Introduction. The main directions of fire safety activities, as it is known, are prevention and extinguishing of fires. This provision is enshrined in the law “Fire Safety”, as well as in other regulatory legal acts and regulatory documents of the Ministry of Emergency Situations of Russia, regulating the activities of supervisory bodies and firefighting services. To improve the effectiveness of fire and rescue units, it is necessary to determine the indicators (quantitative and qualitative) of the complexity of fires and the necessary composition of forces and means for combat operations.

The aim. The genesis and practice-oriented justification of the concepts of “large fire”, “complex (protracted) fire”.

Objectives. Analysis of the genesis of the concepts of complexity of firefighting organization from the point of view of firefighting tactics; determination of indicators (quantitative and qualitative) of fire complexity and the ne­cessary composition of forces and means for combat operations; practice-oriented justification of the concepts of “large fire”, “complex (protracted) fire”.

Analytical part. The analysis of open statistical data on fires in Russia (for 1998–2021 years) with the duration of fire suppression in buildings up to seven hours inclusive, taking into account the changes reflected in the order of state statistical accounting of fires and consequences of them in the Russian Federation made it possible to determine the indicators of complexity of fires and the necessary composition of forces and means for their suppression. On the basis of the data analysis we identified the indicators of fire complexity and the ne­cessary composition of forces and means for combat operations, taking into account: material damage from the fire; safety of fire extinguishing participants and danger of people; number (rank) of the fire; fire area; time of occupancy of GRS units at the fire and their number; weather and climatic conditions of work at the fire; objects of combat operations; presence of radioactive, highly toxic chemical and explosive substances, etc.

Results and their discussion. On the basis of the analysis of the classification of ways to stop burning, general classification of fires given in educational and methodical special literature, statistical data, descriptions of large and characteristic fires that occurred in the country and abroad, the justification of the concepts are offered: a way and technique of fighting at the scene of fire, large fire, complex (protracted) fire.

Conclusions. In order to successfully solve the current problems and implement the concept of improving fire safety of the country, it is proposed to add and/or change the wording of the concepts and definitions of large fire, complex (protracted) fire in the texts of regulations and other documents on fire safety. Indicators characterizing an ordinary, large, complex (protracted), long duration, tactically complex fire are proposed and definitions of the method and technique of combat operations at the fire scene are given. It is suggested to apply the Parzen-Rosenblatt method (nuclear estimation of distribution density) to estimate the density of random variables characterizing the parameters of combat operations by fire-rescue units in fire extinguishing.

Introduction. To prepare a high-quality gas-air mixture, fans are often used, which not only agitate the mixture, but also create flows with significant pulsation components. This leads to significant errors and poor repeatability of experiments.

Aim. The main purpose of this study was to determine the time required for high-quality mixing of combustible gas and air in the experimental chamber. The spatial uniformity of the gas concentration of the combustible mixture is crucial for the results of the experiments.

Research methods. The paper presents the results of calculations for programmes, the reliability of calculations of which is verified by the results of test calculations of problems with analytical solutions. The well-known diffusion equations were used as the initial equations describing the distribution of gas concentration over the space of the experimental chamber. The calculations used the coefficient of turbulent diffusion, the numerical value of which corresponds to the minimum value for enclosed spaces: D = 0.005 m2/s. The calculations were carried out according to an explicit difference scheme in the MatLab package.

Calculation results. The paper presents the results of calculations of the spatial distribution of the gas concentration in the experimental chamber for various time points. The minimum time required for the formation of a high-quality gas-air mixture in the chamber was obtained. The instantaneous photographs of the deflagration explosion shown in the paper show that a homogeneous mixture of good quality has been formed due to natural diffusion. The time intervals that were used to mix the combustible gas and air in the test chamber corresponded to the calculated values of the time required for high-quality preparation of the combustible mixture.

Conclusions. This paper shows that fans should not be used to prepare a high-quality gas-air mixture and that natural turbulent gas diffusion copes well with this problem. The minimum time intervals necessary for the formation of a high-quality gas-air mixture in a cubic chamber of arbitrary size were calculated.

Introduction. In connection with the solution of problems in the field of hydrogen safety as priority methods of large-tonnage hydrogen transportation is considered the transportation of hydrogen carriers in the form of ammonia or liquid organic carriers by pipelines, various types of transport in liquefied or compressed state. Metal hydrides, nanostructures and other hydrogen-rich compounds can also serve as carriers. Ammonia is considered as the most efficient and hydrogen-intensive hydrogen carriers.

Aim. To ensure fire safety during storage and transport of liquid ammonia.

Objectives. Analysis of industrial means and methods of storage and transportation of liquid ammonia, development of measures for localization of large accidents, extinguishing of fires caused by ammonia vapour emissions and its spills in the form of cryogenic liquid.

Analytical part. When ammonia is released from pressurized equipment, the resulting mixture of product with air may vary in density from the formation of gas-air clouds below air density to buoyancy and exceeding air density depending on the conditions of release: pressure and temperature in the equipment; size of the hole through which ammonia enters the surrounding space; location of the hole in the equipment. Liquid ammonia leaks produce spills from the surface of which the product evaporates due to the temperature gradient when it is high, especially violently in the first moments after the spill. Calculations and experience show that the most dangerous area for liquid ammonia spills is a radius around the source of up to several hundred metres. Heat from the upper layer of soil (underlying surface) and the surrounding air is used for evaporation, and to a greater extent in the initial period this depends on the nature of the underlying surface.

Conclusions. Localization and elimination of pressure emissions and ammonia spills can be achieved through application of the following methods: acceleration of evaporation by air jets; reduction of ammonia evaporation surface using pits, pallets, drains into emergency tanks; dissolution in water and application of water curtains; application of water-foam compositions for polar liquids resistant to destruction.

Introduction. In the modern ceramic industry, the composition of the clay charge is adjusted by the introduction of polyfunctional additives, among which silicate fillers on the base of large-tonnage industrial waste are widespread. Synthetic diopside derived from rice husk ash and dolomite, having a number of valuable characteristics, is of undoubted interest as the main crystalline phase in the production of different types of ceramics.

The aim. To investigate the modifying effect of synthetic diopside (SD) derived from rice husk ash (RHA) and dolomite in the composition of ceramic charge based on different types of clay raw materials.

Materials and methods. In this study, there were investigated the clays of Bashkir and Yaush deposits, unmodified compositions based on them, as well as compositions filled with synthetic diopside. Standard experimental methods were used to study the phase and particle size distribution of clays, plasticity, true density and water resistance of base and modified compositions, fire, total and air shrinkage were determined.

Results and discussion. Differences in the phase and particle size distribution of clays do not significantly affect the plasticity of the clay charge, but cause different true density. It was found that water resistance and overall unmodified ceramics based on these clay raw materials differ on average by 10 %.

Conclusions. Synthetic diopside has shown its effectiveness as a modifier of clay raw materials, reducing the shrinkage of ceramic materials and plasticity, with the clay of the Yaush deposit being more promising for application.

Introduction. As a fire hazard in the scientific and regulatory literature, only one hazardous property of smoke is taken into account — reduced visibility. Therefore, estimating the blocking time of escape routes by the volumetric counting concentration of solid smoke particles is an urgent scientific task.

Aims and objectives. The aim of the work is experimental and theoretical estimation of the blocking time of evacuation routes during a fire in a room by the volume concentration of solid smoke particles. To achieve this goal, it is necessary to conduct an experimental study of the smoke-forming ability of combustible materials by the number of smoke particles and obtain a formula for calculating the time for blocking escape routes by the volumetric counting concentration of solid smoke particles.

Methods. An experimental method of measuring the amount, size and mass of suspended solids in a gaseous medium forming in a small-scale pilot plant during combustion of various substances and materials. Analytical method for calculation of evacuation route blocking time by fire hazards is used.

Results and discussion. Formula for calculation of evacuation route blocking time by volume concentration of solid smoke particles is proposed.
Experimental time dependences of the specific mass rate of gasification and specific smoke formation coefficients based on the volumetric count concentration of solid smoke particles with an equivalent diameter less than 2.5 μm were obtained during testing of specimens of wood, cable insulation, and microelectronic elements.
The results of numerical experiments on calculation of time of blocking evacuation routes due to loss of visibility in smoke and the volumetric count concentration of solid smoke particles are presented.
It was found that the volumetric concentration of smoke particles can be the first fire hazard blocking escape routes.

Conclusions. Solid smoke particles with an equivalent diameter less than 2.5 μm, which are the most dangerous to the human body during evacuation in case of fire, can be a fire hazard that first blocks the escape routes.

Introduction. One of the main problems of modern volumetric fire extinguishing with aqueous media is the use of agents having a single extinguishing mechanism. Introduction of water-soluble inhibitors into aqueous media is the most effective way to increase their extinguishing ability. However, at the moment there are no theoretical and experimental studies to establish the increase of fire extinguishing efficiency of aqueous media with the introduction of two or more inhibitors.

Purpose. To study the effect of introduction of two and more water-soluble inhibitors on the fire-extinguishing efficiency of aqueous media.

Materials and methods. The method of analysis and synthesis was applied for the selection of complex inhibitory compositions. The method of validation of mathematical models was applied to check the adequacy of the compiled model. The theory of mathematical analysis was used to determine the effective concentration of complex inhibitors. The evaluation of the effectiveness of the introduction of complex inhibitor composition was carried out by mathematical modelling in FDS environment.

Theoretical bases. The choice of complex inhibitory composition was carried out in accordance with the theory of branched chain combustion processes.

Results and discussions. A mathematical model of combustion suppression in a closed volume by complex water-soluble inhibitors has been developed. Successful validation of this model on the basis of available experi­mental data has been carried out. Mathematical modelling of combustion suppression by aqueous solutions of: ammonium sulphate and magnesium chloride, potassium carbonate and potassium acetate was carried out.

Conclusions. It has been established by the conducted studies that the effective mass concentration of the complex inhibitor of ammonium sulphate and magnesium chloride in aqueous solution corresponds to the value of 3.4 %, which is more than 4 times less than the effective concentration of each of the substances taken separately. The two-component inhibitor of potassium carbonate and potassium acetate are mutually suppressive and do not lead to suppression of combustion by chemical inhibition. Decrease of suppression time with increasing concentration of potassium carbonate and potassium acetate occurs due to increase of carbon dioxide release, as a result of thermal decomposition of these inhibitors.

Introduction. Much attention is paid to the regulatory regulation of fire safety. However, the process of forming a new regulatory and technical framework and applying the relevant requirements has a number of problems.

Goals and objectives. The purpose of the paper is to study the problems of a set of regulatory requirements for fire safety, as well as to analyze the problems and effectiveness of their application, including the concept of a risk-based approach, calculation methods and tools in the form of special technical specifications.

The main part. The prerequisites for the emergence of a new regulatory and technical framework in the field of fire safety are considered. The problems of each of the parts of the existing system are described: the legal component, federal laws, regulatory documents, calculation methods and special technical conditions. The contradictions and disadvantages of the existing risk-based approach are revealed. Solutions to these problems are proposed and appropriate approaches are formulated.

Conclusions. The approach to ensuring fire safety, laid as a basis in the concept of the existing regulatory framework in the field of fire safety, should not be based only on standards, calculations and, in general, on technical requirements. A significant part of it, which currently requires serious study and implementation, is the legal component, which includes the most important component in the form of control (supervision). This will significantly optimize and improve the situation not only in the construction industry, but also in other sectors of the economy, and bring the approach to the fire safety system to a qualitatively new level, taking into account the prevailing economic and political realities.