Introduction. Regulations, governing the fire safety of mobility impaired persons, have been in the spotlight over the last few years. However, problems arise in the process of developing and applying relevant requirements.

Goals and objectives. The purpose of the article is to study the process of developing a set of regulatory requirements focused on protection of mobility impaired population groups, including initial introduction of accessibility and fire safety requirements, analysis of current fire safety requirements in the regulatory documents, and effectiveness of their application at the present time.

The main body. The author analyzes preconditions for the introduction of requirements concerning the fire safety of impaired mobility groups. The process of updating these requirements in building codes and regulations is described; their strengths are demonstrated; contradictions and weaknesses are identified. Construction Regulations 1.13130.2020 are analyzed in terms of the fire safety of impaired mobility groups. Comments are made by a developer, and the conclusion is drawn about the need to revise these Construction Regulations.

Conclusions. There is a need to ensure the fire safety of impaired mobility groups within the framework of regu­latory fire safety requirements. However, these requirements should develop into well-balanced and effective solutions aimed at improving the fire safety of both impaired mobility persons and everybody else inside a construction facility, and to take into account the practice of implementing advanced structural solutions, issues of economics, and other aspects of the present-day reality.

Introduction. Widespread and effective introduction of cross-laminated timber structures into construction of residential buildings substantiates the need to develop modern requirements for the design of fire protection systems for these buildings to limit the spread of fire, ensure safe evacuation and rescue of people from these buildings, increase the effectiveness of firefighters performing rescue operations and fire suppression, and optimize the cost of space-planning and design solutions.

Goals and objectives. The purpose of the article is to substantiate modern requirements for the design of fire protection systems of residential buildings having not more than four storeys, if their structures are made of cross-laminated timber, and to develop engineering solutions to implement these requirements in compliance with provisions of the Federal Law of the Russian Federation dated July 22, 2008 No. 123-FZ “Technical regulations on fire safety requirements” (hereinafter — No. 123-FZ).

Methods. An analytical method is used to substantiate and formulate requirements for the design of fire protection systems for residential buildings whose structures are made of cross-laminated timber, as well as
the engineering solutions needed to implement these requirements for buildings having up to 4 floors in compliance with provisions of No. 123-FZ, the design experience, results of ire resistance and fire hazard testing of building structures and analysis of the influence of the fire resistance factor of building structures on human safety in case of fire.

Results. The results of the work, if integrated into standards of corporate entities and codes of practice, allow for the mass construction of residential buildings having structures made of cross-laminated timber.

Conclusions. This research project substantiated modern fire safety requirements for space-planning and design solutions, fire resistance limits and fire hazard classes of cross-laminated timber structures of residential buildings, as well as requirements for emergency exits and evacuation routes, composition of active fire protection systems and the functional efficiency of these systems.

The results of the work allow for the mass construction of 4-storey residential buildings whose structures are made of cross-laminated timber.

Introduction. Stuffed children’s toys in children’s entertainment areas at multifunction shopping malls are among the most dangerous combustible materials. However, flammable properties of stuffed toys, especially the qualitative and quantitative composition of resulting toxic gases, have not been studied.

Goals and objectives. The aim of the work is to identify specific coefficients of generation and partial density of toxic gases released during the combustion of stuffed toys.

To achieve the goal, a small experimental unit was upgraded and experimental studies of the above parameters were carried out to learn more about the most dangerous toxic gases released during the combustion of specimens of staffed toys made in China.

Methods. An experimental method was used to study the generation of toxic substances during the thermal decomposition of specimens of staffed toys in a small experimental unit. The results of the experiment were analyzed.

Results and discussion. The small experimental unit was upgraded so that it could measure concentrations of nitrogen dioxide and phosgene.

Dependences between time and the specific mass burn up rate, the average volumetric partial density, as well as carbon monoxide, hydrogen cyanide, phosgene, and nitrogen dioxide generation coefficients were obtained for the period starting from the launch of the experiment.

It was found that only partial densities of hydrogen cyanide and phosgene reached their critical values. In this case, the partial density of hydrogen cyanide exceeded its critical value by 2.5 times, and that of phosgene by 17 times. Therefore, it is necessary to calculate the time for blocking evacuation routes for hydrogen cyanide and phosgene to determine fire risks in children’s play areas.

Conclusions. When stuffed children’s toys are in combustion, highly toxic gases as carbon monoxide, hydrogen cyanide and phosgene are released in concentrations dangerous to human life and health. This fact must be taken into account when fire risks in children’s play areas are analyzed.

Introduction. In many countries, regulations consider combustible dust with a particle size of more than 500 μm as dispersed material non-explosive if mixed with air. The explosiveness of mixtures of air and some substance arouses researchers’ interest. In particular, the explosiveness of whey powder specimens (hereinafter referred to as whey powder) with an average particle size of 41, 162 and 750 μm, was identified in the process of their testing in a 1 m3 chamber. The task is to find out the maximum particle size of whey powder dcr using the earlier developed procedure and to demonstrate its failure to conform to the rule specified above.

Method to process experimental data. Continuous functions F of particle size distribution d were constructed for three whey powder specimens having the following values of the lower explosive limit (LEL1 = 250 g/m3, LEL2 = 250 g/m3 and LEL3 = 500 g/m3, respectively). Resulting functions F1(d), F2(d) and F3(d) were presented using Rosin – Rammler distributions that filled the gaps between the discrete data obtained as a result of the sieve analysis.

dcr evaluation. We used information about the first and third whey powder specimens in compliance with the well-known procedure (Poletaev, 2014). dcr values were identified using equation F1(dcr)/F3(dcr) = LEL3/LEL1. Having solved the equation, we found that dcr = 750 μm.

Discussion. The obtained evaluation of dcr is much higher than the limit value of the parameter proposed in the regulations. This evaluation is of objective origin, and it cannot be explained by the grinding of large particles during the spraying process. The latter statement is supported by a characteristic decrease in the explosibility index of whey powder and an increase in the average particle size (for explosive fractions) of the three specimens in question.

Conclusions. The maximum particle size of the explosive whey fraction is about 750 µm.

Introduction. To date, there are many (over 150) different mathematical models developed in the field of fire safety. These models are designed to (1) solve problems of heat engineering, heat and mass transfer, human flows, indoor and outdoor fire behaviour, and (2) determine parameters of operation of fire service departments. System research into fire safety models was initiated in the 1970s, and it has been conducted since then. This article presents the results of scientific generalization of mathematical methods of fire safety and provides a brief historical background of the issue.

Targets and goals. Scientific generalization of basic mathematical models used to solve research and engineering problems of fire safety.

Methods. Methods of systems analysis.

Results. The article presents the results of a review of various mathematical models of fire safety. The study encompasses many theories (theories of fire safety of substances and materials, technologies, buildings and structures, fire resistance of building structures and buildings, fire prevention, organization, operation and management of fire service departments, etc.). Principal mathematical methods (analytical and probabilistic ones, as well as simulation), employed by the above theories of fire safety, are considered.

Discussion. The authors list more than 150 fire models of different types and classes. Most of them deal with processes of heat and mass transfer during fires, the fire behaviour, the behavior of substances, materials, building structures, etc. on fire. The study also focuses on probabilistic models of the theory of emergency rescue services operation.

Conclusions. Currently, a general theory of fire safety is being developed. It is a combination of physicochemical, mathematical, economic-mathematical and other models describing the break-out, development and elimination of fires inside and outside of buildings in case of application of passive and active fire-fighting appliances.

Introduction. Evaluation of actual fire resistance of load-bearing building structures made of various materials and reinforced concrete, in particular, encompasses a rather complex and research-intensive case of analysis of integrated, mechanical and fire safety of buildings and structures. Current methods of analyzing the fire resistance of reinforced concrete structures do not take into account any thermal characteristics of reinforcement. Hence, values of the fire resistance limit of structures can only be consistent with experimental results only if the percentage of reinforcement in analyzed concrete structures and reinforced concrete structures is below 3.5 %.

The purpose of the work. Is (1) the pilot testing of a hybrid experiment method and (2) evaluation of convergence between (a) results of experimental laboratory studies on fire resistance of compressed reinforced concrete elements with a higher percentage of reinforcement, (b) theoretical data and (c) numerical calculations. The following tasks were solved:

• in accordance with the developed method, analytical, experimental laboratory and numerical studies of fire resistance of compressed concrete and reinforced concrete elements (including those that have a higher percentage of reinforcement) were carried out;
• convergence between the obtained results was evaluated;
• conclusions were made about the issues under consideration.

Research methods. Theoretical data, applied for comparison purposes, were obtained analytically (using formulas and nomograms of SP (Construction Regulations) 468.1325800.2019), experimental and calculated data were obtained in the course of concurrent experimental studies conducted at the fire testing laboratory of NRU MGSU, and numerical studies were obtained using the Abaqus PC software package. In the course of a laboratory experiment made using the loading equipment, the strength of reference concrete templates was identified, using the tensile machine to find the physical and mechanical characteristics of reinforcing steel. Next, reference concrete and reinforced concrete specimens with pre-set characteristics were made. Then temperature fields in concrete and cross sections of specimens, containing reinforced concrete, were identified using the thermocouple data. Centrally compressed concrete and reinforced concrete specimens were tested in a fire chamber at a standard fire temperature. The behaviour of concrete and reinforced concrete specimens was simulated using volumetric finite elements, having the size of up to 10 mm, and a built-in Heat Transfer Solver (Heat transfer). Temperature field distribution and fire resistance of reinforced concrete elements were analyzed at a standard fire temperature in concrete and reinforced concrete elements.

Results and their discussion. The following knowledge was gained by means of this research project:

• convergence between temperature values at control points in concrete specimens (according to thermocouples), acceptable for practical purposes. These values were obtained in the course of experimental laboratory studies and calculations made according to current standards, which confirms the validity of the experiment;
• convergence between temperature values at control points in concrete specimens (according to thermocouples), acceptable for practical purposes. These values were obtained in the course of experimental laboratory studies and calculations made according to current standards, which confirms the validity of the proposed hybrid experi­ment method and the trustworthiness of the research;
• a great difference reaching 10 to 30 % (19.3 % on average for a group of specimens) between experimental and analytical values of fire resistance of reinforced concrete elements, which proves the hypothesis about a reduction in the heating temperature of concrete in a reinforced concrete section if the thermal influence of reinforcement is taken into account;
• convergence between fire resistance values (the difference is 7 to 10 %) in reinforced concrete specimens, which is acceptable for practical purposes. These values were obtained in the course of experimental laboratory studies and calculations, and their convergence proves the applicability of the proposed hybrid experi­ment method with account taken of the hypothesis about less intensive heating of concrete, if the thermal impact of reinforcement is taken into account.

Conclusions. The hypothesis about a reduction in the heating temperature of concrete in the reinforced concrete section that has a high percentage of reinforcement (more than 3.5 %) was proven, taking into account the thermal influence of reinforcement. The consequence is the underestimated values of fire resistance of reinforced concrete elements, identified in accordance with a standardized approach. The applicability of the proposed hybrid experiment technique is also proven, taking into account the hypothesis about a reduction in concrete heating due to the thermal influence of reinforcement.

Introduction. The fire hazard of explosive regimes of liquefied natural gas (LNG) evaporation was analyzed on the basis of the published research findings. These regimes include the rollover and the rapid phase transition (RPT).

Characteristics of explosive regimes of LNG evaporation. Rollover occurs in LNG storage tanks in case of spontaneous mixing of LNG layers having different temperatures and densities. These layers emerge when the “fresh” product is loaded into a vessel containing the residual amount of product stored there before. A rapid increase in the LNG evaporation rate accompanies a pressure rise inside the tank, which can exceed an allowable pressure of the tank. RPT occurs at a contact of LND and water in the case of a release of liquefied natural gas onto a water surface. An explosive evaporation of LNG can cause in this case a formation of a shock wave and a large-scale vapor cloud.

Investigations of rollovers. It was mentioned that a stratification of LNG in a storage tank is a necessary condition of a rollover. Two layers with different temperatures and densities are formed during this stratification. A superheating of a lower layer occurs at a heat exchange between the LNG and tank walls with a decrease of a density of this layer. A preferential evaporation of light components of LNG (methane, nitrogen) takes place in the upper layer, and the density of this layer increases. When the densities of these layers are equalized a spontaneous mixing of these layers occurs with an explosive evaporation of the product in the lower superheated layer. A time delay of rollover can reach 60–70 hours after the supply of the “fresh” product into the tank with “old” product.

Investigations of a rapid phase transition. An energy released at the explosive evaporation and a pressure in a shock wave depend on many factors such as a LNG release rate, a position of a source of the LNG release — over or under a water level, a product composition, water temperature etc. It was found that a pressure hazardous for buildings and structures can take place at distances 250–500 m from the point of the release. The empirical correlation was proposed connecting a water temperature at the RPT occurrence and the superheating tempe­rature of LNG at which a boiling takes place in the regime of a homogeneous nucleation.

Conclusions. It was shown that a realization of the explosive regimes of the LNG evaporation increases a fire hazard of objects for a storage and a transportation of liquefied natural gas. Recommendations for a prevention of such regimes are formulated.

The fire hazard of various types of lithium-ion batteries was analyzed. Options for implementing passive extinguishing (cooling) of damaged cells and methods of creating non-flammable electrolyte compounds were presented. The author summarized possible engineering solutions, aimed at reducing the likelihood of fire spread to neighbouring cells within a separate pack. The author also considered ways of preventing and mitigating battery ignition consequences using various fire extinguishing substances, described the main features of application and operating principles underlying advanced methods of extinguishing lithium-ion batteries.