal insulation on the surface of the burning material. This property, in combination with the previous ones, allows it to be used not only for extinguishing, but also to protect materials from ignition.
The low viscosity and non-compressibility of water allow it to be supplied through hoses over considerable distances and under high pressure.
Water can dissolve some vapors, gases and absorb aerosols. This means that combustion products from fires in buildings can be deposited with water. For these purposes, sprayed and finely sprayed jets are used.
Some flammable liquids (liquid alcohols, aldehydes, organic acids, etc.) are soluble in water, therefore, when mixed with water, they form non-flammable or less flammable solutions.
But at the same time, water has a number of disadvantages that narrow the scope of its use as a fire extinguishing agent. A large amount of water used in extinguishing can cause irreparable damage 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 well hard 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 limit the access of air to the combustion zone, but, spreading, contributes to the spread of fire even more).
3. Intensity of water supply for extinguishing
Fire extinguishing agents are of paramount importance in stopping a fire. However, a fire can only be extinguished if a certain amount of fire extinguishing agent is supplied to stop it.
In practical calculations, the amount of fire extinguishing agents required to stop a fire is determined by the intensity of their supply. The supply intensity is the amount of fire extinguishing agent supplied per unit of time per unit of the corresponding geometric parameter of the fire (area, volume, perimeter or front). The intensity of the supply of fire extinguishing agents is determined experimentally and by calculations when analyzing extinguished fires:
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 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 of 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 (when supplying mist water) |
||
|
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% (at specific consumption water 110 - 140 l/m2 and extinguishing time 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 class of functional fire danger object, its fire resistance, fire hazard category (for industrial premises), volume in accordance with SP 8.13130.2009, for external fire extinguishing and SP 10.13130.2009, for internal fire extinguishing.
4. Methods of 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 fire extinguishing agents are used: inert gas - freon, carbon dioxide, foam (low, medium, high expansion), fire extinguishing powders, aerosols and water.
fire extinguishing water fire extinguishing efficiency
“Water” installations are divided into sprinkler 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 that differ from each other different temperatures triggering.
Sprinklers with preliminary action 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 significantly large quantity water to the protected area. Typically, deluge systems are used to create water curtains and cool particularly heat-sensitive and flammable objects.
To supply water to the deluge system, a so-called deluge control unit is used. The unit is activated electrically, pneumatically or hydraulically. The signal to start the deluge fire extinguishing system is given as in an automatic way- system fire alarm, and manually.
One of the new products on the fire extinguishing market is an installation with a mist water supply system.
The smallest particles of water supplied under high pressure have high penetrating and smoke-precipitating properties. This system significantly enhances the fire extinguishing effect.
Water mist fire extinguishing systems are designed and created based on equipment low pressure. This allows for highly 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, or a gas-water mixture.
Water sprayed through a fine hole increases the impact area, thus increasing the cooling effect, which is then increased due to the evaporation of the water mist. This 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 the water needs to be given impact force, as well as fires when it is not possible to get close to the source, when cooling neighboring and burning objects from large distances, structures, devices. This method of extinguishing is the simplest and most common.
Continuous jets should not be used where there may be flour, coal and other dust that can form explosive concentrations.
5. Area of application of water
Water is used to extinguish fires of the following classes:
A - wood, plastics, textiles, paper, coal;
B - flammable and combustible liquids, liquefied gases, oil products (extinguishing with finely sprayed water);
C - flammable gases.
Water should not be used to extinguish substances that release heat, flammable, toxic or corrosive gases upon contact with it. Such substances include some metals and organometallic compounds, metal carbides and hydrides, hot coal and iron. The interaction of water with burning alkali metals is especially dangerous. As a result of this interaction, explosions occur. If water gets on hot coal or iron, an explosive hydrogen-oxygen mixture may form.
Table 2 lists substances that cannot be extinguished with water.
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.
Absence quantitative criteria 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. 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. Corrosion of metal products in contact with water (fire extinguisher housings, pipelines, etc.) can be prevented either by applying special coatings to them or by adding corrosion inhibitors to water. The latter are inorganic compounds (acid phosphates, carbonates, alkali metal silicates, oxidizing agents such as sodium chromate, potassium chromate or sodium nitrite, which form on the surface protective layer), organic compounds (aliphatic amines and other substances that can absorb 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 - surface - active substances: DB wetting agent, OP-4 emulsifier, OP-7 and OP-10 auxiliary substances, 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 its high specific surface area fine particles, which increases the cooling effect due to the uniform penetrating action 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, Matveykin)
Posted on Allbest.ru
Similar documents
The role of water in human life. Water content in the human body. Drinking regime and water balance in the body. Main sources of drinking water pollution. Influence water resources on human health. Methods of water purification. Thermal sanitary treatment.
test, added 01/14/2016
Water from a tap, filter, well. Mineral and protium water. A survey of the population about the benefits of water, what kind of water they prefer to drink. The importance of water for human life. Which water is most beneficial for human health. Water purification technologies.
presentation, added 03/23/2014
Estimated water consumption for fire extinguishing. Hydraulic calculation of water supply network. Basic fire safety requirements for outdoor fire water supply. Drawing up a preliminary design diagram of the water supply network for fire fighting.
course work, added 06/02/2015
Factors influencing human needs for water. Organization of water consumption in taiga and mountain taiga zones. Collecting water from plants. Search for a water source based on the flight patterns of birds, the behavior of animals and insects. Methods for disinfecting and filtering water.
abstract, added 04/03/2017
Physiological, hygienic and epidemiological significance of water. Diseases associated with biological quality and chemical composition water. Calculation of water consumption rates according to Cherkins theory. Analysis of microelement composition and mineralization level.
presentation, added 10/09/2014
Dust cleaning devices are divided according to the method of spraying liquid. The rate of deposition of dust particles on water droplets. Types of filters. Ionizing devices for air purification from dust. Methods for collecting dust in pipelines of industrial enterprises.
abstract, added 03/25/2009
Characteristics, scope of application, mechanism for stopping combustion and intensity of supply of fire extinguishing agents with an inhibitory effect (chemical inhibition of the combustion reaction). Calculation of the required number of tank trucks to transport water to extinguish a fire.
test, added 09.19.2012
Familiarization with the basic principles of using helicopters to extinguish fires in urban areas. Characteristic necessary conditions for supplying fire extinguishing liquid. Determination of the main disadvantages of horizontal fire extinguishing systems.
abstract, added 10/08/2017
Modeling the process of occurrence and spread of fire in a furniture center, the formation of a smoke-filled area of the room. Determination of fire load. Calculation of the forces and means of the fire department to extinguish the fire. Required water flow for fire protection.
test, added 09/24/2013
Determination of the airport category according to the level of required fire protection. Calculation of the amount of water required to extinguish a fire. Drawing up an emergency notification scheme and airport plan. Organization of fire fighting, evacuation of passengers and crew members.
3.4.1. What fire extinguishing agents exist and what are their advantages and disadvantages?
1. WATER . Mainly it has a cooling effect. Additional benefit: When large volumes of water vapor are formed, oxygen is displaced. When 1 liter of water evaporates, 1.7 m³ is formed. saturated steam. Water is an ideal cooling medium for many flammable substances.
Advantages:
· the sea provides an unlimited supply of water; high level heat absorption; versatility; has low viscosity, the jet can penetrate deeply into the fire and create a film on the surface of the burning liquid ( light water);
· spraying to cool large areas or to cool the boundaries of a fire;
● turning into steam, it displaces air (volumetric quenching).
Flaws:
· possible impact on the stability of the vessel;
· extinguishing burning liquids with water can contribute to the spread of fire;
· water is not suitable for extinguishing fires in the presence of electrical equipment or in the presence of live cables near the fire;
· water reacts with some substances, forming toxic fumes, and interaction with calcium and sodium carbide leads to an explosion.
· water causes some cargo to swell (spoils the cargo).
2. CARBON DIOXIDE (CO 2). On ships, carbon dioxide CO 2 is used to extinguish fires in machinery and cargo spaces, storerooms, and is effective for extinguishing electrical and electronic equipment using stationary installations and fire extinguishers.
At a temperature of O 0 C and a pressure of 36 kg/cm 2 CO 2 goes into a liquid state. From one liter of liquid CO 2, upon expansion, 500 liters of gas are obtained. Carbon dioxide on ships is stored in pressurized cylinders. When supplied to a room, it goes into a gaseous state with rapid expansion, which leads to supercooling. As a result of hypothermia, gas is ejected from the installation (fire extinguisher pipe) in the form of flakes of sublimated snow (“ artificial ice") with a temperature of minus 78.5 0 C. Getting into the combustion center, CO 2 passes from a solid state to a gaseous state.
Carbon dioxide is 1.5 times heavier than air and therefore gradually concentrates in the lower part of the protected room. Extinguishing with carbon dioxide requires time and the required concentration with the volumetric extinguishing method. Combustion can be stopped when its concentration indoors is in the range of 30-45% by volume.
Advantages:
· inertia; relatively low cost; does not damage the cargo, does not leave marks, does not conduct electricity;
does not form toxic or explosive gases in contact with most substances.
Flaws:
· limited stock; does not have a cooling effect with the volumetric method; creates a suffocation hazard at air concentrations of 15–30%;
· not very effective when used on outdoors;
· when extinguishing magnesium reacts with it (oxygen is released).
3. FOAM. Suppresses fire by forming an airtight layer. This layer prevents flammable vapors from leaving the surface and oxygen from penetrating the flammable substance. This prevents fire above the foam cover. Due to heating, the foam bubbles burst, forming water mist, which turns into steam. All this together stops the combustion process.
Advantages:
· covers the surface freely and quickly; extinguishes burning petroleum products, alcohols, ethers, ketones. Due to the water contained in the solution, it has a cooling effect (extinguishing class A fires);
· used in conjunction with fire extinguishing powders;
· foam creates a vapor barrier that prevents vapors from escaping;
· fresh, sea or soft water is used to obtain foam;
· economical water consumption, does not overload fire pumps;
· foam concentrates are light in weight, the systems do not require much space for placement (they are compact).
Flaws:
· conducts electricity; cannot be used to extinguish flammable metals; limited stock; does not extinguish gases.
4 . FIRE EXTINGUISHING POWDERS . Fire extinguishing agents in the form of powders are divided into two groups - these are fire extinguishing powders general purpose– for extinguishing fires of classes A, B, C, E and fire extinguishing powders special purpose, which are used to extinguish only flammable metals. Typically, sodium bicarbonate is used as a dry powder with various additives that improve fluidity, mutual miscibility with foam, water resistance and shelf life. Ammonium phosphate, potassium bicarbonate, potassium chloride, etc. are also used as dry powder.
Advantages. Dry powder quickly puts out the flame. A powder cloud entering the combustion zone inhibits the combustion reaction. In addition, burning substances are diluted with non-flammable gases released as a result of thermal decomposition of powder particles. The powders used are non-toxic, however, it is recommended to protect the respiratory tract when extinguishing. Powders do not have a harmful effect on ship equipment.
Flaws. Limited supply causes respiratory tract irritation and damage to electronics. They have a low cooling effect. They do not have penetrating ability.
5 . CHILDONS, (FREONS). Freons, halons, (freons) - halogenated hydrocarbons consist of carbon and one or more halogens: fluorine, chlorine, bromine and iodine. Extinguishing fires with freons is based on chemical inhibition of the combustion reaction, i.e. binding of active centers of atoms and radicals.
Easily evaporating, the vapors of these liquids fill the entire volume of the burning room. Having reached the source of the fire, they slow down the combustion reaction and interrupt it, as a result of which the fire stops.
Advantages:
· used in small quantities; they put out fire very quickly and do not damage cargo and equipment; in gas injection systems they form a homogeneous gas environment; “penetrating” gas, spreads throughout the room, applicable for extinguishing fires with electrical equipment.
Flaws:
● limited stock, relatively high cost. There is no cooling effect and visibility is impaired. When used at very high temperatures (500˚C), toxic by-products may form (i.e. high toxicity). Not effective on deep fires (eg mattresses, wool bales, etc.). Inhaling gallons causes dizziness and loss of coordination. Destroy ozone layer.
In Russia, the most widely used refrigerants are 13B1, 12B1, freon 114-B2, as well as a mixture of ethyl bromide (73%) and freon 114 - B2 (27%) for extinguishing solid and liquid flammable substances. When the vapor in the emergency room reaches 215 g per 1 cm3. free volume, the combustion chain reaction stops. Effectively extinguishes smoldering materials. Further supplies of these types of refrigerants are prohibited, as they destroy the ozone layer.
6. REFRIGERANT REPLACEMENTS (HALON) ). After the Montreal Protocol banned the use and production of ozone-depleting refrigerants, an intensive search began for alternative bulk extinguishing agents. Both in our country and abroad, the latest fire extinguishing systems using finely sprayed water are manufactured and installed on ships. aerosol generators, inert gases and non-ozone-depleting refrigerants. Currently, gas extinguishing systems have been created using freon FM - 200 (heptofluoropropane). Approved for use in fire extinguishing systems to protect both inhabited and uninhabited premises. To stop a fire, a low concentration of freon is required (7.5%), which does not affect the human respiratory system.
7 . INERT GASES (IG). An inert gas is a gas or mixture of gases that does not contain sufficient oxygen to support combustion.
IGs are obtained from the combustion of organic fuel in ship boilers and separate gas generators on diesel fuel. Nitrogen generators produce IG - NITROGEN from the air. The fire extinguishing effect of IG is reduced to a decrease in the oxygen concentration in the combustion area. They are used to fill the free space of tanks, holds for protection against fires and explosions, as well as to extinguish fires in holds. Nitrogen (N) is widely used in inert gas systems for inerting tanks on chemical tankers and gas tankers. For effective application system, the oxygen content in the gas should be no more than 5% at a gas temperature of no more than 40˚C. When unloading petroleum products, the supply of gases to tanks should be 25% higher than maximum speed unloading
8 . FINE MISTRIZED WATER . Finely sprayed water is an effective and promising extinguishing agent. It is recommended for extinguishing crushed solids, fibrous materials and flammable liquids.
To obtain finely atomized water, screw and vortex atomizers are required at a water pressure in the line of 25-30 kg/cm 2 . In this case, water particles ranging in size from 0.1 mm to 0.5 are obtained. Such finely sprayed water turns into steam in the flame, having previously taken away a significant part of the heat from the fire, and the steam, diluting the oxidizer in the fire zone, helps stop the combustion.
The required spray dispersion depends on the nature of the burning substances. For example, to extinguish gasoline and dusty substances, the droplet diameter should be no more than 0.1 mm, for alcohols - 0.3 mm, for flammable liquids such as transformer oil and fibrous materials - 0.5 mm.
Finely sprayed water is now more often used in stationary fire extinguishing installations in municipalities, incinerators, and separator rooms, and automatically, since it is not dangerous to humans.
9. WATER VAPOR. Water steam for extinguishing fires is supplied to the combustion zone through special pipelines from the steam power plant. Saturated steam has the best fire extinguishing properties. Fire extinguishing concentrations of water vapor depend on the type of combustible materials and do not exceed 35% by volume. The use of water steam to extinguish fires is effective in rooms with a volume of up to 500 m 3 . Heat, danger to personnel, low filling rates of the emergency room limit the use of water vapor as a fire extinguishing agent. Steam cannot be used to extinguish heated iron up to 700 0 C and burning soot, because there is an increase in combustion and the possibility of an explosion of the released hydrogen.
10. FIRE EXTINGUISHING AEROSOLS. The principle of operation of fire extinguishing aerosols is based on the inhibition of redox reactions by finely dispersed products (aerosol) of salts and oxides of alkali and alkaline earth metals, formed during the combustion of an aerosol-forming charge located in the generator housing, and capable of being suspended for 30-50 minutes.
The gas-aerosol mixture released when the generator is activated is toxic and has an irritating effect on the mucous membranes of the respiratory system, so you can enter the room in which the generators were used no earlier than 30 minutes later. after stopping their work, wear respiratory protection or after ventilation.
11. COMBINED EXTINGUISHING MEANS .
Combined gas-powder fire extinguishing is a new promising direction in the development of automatic protection. The principle of such extinguishing is as follows: a jet consisting of a mixture carbon dioxide and fine powder based on ammonium phosphate is fed into the protected volume at high speed. This suspension, entering the zone of the gas-phase flame, extinguishes it by diluting the oxidizer with gas and absorbing the active centers of the flame by powder particles. Powder particles passing through the gas phase of the flame fall on the surface of the material and block the processes of evaporation and sublimation, forming a dense glassy phosphate film on the surface, i.e. the powder works in two zones, which is why such modules were called “Bison” (two zones). The Bison fire extinguishing module is located on the bulkhead (wall) of the protected volume at a height of up to 3.5 meters.
