Introduction. The well-known results of experimental study of the minimum explosive concentration (MEC) polydisperse iron dust air suspension in a 1-m3 chamber (Clouthier, Taveau, Dastidar et al., 2019) and a 20-L chamber (Cashdollar, 1994) are considered. An analysis of these results at a qualitative level, carried out by the authors of these studies, showed that the maximum size of iron particles dcr responsible for the explosion hazard belongs to the range from 30 microns to 75 microns. The task is to clarify the dcr based on a quantitative analysis of the results of the study in a 1-m3 chamber by the known method (Poletaev, 2014).

Selection and processing of initial data. For two polydisperse iron specimens with different MEC in a 1-m3 chamber (MEC1 = 250 g/m3 for a fine specimen and MEC2 = 1,250 … 1,500 g/m3 for a coarse specimen), continuous particle size distribution functions are constructed: F1(d) and F2(d), respectively. Here, F(d) is the mass fraction specimen particles having size less than d.

Estimation of dcr and discussion of the result. Following the procedure of the quantitative dcr estimation method, the equation F1(dcr)/F2(dcr) = MEC2/MEC1 was solved in a visual graphical form. The result of the solution: dcr = 36 ± 3 microns. The obtained quantitative result significantly clarified the known qualitative assessment of the dcr.

Conclusions. The ability of polydisperse air suspension of iron dust to spread the flame (i.e. its explosiveness) is determined by the content of fine fraction “less than dcr”. The minimum amount of this fraction should exceed the value of about 150 g/m3.

Introduction. Intumescent fire retardant materials (IFRM) are widely used as passive fire protection means. The principle of their action providing increase of fire resistance of a structure is based on foaming and formation of heat-insulating coked cellular material layer under conditions of fire exposure. Active research conducted in this field formulated general principles for the development of IFRM based on functional components (FC) responsible for the fire protection function of coverings.

Purpose. To propose a new systematic approach to the development of IFRM, which takes into account the quantitative influence of all FC included in the composition of IFRM and to demonstrate its effectiveness on the example of developing the formulation of water-base IFRM.

Methodology. A method of multifactor quantitative optimization was developed and described to enhance the fire retardant effectiveness (FRE) of IFRM. The optimization of the composition is carried out by changing the quantitative ratio of the FC within the IFRM formulation by a selected coefficient of variation. The optimization is carried out through an iterative mechanism, which allows to detect new maximums of FRE. Each stage corresponds to a design matrix describing all possible combinations of FC, the number of which is determined by the number of FC. To assess the maximum FRE and the progress of optimization, fire tests were conducted under standard fire temperature conditions. The method was validated on a base IFRM formulation based on polyvinyl acetate dispersion and four FC: ammonium polyphosphate, melamine, pentaerythritol, and titanium dioxide.

Results and its discussion. Through two stages of multifactor quantitative optimization, the investigated formulation of the IFRM achieved its optimum in terms of FRE. The FRE of the IFPM was increased from 31 to 45 minutes, accompanied by qualitative improvements in the appearance of the coked cellular material.

Conclusions. The multifactor optimization method allowed to find the optimal ratio of the FC and to increase the FRE by 45 % as a result of well-structured experimental procedures. This optimization method is recommended for implementation in the development process of new IFRM.

Introduction. Forest fires lead to economic damage to the state, for example, damage and destruction of civil and in­dustrial buildings in rural areas. The purpose of the study is to develop physical and mathematical models of the forest fire front impact on the building enclosures. Research objectives: 1) formulation of physical and mathe­matical models; 2) software implementation of a mathematical model in a high-level programming language; 3) numerical study of heat transfer processes in building enclosures.

Methods. A low-intensity surface forest fire, a high-intensity surface forest fire, a crown forest fire, and a fire storm are considered. An element of a two-layer enclosing structure of a wooden building with a window opening is considered. The effect of convective heat flow is considered. Heat transfer processes in the building enclosures are described by a system of non-stationary heat conduction equations with the corresponding initial and boundary conditions. Two-­dimensional heat equations were solved using the locally one-dimensional method. For numerical implementation of the presented mathematical model, the finite difference method was used. Difference analogues of partial differential equations are solved by the marching method.

Results and discussion. Temperature distributions in a structurally inhomogeneous element of the building enclosures were obtained. The analysis shows that the temperature fields are almost the same for different seasons of forest fires. The noticeable difference is only near the contact of the enclosing structure with the soil. In general, higher temperatures are observed in the upper part of the building enclosures at the border with the roof of the building. The glass in the window opening is heated up to sufficiently high temperatures. This will lead to its destruction during the period of exposure to the forest fire front. The window opening is the most vulnerable area to flame in the building enclosures. In addition, as a result of numerical modelling, it was established that maximum temperature gradients occur in the cladding material.

Conclusion. Recommendations are proposed for improving the fire safety of buildings in rural areas and the application of the proposed physical and mathematical model were suggested.

Introduction. Every year, new types of polymer composite materials appear, which are used for the manufacture of quickly erected soft tanks. These materials are tested for mechanical and chemical resistance, while much less attention is paid to the study of their fire-hazardous properties. Due to the fact that composite materials for elastic tanks are combustible, the experimental study of the process of their thermal destruction process, in particular by the method of thermal analysis, is an urgent task.

Purpose and objectives. The aim of the study was to assess the fire hazard of elastic tanks based on thermogravimetric analysis of three specimens of composite materials, which are widely used in the manufacture of elastic tanks for the storage of flammable liquids. The paper analyzes the results of synchronous thermal analysis of composite materials similar in structure, as well as surface layer temperatures during burning of oil and petroleum products; the intervals of thermal destruction, mass loss rates, and thermal effects of thermo-oxidative destruction in the nitrogen-oxygen environment of the studied materials are determined.

Materials and methods. To assess the thermal resistance of polymer composite materials used in the manu­facture of soft storage tanks for flammable liquids, the physical and mechanical properties of the following material grades were studied: Yan Yang YY1600; Jinlong JL1600; L3690 NESU. Thermal destruction of these materials in nitrogen-oxygen atmosphere was studied by the method of synchronous thermal analysis (TGA+DSC) using Setsys Evolution 16 device.

Results of the study. The experiments carried out made it possible to establish that thermal destruction of the materials under study occurs at temperatures of 280–290 °С, which is close to the temperature of the surface layer during combustion of dark petroleum products. The maximum rate of destruction in all specimens was observed at 410–420 °С, and the maximum coke residue did not exceed 4.5 %. The time of complete destruction of the studied materials at the maximum rate of mass loss ranged from 9 to 14 minutes, depending on the type of specimen.

Conclusions. The temperature of the beginning of thermal destruction of the three grades of polymer composite materials under study is close to the temperature of the surface layer during the combustion of high-boiling liquids, which creates danger of depressurization during ignition of a spill of dark petroleum products on the surface of the materials under study.

Introduction. The paper is devoted to experimental and analytical study of the load-bearing capacity of bending structures made of ordinary and fire-resistant rolled steel under standard temperature conditions. Fire tests were carried out with rolled I-beams No. 20B1 manufactured according to GOST R 57837–2017 from steels of strength classes C255, C390 and welded I-beams 180 × 90 × 10 from steels C355, C390, C355P, C390P with the length of 3,500 mm. Experiments on determination of high-temperature mechanical properties of new steel grades were carried out.

Materials and methods. The values of actual fire resistance limits of beams obtained experimentally are determined according to GOST 30247.1–94 and GOST 30247.0–94. The thermotechnical part of the calculation of the temperature in the cross-section of steel beams was performed in the ANSYS Mechanical programme complex. The calculation of bearing capacity was carried out according to the developed method and the registered programme for computer. Experiments on determination of mechanical properties of rolled metal products under high-temperature heating were carried out on small-sized specimens in accordance with GOST 9651–84.

Results and discussion. Experimentally obtained values of actual fire resistance limits for I-beams made of ordinary and fire-resistant rolled steel. The averaged values of coefficients of change of yield strength at elevated temperatures of construction rolled steel, including fire-resistant steel, which can be used in calculation models of fire resistance assessment of steel structures, were determined. A programme complex for calculation of fire resistance limit taking into account non-uniform temperature distribution in the cross-section of the structure was developed. The results of calculations of fire resistance limits according to the proposed model are close to the experimental data obtained on I-beams made of building steels, including fire-resistant ones.

Conclusions. The fire resistance limit of beams made of fire-resistant rolled steel C355P, C390P at standard temperature regime occurs 10–15 minutes later than beams made of ordinary construction steel. The results of experimental and analytical studies of fire resistance limits of structures made of new types of fire-resistant steels confirm the increase in the time of metal heating from the beginning of fire exposure to the achievement of critical temperature in the design cross-section, which allows to justify their use in the design of buildings and structures in accordance with the requirements of standardized documents on fire safety, as well as to reduce the use of fireproof materials, reduce the metal intensity and cost of construction.

Introduction. When designing buildings it is necessary to estimate the actual fire resistance limits of unprotected steel structures. Nomograms are a convenient tool for obtaining such an assessment. Practical necessity of integration of “manual” technology and modern means of design automation makes the task of “digitization” of nomo­grams by creating computational data models urgent.

Goals and objectives. The purpose of the work was to obtain a rather simple formula for calculating the fire resistance limits of unprotected steel structures. The following tasks were solved: comparison of the literature data on fire resistance limits with the results of calculations according to the normative document on fire safety “VNPB 73–18”; calculation of a four-digit table of fire resistance limits for the subsequent approximation of functional dependence.

Research methods. The table of fire resistance values is calculated with four correct digits using the Adams multistep method of variable order. The formula for calculation of fire resistance limit of unprotected steel structures was obtained by successive approximation of tabular data first by one variable (thickness, i.e. reciprocal of the section factor) and then by another (critical temperature).

Results and discussion. Calculation according to the methodology VNPB 73–18 gives the fire resistance limits close to the reference values, which were published by A.I. Yakovlev in 1985. The values of convective and radiation heat transfer coefficients adopted in the VNPB 73–18 method correspond to the fire resistance tests according to GOST 30247.0–94 (ISO 834–75).

Conclusions. An approximation formula was obtained, the calculations according to which give the same fire resistance limits as the calculations according to the VNPB 73–18 method. Relative error of approximation does not exceed 0.5 % in the range of parameters change: critical temperature — from 500 to 700 °C; thickness — from 3 to 12 mm.

Introduction. According to the Ministry of Labour and Social Protection of the Russian Federation, annually for the period from 2018 to 2022 in the organizations out of the total number of accidents with severe consequences, the share of accidents as a result of falling at height and depth differences was 23 %. The main reasons for this are non-compliance with the rules on labour protection when working at height, falling objects from height, conscious non-use of personal protective equipment (PPE) against falls from height, violation of work techniques at height, misuse of PPE or improper use of components of safety systems, lack of collective protection equipment (guardrails, safety catch nets).

Purpose. Increase of safety during rescue and evacuation measures of the victim, who is suspended after a fall, in the means of personal protection against falls from height.

Objectives. 1. To consider the process of the block pulley certification for compliance with the requirements of TR CU 019/2011, the requirements and methods used in the verification of the block pulley. 2. To analyze the correctness of the block pulley certification when using standards to verify the quality of the product. 3. To determine the safety margin, dynamic characteristics of the block pulley by experimentation. 4. To determine the necessary requirements for the block pulley and develop methods of testing the product to introduce another class of product in GOST EN 1496–2020.

Analytical part. The paper analyses the group of standards according to which rescue and evacuation devices are certified in the Customs Union countries. The paper also considers the European experience of certification and verification of technical requirements for the block pulley.
The standards used to verify the technical requirements of TR CU 019/2011 to identify deficiencies and correctness of methods were analyzed.
The authors conducted research tests of the block pulley for various characteristics with the subsequent development of requirements and test methods for these devices.

Conclusions. In the course of the work the criteria of requirements with regard to the characteristics of the block pulley and the methods of testing dynamic and static strength were developed. Functionality check of the free end of the rope used in the block pulley was realized. A term defining a block pulley used in rescue and evacuation and positioning systems was proposed.

Introduction. The paper presents an integrated security system (ISS), for which a quantitative measure of the influence of subsystems of industrial and fire safety (IS and FS), labour protection (LP), production structural units (PSU) is obtained.

Goals and objectives. The purpose of the presented paper is to improve the state of the ISS at the enterprise by assessing the influence of personnel (IS and FS; LP; PSU) on it, which performs labour functions to ensure the quality functioning of the system under consideration, it was necessary to solve two problems.

Results. In the course of solving problem No. 1, the substantiation of the preferability of using the method of prioritisation is presented, which together with the Gaussian normal distribution functional, allows solving problems of experts choosing a specific subsystem (IS and FS; LP; PSU) in which there are drawbacks. In the course of solving problem No. 2, an example substantiating the adequacy of the joint application of the considered method in practice is presented.

Conclusions. On the basis of the system analysis of the methods used in practice, the justification for the use of such an expert method is presented, with the help of which quantitative values are displayed in the form of the influence coefficient, which indicates certain deviations and allows to correct the personnel management model (IS and FS; LP; PSU).
An example is demonstrated that allows us to prove the adequacy of using the method of assessing the state of the ISS created at a manufacturing enterprise.
The application of the developed model for the development of the ISS at Russian manufacturing enterprises makes it possible in practice to solve the problem of reducing damage from accidents and fires in the system under consideration, i.e. to solve the problem of important socio-economic importance for Russia.