Calculation of automatic gas fire extinguishing systems. Methodology for calculating gas fire extinguishing List of initial data for development

Installation Responsibility gas fire extinguishing always carried by the designer. For successful work It is necessary, first of all, to make the calculations correctly. 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 will present the formulas necessary for the calculations and reveal their content.

First, 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 with carbon dioxide.

Gas mass calculation

The first step is to select a gas fire extinguishing agent (as we already know, the choice of fire extinguishing agent is the prerogative of the designer). Since gas fire extinguishing is volumetric, the main initial data for its calculation will be the length, width and height of the room. Knowing the exact volume of the room, you can calculate the mass of gas extinguishing agent required to extinguish this volume. The mass of gas that must be stored in the installation is calculated using the formula:

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

Where M p- a mass of fire extinguishing agent intended to create a fire extinguishing concentration in the volume of the room in the absence of artificial ventilation air. Determined by the formulas:
for GOTV - liquefied gases, excluding carbon dioxide:

For GFFS - compressed gases and carbon dioxide:

Where V p — design volume of the protected space, m3.
The calculated volume of the room includes its internal geometric volume, including the volume of the ventilation, air conditioning system, air heating(up to sealed valves or dampers). The volume of equipment located in the room is not deducted from it, with the exception of the volume of solid (impenetrable) building elements (columns, beams, foundations for equipment, etc.);
K 1 — coefficient taking into account leaks of gas extinguishing agent from vessels;
K 2 — coefficient taking into account the loss of gas extinguishing agent through room openings;
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 room temperature T m, kg/m 3, is determined by the formula:

p 0 — vapor density of the gas fire extinguishing agent at temperature T0 = 293 K (20°C) and atmospheric pressure 101.3 kPa;
T 0 — minimum temperature air in the protected area,
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);
S n — standard volume concentration, % (vol.).
The values ​​of standard fire extinguishing concentrations Cn are given in Appendix D (SP 5.13130.2009);

The mass of the remaining GFFS in pipelines, M tr/kg, is determined by the formula:

Where V tp — volume of the entire installation piping, m 3 ;
r ready — density of the fire extinguishing agent residue at the pressure that exists in the pipeline after the end of the flow of the mass of gaseous fire extinguishing agent M p into the protected room;
M bp — the product of the remaining GFFS in the module M b, 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 three quantities: the mass of the fire extinguishing agent necessary to create a fire extinguishing concentration in the volume, the mass of the remaining fire fighting substances in the pipeline, and the mass of the remaining fire fighting substances in the cylinder. We multiply the resulting amount by the coefficient of flue gas leakage from cylinders (usually 1.05) and obtain the exact mass of flue gas required to protect a specific volume. Don’t forget that for gas and liquid fuels located at normal conditions in the liquid phase, as well as mixtures of fire extinguishing agents, 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.

Relieving excess pressure

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

Where R pr — maximum permissible overpressure, which is determined from the conditions of preservation and strength building structures protected premises or equipment located in it, MPa;
R a — atmospheric pressure, MPa;
r in — air density under 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 — time of GFFS supply, determined from hydraulic calculation, s;
∑F - area of ​​permanently open openings (except for the discharge opening) in the enclosing structures of the room, m2.
The values ​​of M p, K 1, p 1 are determined based on the calculation of the mass of the GFFS.
For GFFS - liquefied gases, coefficient K 3 = 1.
For GOTV - compressed gases, the coefficient K 3 is taken equal to:

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

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

    Fire extinguishing module selection

    We have sorted out the mass and area of ​​the opening for releasing excess pressure, now you need to select a gas fire extinguishing module. Depending on the module manufacturer, as well as the physical and chemical properties of the selected GFFS, the module filling coefficient 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 GFFS is used liquefied gas;
      with the same pressure of the GFSF, if compressed gas is used as the GFSF;
      with the same GFFS filling, if liquefied gas without propellant gas is used as GFFS.”

    Module location

    Once you have decided on the number and types of modules, you need to agree with the customer on their location. Oddly enough, such a seemingly simple question can cause many design problems. In most cases, the construction of server rooms, electrical switchboards and other similar rooms 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. However, when choosing a location for modules, you must be guided by a 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.) must be at least 1 m. Modules should be placed as close as possible to the protected premises. However, they should not be located in places where they may be exposed to dangerous fire (explosion) factors, mechanical, chemical or other damage, or direct exposure to sunlight.”

    Piping

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

    Hydraulic calculation

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

      calculation of the diameter of pipelines along the entire length of the pipe distribution;
      calculation of the time of exit of the GFFE from the module;
      calculation of the area of ​​nozzle outlet openings.

    For hydraulic calculations, we again turn to the manufacturer of gas fire extinguishing systems. There are hydraulic calculation methods that were developed for a specific manufacturer of modules with the filling of a specific gas fire extinguishing composition. But in Lately is becoming increasingly widespread software, which allows you not only to calculate the parameters described above, but also to draw the pipework in a graphical user-friendly interface, calculate the pressure in the pipeline and on the nozzle, and even indicate the diameter of the drill that needs to be drilled into the nozzles. Of course, the program makes all calculations based on the data you enter: 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 possible to purchase a hydraulic calculation program, undergo training and no longer depend on a specific manufacturer.

    Finish

    Well, all stages have been completed. All that remains is to issue 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

E.1 The estimated mass of GFFS, which must be stored in the installation, is determined by the formula

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

For GFFS - liquefied gases, with the exception of carbon dioxide:

For GOTV - compressed gases and carbon dioxide

here - the calculated volume of the protected room, m. The calculated volume of the room includes its internal geometric volume, including the volume of the ventilation, air conditioning, air heating system (up to sealed valves or dampers). The volume of equipment located in the room is not deducted from it, with the exception of the volume of solid (impenetrable) building elements (columns, beams, foundations for equipment, etc.);

Coefficient taking into account leaks of gas extinguishing agent from vessels;

A coefficient that takes into account the loss of gas extinguishing agent through room openings;

The density of the gas fire extinguishing agent, taking into account the height of the protected object relative to sea level for the minimum room temperature, kg/m, is determined by the formula

here is the vapor density of the gas fire extinguishing agent at a temperature of 293 K (20 °C) and an atmospheric pressure of 101.3 kPa;

Minimum air temperature in the protected room, K;

A correction factor that takes into account the height of the object relative to sea level, the values ​​of which are given in Table E.11 of Appendix E;

Standard volume concentration, % (vol.).

The values ​​of standard fire extinguishing concentrations are given in Appendix D.

The mass of GFFS residue in pipelines, kg, is determined by the formula

where is the volume of the entire piping of the installation, m;

The density of the residual fire extinguishing agent at the pressure that exists in the pipeline after the end of the flow of the mass of gaseous fire extinguishing agent into the protected room;

The product of the remaining GFFS in the module, which is accepted according to the TD per module, kg, by the number of modules in the installation.

Note - For liquid flammable substances not listed in Appendix E, the standard volumetric fire extinguishing concentration of GFFS, all components of which are in the gas phase under normal conditions, can be determined as the product of the minimum volumetric fire extinguishing concentration by a safety factor equal to 1.2 for all GFFS , with the exception of carbon dioxide. For SO, the safety factor is 1.7.

For GFFS that are in the liquid phase under normal conditions, as well as mixtures of GFFS, 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.

Methods for determining the minimum volumetric fire extinguishing concentration and fire extinguishing concentration are set out in GOST R 53280.3.

E.2 The coefficients of equation (E.1) are determined as follows.

E.2.1 Coefficient taking into account leaks of gas extinguishing agent from vessels 1.05.

E.2.2 Coefficient taking into account the loss of gas extinguishing agent through room openings:

where is a parameter that takes into account the location of openings along the height of the protected room, m s.

The numerical values ​​of the parameter are selected as follows:

0.65 - when openings are located simultaneously in the lower (0-0.2) and upper zones of the room (0.8-1.0) or simultaneously on the ceiling and floor of the room, and the areas of the openings in the lower and upper parts are approximately equal and constitute half of the total area of ​​the openings; 0.1 - when the openings are located only in the upper zone (0.8-1.0) of the protected room (or on the ceiling); 0.25 - when the openings are located only in the lower zone (0-0, 2) the protected room (or on the floor); 0.4 - with an approximately uniform distribution of the area of ​​openings over the entire height of the protected room and in all other cases;

Room leakage parameter, m,

where is the total area of ​​openings, m;

Room height, m;

Standard time for supplying GFFS to the protected premises, s.

E.3 Extinguishing fires of subclass A (except for smoldering materials specified in 8.1.1) should be carried out in rooms with a leakage parameter of no more than 0.001 m.

The mass value for extinguishing fires of subclass A is determined by the formula

where is the mass value for the standard volumetric concentration when extinguishing n-heptane, calculated using formulas (2) or (3);

A coefficient that takes into account the type of combustible material.

The coefficient values ​​are taken equal to: 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 for firefighters after the end of the AUGP operation is excluded. For other fires of subclass A, except those specified in 8.1.1, the value is assumed to be 1.2.

In this case, it is allowed to increase the standard time for supplying GFFS by a factor.

If the estimated quantity of GFFS is determined using a factor of 2.25, the GFFS reserve can be reduced and determined by calculation using a factor of 1.3.

You should not open the protected room to which access is permitted, or break its tightness in any other way within 20 minutes after the activation of the AUGP (or until the fire department arrives).

Appendix G

Hydraulic calculation is the most difficult stage in creating an AUGPT. It is necessary to select the diameters of the pipelines, the number of nozzles and the outlet cross-sectional area, and calculate real time GOTV output.

How will we count?

First you need to decide where to get the methodology and formulas for hydraulic calculations. We open the set of rules SP 5.13130.2009, Appendix G and see there only the 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 other installations, it is recommended to carry out calculations using methods agreed upon in the prescribed manner.”

Calculation programs

Let's turn to manufacturers of gas fire extinguishing equipment for help. In Russia, there are two methods for hydraulic calculations. One developed and copied many times by leading Russian manufacturers equipment and approved by VNIIPO, on its basis the software “ZALP” and “Salyut” was created. The other was developed by the TACT company and approved by the DND of the Ministry of Emergency Situations, on its basis the TACT-gaz software was created.

The techniques are closed to most design engineers and serve to internal use manufacturers automatic installations gas fire extinguishing. If you agree, they will show it to you, but without special knowledge and experience, it will be difficult to perform hydraulic calculations.

Calculation of gas fire extinguishing is carried out during the development of projects and is carried out by a specialist - design engineer. It involves determining the amount of substance required for extinguishing, the required number of modules, and hydraulic calculations. It also includes work on installation suitable diameter pipeline, determining the time required to supply gas to the room, taking into account the width of the openings and the area of ​​each individual protected room.

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

  • carbon dioxide;
  • nitrogen;
  • argon inergen;
  • sulfur hexafluoride;
  • freons (227, 23, 125 and 218).
Fire extinguishing system gas type for 6 cylinders

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

  1. Deoxidants are substances that act as a fire extinguishing concentration, creating a dense cloud around the flame. This concentration prevents the access of oxygen necessary to maintain the combustion process. As a result, the fire goes out.
  2. Inhibitors are special fire extinguishing compounds that can interact with burning substances. As a result, combustion slows down.

Calculation of the mass of gas extinguishing agent

Calculation of the standard volume concentration allows you to determine what mass of gaseous substances will be required to extinguish the fire. 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 the refrigerant required to create the gas concentration required for fire extinguishing in the volume of the room, the density of the compositions, as well as the coefficient of leakage of the concentration for fire extinguishing from containers and other data.

Design of 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;
  • the location of the openings, as well as the number and width of constantly open openings;
  • temperature and humidity indicators in the room;
  • features, number of people on site.

Scheme of operation of the gas fire extinguishing system

Other factors are also taken into account, depending on individual characteristics design, 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 includes such a moment as the choice of module. This is done taking into account the physical and chemical properties of the concentrate. The filling coefficient is determined. More often this value is in the range: 0.7-1.2 kg/l. Sometimes it is necessary to install several modules to one collector. In this case, the volume of the pipeline is important, the cylinders must be the same size, one type of filler is selected, and the pressure of the propellant gas is the same. Location is allowed in the protected premises itself, or outside it - in close proximity. The distance from the gas container to the heating system object is at least one meter.


Connected module gas system industrial fire extinguishing

After choosing the location for gas fire extinguishing installations, a hydraulic calculation should be made. During the hydraulic calculation, the following parameters are determined:

  • pipeline diameter;
  • time of departure of the train from the module;
  • area of ​​nozzle outlet openings.

You can make hydraulic calculations either independently or using special programs.

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


Personnel briefing and training on the use of funds personal protection in case of fire

Authorized supervisory authorities

Institutions exercising control:

  • Mrs. Supervision;
  • safety department;
  • fire technical commission.

Compact gas fire extinguishing module for small spaces

Tasks of regulatory authorities

Responsibilities include monitoring compliance regulatory framework, ensuring the proper level of safety and security of objects. Such authorities require:

  • bringing the working conditions of employees to established standards;
  • installation of warning systems and automatic fire extinguishing systems;
  • eliminating the use of flammable materials for repairs and finishing;
  • requirement to eliminate any fire safety violations.

Conclusion

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

Selection and calculation of a gas fire extinguishing system

The main factors influencing optimal choice gas fire extinguishing installations (GFP): type of flammable load in the protected premises (archives, storage facilities, radio-electronic equipment, technological equipment etc.); the size of the protected volume and its leakage; type of gas fire extinguishing agent (GOTV); the type of equipment in which GFFS should be stored, and the type of UGP: centralized or modular.


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


The main factors influencing the optimal choice of gas fire extinguishing installation. Firstly, the type of flammable load in the protected premises (archives, storage facilities, radio-electronic equipment, technological equipment, etc.). Secondly, the size of the protected volume and its leakage. Thirdly, the type of gas extinguishing agent. Fourth, the type of equipment in which the gas extinguishing agent should be stored.


Fifthly, the type of gas fire extinguishing installation: centralized or modular. The last factor can only occur if necessary fire protection two or more premises on one site. Therefore, we will consider the mutual influence of only the four factors listed above, i.e. on the assumption that the facility requires fire protection for only one room.


Certainly, right choice gas fire extinguishing installations should be based on optimal technical and economic indicators.


It should be especially noted that any of the gas fire extinguishing agents approved for use will extinguish a fire, regardless of the type of combustible material, but only when the standard fire extinguishing concentration is created in the protected volume.


The mutual influence of the above factors on the technical and economic parameters of a gas fire extinguishing installation will be assessed 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, N2, Ar and mixture (N2 , Ar and CO2), having trademark Inergen.


According to the method of storage and methods of control of gaseous fire extinguishing agents in gas fire extinguishing modules (GFM), all gaseous fire extinguishing agents can be divided into three groups.


The first group includes freon 125, 318C and 227ea. These refrigerants are stored in a 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 operating pressure, not exceeding 6.4 MPa. The amount of refrigerant during operation of the installation is monitored 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 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 gas 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 monitoring of the mass of freon 23 or CO2.


The third group includes N2, Ar and Inergen. These gaseous fire extinguishing agents are stored in gaseous fire extinguishing modules in a 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 mass of the listed gas fire extinguishing agents is controlled using a pressure gauge. N2, Ar 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 quite a large number of restrictions on their use in accordance with the specified rules.


The exception is isothermal modules for liquid dioxide carbon (MIZHU) with a capacity from 3.0 to 25.0 m3. These modules are designed and manufactured to store carbon dioxide in quantities exceeding 2500 kg in gas fire extinguishing installations. Isothermal modules for liquid carbon dioxide are equipped with refrigeration units and heating elements, which allows you to maintain the pressure in the isothermal tank in the range of 2.0 - 2.1 MPa at temperature environment from minus 40 to plus 50 °C.


Let's look at examples of how each of the four factors influences 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 set out 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 sealed, i.e. K2 = 0. We summarize the calculation results in table. 1.


Economic justification table. 1 in specific numbers has a certain difficulty. This is due to the fact that the cost of equipment and gas extinguishing agent from manufacturers and suppliers varies. However, there is a general tendency that as the cylinder capacity increases, the cost of the gas fire extinguishing module increases. 1 kg CO2 and 1 m3 N2 are close in price and two orders of magnitude less than the cost of refrigerants. Analysis of the table 1 shows that the cost of installing a gas fire extinguishing system with freon 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 fire extinguishing module with an 80 liter cylinder weighing device.


We can definitely state that the cost of installing a gas fire extinguishing system with nitrogen is significantly higher compared to the two previously considered options, because Two modules with maximum capacity are required. More space will be required to place two modules in the room and, naturally, the cost of two modules with a volume of 100 liters will always be higher than the cost of a module with a volume of 80 liters, which is usually 4 - 5 times cheaper than the module itself.

Table 1

Example 2

The room parameters are similar to example 1, but it is not the radio-electronic equipment that needs to be protected, but the archive. The calculation results are similar to the first example and are summarized in table. 2.


Based on the analysis of table. 2, we can clearly say that in this case, the cost of installing a gas fire extinguishing system with nitrogen is significantly higher than the cost of installing gas fire extinguishing systems with freon 125 and carbon dioxide. But unlike the first example, in this case it can be more clearly noted that the installation of gas fire extinguishing with carbon dioxide has the lowest cost, because 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 a weighing device.


Similar dependencies will be traced if the volume of the protected premises increases and/or its leakage increases, because all this causes a general increase in the amount of any type of gas extinguishing agent.


Thus, just based on two examples it is clear what to choose optimal installation gas fire extinguishing for fire protection of the premises is possible only after considering at least two options with various types 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 extinguishing agents.

table 2


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