The analysis of emergency situations related to fires at nuclear power plants

Introduction. The article provides a system and statistical analysis of emergency situations associated with fires at nuclear power plants (NPPs) in various countries of the world for the period from 1955 to 2019. The countries, where fires occurred at nuclear power plants, were identified (the USA, Great Britain, Switzerland, the USSR, Germany, Spain, Japan, Russia, India and France). Facilities, exposed to fires, are identified; causes of fires are indicated. The types of reactors where accidents and incidents, accompanied by large fires, have been determined.The analysis of major emergency situations at nuclear power plants accompanied by large fires. During the period from 1955 to 2019, 27 large fires were registered at nuclear power plants in 10 countries. The largest number of major fires was registered in 1984 (three fires), all of them occurred in the USSR. Most frequently, emergency situations occurred at transformers and cable channels — 40 %, nuclear reactor core — 15 %, reactor turbine — 11 %, reactor vessel — 7 %, steam pipeline systems, cooling towers — 7 %. The main causes of fires were technical malfunctions — 33 %, fires caused by the personnel — 30 %, fires due to short circuits — 18 %, due to natural disasters (natural conditions) — 15 % and unknown reasons — 4 %. A greater number of fires were registered at RBMK — 6, VVER — 5, BWR — 3, and PWR — 3 reactors.Conclusions. Having analyzed accidents, involving large fires at nuclear power plants during the period from 1955 to 2019, we come to the conclusion that the largest number of large fires was registered in the USSR. Nonetheless, to ensure safety at all stages of the life cycle of a nuclear power plant, it is necessary to apply such measures that would prevent the occurrence of severe fires and ensure the protection of personnel and the general public from the effects of a radiation accident.

An experimental study of the fire extinguishing ability of modular fire extinguishing installations if astralene-modified water mist is used

Introduction. The aim of the research project is to study the effect produced by one type of carbon nanostructures, or astralenes, on processes of extinguishing oil product flame using finely sprayed water. Materials and research methods. The research is focused on fire extinguishing suspensions used in modular water mist installations for the fire extinguishing of oil products. Astralene-modified distilled water, having the volumetric concentration of nanostructures equal to 0.05–1.0 percent, was used as a fire extinguishing substance under research. The experiment was focused on the study of thermophysical characteristics of fire extinguishing liquids, such as density, dynamic viscosity, surface tension, specific heat of vaporization. Also, studies were carried out to identify the rate of evaporation, the distribution of droplet sizes of sprayed fire extinguishing compositions, and the time needed to extinguish the model source of ignition of oil products.Research results. The dispersion of nanostructures of fire-extinguishing liquids allows to increase their density, surface tension by 20.6 %, increase the specific heat of vaporization if the volumetric concentration of astralenes is equal to 0.25 and 0.5 %, and boost the dynamic viscosity by 6.68–15.38 % at the temperature of 20 °С. The research was carried out to find the rate of evaporation of droplets of the modified fire-extinguishing liquid. It was found that an increase in the volumetric concentration of nanostructures from 0.05 to 0.5 % causes reduction in the evaporation rate.The droplet speed increases if the volumetric dispersion of astalenes goes up to 0 to 0.25 %. However, a further increase in the volumetric concentration of astralenes to 1.0 % causes a reduction in their speed. The extinguishing time was identified using a laboratory fire extinguishing installation. The distribution of droplet sizes of fire-extinguishing compositions is in the range of 20 to 160 microns. The fire extinguishing capacity of the installation was highest if a fire extinguishing composition had a 0.5 % volumetric concentration of astralenes.Conclusions. The modification of a fire extinguishing composition by carbon nanostructures leads to a change in its thermophysical characteristics. The addition of this composition to the installation, used at facilities involved in the processing of petroleum products, will increase its fire extinguishing ability. Further areas of research may include the development of astralene stabilization methods for suspensions and adaptation to low temperatures.

Trends in the development of fire alarm system controllers for fire alarm systems

Introduction. Fire alarm system controllers are the main technical aids that serve as the backbone of a fire alarm system (a unit) at a facility. They consolidate fire alarm messages, coming from fire detectors, analyze, process, and deliver them to the user and display them in the pre-set format. The technical capacity of fire alarm system controllers is constantly improving in line with the technical progress and tightening fire safety requirements.Aims and purposes. The purpose of the article is to analyze the state of and trends in the development of fire alarm system controllers, that improve the fire safety of protected facilities. The task encompasses the retrospective review of principal tactical and technical characteristics of fire alarm devices for the period starting from the early 1950s to the present time in Russia, as well as the statistical analysis of the pace of their supply on the market of automatic fire fighting systems.Methods. Methods of system analysis and mathematical statistics were used.Results and discussion. The main stages of development of instruments for fire alarm systems that are reflective of the technical progress, primarily in the field of radio electronics, as well as the socio-economic transformations in Russia are specified. The article presents the results of statistical studies, carried out by the co-authors at different times and characterizing a change in the Russian market based on the comparative data on domestic and foreign alarm systems. The main trends in the development of the product mix and technical specifications of devices during the analyzed period are identified. The co-authors focus on the generalized layout of a blockmodular apparatus of a fire alarm system controller and determine the requirements for communication between functional modules to ensure the reliable operation of a fire alarm system.Conclusions. The main trends in the development of fire alarm system controllers, designated for fire alarm systems, focus on the application of new communication technologies and microelectronic devices that solve comprehensive safety problems with regard for the top-priority requirements of fire safety. The pace of improvement of tactical technological characteristics of devices is reflective of the state of and trends in the development of automatic fire fighting systems in Russia.

The calculation of required fire resistance limits for engineering structures of technological pipe racks at oil and gas processing plants on the basis of an evaluation of the time needed for personnel evacuation and rescue in case of fire

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.

A comparative analysis of the requirements of Russia and the United States to the fire resistance of building structures of oil refineries and petrochemical plants

Introduction. Currently, national standards and codes of practice contain deterministic values of the fire resistance of building structures of facilities of the Russian fuel and energy complex (FEC), while a probabilistic approach to determining their fire resistance is not specified in the Russian regulatory documents. The methodology of the probabilistic approach to the fire resistance of structures is detailed in API 2218 “Fireproofing Practices in Petroleum and Petrochemical Processing Plants”, developed by the American Petroleum Institute.Methods. A comparative analysis of the Russian regulatory documents on fire safety and API 2218 in terms of the established concepts of fireproofing and requirements for the fire resistance limits of building structures of oil and gas industry facilities, is carried out.Results. It was established that the Russian Federation has no regulatory documents establishing methods based on the probabilistic approach, including determination of the required fire resistance limits and points of application of fire-resistant coatings at facilities of the fuel and energy complex by analogy with international standard API 2218.Conclusion. Based on the analysis, it was concluded that approaches to the philosophy of the fire resistance of structures of buildings and structures of the fuel and energy complex in the documents under consideration are fundamentally different. In order to improve the Russian regulatory and technical framework, governing fire safety and fire resistance, it is proposed to consider the requirements of foreign documents that take into account proven international engineering and technical practices, in particular, the use of a probabilistic approach taking into account hydrocarbon fires.

Flameless combustion of wood: charring and heat release characteristics

Introduction. The article presents the results of a research on the two stages of thermal decomposition of timber. The first stage of thermal decomposition is flame combustion, which is followed by a transition to flameless combustion due to the formation of a char layer on the surface of wood. The flameless process is accompanied not only by heterogeneous combustion, but, at least, three reactions: pyrolysis, thermal oxidative destruction of wood and oxidation of resulting coke.Goals and objectives. The goal is to identify the criteria of charring and heat release under the influence of an external radiative heat flux on samples of coniferous and deciduous species of wood using a standard flowthrough calorimeter with a focus on flameless combustion. Methods. A standard OSU flow-through calorimeter, produced by Atlas (USA), was used to identify heat release characteristics under the influence of external radiative heat fluxes that had the density of 20, 35 and 52 kW/m2. The lower limit of heat, released in the complete combustion of samples, that had a char layer, was identified using bomb calorimeter C-5000.Results. The co-authors analyzed the charring process and characteristics of heat release using samples of wood species that were 10 and 25 cm thick. Wood samples were exposed to combustion under the influence of an external radiative heat flux that had the density of 20, 35 and 52 kW/m2 subsequent to the results of tests, conducted using the OSU calorimeter. The co-authors evaluated the charring velocity and the coke layer thickness for the cases of flame and flameless combustion; efficient combustion heat release and the combustion completeness coefficient, as well as the sample shrinkage. The co-authors demonstrated that a transition from flame combustion to heterogeneous combustion occurs upon completion of the quasi-neutral burning of wood samples, which corresponds to the final point of heat release velocity curves and marks a transition from the behaviour of a thermally thick material to that of a thermally thin material.Conclusion. The obtained experimental data allow to forecast a change in the physical and heat engineering properties, characteristics of heat release in the processes of flame and flameless combustion of different wood species with account taken of the char layer formed on its surface under the influence of various heat fluxes.

A model of response efficiency in the hierarchical control system based on the assessment of readiness of fire departments

Introduction. The readiness of all levels of subsystems that comprise the Unified State System for Emergency Prevention and Liquidation (USSEPL) is one of the most important characteristics that determine its effectiveness. To support decision-making at the upper levels of the management hierarchy, it is important to have a set of models that adequately represent the dependence between key response efficiency indicators and particular indicators of lower levels of the system (fire and rescue departments). In most cases, a regulatory approach to the construction of such models, by virtue of which analysts set their structure and parameters, turns out to be unproductive due to their non-adaptive nature in the context of dynamically changing external conditions and technological capabilities of modern devices. The use of an approach based on solving inverse problems that close the feedback loop and provide for an adaptive adjustment of parameters and the structure of models, ensures the current adequacy of models amid changing conditions.The relevance of the study lies in the development of a technology for constructing polynomial models that allow to assess the USSEPL response effectiveness based on estimated indicators of readiness of subsystems at lower levels obtained using expert evaluation techniques (testing) by means of internal control.Goals and objectives. The aim of the work is to build and test the technology for developing analytical polynomial models that allow to adequately assess performance indicators of the USSEPL response depending on the readiness indicators of lower-level subsystems (fire and rescue departments). In compliance with this goal, the tasks of choosing the type of model and methods of obtaining the necessary initial data are also set.Methods. The study uses methods of analysis of hierarchically organized systems, mathematical statistics, simulation modelling, and methods of expert evaluation. The research is backed by materials from domestic and foreign publications.Results and discussion. The proposed method of constructing an efficiency model of the USSEPL operation, relying on the readiness of subsystems, serves as the basis for constructing models that can take into account other indicators of subsystems.Conclusions. The solution to the problem of constructing a polynomial model, that features dependence between the USSEPL response efficiency and lower-level readiness indicators, serves as the basis for other similar models that will support decision making systems.

A change in the air temperature inside a 20-liter chamber when air is added from the receiver

Introduction. One of the reasons for the overestimation of the explosion hazard of dust inside a (20 ± 2)-liter chamber is the elevated initial temperature of the air suspension. The initial temperature is also raised by the process of filling the pre-emptied chamber with air from the receiver, used to distribute dust over the chamber. In this work, an increase in the air temperature inside an 18.7-liter chamber was identified in an experiment for the case of addition of air from the receiver.The methodology of an experiment. The air temperature in the chamber was measured at the time when the air from the receiver was added using a WR 5/20 thermoelectric converter (a thermocouple). The thermocouple junction was located at the distance of 70 mm from the inner wall of the chamber. The thermocouple signal was processed by an MCLab PRO programmable logic controller (the time resolution is 1 ms).Research results. The measuring instruments recorded an increase in the temperature of the thermocouple junction by +14 degrees. Due to the comparability of the inertia of the thermocouple (3 s) and the characteristic time of air cooling by the chamber walls (5 s), the measurement results underestimated the real value of a jump in the air temperature inside the chamber. Measurement results were refined using a simple model of heat transfer between the objects involved in the process (thermocouple junction – air – chamber wall) that entailed the exponential relaxation of the temperature difference over time. As a result, an estimated increase in the initial temperature inside the chamber of +30 degrees was identified.Results and discussion. The temperature jump by +30 degrees makes a noticeable contribution to the total jump in the initial temperature, which was previously tied solely to the burnout of the ignition source (+80 degrees).Conclusions. Given the known increase in the temperature inside the chamber caused by the burnout ofa standard ignition source (2 kJ), the real value of the initial temperature of the environment can reach 135 °C in the course of studying dust in a (20 ± 2)-liter chamber.

New milestones of professional culture for the persons regulating relations in the field of fire safety

The article addresses the problem of bridging the divide between the present-day technological advancement, primarily in the field of normative legal and technical regulation of fire safety, and the qualification of persons, authorized to regulate relations in fire safety assurance (hereinafter — “Authorized persons”) in the context of transition of the state regulation of fire safety relations from an obsolete standard target model to a new analytical and scenario-based (risk-oriented) target model used to make decisions in the area of control over the safe condition of the technosphere in view of a sudden increase in the dynamics of sociocultural processes.The Education and Research Supervision Unit of the State Fire Academy of the EMERCOM of Russia (the Ministry for Civil Defense, Emergencies, and Elimination of Consequences of Natural Disasters), responsible for the drafting of suggestions concerning the implementation of point 10, Minutes № 1 of the meeting of the workgroup of EMERCOM of Russia on May 20, 2019 “Regarding the arrangement of interaction with the management authorities of the institutional firefighting service of executive federal authorities and organizations”, has developed “The list of milestones of professional culture for the persons responsible for regulating relations in the field of fire safety for the period of transition from a standard target model to the risk model of controlling, supervisory, and authorization-related activities” (hereinafter — “the List”).This List represents a basic set of conceptual professional milestones, whose attainment enables authorized persons to re-focus their conscience from an obsolete standard paradigm, used to make decisions in the area of fire safety, to a new risk-oriented one.Given the focus of this article, it defines some, or the most significant, milestones of professional risk-oriented culture of authorized persons.