Hydraulic calculation of gas fire extinguishing online calculator. Calculation of automatic gas fire extinguishing systems. Selection and calculation of a gas fire extinguishing system

11.03.2020

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Fire fighting

SELECTION AND CALCULATION OF THE GAS FIRE EXTINGUISHING SYSTEM

A. V. Merkulov, V. A. Merkulov

CJSC "Artsok"

The main factors influencing the optimal choice of a gas fire extinguishing installation (GFS) are given: the type of combustible load in the protected room (archives, storage facilities, radio-electronic equipment, technological equipment, etc.); the value of the protected volume and its leakage; type of gas fire extinguishing agent (GOTV); the type of equipment in which the DHW must be stored, and the type of the gas supply unit: centralized or modular.

The correct choice of gas fire extinguishing installation (UGP) depends on many factors. Therefore, the purpose of this work is to identify the main criteria that affect the optimal choice of a gas fire extinguishing installation and the principle of its hydraulic calculation.

The main factors influencing the optimal choice of gas fire extinguishing installation. Firstly, the type of combustible load in the protected room (archives, storage facilities, electronic equipment, technological equipment, etc.). Secondly, the value of the protected volume and its leakage. Thirdly, the type of gas fire-extinguishing agent. Fourth, the type of equipment in which the gas extinguishing agent must be stored. Fifth, the type of gas fire extinguishing installation: centralized or modular. The last factor can take place only if it is necessary to provide fire protection for two or more rooms at one facility. Therefore, we will consider the mutual influence of only the above four factors, i.e. assuming that only one room needs fire protection at the facility.

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 gas fire extinguishing agents permitted for use eliminates a fire regardless of the type of combustible material, but only when a standard fire extinguishing concentration is created in the protected volume.

The mutual influence of the factors listed above on the technical and economic parameters of the gas fire extinguishing installation will be estimated

It can be taken from the condition that the following gas fire extinguishing agents are allowed for use in Russia: freon 125, freon 318C, freon 227ea, freon 23, CO2, K2, Ag and a mixture (No. 2, Ag and CO2), which has the Inergen trademark.

According to the method of storage and methods of control of gas fire extinguishing agents in gas fire extinguishing modules (MGP), all gas fire extinguishing agents 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 refrigerants, as a rule, have an operating pressure not exceeding 6.4 MPa. Control of the amount of freon during the operation of the unit is carried out by the 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 forced out of the gas fire extinguishing module under the pressure of their own saturated vapors. The working pressure of modules with the listed gaseous fire-extinguishing agents must have a working pressure of at least 14.7 MPa. During operation, the modules must be installed on weighing devices that provide continuous control of the mass of freon 23 or CO2.

The third group includes K2, Ag and Inergen. These gas fire extinguishing agents are stored in the gas fire extinguishing modules in the gaseous state. Further, when we consider the advantages and disadvantages of gas fire extinguishing agents from this group, we will focus only on nitrogen.

This is due to the fact that N2 is the most effective (lowest extinguishing concentration) and has the lowest cost. The control of the mass of the listed gas fire extinguishing agents is carried out by a pressure gauge. Lg or Inergen are stored in modules at a pressure of 14.7 MPa or more.

Gas fire 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.

An 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 storage in gaseous fire extinguishing installations of carbon dioxide in quantities exceeding 2500 kg. Isothermal modules for liquid carbon dioxide are equipped with refrigeration units and heating elements, which makes it possible to maintain pressure in the isothermal tank in the range of 2.0 - 2.1 MPa at an ambient temperature of minus 40 to plus 50 °C.

Let's look at examples of how each of the four factors affects the technical and economic indicators of a gas fire extinguishing installation. The mass of the gas fire extinguishing agent was calculated according to the method described in NPB 88-2001.

Example 1. It is required to protect electronic equipment in a room with a volume of 60 m3. The room is conditionally hermetic, i.e. K2 « 0. The results of the calculation are summarized in Table. 1.

Economic justification of the table. 1 in specific numbers has a certain difficulty. This is due to the fact that the cost of equipment and gas extinguishing agent varies from manufacturers and suppliers. However, there is a general trend that with an increase in the capacity of the cylinder, the cost of the gas fire extinguishing module increases. 1 kg CO2 and 1 m3 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 l cylinder will be comparable or even somewhat lower than a set of carbon dioxide - a gas fire extinguishing module with a 80 l cylinder - a weighing device. It can be unambiguously stated that the cost of a gas fire extinguishing installation with nitrogen is significantly higher compared to the two previously considered options, because two modules with a maximum capacity are required. Need more space to accommodate

TABLE 1

Freon 125 36 kg 40 1

CO2 51 kg 80 1

two modules in a room and, of course, the cost of two modules with a volume of 100 l will always be higher than the cost of an 80 l module with a weighing device, which, as a rule, is 4–5 times cheaper than the module itself.

Example 2. The parameters of the room are similar to example 1, but it is required to protect not the electronic equipment, but the archive. The results of the calculation, similarly to the first example, are summarized in Table. 2.

Based on the analysis of Table. 2, we can unequivocally say that in this case, the cost of a gas fire extinguishing installation with nitrogen is much higher than the cost of gas fire extinguishing installations with freon 125 and carbon dioxide. But unlike the first example, in this case it can be more clearly noted that the gaseous fire extinguishing installation with carbon dioxide has the lowest cost, because. with a relatively small difference in cost between the 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 a weighing device.

Similar dependencies will be traced if the volume of the protected room increases and/or its non-hermeticity increases, since all this causes a general increase in the amount of any kind of gas fire 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 a room only after considering at least two options with different types of gas fire 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 fire extinguishing agents.

TABLE 2

Name of GOTV Quantity of GOTV Tank capacity MGP, l Quantity of MGP, pcs.

Freon 125 56 kg 80 1

CO2 66 kg 100 1

These restrictions primarily include the protection of critical facilities in a seismically hazardous area (for example, nuclear power facilities, etc.), where the installation of modules in seismic-resistant frames is required. In this case, the use of freon 23 and carbon dioxide is excluded, since modules with these gaseous fire extinguishing agents must be installed on weighing devices that exclude their rigid fastening.

The fire protection of premises with permanently present personnel (air traffic control rooms, halls with control panels of nuclear power plants, etc.) is subject to restrictions on the toxicity of gaseous fire extinguishing agents. In this case, the use of carbon dioxide is excluded, because. 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 filled into an isothermal module for liquid carbon dioxide, in comparison with all other gas fire extinguishing agents.

After the feasibility study, the amount of gas fire extinguishing agents required to extinguish the fire and the preliminary number of gas fire extinguishing modules become known.

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 (ceiling, false ceiling) should not exceed 0.5 m when using all gas fire extinguishing agents, with the exception of K2.

Piping, as a rule, should be symmetrical, i.e. nozzles must be equally removed from the main pipeline. In this case, the flow rate of gas fire 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, one should also take into account the correct connection of the outlet pipelines (rows, bends) from the main one.

A cruciform connection is possible only if the flow rates of gas fire extinguishing agents 01 and 02 are equal in value (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 fire extinguishing agents at a distance b 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 when designing the piping of a gas fire extinguishing installation when using gas fire extinguishing agents belonging to the second and third groups. And for the piping of a gas fire extinguishing installation with gas fire extinguishing agents of the first group, there are a number of restrictions. This is caused by the following.

When freon 125, 318Ts or 227ea is pressurized in the gas fire extinguishing module with nitrogen to the required pressure, nitrogen is partially dissolved in the listed freons, and the amount of dissolved nitrogen in freons is proportional to the boost pressure.

b>10D ^ N

After the opening of the locking and starting device of the gas fire extinguishing module under the pressure of the propellant gas, the freon with partially dissolved nitrogen enters the nozzles through the piping and exits through them into 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 freon displacement and the hydraulic resistance of the piping. There is a partial release of nitrogen from the liquid phase of the freon and a two-phase medium is formed "a mixture of the liquid phase of the freon - gaseous nitrogen". Therefore, a number of restrictions are imposed on the piping of a gas fire extinguishing installation using the first group of gas fire extinguishing agents. The main purpose of these restrictions is to prevent stratification of the two-phase medium inside the piping.

During the design and installation, all pipe connections of the gas fire extinguishing installation must be made as shown in fig. 5, and it is forbidden to perform them in the form shown in fig. 6. The arrows in the figures show the direction of the flow of gaseous fire extinguishing agents through the pipes.

In the process of designing a gas fire extinguishing installation in an axonometric view, a piping layout, pipe length, number of nozzles and their elevations are determined. To determine the inner diameter of the pipes and the total area of the outlets of each nozzle, it is necessary to perform a hydraulic calculation of the gas fire extinguishing installation.

The method for performing a hydraulic calculation of a gas fire extinguishing installation with carbon dioxide is given in the work. The calculation of a gas fire extinguishing installation with inert gases is not a problem, because in this case, the flow is inert

ny gases occurs in the form of a single-phase gaseous medium.

The hydraulic calculation of a gas fire extinguishing installation using freons 125, 318C and 227ea as a gas fire-extinguishing agent is a complex process. The application of the hydraulic calculation method developed for freon 114B2 is unacceptable due to the fact that in this method the flow of freon through pipes is considered as a homogeneous liquid.

As noted above, the flow of freons 125, 318C and 227ea through pipes occurs in the form of a two-phase medium (gas - liquid), and with a decrease in pressure in the system, the density of the gas-liquid medium decreases. Therefore, in order to maintain a constant mass flow rate of gas fire extinguishing agents, it is necessary to increase the velocity of the gas-liquid medium or the inner diameter of pipelines.

Comparison of the results of full-scale 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 a 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 freon 13B1 is used as a gas fire extinguishing agent. These methods are not general. Designed for hydraulic calculation of a gas fire extinguishing installation only with freon 13V1 at two values of the MGP boost pressure with nitrogen - 4.2 and 2.5 MPa and; at four values in operation and six values in operation of the fill factor of the modules with refrigerant.

Given the above, the task was set and a method was developed for hydraulic calculation of a gas fire extinguishing installation with freons 125, 318C and 227ea, namely: for a given total hydraulic resistance of the gas fire extinguishing module (the entrance to the siphon tube, the siphon tube and the shut-off and starting device) and the known pipe in the wiring of the gas fire extinguishing installation, find the distribution of the mass of refrigerant that has passed through individual nozzles, and the time of expiration of the calculated mass of freon from the nozzles into the protected volume after the simultaneous opening of the shut-off device of all modules. When creating the methodology, the non-stationary 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 dependence between pressure and density in the equation of state of the gas-liquid mixture was associated with the relation using Henry's law under the assumption of uniformity (homogeneity) of the gas-liquid mixture. The nitrogen solubility coefficient for each of the considered freons was determined experimentally.

To perform hydraulic calculations of the gas fire extinguishing installation, a calculation program was developed in the Fortran language, 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 fire extinguishing agents with nitrogen pressurization up to pressure Рн;

Collector and main pipeline;

Distribution devices;

Distribution pipelines;

Nozzles on outlets, to be determined:

Installation inertia;

Time of release of the estimated mass of gaseous fire-extinguishing agents;

Release time of the actual mass of gaseous fire-extinguishing agents; - mass flow rate of gas fire extinguishing agents through each nozzle. Approbation of the hydraulic calculation method "2ALP" was carried out by the operation of three operating gas fire extinguishing installations and on an experimental stand.

It was found that the results of the calculation according to the developed method satisfactorily (with an accuracy of 15%) coincide with the experimental data.

Hydraulic calculation is performed in the following sequence.

According to NPB 88-2001, the calculated and actual masses of freon are determined. From the condition of the maximum allowable filling factor of the module (freon 125 - 0.9 kg / l, freons 318C and 227ea - 1.1 kg / l), the type and number of gas fire extinguishing modules is determined.

The boost pressure Рн of gaseous fire extinguishing agents is set. As a rule, pH is taken in the range from 3.0 to 4.5 MPa for modular and from 4.5 to 6.0 MPa for centralized installations.

A diagram of the piping of the gas fire extinguishing installation is drawn up, indicating the length of the pipes, elevation marks of the junctions of the piping and nozzles. The internal diameters of these pipes and the total area of nozzle outlets are preliminarily set from 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 "2ALP" program and a hydraulic calculation is performed. The results of the calculation can have several options. Below we consider the most typical.

The release time of the estimated 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 costs between 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 calculated mass of the gaseous fire extinguishing agent is less than the values indicated above, then the inner diameter of the pipelines and the total area of the openings of the nozzles should be reduced.

If the standard time for the release of the calculated mass of the gas fire extinguishing agent is exceeded, the boost pressure of the gas fire 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 fill factor of the gas extinguishing agent module, which entails an increase in the total number of modules in the gas fire extinguishing installation.

Compliance with the regulatory requirements for the difference in flow rates between nozzles is achieved by reducing the total area of nozzle outlets.

LITERATURE

1. NPB 88-2001. Fire extinguishing and signaling installations. Design norms and rules.

2. SNiP 2.04.09-84. Fire automatics 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 calculation of gas fire extinguishing is carried out during the development of projects and is carried out by a specialist - a design engineer. It provides for determining the amount of substance required for extinguishing, the required number of modules, and hydraulic calculation. It also includes work on setting a suitable pipeline diameter, determining the time it will take to supply gas to the room, taking into account the width of the openings and the area of \u200b\u200beach protected room.

Calculating the mass of a gas fire extinguishing agent allows you to calculate the required amount of freon used for. The following fire extinguishers are used to extinguish fire:

carbon dioxide;
nitrogen;
argon inergen;
sulfur hexafluoride;
freons (227, 23, 125 and 218).

Gas type fire extinguishing system for 6 cylinders

Depending on the principle of action, fire extinguishing compositions are divided into groups:

Deoxidants are substances that act like a fire extinguishing concentration that creates a dense cloud around the flame. This concentration prevents the access of oxygen necessary to maintain the combustion process. As a result, the fire is extinguished.
Inhibitors are special fire-extinguishing compositions that are capable of interacting with burning substances. As a result, combustion slows down.

Calculation of the mass of gas fire extinguishing agent

The calculation of the standard volume concentration allows you to determine what mass of a gaseous substance is required to extinguish a fire. The calculation of gas fire extinguishing is carried out taking into account the main parameters of the protected premises: length, width, height. You can find out the required mass of the composition using special formulas, which take into account the mass of freon necessary to create the gas concentration necessary for fire extinguishing in the volume of the room, the density of the compositions, as well as the concentration leakage coefficient for fire extinguishing from containers and other data.

Designing a gas fire extinguishing system

The design of a gas fire extinguishing system is carried out taking into account the following factors:

number of rooms in the room, their volume, installed structures in the form of suspended ceilings;
location of openings, as well as the number and width of permanently open openings;
temperature and humidity in the room;
features , the number of people at the facility.

Scheme of operation of the gas fire extinguishing system

Other factors are also taken into account, depending on the individual design features, target affiliation, staff work schedule, if we are talking about an enterprise.

Selection and location of gas fire extinguishing modules

The calculation of gas fire extinguishing also provides for such a moment as the choice of a module. This is done taking into account the physical and chemical properties of the concentrate. The charging factor is determined. More often this value is from the range: 0.7-1.2 kg / l. Sometimes it is required to install several modules to one collector. In this case, the volume of the pipeline is important, the cylinders must match in size, one type of filler is selected, the same pressure of the propellant gas. The location is allowed in the protected room itself, or outside it - in the immediate vicinity. The distance from the gas tank to the heating system object is at least one meter.

Connected module of gas fire extinguishing system in production
After choosing the location of gas fire extinguishing installations, a hydraulic calculation should be made. During the hydraulic calculation, the following parameters are determined:

pipeline diameter;

train exit time from the module;

nozzle outlet area.

You can make a hydraulic calculation both independently and using special programs.

When the results of the calculation are received and the installation is completed, it is necessary to instruct the personnel in accordance with. Special attention is paid to the regulatory framework, the preparation and placement of an evacuation plan, familiarization with the instructions.

Staff briefing and training on the use of personal protective equipment in case of fire
Authorized supervisory authorities

Instances exercising control:

state fire supervision;

safety department;

fire-technical commission.

Compact gas extinguishing module for small spaces
Tasks of the controlling authorities

Responsibilities include monitoring compliance with the regulatory framework, ensuring the proper level of security, security of facilities. These institutions require:

bringing the working conditions of employees to the established standards;

installation of warning systems and automatic fire extinguishing systems;

exclusion of the use of flammable materials for repairs and decoration;

the requirement to eliminate any violations of fire safety.

Conclusion

Upon completion of the process, the company draws up project documentation in accordance with existing norms and requirements. The results of the work are provided to the customer for review.

The designer is always responsible for the installation of gaseous fire extinguishing. For successful work, it is necessary, first of all, to correctly make calculations. Hydraulic calculations are provided by manufacturers free of charge, upon request. As for other operations, the designer performs them independently. For more successful work, we present the formulas necessary for the calculations and reveal their content.

To begin with, let's look at the areas of application of gas fire extinguishing.
First of all, gas fire extinguishing is fire extinguishing by volume, that is, we can extinguish a closed volume. Local fire extinguishing is also possible, but only on carbon dioxide.

Gas Mass Calculation

First of all, you need to choose a gas fire extinguishing agent (as we already know, the choice of GOTV is the prerogative of the designer). Since gas fire extinguishing is volumetric, then, accordingly, the main initial data for its calculation will be the length, width and height of the room. Knowing the exact volume of the room, it is possible to calculate the mass of the gas fire extinguishing agent required to extinguish this volume. Calculation of the mass of gas to be stored in the installation is made according to the formula:

M g \u003d K 1 [ M p + M tr + M 6 n ] ,

where M p- the mass of GFEA, designed to create a fire-extinguishing concentration in the volume of the room in the absence of artificial air ventilation. It is determined by the formulas:
for GFFS - liquefied gases, except for carbon dioxide:

For GOTV - compressed gases and carbon dioxide:

where Vp - the estimated volume of the protected premises, m 3.
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 located 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.);
K 1 - coefficient taking into account the leakage of gaseous fire extinguishing agent from vessels;
K 2 - coefficient taking into account the loss of gas fire extinguishing agent through the openings of the room;
p t - the density of the gas fire 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 / m 3, is determined by the formula:

p 0 - vapor density of the gaseous extinguishing agent at a temperature of T 0 = 293 K (20°C) and atmospheric pressure of 101.3 kPa;
T 0 - minimum air temperature in the protected room,
TO; K 3 - correction factor, taking into account the height of the object relative to sea level, the values of which are given in Appendix D (SP 5.13130.2009);
C n — normative volume concentration, % (vol.).
The values of standard fire-extinguishing concentrations C n are given in Appendix D (SP 5.13130.2009);

The mass of the GOTV residue in pipelines M tr / kg is determined by the formula:

where V tp - the volume of the entire pipeline distribution of the installation, m 3;
r gotv - the density of the GFFS residue at the pressure that exists in the pipeline after the end of the outflow of the mass of the gas fire extinguishing agent M p into the protected room;
M bp - the product of the remainder of the DHW in the M b module, which is accepted according to the TD per module, kg, by the number of modules in the installation n.

Result

At first glance, it may seem that there are too many formulas, links, etc., but in reality everything is not so complicated. It is necessary to calculate and add up three quantities: the mass of AGW required to create a fire-extinguishing concentration in the volume, the mass of AGV residues in the pipeline and the mass of AGFU residues in the cylinder. We multiply the resulting amount by the coefficient of DHW leakage from cylinders (usually 1.05) and get the exact weight of DHW required to protect a specific volume. Do not forget that for fumes that are in the liquid phase under normal conditions, as well as fumes 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.

Relief of excess pressure

Another very important point is the calculation of the area of the opening to relieve excess pressure. Opening area F c, m 2, is determined by the formula:

where R pr - the maximum allowable overpressure, which is determined from the condition of preservation and strength of the building structures of the protected premises or the equipment located in it, MPa;
R a — atmospheric pressure, MPa;
r in - air density in the operating conditions of the protected premises, kg / m 3;
K 2 — safety factor taken equal to 1.2;
K 3 - coefficient taking into account the change in pressure when it is supplied;
τ under is the GFFS supply time, determined from the hydraulic calculation, s;
∑F - the area of permanently open openings (except for the discharge opening) in the enclosing structures of the room, m 2.
The values of M p, K 1 , p 1 are determined based on the calculation of the mass of GOTV.
For GOTV - liquefied gases, the coefficient K 3 \u003d 1.
For GOTV - compressed gases, the coefficient K 3 is taken equal to:

If the value of the right side of the inequality is less than or equal to zero, then the opening (device) for relieving excess pressure is not required.
To calculate the area of openings, we need to obtain data from the customer on the area of permanently open openings in the protected area. Of course, these can be small holes in cable channels, ventilation, etc. But it should be understood that these openings can be sealed in the future, and therefore, for reliable operation of the installation (if there are no visible open openings), it is better to take the value of the indicator? F = 0. A gas fire extinguishing installation without excess pressure relief valves can only damage effective extinguishing, and in some cases, lead to human casualties, for example, when opening the door of a room.

Choice of fire extinguishing module

We figured out the mass and area of the opening for relieving excess pressure, now you need to select a gas fire extinguishing module. Depending on the manufacturer of the module, as well as the physical and chemical properties of the selected fumes, the filling factor of the module is determined. In most cases, its values are in the range from 0.7 to 1.2 kg/l. If you get several modules (a battery of modules), then do not forget about clause 8.8.5 of SP 5.13130: “When connecting two or more modules to a manifold (pipeline), modules of the same standard size should be used:

Location of modules

After having decided on the number and types of modules, it is necessary to agree with the customer on their location. Oddly enough, such an easy question at first glance can cause many design problems. In most cases, the construction of server rooms, switchboards and other similar premises is carried out in a short time, so some changes in the architecture of the building are possible, which negatively affects the design, especially at the location of the gas fire extinguishing modules. Nevertheless, when choosing the location of the modules, it is necessary to be guided by the set of rules (SP 5.13130.2009): “Modules can be located both in the protected room itself and outside it, in close proximity to it. The distance from the vessels to heat sources (heating devices, etc.) should be at least 1 m. The modules should be placed as close as possible to the protected premises. At the same time, they should not be located in places where they can be exposed to dangerous effects of fire factors (explosion), mechanical, chemical or other damage, direct exposure to sunlight.

Pipe wiring

After determining the location of the gas fire extinguishing modules, it is necessary to draw the piping. It should be as symmetrical as possible: each nozzle must be equidistant from the main pipeline. The nozzles should be arranged according to their radius of action.
Each manufacturer has certain restrictions on the arrangement of nozzles: the minimum distance from the wall, installation height, nozzle sizes, etc., which must also be taken into account when designing.

Hydraulic calculation

Only after calculating the mass of the gas fire extinguishing agent, choosing the location of the modules, drawing a sketch of the piping and arranging nozzles, we can proceed to the hydraulic calculation of the gas fire extinguishing installation. The loud name "hydraulic calculation" hides the definition of the following parameters:

For hydraulic calculation, we again turn to the manufacturer of gas fire extinguishing installations. There are hydraulic calculation methods that have been developed for a specific manufacturer of modules with the filling of a specific gas fire extinguishing composition. But recently, software has become more widespread, which allows not only to calculate the above parameters, but also to draw pipe wiring in a user-friendly graphical interface, calculate the pressure in the pipeline and at the nozzle, and even indicate the diameter of the drill that needs to drill holes in the nozzles. Of course, the program makes all calculations based on the data you entered: from the geometric dimensions of the room to the height of the object above sea level. Most manufacturers provide hydraulic calculations free of charge, upon request. It is also possible to purchase a hydraulic calculation program, undergo training and no longer depend on a particular manufacturer.

Finish

Well, all the steps have been completed. It remains only to draw up project documentation in accordance with the requirements of the current regulatory documents and coordinate the project with the customer.

P.P. Kurbatov, head of the design department of Pozhtekhnika LLC
Magazine "Security Systems", No. 4-2010

AUGP calculation includes:

* determination of the estimated mass of GOTV required to extinguish a fire;
* determination of the duration of the supply of GOTV;
* determination of the diameter of pipelines AUGP, type and number of nozzles;
* determination of the maximum overpressure when applying GOTV;
* determination of the required stock of GOTV and modules.

Extinguishing method - voluminous. GOTV - Freon 125HP (C2F5H).

Determination of the estimated mass of GFEA required to extinguish a fire

The calculated mass of GFFS Mg, which must be stored in the plant, is determined by the formula:

Mg = K1(Mr + Mtr + Mbn),

where Mtr is the mass of the GFEA residue in pipelines, kg, is determined by the formula:

Mtr \u003d Vtr ready,

here Vtr is the volume of the entire piping distribution of the installation, m3; sgotv is the density of the GFFS residue at the pressure that is present in the pipeline after the end of the outflow of the mass of the gas fire extinguishing agent Mp into the protected room. Mbn -- the product of the remaining GOTV in the Mb module, which is received according to the TD per module, kg, by the number of modules in the installation n.

Mtr + Mbn \u003d Bridge \u003d Mg \u003d K1 (Mr + Bridge),

where Bridge is the remainder of GOTV in modules and piping, kg.

Determined by the formula:

Bridge=nmmbridge,

where nm is the number of modules containing the calculated mass of GFEA; mres is the mass of the gas phase of the fire extinguishing agent in the module and in the piping after the liquid phase is released from it, kg. We accept based on the capacity of the received modules.

Table 3.1 presents data for determining the mass of the gas phase of the OTV in the module and in the piping after the release of the liquid phase from it.

Table 3.1 - Mass of the gas phase of the OTV in the module and in the piping after the release of the liquid phase of the OTV, kg.

K1 - the coefficient taking into account the leakage of gaseous fire extinguishing agent from the vessels, is assumed to be 1.05;

Mp - the mass of GFEA, intended to create a fire-extinguishing concentration in the volume of the room in the absence of artificial air ventilation, is determined by the formula:

here Vp is the estimated volume of the protected premises, Vp = 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 located 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 gas fire extinguishing agent through the openings of the room; c1 - density of the gaseous fire 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 c0 is the vapor density of the gas fire-extinguishing agent at a temperature T0 = 293K (20°C) and an atmospheric pressure of 101.3 kPa, for Freon 125 this value is 5.074; Tm - the minimum air temperature in the protected room, K, Tm = 293K .; K3 is a correction factor that takes into account the height of the object relative to sea level. Accept K3=1; Cn -- normative fire extinguishing concentration, vol. The share accepted for ethanol storage rooms is 0.105.

Coefficient taking into account the loss of gas 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 premises, m0.5 s-1. We accept P = 0.1 (with the location of openings in the upper zone of the room); H is the height of the room, H=7.2 m; d - the parameter of leakage of the room, is determined by the formula:

where UFn is the total area of permanently open openings, m2; fpod -- normative time of GOTV supply to the protected premises, s, fpod = 10 s.

Volumetric fire extinguishing AUGP is used in rooms characterized by a non-tightness parameter d not more than 0.004 m-1.

We accept that in the considered room the permanently open opening is the exhaust shaft. In rooms without light and aeration lamps and aeration lamps, which provide for the placement of production facilities of categories A, B, and C, there must be smoke, exhaust shafts made of fireproof materials with valves with manual and automatic opening in case of fire. The cross-sectional area of these shafts should be determined by calculation, and in the absence of calculated data, take at least 0.2% of the area of \u200b\u200bthe room. Shafts should be placed evenly (one shaft for every 1000 m of space). Thus, we assume that in the considered room there is 1 shaft with a cross-sectional area of 0.216 m2. Then the leakage coefficient will be

Head of the design department of the company LLC "Pozhtekhnika"

To begin with, let's look at the areas of application of gas fire extinguishing.

First of all, gas fire extinguishing is fire extinguishing by volume, that is, we can extinguish a closed volume. Local fire extinguishing is also possible, but only on carbon dioxide.

Gas Mass Calculation

First of all, you need to choose a gas fire-extinguishing agent (as we already know, the choice of GOTV is the prerogative of the designer). This topic was the subject of our column in No. 2 of the journal for 2010, so we will not dwell on this stage of work.

Since gas fire extinguishing is volumetric, then, accordingly, the main initial data for its calculation will be the length, width and height of the room. Knowing the exact volume of the room, it is possible to calculate the mass of the gas fire extinguishing agent required to extinguish this volume. Calculation of the mass of gas to be stored in the installation is made according to the formula:

where Mρ is the mass of GFEA, intended to create a fire extinguishing concentration in the volume of the room in the absence of artificial air ventilation. It is determined by the formulas:

For GFFS - liquefied gases, except for carbon dioxide:

For GOTV - compressed gases and carbon dioxide:

where Vr is the estimated volume of the protected premises, m 3. 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 located 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.);

K 1 - coefficient taking into account leakage of gas fire extinguishing agent from vessels;
K 2 - coefficient taking into account the loss of gas fire extinguishing agent through the openings of the room;
ρ 1 - the density of the gas fire extinguishing agent, taking into account the height of the protected object relative to sea level for the minimum temperature in the room Tm, kg / m 3, is determined by the formula:

R o is the vapor density of the gaseous extinguishing agent at a temperature of To = 293 K (20 °C) and an atmospheric pressure of 101.3 kPa;
To - minimum air temperature in the protected room, K;
K 3 - correction factor that takes into account the height of the object relative to sea level, the values of which are given in Appendix D (SP 5.13130.2009);
Сн - normative volume concentration, % (vol.)

The values of standard fire extinguishing concentrations Cn are given in Appendix D (SP 5.13130.2009); The mass of the GFEA residue in pipelines Mtr, kg, is determined by the formula:

where Vtr is the volume of the entire pipeline distribution of the installation, m 3;
p GOTV - the density of the GOTV residue at the pressure that is present in the pipeline after the mass of the gas fire extinguishing agent Mp has flowed into the protected room;
Mbn is the product of the DHW residue in the Mb module, which is received according to the TD per module, kg, by the number of modules in the unit n.

Result

At first glance, it may seem that there are too many formulas, links, etc., but in reality everything is not so complicated. It is necessary to calculate and add up three quantities: the mass of AGW required to create a fire-extinguishing concentration in the volume, the mass of AGV residues in the pipeline and the mass of AGFU residues in the cylinder. We multiply the resulting amount by the coefficient of DHW leakage from cylinders (usually 1.05) and get the exact DHW mass required to protect a specific volume components of which, under normal conditions, is in the liquid phase, the standard fire extinguishing concentration is determined by multiplying the volumetric fire extinguishing concentration by a safety factor of 1.2

Relief of excess pressure

Another very important point is the calculation of the area of the opening to relieve excess pressure. The opening area Fc, m2, is determined by the formula:

where Ppr is the maximum allowable excess pressure, which is determined from the condition of preservation and strength of the building structures of the protected premises or the equipment located in it, MPa; Pa - atmospheric pressure, MPa;
R c - air density in the operating conditions of the protected premises, kg/m3;
K 2 - safety factor, taken equal to 1.2;
K 3 - coefficient taking into account the change in pressure when it is supplied;
τ under - GOTV supply time, determined from the hydraulic calculation, s;
∑ F is the area of permanently open openings (except for the discharge opening) in the enclosing structures of the room, m 2 The values of Mp, K 1, R 1 are determined based on the calculation of the mass of GFFS For GFFS - liquefied gases, the coefficient K 3 = 1. For GFFS - compressed gases, the coefficient K 3 is taken equal

for nitrogen - 2.4;
for argon - 2.66;
for the composition "Inergen" - 2.44

If the value of the right side of the inequality is less than or equal to zero, then the opening (device) for relieving excess pressure is not required.

To calculate the area of openings, we need to obtain data from the customer on the area of permanently open openings in the protected area. Of course, these can be small holes in cable channels, ventilation, etc. But it should be understood that these openings can be sealed in the future, and therefore, for reliable operation of the installation (if there are no visible open openings), it is better to take the value of the indicator ∑F = 0. A gas fire extinguishing installation without excess pressure relief valves can only damage effective extinguishing, and in some cases - lead to human casualties, for example, when opening the door of a room.

Choice of fire extinguishing module

We figured out the mass and area of the opening for relieving excess pressure, now you need to select a gas fire extinguishing module. Depending on the manufacturer of the module, as well as the physical and chemical properties of the selected fumes, the filling factor of the module is determined. In most cases, its values are in the range from 0.7 to 1.2 kg/l. If you get several modules (a battery of modules), then do not forget about clause 8.8.5 of SP 5.13130: "When connecting two or more modules to a manifold (pipeline), modules of the same standard size should be used:

with the same GFFS filling and propellant gas pressure, if liquefied gas is used as GFFS;
with the same DHW pressure, if compressed gas is used as DHW;
with the same GFFS filling, if liquefied gas without propellant is used as GFFS.

Location of modules

After having decided on the number and types of modules, it is necessary to agree with the customer on their location. Oddly enough, such an easy question at first glance can cause many design problems. In most cases, the construction of server rooms, switchboards and other similar premises is carried out in a short time, so some changes in the architecture of the building are possible, which negatively affects the design, especially at the location of the gas fire extinguishing modules. Nevertheless, when choosing the location of the modules, it is necessary to be guided by the set of rules (SP 5.13130.2009): "Modules can be located both in the protected room itself and outside it, in its immediate vicinity. The distance from the vessels to heat sources (heating devices etc.) should be at least 1 m. The modules should be placed as close as possible to the protected premises, and they should not be located in places where they can be exposed to hazardous effects of fire (explosion), mechanical, chemical or other damage, direct exposure to sunlight.

Pipe wiring

Each manufacturer has certain restrictions on the arrangement of nozzles: the minimum distance from the wall, installation height, nozzle sizes, etc., which must also be taken into account when designing.

Hydraulic calculation

calculation of the diameter of pipelines along the entire length of the piping;
calculation of the time for the GOTV exit from the module;
calculation of the area of nozzle outlets.

Of course, the program makes all calculations based on the data you entered: from the geometric dimensions of the room to the height of the object above sea level. Most manufacturers provide hydraulic calculations free of charge, upon request. It is also possible to purchase a hydraulic calculation program, undergo training and no longer depend on a particular manufacturer.