Extinguishing fires
SELECTION AND CALCULATION OF A GAS FIRE EXTINGUISHING SYSTEM
A. V. Merkulov, V. A. Merkulov
CJSC "Artsok"
The main factors influencing the optimal choice installations gas fire extinguishing(UGP): type of combustible load in the protected premises (archives, storage facilities, radio-electronic equipment, technological equipment, etc.); the size of the protected volume and its leakproofness; type of gas extinguishing agent (GFFS); the type of equipment in which the GFFS should be stored, and the type of UGP: centralized or modular.
The correct choice of a gas fire extinguishing installation (GSP) depends on many factors. Therefore, the purpose of this work is to identify the main criteria affecting the optimal choice of a gas fire extinguishing installation and the principle of its hydraulic calculation.
The main factors affecting the optimal choice of a gas fire extinguishing installation. First, the type of combustible load in the protected room (archives, storage facilities, radio-electronic equipment, technological equipment, etc.). Secondly, the size of the protected volume and its leakproofness. Thirdly, the type of gaseous extinguishing agent. Fourth, the type of equipment in which the gas extinguishing agent is to be stored. Fifth, the type of gas fire extinguishing installation: centralized or modular. The last factor can only take place when necessary. fire protection two or more premises in one facility. Therefore, we will consider the mutual influence of only four of the above factors, i.e. on the assumption that the facility needs fire protection for only one room.
Of course, right choice gas fire extinguishing installations should be based on optimal technical and economic indicators.
It should be especially noted that any of the permitted gaseous extinguishing agents will extinguish a fire regardless of the type of combustible material, but only when a standard extinguishing concentration is created in the protected volume.
The mutual influence of the above factors on the technical and economic parameters of the gas fire extinguishing installation will be assessed
from the condition that the following gas extinguishing agents are permitted for use in Russia: freon 125, freon 318C, freon 227ea, freon 23, CO2, K2, Ar and a mixture (No. 2, Ar and CO2), which has trade mark Inergen.
According to the storage method and methods of control of gas fire extinguishing substances in gas fire extinguishing modules (MGP), all gas fire extinguishing substances can be divided into three groups.
The first group includes freon 125, 318C and 227ea. These freons are stored in the gas fire extinguishing module in liquefied form under the pressure of a propellant gas, most often nitrogen. Modules with the listed freons, as a rule, have a working pressure not exceeding 6.4 MPa. The control of the amount of freon during the operation of the installation is carried out using a pressure gauge installed on the gas fire extinguishing module.
Freon 23 and CO2 make up the second group. They are also stored in a liquefied form, but are displaced from the gas fire extinguishing module under the pressure of their own saturated vapors. The working pressure of modules with the listed gaseous extinguishing agents must have an operating pressure of at least 14.7 MPa. During operation, the modules must be installed on weighing devices that ensure continuous monitoring of the mass of Freon 23 or CO2.
The third group includes K2, Ar and Inergen. These gaseous extinguishing agents are stored in gaseous extinguishing modules in a gaseous state. Further, when we consider the advantages and disadvantages of gas extinguishing agents from this group, we will focus only on nitrogen.
This is because N2 is the most effective (lowest extinguishing concentration) and has the lowest cost. Control of the mass of the listed gaseous fire extinguishing substances is carried out using a pressure gauge. Lg or Inergen are stored in modules at a pressure of 14.7 MPa or more.
Gas extinguishing modules, as a rule, have a cylinder capacity not exceeding 100 liters. At the same time, modules with a capacity of more than 100 liters, according to PB 10-115, are subject to registration with the Gosgortekhnadzor of Russia, which entails a fairly large number of restrictions on their use in accordance with the specified rules.
The exception is isothermal modules for liquid carbon dioxide (MIZHU) with a capacity of 3.0 to 25.0 m3. These modules are designed and manufactured for storing carbon dioxide in gas fire extinguishing installations in quantities exceeding 2500 kg. Isothermal modules for liquid carbon dioxide are equipped with refrigeration units and heating elements, which allows maintaining the pressure in the isothermal tank in the range of 2.0 - 2.1 MPa at a temperature the environment from minus 40 to plus 50 ° С.
Let us consider with examples how each of the four factors affect the technical and economic indicators of a gas fire extinguishing installation. The mass of the gaseous extinguishing agent was calculated according to the method described in NPB 88-2001.
Example 1. It is required to protect radio-electronic equipment in a room with a volume of 60 m3. The room is conditionally sealed, i.e. K2 "0. The calculation results are summarized in table. 1.
The economic rationale for table. 1 in concrete numbers has a certain difficulty. This is due to the fact that the cost of equipment and gas extinguishing agent is different for manufacturers and suppliers. However, there is a general trend that as the capacity of the cylinder increases, the cost of the gas extinguishing module increases. 1 kg of CO2 and 1 m3 of N are close in price and two orders of magnitude less than the cost of freons. Analysis of the table. 1 shows that the cost of a gas fire extinguishing installation with refrigerant 125 and CO2 is comparable in value. Despite the significantly higher cost of Freon 125 compared to carbon dioxide, the total price of Freon 125 - a gas fire extinguishing module with a 40 liter cylinder will be comparable or even slightly lower than a set of carbon dioxide - a gas extinguishing module with an 80 liter cylinder - weighing device. It can be unambiguously stated that the cost of a gas fire extinguishing installation with nitrogen is significantly higher in comparison with the two previously considered options, since requires two modules with the maximum volume. More space will be needed to accommodate
TABLE 1
Freon 125 36 kg 40 1
CO2 51 kg 80 1
of two modules in a room and, naturally, the cost of two 100-liter modules will always be higher than the cost of an 80-liter module with a weighing device, which, as a rule, is 4 - 5 times cheaper than the module itself.
Example 2. The parameters of the premises are similar to example 1, but it is required to protect not the electronic equipment, but the archive. The calculation results, similar to the first example, are summarized in table. 2.
Based on the analysis of the table. 2, we can unequivocally say that in this case, too, the cost of a gas fire extinguishing installation with nitrogen is much higher than the cost of gas fire extinguishing installations with chladone 125 and carbon dioxide. But in contrast to the first example, in this case it can be more clearly noted that the least cost is the installation of gas fire extinguishing with carbon dioxide, since with a relatively small difference in cost between a gas fire extinguishing module with a cylinder with a capacity of 80 and 100 liters, the price of 56 kg of Freon 125 significantly exceeds the cost of the weighing device.
Similar dependencies will be traced if the volume of the protected premises increases and / or its leakage capacity increases, because all this causes a general increase in the amount of any kind of gaseous extinguishing agent.
Thus, only on the basis of two examples it can be seen that it is possible to choose the optimal gas fire extinguishing installation for fire protection of the premises only after considering at least two options with different kinds gas extinguishing agents.
However, there are exceptions when a gas fire extinguishing installation with optimal technical and economic parameters cannot be used due to certain restrictions imposed on gas extinguishing agents.
TABLE 2
Name of GFFS Amount of GFUs Capacity of MGP cylinder, l Number of GFU, pcs.
Freon 125 56 kg 80 1
CO2 66 kg 100 1
Such restrictions, first of all, include the protection of especially important objects in an earthquake hazardous area (for example, nuclear power facilities, etc.), where it is required to install modules in earthquake-resistant frames. In this case, the use of freon 23 and carbon dioxide is excluded, because modules with these gaseous extinguishing agents must be installed on weighing devices, excluding their rigid attachment.
For fire protection of premises with permanently present personnel (air traffic control rooms, rooms with control panels of nuclear power plants, etc.), restrictions are imposed on the toxicity of gaseous fire extinguishing substances. In this case, the use of carbon dioxide is excluded, because the volumetric fire extinguishing concentration of carbon dioxide in the air is fatal to humans.
When protecting volumes of more than 2000 m3, from an economic point of view, the most acceptable is the use of carbon dioxide, charged into the isothermal module for liquid carbon dioxide, in comparison with all other gaseous fire extinguishing agents.
After the feasibility study, the amount of gas extinguishing agents required to extinguish the fire and the preliminary number of gas extinguishing modules become known.
The nozzles must be installed in accordance with the spray patterns specified in the technical documentation of the nozzle manufacturer. The distance from the nozzles to the ceiling (floors, false ceiling) should not exceed 0.5 m when using all gas extinguishing agents, with the exception of K2.
Piping should generally be symmetrical, i.e. nozzles should be equally spaced from the main pipeline. In this case, the consumption of gas extinguishing agents through all nozzles will be the same, which will ensure the creation of a uniform fire extinguishing concentration in the protected volume. Typical examples of symmetrical piping are shown in fig. 1 and 2.
When designing piping, you should also take into account the correct connection of the outgoing pipelines (rows, bends) from the main pipelines.
A cruciform connection is possible only if the flow rates of gaseous extinguishing agents 01 and 02 are equal in magnitude (Fig. 3).
If 01 Ф 02, then the opposite connections of rows and branches with the main pipeline must be spaced in the direction of movement of gas extinguishing agents at a distance L exceeding 10 D, as shown in Fig. 4, where D is the inner diameter of the main pipeline.
No restrictions are imposed on the spatial connection of pipes in the design of pipe distribution of a gas fire extinguishing installation when using gas extinguishing agents belonging to the second and third groups. And for the piping of a gas fire extinguishing installation with gas extinguishing agents of the first group, there are a number of restrictions. This is due to the following.
When freon 125, 318C or 227ea is pressurized in the gas fire extinguishing module with nitrogen to the required pressure, nitrogen partially dissolves in the listed freons, and the amount of dissolved nitrogen in freons is proportional to the boost pressure.
B> 10D ^ N Y
After opening the locking and starting device of the gas fire extinguishing module under the pressure of the propellant gas, the freon with partially dissolved nitrogen flows through the piping to the nozzles and through them enters the protected volume. At the same time, the pressure in the "modules - piping" system decreases as a result of the expansion of the volume occupied by nitrogen in the process of displacing the freon and the hydraulic resistance of the piping. There is a partial release of nitrogen from the liquid phase of freon and a two-phase medium "mixture of the liquid phase of freon - gaseous nitrogen" is formed. Therefore, a number of restrictions are imposed on the piping of a gas fire extinguishing installation using the first group of gas extinguishing agents. The main purpose of these restrictions is to prevent stratification of the two-phase fluid within the piping.
During the design and installation, all pipework connections of the gas fire extinguishing installation must be performed as shown in Fig. 5, and it is forbidden to perform them in the form shown in Fig. 6. In the figures, arrows show the direction of flow of gas extinguishing agents through the pipes.
In the process of designing a gas fire extinguishing installation in an axonometric view, the pipe layout, the length of the pipes, the number of nozzles and their height marks are determined. To determine the inner diameter of the pipes and the total area of the outlet openings of each nozzle, it is necessary to perform a hydraulic calculation of the gas fire extinguishing installation.
The method for performing the hydraulic calculation of a gas fire extinguishing installation with carbon dioxide is given in the work. Calculation of the installation of gas fire extinguishing with inert gases is not a problem, because in this case, the flow is inert
gases occurs in the form of a single-phase gaseous medium.
Hydraulic calculation of a gas fire extinguishing installation using freons 125, 318C and 227ea as a gas extinguishing agent is a complex process. The application of the hydraulic calculation method developed for the 114B2 freon is unacceptable due to the fact that in this method the flow of freon through the pipes is considered as a homogeneous liquid.
As noted above, the flow of chladones 125, 318Ts and 227ea through pipes occurs in the form of a two-phase medium (gas - liquid), and with decreasing pressure in the system, the density of the gas-liquid medium decreases. Therefore, to maintain a constant mass flow rate of gaseous fire extinguishing agents, it is necessary to increase the velocity of the gas-liquid medium or the inner diameter of the pipelines.
Comparison of the results of field tests with the release of freons 318C and 227ea from the gas fire extinguishing installation showed that the test data differed by more than 30% from the calculated values obtained by the method that does not take into account the solubility of nitrogen in freon.
The influence of the solubility of the propellant gas is taken into account in the methods of hydraulic calculation of the gas fire extinguishing installation, in which chladon 13B1 is used as a gas extinguishing agent. These techniques are not generalized. Designed for hydraulic calculation of a gas fire extinguishing installation only with freon 13B1 at two values of the pressurization of MGP with nitrogen - 4.2 and 2.5 MPa and; at four values in operation and six values in operation of the module filling factor with freon.
Considering the above, the task was set and a method was developed for the hydraulic calculation of a gas fire extinguishing installation with freons 125, 318Ts and 227ea, namely: at a given total hydraulic resistance of the gas fire extinguishing module (entrance to the siphon tube, siphon tube and shut-off-starting device) and the known pipe in the layout of the gas fire extinguishing installation, find the distribution of the mass of refrigerant that has passed through the individual nozzles, and the time for the estimated mass of the refrigerant from the nozzles to flow into the protected volume after the simultaneous opening of the shut-off and starting device of all modules. When creating the method, the unsteady flow of a two-phase gas-liquid mixture "freon - nitrogen" in a system consisting of gas fire extinguishing modules, pipelines and nozzles was taken into account, which required knowledge of the parameters of the gas-liquid mixture (pressure, density and velocity fields) at any point of the pipeline system at any time ...
In this regard, the pipelines were divided into elementary cells in the direction of the axes by planes perpendicular to the axes. For each elementary volume, the equations of continuity, momentum and state were written.
In this case, the functional relationship between pressure and density in the equation of state of a gas-liquid mixture was related by a relationship using Henry's law under the assumption of homogeneity (homogeneity) of the gas-liquid mixture. The nitrogen solubility coefficient for each of the considered freons was determined experimentally.
To perform hydraulic calculations of a gas fire extinguishing installation, a Fortran calculation program was developed, which was named "ZALP".
The hydraulic calculation program allows for a given scheme of a gas fire extinguishing installation, in the general case, including:
Gas fire extinguishing modules filled with gas extinguishing agents with nitrogen pressurization up to pressure Рн;
Collector and main pipeline;
Distribution pipelines;
Outlets on bends, define:
The inertia of the installation;
Release time of the estimated mass of gaseous extinguishing agents;
Time of release of the actual mass of gaseous fire-extinguishing substances; - mass flow rate of gas extinguishing agents through each nozzle. Approbation of the method of hydraulic calculation "2AbP" was carried out by triggering three operating gas fire extinguishing installations and on an experimental stand.
It was found that the results of the calculation by the developed method agree satisfactorily (with an accuracy of up to 15%) with the experimental data.
Hydraulic calculation is performed in the following sequence.
According to NPB 88-2001, the calculated and actual weights of freon are determined. The type and number of gas fire extinguishing modules is determined from the condition of the maximum permissible filling factor of the module (freon 125 - 0.9 kg / l, freons 318Ts and 227ea - 1.1 kg / l).
The boost pressure Рн of gaseous fire extinguishing agents is set. As a rule, Рн is taken in the range from 3.0 to 4.5 MPa for modular installations and from 4.5 to 6.0 MPa for centralized installations.
A diagram of the pipe distribution of the gas fire extinguishing installation is drawn up, indicating the length of the pipes, the elevation marks of the joints of the pipe distribution and nozzles. The internal diameters of these pipes and the total area of the nozzle outlet openings are preset on the condition that this area should not exceed 80% of the area of the internal diameter of the main pipeline.
The listed parameters of the gas fire extinguishing installation are entered into the 2ABP program and the hydraulic calculation is performed. The calculation results can have several variants. Below we will consider the most typical ones.
The release time of the calculated mass of the gas extinguishing agent is Tr = 8-10 s for a modular installation and Tr = 13 -15 s for a centralized one, and the difference in flow rates between the nozzles does not exceed 20%. In this case, all parameters of the gas fire extinguishing installation are selected correctly.
If the release time of the estimated mass of the gaseous extinguishing agent is less than the values indicated above, then the inner diameter of the pipelines and the total area of the nozzle openings should be reduced.
If the standard release time of the estimated mass of the gaseous extinguishing agent is exceeded, the boost pressure of the gaseous extinguishing agent in the module should be increased. If this measure does not allow meeting the regulatory requirements, then it is necessary to increase the volume of propellant in each module, i.e. to reduce the filling factor of the gas extinguishing agent module, which entails an increase in the total number of modules in the gas fire extinguishing installation.
Performance regulatory requirements the difference in flow rates between the nozzles is achieved by reducing the total area of the nozzles outlet openings.
LITERATURE
1. NPB 88-2001. Fire extinguishing and signaling installations. Norms and rules of design.
2. SNiP 2.04.09-84. Fire automation of buildings and structures.
3. Fire Protection Equipment - Automatic Fire Extinguishing Systems using Halogenated Hydrocarbns. Part I. Halon 1301 Total Flooding Systems. ISO / TC 21 / SC 5 N 55E, 1984.
The main factors influencing the optimal choice of the gas fire extinguishing installation (GSP) are given: the type of combustible load in the protected room (archives, storage facilities, radio electronic equipment, technological equipment, etc.); the size of the protected volume and its leakage; type of gas extinguishing agent (GFFS); the type of equipment in which the GFFS should be stored, and the type of UGP: centralized or modular.
The correct choice of a gas fire extinguishing installation (GSP) depends on many factors. Therefore, the purpose of this work is to identify the main criteria affecting the optimal choice of a gas fire extinguishing installation and the principle of its hydraulic.
The main factors affecting the optimal choice of a gas fire extinguishing installation. First, the type of combustible load in the protected premises (archives, storage facilities, radio-electronic equipment, technological equipment, etc.). Secondly, the size of the protected volume and its leakproofness. Third, the type of gas extinguishing agent. Fourth, the type of equipment in which the gas extinguishing agent is to be stored.
Fifth, the type of gas fire extinguishing installation: centralized or modular. The latter factor can take place only when it is necessary to protect two or more premises in one facility. Therefore, we will consider the mutual influence of only four of the above factors, i.e. on the assumption that the facility needs fire protection for only one room.
Of course, the correct choice of a gas fire extinguishing installation should be based on optimal technical and economic indicators.
It should be especially noted that any of the permitted gaseous extinguishing agents will extinguish a fire regardless of the type of combustible material, but only when a standard extinguishing concentration is created in the protected volume.
The mutual influence of the above factors on the technical and economic parameters of the gas fire extinguishing installation will be estimated from the condition that the following gas extinguishing agents are permitted for use in Russia: freon 125, freon 318C, freon 227еа, freon 23, CO2, N2, Ar and mixture (N2 , Ar and CO2) having the trademark Inergen.
According to the storage method and methods of control of gas fire extinguishing substances in gas fire extinguishing modules (MGP), all gas fire extinguishing substances can be divided into three groups.
The first group includes freon 125, 318C and 227ea. These freons are stored in the gas fire extinguishing module in liquefied form under the pressure of a propellant gas, most often nitrogen. Modules with the listed freons, as a rule, have a working pressure not exceeding 6.4 MPa. The control of the amount of freon during the operation of the installation is carried out using a pressure gauge installed on the gas fire extinguishing module.
Freon 23 and CO2 make up the second group. They are also stored in a liquefied form, but are displaced from the gas fire extinguishing module under the pressure of their own saturated vapors. The working pressure of modules with the listed gaseous extinguishing agents must have an operating pressure of at least 14.7 MPa. During operation, the modules must be installed on weighing devices that ensure continuous monitoring of the mass of Freon 23 or CO2.
The third group includes N2, Ar and Inergen. These gaseous extinguishing agents are stored in gaseous extinguishing modules in a gaseous state. Further, when we consider the advantages and disadvantages of gas extinguishing agents from this group, we will focus only on nitrogen. This is because N2 is the most effective (lowest extinguishing concentration) and has the lowest cost. Control of the mass of the listed gaseous fire extinguishing substances is carried out using a pressure gauge. N2, Ar or Inergen are stored in modules at a pressure of 14.7 MPa or more.
Gas extinguishing modules, as a rule, have a cylinder capacity not exceeding 100 liters. At the same time, modules with a capacity of more than 100 liters, according to PB 10-115, are subject to registration with the Gosgortechnadzor of Russia, which entails a fairly large number of restrictions on their use in accordance with the specified rules.
The exception is isothermal modules for liquid carbon dioxide (MIZHU) with a capacity of 3.0 to 25.0 m3. These modules are designed and manufactured for storing carbon dioxide in gas fire extinguishing installations in quantities exceeding 2500 kg. Isothermal modules for liquid carbon dioxide are equipped with refrigeration units and heating elements, which allows maintaining the pressure in the isothermal tank in the range of 2.0 - 2.1 MPa at ambient temperatures from minus 40 to plus 50 ° C.
Let us consider with examples how each of the four factors affect the technical and economic indicators of a gas fire extinguishing installation. The mass of the gaseous extinguishing agent was calculated according to the method described in NPB 88-2001.
It is required to protect electronic equipment in a room with a volume of 60 m3. The room is conditionally sealed, i.e. K2 = 0. The calculation results are summarized in table. 1.
The economic rationale for table. 1 in concrete numbers has a certain difficulty. This is due to the fact that the cost of equipment and gas extinguishing agent is different for manufacturers and suppliers. However, there is a general trend that as the capacity of the cylinder increases, the cost of the gas extinguishing module increases. 1 kg of CO2 and 1 m3 of N2 are close in price and two orders of magnitude less than the cost of freons. Analysis of the table. 1 shows that the cost of a gas fire extinguishing installation with HFC 125 and CO2 is comparable in value.
Despite the significantly higher cost of freon 125 compared to carbon dioxide, the total price of freon 125 - a gas fire extinguishing module with a 40 l cylinder will be comparable or even slightly lower than a set of carbon dioxide - a gas fire extinguishing module with an 80 l cylinder weighing device.
It can be unambiguously stated that the cost of a gas fire extinguishing installation with nitrogen is significantly higher in comparison with the two previously considered options, since requires two modules with the maximum volume. More space will be required to accommodate two modules in the room and, naturally, the cost of two 100-liter modules will always be higher than the cost of an 80-liter module with a weighing device, which, as a rule, is 4 - 5 times cheaper than the module itself.
Table 1
The parameters of the room are similar to example 1, but it is required to protect not the electronic equipment, but the archive. The calculation results, similar to the first example, are summarized in table. 2.
Based on the analysis of the table. 2, we can unequivocally say that in this case, too, the cost of a gas fire extinguishing installation with nitrogen is much higher than the cost of gas fire extinguishing installations with chladone 125 and carbon dioxide. But in contrast to the first example, in this case it can be more clearly noted that the least cost is the installation of gas fire extinguishing with carbon dioxide, since with a relatively small difference in cost between a gas fire extinguishing module with a cylinder with a capacity of 80 and 100 liters, the price of 56 kg of Freon 125 significantly exceeds the cost of the weighing device.
Similar dependencies will be traced if the volume of the protected premises increases and / or its leakage capacity increases, because all this causes a general increase in the amount of any kind of gaseous extinguishing agent.
Thus, only on the basis of two examples it can be seen that it is possible to choose an optimal gas fire extinguishing installation for fire protection of a room only after considering at least two options with different types of gas extinguishing agents.
However, there are exceptions when a gas fire extinguishing installation with optimal technical and economic parameters cannot be used due to certain restrictions imposed on gas extinguishing agents.
table 2
Such restrictions, first of all, include the protection of especially important objects in an earthquake hazardous area (for example, nuclear power facilities, etc.), where it is required to install modules in earthquake-resistant frames. In this case, the use of freon 23 and carbon dioxide is excluded, because modules with these gaseous extinguishing agents must be installed on weighing devices, excluding their rigid attachment.
1. The estimated mass of GFFS M_g, which must be stored in the installation, is determined by the formula
M = K, (1)
where M is the mass of GFFS intended for creation in volume
premises with a fire-extinguishing concentration in the absence of artificial
air ventilation, is determined by the formulas:
for GFFS - liquefied gases, excluding carbon dioxide
M = V x ro x (1 + K) x ──────────; (2)
p p 1 2 100 - C
for GFFS - compressed gases and carbon dioxide
M = V x ro x (1 + K) x ln ──────────, (3)
p p 1 2 100 - C
where V is the estimated volume of the protected premises, m3.
The calculated volume of the room includes its internal geometric volume, including the volume of the ventilation, air conditioning, air heating(up to hermetic valves or dampers). The volume of equipment in the room is not deducted from it, with the exception of the volume of solid (impermeable) building elements (columns, beams, foundations for equipment, etc.); К_1 - coefficient taking into account leaks of gas extinguishing agent from vessels; K_2 - coefficient taking into account the loss of gaseous extinguishing agent through the openings of the room; ro_1 is the density of the gas extinguishing agent, taking into account the height of the protected object relative to sea level for the minimum temperature in the room T_m, kg x m (-3), is determined by the formula
ro = ro x ──── x K, (4)
where ro_0 is the vapor density of the gaseous extinguishing agent at a temperature T_0 = 293 K (20 ° C) and atmospheric pressure 101.3 kPa; T_m is the minimum air temperature in the protected room, K; K_3 is a correction factor that takes into account the height of the object relative to sea level, the values of which are given in Table 11 appendix 5; С_н - standard volumetric concentration,% (vol.).
The values of standard fire extinguishing concentrations C_n are given in Appendix 5.
The mass of the remainder of the GFFS in the pipelines M_tr, kg, is determined by the formula
M = V x ro, (5)
TR TR GOTV
where V is the volume of the entire pipeline distribution of the installation, m3;
ro is the density of the GFFS residue at the pressure that is available in
pipeline after the end of the expiration of the mass of gas fire extinguishing
substance M to the protected area; M x n is the product of the remainder of the GOTV in
module (M), which is accepted by TD per module, kg, per quantity
modules in installation n.
Note. For liquid combustible substances not listed in Appendix 5, the normative volumetric fire extinguishing concentration of GFFS, all components of which are in the gaseous phase under normal conditions, can be defined as the product of the minimum volumetric fire extinguishing concentration by a safety factor equal to 1.2 for all GFFS, except for carbon dioxide. For CO2, the safety factor is 1.7.
For GFFS that are in the liquid phase under normal conditions, as well as for GFFS mixtures, at least one of the components of which is in the liquid phase under normal conditions, the standard fire extinguishing concentration is determined by multiplying the volumetric fire extinguishing concentration by a safety factor of 1.2.
The methods for determining the minimum volumetric fire extinguishing concentration and fire extinguishing concentration are set out in NPB 51-96 *.
1.1. Equation coefficients (1) are defined as follows.
1.1.1. Coefficient taking into account leaks of gaseous extinguishing agent from vessels:
1.1.2. Coefficient taking into account the loss of gaseous fire extinguishing agent through the openings of the room:
K = P x delta x tau x square root (H), (6)
where P is a parameter that takes into account the location of openings along the height of the protected room, m (0.5) x s (-1).
The numerical values of the parameter P are selected as follows:
P = 0.65 - when the openings are located simultaneously in the lower (0-0.2) N and the upper zone of the room (0.8-1.0) N or simultaneously on the ceiling and on the floor of the room, and the area of the openings in the lower and upper parts are approximately equal and make up half of the total area of the openings; P = 0.1 - when the openings are located only in the upper zone (0.8-1.0) N of the protected room (or on the ceiling); P = 0.25 - when the openings are located only in the lower zone (0-0.2) N of the protected room (or on the floor); P = 0.4 - with an approximately uniform distribution of the area of the openings over the entire height of the protected room and in all other cases;
delta = ───────── - room leakage parameter, m (-1),
where the sum F_H is the total area of the openings, m2, H is the height of the room, m; tau_pod is the standard time for the supply of GFFS to the protected premises, s.
1.1.3. Extinguishing fires of subclass A_1 (except for smoldering materials specified in clause 7.1) should be carried out in rooms with a leakage parameter of no more than 0.001 m (-1).
The value of the mass M_p for extinguishing fires of subclass A_i is determined by the formula
p 4 p-hept
where M is the value of the mass M for the standard volumetric concentration C
p-hept p n
when quenching n-heptane, calculated by formulas (2) or (3) ;
K is a coefficient that takes into account the type of combustible material.
The values of the coefficient K_4 are taken equal: 1.3 - for extinguishing paper, corrugated paper, cardboard, fabrics, etc. in bales, rolls or folders; 2.25 - for premises with the same materials, to which access by firefighters after the end of the work of the AUGP is excluded, while the safety stock is calculated with a value of K_4 equal to 1.3.
The time of supplying the main stock of GFFS with a value of K_4 equal to 2.25 can be increased by a factor of 2.25. For other fires of subclass A_1, the value of K_4 is taken equal to 1.2.
Do not open the protected room, which is allowed access, or break its tightness in another way within 20 minutes after the AUGP is triggered (or before the arrival of the fire brigade).
AUGP calculation includes:
The extinguishing method is volumetric. GOTV - Freon 125HP (C2F5H).
The estimated mass of GFFS Mg, which must be stored in the installation, is determined by the formula:
Mg = K1 (Mp + Mtr + Mbn),
where Mtr is the mass of the GFFS residue in pipelines, kg, determined by the formula:
Mtr = Vtr sgotv,
here Vtr is the volume of the entire pipeline distribution of the installation, m3; sgotv is the density of the GFFS residue at the pressure that exists in the pipeline after the end of the outflow of the mass of gaseous fire extinguishing agent Mp into the protected room. Mbn is the product of the remainder of the GEF in the MB module, which is received by the TD per module, kg, by the number of modules in the installation n.
Mtr + Mbn = Bridge => Mg = K1 (Mр + Bridge),
where Bridge is the remainder of the GFFS in modules and piping, kg.
Determined by the formula:
Bridge = nmm Bridge,
where nm is the number of modules containing the estimated mass of the GFFS; mb is the mass of the OTV gas phase in the module and in the piping after the liquid phase is discharged from it, kg. We accept it based on the capacity of the accepted modules.
Table 3.1 shows the data for determining the mass of the gas phase of the OTS in the module and in the piping after the liquid phase is discharged from it.
Table 3.1 - Mass of the OTV gas phase in the module and in the piping after the OTV liquid phase is discharged, kg.
K1 - coefficient taking into account leaks of gaseous extinguishing agent from vessels, is taken equal to 1.05;
Mp is the mass of GFFS intended to create a fire extinguishing concentration in the volume of the room in the absence of artificial ventilation air, is determined by the formula:
here Vр is the estimated volume of the protected premises, Vр = 777.6 m3. The calculated volume of the room includes its internal geometric volume, including the volume of the ventilation, air conditioning, air heating system (up to hermetic valves or dampers). The volume of equipment in the room is not deducted from it, with the exception of the volume of solid (impermeable) building elements (columns, beams, foundations for equipment, etc.); K2 - coefficient taking into account the loss of gaseous fire extinguishing agent through the openings of the room; с1 is the density of the gas extinguishing agent, taking into account the height of the protected object relative to sea level for the minimum temperature in the room Tm, kg / m3, is determined by the formula:
here с0 is the vapor density of the gaseous fire extinguishing agent at a temperature of T0 = 293K (20 ° C) and an atmospheric pressure of 101.3 kPa, for Freon 125 this value is 5.074; Tm is the minimum air temperature in the protected room, K, Tm = 293K; K3 - correction factor, taking into account the height of the object relative to sea level. We accept K3 = 1; Cн - standard fire extinguishing concentration, vol. The fraction accepted for ethanol storage facilities is 0.105.
Coefficient taking into account the loss of gaseous extinguishing agent through the openings of the room:
where P is a parameter that takes into account the location of openings along the height of the protected room, m 0.5 s-1. We accept P = 0.1 (when the openings are located in the upper zone of the room); H - room height, H = 7.2 m; d - parameter of room leakage, determined by the formula:
where УFн - the total area of constantly open openings, m2; fpod is the standard time for the supply of GFFS to the protected room, s, fpod = 10 s.
Volumetric fire extinguishing AUGP is used in rooms characterized by a leakproofness parameter d not more than 0.004 m-1.
We assume that an exhaust shaft is a permanently open opening in the room under consideration. In rooms without light-aeration lanterns and aeration lanterns, where production facilities are to be located categories A, B, and B, there should be smoke, exhaust shafts made of non-combustible materials with valves with manual and automatic opening in case of fire. Square cross section these mines should be determined by calculation, and in the absence of calculated data, take at least 0.2% of the area of the room. The shafts should be evenly spaced (one shaft for every 1000 m of the room). Thus, we assume that in the room under consideration there is 1 shaft with a cross-sectional area of 0.216 m2. Then the leakage coefficient will be.
Hydraulic calculation is the most difficult stage in the creation of AUGPT. It is necessary to select the diameters of pipelines, the number of nozzles and the area of the outlet section, calculate real time exit GOTV.
First you need to decide where to get the methodology and formulas for hydraulic calculation. We open the set of rules of SP 5.13130.2009, Appendix G and see there only a method for calculating carbon dioxide fire extinguishing low pressure, and where is the methodology for other gaseous fire extinguishing agents? We look at paragraph 8.4.2 and see: "For the rest of the installations, it is recommended to make the calculation according to the methods agreed upon in the prescribed manner."
Let's turn to the manufacturers of gas fire extinguishing equipment for help. In Russia, there are two methods for hydraulic calculations. One was developed and copied many times by leading Russian equipment manufacturers and approved by VNIIPO, on its basis the software"ZALP", "Salute". The other was developed by the TAKT company and approved by the Ministry of Emergency Situations DND, on its basis the TAKT-gas software was created.
Techniques are off limits to most design engineers and are used internally by manufacturers automatic installations gas fire extinguishing. If you agree, then you will be shown it, but without special knowledge and experience to perform hydraulic calculation it will be difficult.
