Key Engineering Materials Vol. 952

Abstract: Consideration was given to the issue of the integrated evaluation of the flammable properties and factors of wooden products (Oriented Strand Boards, OSB and Wood Particle Boards, WPB) as basic flammable construction materials exposed to the action of fire. The experimental data obtained for flammable wooden products during the experiments carried out to define the dependence of temperature on the time of fire impact, to measure and substantiate the charring depth of wooden products, to determine degradation zones affected by fire and their sizes (area, width and length) and to compare a change in the specimen mass before and after the tests have been given. The experimental data confirm and substantiate the pyrolysis processes of wooden products during the fire spread.

Abstract: Consideration was given to the issue of flammability during the thermal decomposition of synthetic materials used for the constructions to isolate the process equipment and building structures. The experimental research data obtained for the thermal decomposition of synthetic materials with the measurements of temperature as a function of the time of thermal radiation were given including a change in the mass and structure of the specimens of synthetic materials exposed to the thermal radiation during the fire. The obtained experimental data enabled the substantiation of the process of the thermal decomposition of synthetic materials depending on time and temperature and also a change in the mass of the specimens of synthetic materials before and after the tests.

Abstract: This article presents the results of fire properties of modern materials, namely geopolymer fire-insulating mixtures of domestic production to provide fire protection of reinforced concrete structures of the agroindustrial complex. According to the data of the fire test, it has been established that with the thickness of a fire-proof geopolymer coating of 10 mm no heating of the surface of a reinforced concrete specimen (300<380 °С) or of the armature at the depth of its embedding (124.5<500 °С) up to the limit states has been noted. It they shown that the protective coating reduces the critical temperature of brittle fracture of reinforced concrete by a factor of 1.3 during 180 minutes of the test. It has been note that due to the protective properties of the coating, the temperature of armature heating at the depth of its laying decreases 4 times in comparison with the unprotected reinforced concrete specimen during 180 minutes of the test. The mechanism of formation of an effective fine-pore structure in the coating with its developed and high heat-absorbing and dissipating capacity has been reveale due to the transition of the binder into the glass-like state, which prevents both physically and chemically bound water vapor from escaping into the hydrate new formations of the geopolymer binder.

Abstract: Composite materials are widely used in various industries. Both ordinary household items and specialized equipment used, in particular, in emergency and rescue formations, are made from them. Each equipment has a different level of reliability. One of the types of such equipment with the lowest level of reliability is fire hoses. Fire hoses work under different internal working pressures, and depending on this indicator, during their manufacture, such materials are chosen that are able to withstand it. High-pressure fire hoses are a separate type of fire hoses. In order to ensure the necessary strength of the material, it includes an internal reinforcing layer, which is a weaving of textile threads or metal wire. The composite structure of the material greatly complicates the process of checking the technical condition of high-pressure fire hoses, which may have hidden defects. These defects can cause their destruction during operation and lead to non-fulfillment of the tasks assigned by units of emergency and rescue formations. Therefore, the study of changes in the properties of the composite material from which high-pressure fire hoses are made due to the influence of various factors on it is relevant.

Abstract: The main purpose of this study is a numerical assessment of the consequences of an explosion of a hydrogen-air cloud on the personnel of a hydrogen fueling station and the strength of a protective solid wall of certain dimensions. An explosive gas mixture is formed as a result of the destruction of high-pressure cylinders, the number of which determines the size of the cloud, the power of the explosion, and the scale of the consequences of environmental impact. To obtain the spatio-temporal distribution of the maximum overpressure and the impulse of the shock wave compression phase, a mathematical model of the dispersion of an active gaseous admixture is used, taking into account the chemical interaction with air oxygen. The probable consequences of the shock-impulse impact on the personnel at the control point are carried out using probit analysis. The values of the maximum bending moment and stress at the base of the protective wall, which result from the impact of the blast wave, are used to deterministically estimate the minimum wall thickness necessary for the safe operation of the protective device. The mathematical model takes into account the complex terrain and the three-dimensional non-stationary nature of the shock wave propagation process, and it is a source of data necessary to solve the problem of the strength of solid objects located in the area of baric perturbation of the gaseous medium. The developed methodology makes it possible to carry out a comparative analysis of the effectiveness of protective structures in relation to the power of the explosion.

Abstract: The relationship between substance characteristic temperatures: autoignition, melting, flash, boiling is demonstrated and analyzed. Based on the oscillatory and step changes presence, a conclusion was made about the supramolecular structures presence and periodicity in the n-alkanes homologous series. A method for modeling equivalent lengths of peroxide supramolecular structures for predicting the explosion and fire hazard parameters of n-alkanes is proposed. An approximation dependence was developed for predicting autoignition temperatures t_ai of n-alkanes. It is shown that stoichiometric concentrations of the various supramolecular peroxide structures formation accord to different flammability and explosion limits. A correlation between t_ai and Anti-Knock Index (AKI) was established. An approximation dependence was developed for predicting n-alkanes AKI. The detonation propensity index К_D was introduced based on cluster supramolecular structures modeling and melting temperatures. It is shown that К_D indicator correlates with the n-alkanes AKI and with the explosives detonation velocity. The possibility of taking into account during calculations the supramolecular structures presence at the combustion stage confirms their existence.

Abstract: The components of the most common explosive ordnance in Eastern Europe have been analysed. The most dangerous explosive materials that rescuers may encounter when disposing explosive ordnance and clearing territories from mines have been identified. Such hazardous materials include tetryl, texogen, trinitrotoluolol, mercury fulminate, lead azide, lead trinitroresorcinate. An analysis of the chemical structure and physical and chemical properties of such materials has been carried out. It has been established that explosive materials can be divided into two classes with similar values based on such parameters as detonation velocity, volume of explosion products, and explosion heat. It has been established that the chemical structure of their molecules corresponds to the said two classes of physical and chemical properties. The first class includes materials based on hydrocarbons, the second includes materials based on heavy metals. It has been established that the specific volume values for the second class materials increase significantly, and exceed the indicators for the first class materials. This is due to the difference in the density of such materials by 2 to 4 times. The established features of the physical and chemical and explosive parameters of explosive materials can be used in the development of standard operating procedures and plans of actions of rescuers in order to increase the safety of handling the explosive ordnance.

Abstract: A study was made of the regularities of the influence of the main parameters of external thermal effects (elevated heating temperatures and external pressures) on the rate and explosive modes of combustion development of compacted mixtures of magnesium, aluminum and sodium nitrate with fluoride additives metals for different values of technological parameters (excess ratio of the oxidizing agent, nature and content of the additive, dispersion of the components). The effect of technological parameters (ratio and dispersion of components, compaction coefficient, charge diameter, shell material, etc.) on the dependence of the burning rate of mixtures on elevated heating temperatures and external pressures was established; critical ranges of changes in these parameters are determined, the excess of which leads to premature explosive development of combustion of mixtures and fire hazardous destruction of products. On the basis of the research, methods were developed to prevent these destructions of products by regulating technological parameters at the stage of preparation of charge mixtures, which increases the stability of the combustion process of mixtures to external thermal influences. A database has been obtained on the burning rates of compacted mixtures of metal powders (Mg, Al), nitrate-containing oxidizer (NaNO₃ ) and additives of inorganic substances (metal fluorides (LiF, NaF, BaF₂ , SiF₂ , SrF₂ , AlF₃ )) under conditions elevated heating temperatures and external pressures for various values of technological parameters, which makes it possible to determine the explosive modes of their combustion.