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Introduction. GOST R 12.3.047-2012 standard offers a methodology for determination of required fire resistance limits of engineering structures. This methodology is based on a comparison of values of the fire resistance limit and the equivalent fire duration. However, in practice incidents occur when, in absence of regulatory fire resistance requirements, a facility owner, who has relaxed the fire resistance requirements prescribed by GOST R 12.3.047–2012, is ready to accept its potential loss in fire for economic reasons. In this case, one can apply the probability of safe evacuation and rescue to compare distributions of fire resistance limits, on the one hand, and evacuation and rescue time, on the other hand.A methodology for the identification of required fire resistance limits. The probabilistic method for the identification of required fire resistance limits, published in work [1], was tested in this study. This method differs from the one specified in GOST R 12.3.047-2012. The method is based on a comparison of distributions of such random values, as the estimated time of evacuation or rescue in case of fire at a production facility and fire resistance limits for engineering structures.Calculations of required fire resistance limits. This article presents a case of application of the proposed method to the rescue of people using the results of full-scale experiments, involving a real pipe rack at a gas processing plant [2].Conclusions. The required fire resistance limits for pipe rack structures of a gas processing plant were identified. The calculations took account of the time needed to evacuate and rescue the personnel, as well as the pre-set reliability of structures, given that the personnel evacuation and rescue time in case of fire is identified in an experiment.

Due to the lack of national analogies a prototype of enzyme-linked immunosorbent assay (ELISA) test system was developed for the qualitative determination of antibodies class G to hepatitis E virus (HEV) based on the using of antigenic polypeptides ORF2 and ORF3 of the 3rd genotype (FSBSI «I.I. Mechnikov Research Institute of Vaccines and Serums», Russia). The results of experimental ELISA conducted in parallel with the reference test system «DS-ELISA-ANTI-HEV-G» (NPO Diagnostic Systems, Russia) are presented. The working concentrations of ORF2 and ORF3 antigens were 2.5 µg/mL and 0.25 µg/mL, respectively. They were tested with 200 donors and patients’ serum samples. The article reflects the determination of sensitivity, specificity and reproducibility results. The developed test system demonstrated high efficiency in the detection of specific anti-HEV-IgG.

In this paper, we experimentally studied the limiting conditions for the combustion of hydrogen, methane, and propane in mixtures with air or oxygen at pressures below atmospheric. A significant effect is shown for the size of the reaction vessel and the ignition energy on both the minimal pressure value and the change in the concentration range of flame propagation. The dimensions of the reaction vessel and the magnitude of the ignition energy, the increase of which does not lead to a change in the minimal pressure and concentration region of flame propagation, are established. The minimal pressures Pmin of gas mixtures, below which flame propagation is impossible, were determined. A qualitative interpretation of the data is presented.

This paper presents a method of testing structural materials for spark safety and the results of testing this method for several pairs of materials and samples of combustible gases and vapors. Hydrogen, acetylene, AI-92 gasoline vapor, methane and liquefied petroleum gas were used as combustible gases and vapor, and samples of various types of steel, aluminum, and brass as structural materials.

Because fluorinated hydrocarbons are now widely used for fire extinguishing, it is interesting to use them for explosion prevention for oxidizers with different oxygen contents. An experimental investigation of the influence of the oxygen content of the oxidizer (mixture of O 2 and N 2 ) on the characteristics of combustion of nearly stoichiometric mixtures of flammable gas (hydrogen, methane) – oxidizer – fluorinated hydrocarbon (trifluoromethane CHF 3 , pentafluoroethane C 2 HF 5 , perfluorobutane C 4 F 10 ) was carried out. The oxygen content of the oxidizer was 15, 20.6 (air) and 25% (vol.). The dependences of the maximum explosion pressure Δ P max , the maximum pressure rise rate upon explosion ( dP/dt ) max and the laminar burning velocity S ui on the concentrations of the fluorinated agents for various oxygen contents were determined using standard methodologies. It was found that influence of CHF 3 on Δ P max is rather weak, while C 2 HF 5 and C 4 F 10 are much more effective for the reduction of the maximum explosion pressure. For all investigated fluorinated agents, the influence of the maximum pressure rise rate on the explosion and the laminar burning velocity was very strong. A qualitative explanation of the obtained results is presented.

The effect of the oxygen content in the oxidizing medium (O2–N2 mixture) on the characteristics of the combustion of gaseous fuel (hydrogen, methane)–oxidizing medium–hydrofluorocarbon (trifluoromethane CHF3, pentafluoroethane C2HF5, or perfluorobutane C4F10) is experimentally studied. The oxygen concentrations in the oxidizing medium are 15, 20.6 (air), and 25 vol %. The dependences of the maximum explosion pressure ΔP max, maximum explosion pressure rise rate (dP/dt)max, and laminar burning velocity Sui on the hydrofluorocarbon content at various oxygen concentrations in the oxidizing medium are determined. It is shown that, at a relatively low deterrent content Cd (up to 30–50% of the minimum inhibitory concentration of the hydrofluorocarbon, i.e., up to 30–50% of the hydrofluorocarbon content at the “peak” point of the inhibition curve), the maximum explosion pressure is only slightly dependent on C d. It is demonstrated that the larger the molecule of the hydrofluorocarbon, the higher is its inhibitory ability in terms of (dP/dt)max and Sui. A qualitative interpretation of the results is given, based on the concept of additional heat release in the flame front by reactions involving hydrofluorocarbons.

An experimental investigation of flammability limits of hydrogen, methane and propane in air and oxygen at reduced pressures was carried out. A slow influence of sizes of an experimental vessel of a diameter higher than 125 mm on the flammability limits was revealed, but an influence of a type of an oxidizer (air or oxygen) and an ignition energy is significant. Critical values of an initial pressure for a possibility of a flame propagation were determined. The limiting values of the ignition energy were determined, for which an elevation of this parameter does not influence the critical pressure and the flammability region. A qualitative interpretation of obtained experimental results is given, which is based on a peculiarities of a flame initiation.

This article describes a method for testing the safety of construction materials with respect to mechanical sparks (spark safety). This method was tested on examples of various materials and flammable gases. Hydrogen, acetylene, petrol, methane and LPG were used as the flammable gases. Various types of steel, aluminium, and copper and aluminium alloys were used as the construction materials. On the basis of the experiment a criterion for spark safety was proposed.

The BLEVE (boiling liquid expanding vapor explosion) effect that involves the formation of a fireball occurs at the engulfment by fire of a tank with a highly flammable liquid or a liquid gas. Heating of the tank causes elevation of the liquid phase temperature and pressure inside the tank. A partial rupture of the dry tank walls is possible, with the formation of a rarefaction wave propagating into the liquid phase. An evaporation wave moves after the rarefaction wave and cause a rapid increase of pressure, exceeding the initial pressure before depressurization. Rapid violent destruction of the tank occurs. The mechanism of a BLEVE initiation is considered using Van der Waals isotherms. The following criterion for the possibility of a BLEVE was formulated. If the final state is located on an unstable part of the Van der Waals isotherm, a BLEVE takes place. Limiting values of the temperatures for overheating of certain highly flammable liquids and liquid gases (propane, n-butane, n-pentane, isopentane) were calculated using the proposed method, and were found to be in good agreement with experimental data available in the literature.

The flammability limits for combustible gas (methane, hydrogen)-nitrous oxide-fluorinated hydrocarbon (trifluoromethane CHF3, pentafluoroethane C2HF5, perfluorobutane C4F10) mixtures are experimentally determined. The upper and lower flammability limits turned out to be, respectively, significantly higher and lower as compared to those characteristic of the combustion in air. The compositions of the mixtures at the peaks of the flammability curves are characterized by lower values of the fuel equivalence ratio φ (in most cases, φ 0.5). It was established that the inhibiting concentrations of fluorinated hydrocarbons for the combustion of methane and hydrogen in nitrous oxide are similar, in contrast to the combustion in oxygen- nitrogen oxidative media. A qualitative interpretation of the results is given.

An experimental investigation of an influence of trifluoromethane CHF3, pentafluoroethane C2HF5 and perfluorobutane C4F10 on near-limit hydrogen-nitrous oxide and methane-nitrous oxide premixed flames was performed. Flammability limits, a maximum explosion pressure ΔPmax, maximum rate of pressure rise (dP/dt)max, and a laminar burning velocity Su were determined. The flammability area in the case of N2O as an oxidizer is substantially wider than for the case of the oxidizer which is the mixture of oxygen and nitrogen with the O2 content 25% (vol.). The dependences of Su, ΔPmax and (dP/dt)max on concentration of the fluorinated hydrocarbons are characterizing by an availability of maxima which positions are close to the peak concentrations of the flammability regions. A qualitative interpretation of the results obtained is given.

The combustion of hydrogen-air mixtures near the lower composition flammability limit in cylindrical reactors of various diameters is studied. The speed of flame propagation in the horizontal direction is lower than that in the upward direction. Chromatographic analysis showed that, during the combustion of these mixtures, hydrogen is consumed only partially. That the flame propagates despite a low adiabatic temperature can be explained by the formation of the well-known cellular structure.

Experimental data on the combustion characteristics of methane-oxidative gas (O2 + N2)-inhibitor (CHF3, C2HF5, and C4F10) mixtures and an analysis thereof show that fluorinated hydrocarbons (HFC and FC) exhibit the properties of both flame inhibitors and promoters. The flammability concentration limits, maximum explosion pressure ΔP max, maximum explosion pressure rise rate (dP/dt)max, and laminar flame speed S u are measured for near-limit methane-oxidative gas-fluorinated hydrocarbon mixtures. It is demonstrated that, when added to lean near-limit mixtures, HFC and FC behave as an additional fuel. Calculations of the thermodynamic characteristics of reactions involving fluorinated hydrocarbons capable of acting as both an inhibitor and oxidizer show that such reactions have significant heat effects, 150–700 kJ/mol, with the respective adiabatic temperatures being as high as 900–1800 K. The results of the present study suggest that the procedure of selecting fluorinated hydrocarbons for practical applications as fire and explosion suppressants should include careful tests of their promoting effect.

The influence of additives of various chemical natures (CH 4 , N 2 , CO 2 , and steam) at a laminar burning velocity S u of hydrogen in air has been studied by numerical modelling of a flat flame propagation in a gaseous mixture. It was found that the additives of methane to hydrogen–air mixtures cause as a rule monotonic reduction in the S u value with the exception of very lean mixtures (fuel equivalence ratio ϕ = 0.4), for which a dependence of the laminar burning velocity on the additive's concentration has a maximum. In the case of the chemically inert additives (N 2 , CO 2 , H 2 O) the laminar burning velocity of rich near-limit hydrogen–air flames drops monotonically with an increase in the additive's content, but no more than 1.5 times, and the adiabatic flame temperature changes slowly in this case. In the case of methane as the additive, the laminar burning velocity is diminished approximately 5 times with an increase in the adiabatic flame temperature from 1200 to 2100 K. Deviations from the known empirical rule of the approximate constancy of the laminar burning velocity for near-limit flames are shown.

The normal rate of combustion S ui of rich near-limit hydrogen-oxidizing medium-retarder mixtures was determined experimentally. The oxidizing medium was a mixture of nitrogen and oxygen with oxygen contents of 15, 20.6, and 25 vol%; the retarding agents were trifluoromethane CF3H, pentafluoroethane C2F5H, and perfluorobutane C4F10, and the inhibitor was AKM. Deviations from the empirical rule of approximately constant normal rate of combustion of near-limit mixtures were observed. In the presence of pentafluoroethane, the dependence of S ui on the content of the retarder contained a pronounced maximum. The AKM inhibitor was found to be highly effective with respect to the combustion of near-limit mixtures in oxidizing media enriched in oxygen.

An analysis of published experimental data characterizing the influence of diluents of various chemical nature (both halogenated and chemically inert) on upper flammability limits of flammable gases in air (methane and hydrogen have been considered as examples) has been done. Dependences of critical oxygen concentration C O 2 cr and critical fuel equivalence ratio ϕcr for mixtures combustible–air–diluent at upper flammability limits on diluent concentration were determined. The obtained data were interpreted on the basis of the concept of self-inhibition at combustion of rich mixtures of organic combustibles in air. A method for evaluation of relative effectiveness of various inhibitors and for determination of availability of self-inhibitive properties of a combustible gas has been proposed.

An experimental investigation of the influence of inhibitors of various chemical natures on flammability limits in mixtures H 2 +oxidizer (O 2 +N 2 )–suppressant (C 2 HF 5 ; CHF 3 ; C 4 F 10 ; inhibitor AKM, which is a mixture of olefins) was carried out. Compositions of N 2 and O 2 with elevated (25 vol%) and reduced (15 vol%) oxygen concentrations and air were used as oxidizing atmospheres. Experiments were done at room temperature and atmospheric pressure. Flammability limits were determined in a closed vessel of volume of 4.2 dm 3 (internal diameter 20 cm). Mixtures were prepared immediately in the preliminary evacuated reaction vessel by partial pressures. The mixtures were ignited by an electrical spark of energy near 1 J in the center of the reaction vessel. A flame propagation was detected by a pressure transducer. Twelve flammability curves were measured, which allowed to compare effectiveness of the inhibitors at various oxygen contents in the atmosphere. A qualitative analysis of the obtained results was done, which showed an important role of an inhibitor regeneration.

The absence of correlations between the heat of combustion of substances and substance combustion characteristics is shown to be caused by the special features of competition between reaction chain branching and termination, including partial participation of fuels in the inhibition of their oxidation. By way of example, differences in the characteristics of combustion of hydrocarbons and hydrogen at atmospheric pressure and the mechanisms of the development of chain avalanches in these processes are considered.