Preview

Pozharovzryvobezopasnost/Fire and Explosion Safety

Advanced search
Vol 31, No 1 (2022)
View or download the full issue PDF (Russian)

COMBUSTION, DETONATION AND EXPLOSION PROCESSES

6-13 406
Abstract

Introduction. Critical values of the partial density of gas, the toxic dose or relative mass of carboxyhemoglobin in human blood serve as the criteria determining the time to the blocking of escape routes due to the presence of carbon monoxide. However, the comparative analysis of the effect produced by the selected criterion on the time to the blocking of escape routes due to the presence of this gas has not been conducted yet.

Goals and objectives. The purpose of the article is to compare the values of the time to the blocking of escape routes by carbon monoxide obtained using various methods of determining the critical values of the carbon monoxide density. Towards this end, experimental studies on combustion processes of various solid and liquid combustible substances and materials were conducted in a small-scale test unit, and calculations of the time to the blocking of escape routes with carbon monoxide were made on their basis.

Theoretical fundamentals. The amount of carbon monoxide, inhaled during a fire, is calculated using experimentally measured partial densities of CO and mathematical models designated for the calculation of the toxic dose of this gas and formation of carboxyhemoglobin in human blood.

Results and discussion. Experimental dependencies between the testing time and medium-volume densities of monoxide emitted during the combustion of the “low smoke” PVC cable sheathing, timber (pinewood), chocolate, transformer oil and vegetable oil are presented. The authors obtained theoretical dependencies between
the toxic dose and mass concentration of carboxyhemoglobin in human blood, on the one hand, and the time for the combustible materials, analyzed in the article. It has been found that the values of time to the blocking of escape routes due to the presence of carbon monoxide may differ significantly depending on the method used to determine the critical values of the carbon monoxide density.

Conclusions. Standard methods, used to calculate the time to the blocking of escape routes due to the presence of carbon monoxide, employ the value of the critical partial density which may involve a substantial overestimation of the above time frame and the underestimation of the toxic effect produced on a person in the process of his/her evacuation. Therefore, it is necessary to apply all methods, discussed in the article, to select the minimum value of the above time frame.

14-20 260
Abstract

Introduction. A fire investigation assumes that electric arc welding sparks (hereinafter referred to as “sparks”) are effective sources of ignition. However, the spark ignition of a combustible material depends on the contact time. This work has experimentally proven that a smooth vertical wall, made of combustible rigid polyurethane foam (PUF), is not subjected to spark ignition. To explain this fact, the author calculated the time of contact between the spark and the wall τint, and compared it with the minimal estimated contact time τmin required to ignite the wall.

The sample and the testing procedure. Sparks (the arc power up to 6 kW, the current up to 160 A) reached the PUF wall located at a distance of 0.1–0.15 m from the arc. An everyone experiment was continued until the electrode was burned down.

Research results and discussion. Neither attempt to inflame the PUF sample by a spark was successful. Sparks bounced off the PUF sample and fell down. The characteristic dimensions of cooled iron droplets ranged from 0.2 to 3 mm.

An evaluation of τint. The authors applied a model of elastic interaction between a drop of molten iron and a rigid wall, assuming that the sum of the potential energy of the drop, associated with its surface, and the kine­tic energy of a spreading drop, if flattened, is conserved. The longest contact time is achieved for drops, featuring the maximum diameter of 3 mm: τint ≈ 0.004 s.

Estimation τmin. The authors applied the experimental modeling of the process, whereby the effect of an iron drop on PUF was replaced by the time-controlled effect, produced by a wooden cylinder (6 mm in diameter), inflamed at one edge. τmin ≈ 0.3 s. The ratio τint << τmin explains the inability of electric arc welding sparks to ignite the PUF wall.

Conclusions. Electric arc welding sparks, having a diameter of up to 3 mm, cannot ignite a vertical wall, made of rigid combustible polyurethane foam, in case of a side impact. The lack of ignition is explained by the short-term contact between the spark and the surface of the polyurethane foam.

SAFETY OF SUBSTANCES AND MATERIALS

21-39 497
Abstract

Introduction. The article addresses the fireproofing limit of the cast-iron tubing that lines subway tunnels. These structures have been fire tested neither in our country, nor abroad, and therefore, no fire test results have been analyzed, although this analysis is necessary to guarantee structural performance.

Purpose and objective. The purpose of the study is to analyze the results of two fire experiments, including the testing of the cast iron tubing without fire proofing, and the testing of the tubing protected by a fireproof plate. The objective of the study is to choose and use a rational thermal analysis methodology.

Methods. A standardized methodology was applied to test the fire resistance of loaded full-scale tubing specimens in a fire furnace, where thermocouple measurements of tested specimens were taken. The thermal analysis of these measurement results was conducted, using the methods and software for the numerical calculation of non-stationary temperature fields inside fireproof structures in one- and two-dimensional settings.

Results. It has been established that the fire resistance limit of the 5.6-25-NU cast-iron tubing tested under constant static loading (150 kN) without any fire protection is 54 minutes, which corresponds to classification R 45, while the fire resistance limit of the same tubing, fireproofed by PROSASK fire panel plates, that are 25 mm thick, is, at least, 121 min (R 120). Calculations allow to prognosticate a change in the fire resistance, if account is taken of the difference between the test environment and the one of the tubing when in operation. The authors present the results of calculations for various fire protection options and show that the fire protection and fire resistance limits of the cast-iron tubing are high, if PROSASK fire plates are used. The authors also demonstrate the projectability of the fire resistance values, if the modes of exposure differ from the standard temperature mode.

Conclusions. The thermal analysis of the results of two fire experiments, conducted to evaluate the fire resistance of the cast-iron tubing as the tunnel lining allows to obtain the information that is essential for the fire protection and pre-set fire resistance of critical subway structures as well as the further development of this area of experimental and theoretical research. The authors demonstrate the efficiency of thermal calculations as an instrument for the evaluation of fire protection parameters/fire resistance of tubing and the reduction in the number of costly fire tests.

MATHEMATICAL MODELING, NUMERICAL METHODS AND PROGRAM COMPLEXES

40-48 337
Abstract

Introduction. The authors draw attention to the importance of the pre-explosive concentration detectors to assure the fire safety (FS) of fire and explosion hazardous facilities at oil refineries. The problem of the principle of pla­cing detectors close to sources of potential leaks is identified. The subject of research is the process of the maintenance of stationary thermochemical gas analyzers and their detectors installed around open-air facilities (OAF).

Theoretical fundamentals. The notion of the discipline of the maintenance of stationary thermochemical gas analyzers is addressed in this section. The authors justify the choice of this type of devices according to the classification based on physical methods of analysis. Maintenance as a process, focused on the fire and explosion safety at oil refineries, depends on environmental and meteorological parameters, as well as the parameters of the process equipment. The release of catalytic poisons in the process of oil refining at OAFs, which negatively affect the sensitive elements (SE) of thermochemical detectors, and weather conditions may reduce calibration adjustment intervals or cause an accelerated failure of sensitive elements. The impact of environmental factors makes it necessary to adjust the detector calibration dates with account taken of the standard ones specified in the engineering documentation.

Research results. The work sets the goals in terms of the values of the function of groups of parameters that substantiate the implementation of measures focused on the maintenance of detectors in the condition required by the documentation. The maintenance evaluation criterion is expressed as a vector of objective functions that convey the dependencies between groups of climatic, personnel work performance, specific, and other parameters. The integral criterion of the maintenance efficiency is provided in the form of a rectangular matrix and a convolution that takes into account three vectors of objective functions. The discipline of the maintenance of gas analyzers is presented in the form of a discrete subprocess of the process of fire and explosion safety assurance.

Conclusions. This research work addresses an approach to modeling the discipline of the maintenance of stationary thermochemical gas analyzers installed around the open-air facilities (OAF) of an oil refinery. In further studies it is necessary to analyze the spatial location of the gas analyzer detectors to determine their number depending on the perimeter of the oil refinery’s open-air facilities.

49-64 480
Abstract

Introduction. The article addresses the choice of a method used to analyze hierarchies and pairwise comparisons (hereinafter — MAH), that serve as a framework for an integrated corporate safety assessment methodology. Its application ensures the transformation of input information, obtained in the form of a characteristic description of an assessed event, into the resulting assessment that has a weighted numerical value.

Goals and objectives. The main purpose of the article is to obtain an assessment result in respect of the actions that are added to industrial and fire safety checklists applied to assure the integrated safety of an enterprise. A selected MAH is used to make pairwise comparisons of factors and alternatives. Values of local and global priorities can be determined for each element under study. Weighted coefficients, obtained in the form of local priorities, are related to the activities being checked, while global priorities are directly related to the services (structural units) that ensure the sustainable integrated security of an enterprise.

Methods. The authors provide a rationale for the choice of MAH, which allows itemizing the values demonstrating the intensity of influence of factors and break them down into components. At the stage of synthesizing the obtained analytical results with the help of MAH, the results obtained by expertise must be verified by determining the value of the expert consistency ratio to confirm the adequacy of the obtained result.

Results. The probability of influence of analyzed hazards, related to accidents and fires at the enterprises under consideration, was assessed as a function of their causes during the 7-year period under review. The article presents calculated coefficients of communication, impacts and influence made by specialists employed with respective services (structural units) on the industrial and fire safety subsystems that encompassed the integra­ted safety of an enterprise. The results of introducing correction factor g, whose dependence is expressed by final indicators of damage measured in economic (ruble) and social (human) losses, are presented.

Discussion. The article focuses on the fact that the sustainable operation of industrial enterprises depends on the reliability margin of integrated corporate safety, the maintenance of which requires particular resources (financial, material resources, as well as the time, needed for the personnel to eliminate any identified deviations, etc.). Given that the resources focused on the integrated safety assurance are limited, they cannot meet all requests made by the heads of services (departments), while highly risky targeted activities need more research.

ELECTRICAL ENGINEERING

65-76 394
Abstract

Introduction. The data, provided in the article, demonstrate the relevance of the socket fire safety improvement in the course of operation. The purpose of the article is to develop a research-backed method of examining the socket contacts that feature high transient resistance or change in shape. The method can be subsequently used to identify causes of damages in a fire investigation.

Materials and methods. A JSM-6390LV scanning electron microscope with a module designated for the energy dispersive microanalysis is used in the research. The subjects of research are type C (EU Type C) and type F (EU Type F) sockets. The failure surfaces of socket contacts were analyzed without preliminary sample preparation.

Theoretical fundamentals (theory and calculations). A physical and mathematical model of the limit bearing capacity of socket contacts, similar to the real construction, has been developed. The model serves as the framework for a practical computational algorithm of the expert analysis of mechanical and geometrical characteristics. The solution is reduced to short calculation formulas, that can be used to evaluate the bearing capacity of so­cket contacts. The applicability of the developed mathematical model to fire investigations is proven in a specific ­example.

Results and discussion. The authors analyze cases of socket fires, caused by the loss of the bearing capacity of socket contacts in the process of operation. Photos of the oxide film on the contact surface and its elemental composition are provided in the article. The experimental data have proven that the fusion of contacts and the presence of an oxide film, featuring high specific resistivity, are a significant criminalistic evidence that helps to identify causes of fire.

Conclusions. The authors propose a method for the identification of the bearing capacity of socket contacts. The method can be used to determine if a subsequent fire is related to the socket ignition. The information, provided in the article, can be used by specialists in the course of an expert examination of socket contacts withdrawn from the site of the fire to identify the failure mechanisms and, ultimately, causes of fire.

SAFETY OF BUILDINGS, STRUCTURES, OBJECTS

77-87 353
Abstract

Introduction. The problem of car parks and parking spaces is relevant in many large cities, and it requires
the optimization of parking spaces. The arrangement of open car parks on the ground floors of apartment buil­dings is an effective way to organize car parks in a house in addition to covered parking lots. In this regard, in order to assess the fire hazard of such a design solution, it is necessary to study the spreadability of fire from an open ground floor parking lot to upper floors and develop reasonable proposals for the development of new and optimization of effective fire safety requirements.

Goals and objectives. The goal of this work is to study the spread of fire hazards using the field modeling of the car burning process in an open parking lot on the ground floor of an apartment building and to assess the possibility of the fire safe arrangement of such parking lots in residential buildings.

Method. To achieve the purpose of the study, the field (CFD) modeling of the fire development pattern was performed using FDS computer software. In the course of modeling, the authors analyzed the spread of the fire hazard from an open parking lot, located on the ground floor, to the upper floors of a residential building.

Results and discussion. Temperature distributions, smoke and heat flows at various points in time were obtained as a result of modeling the development of fire in a parking lot. The results of calculations allowed to evaluate the effectiveness of various types of fire barriers and determine their parameters to meet the condition of the non-proliferation of fire. The most optimal solution is a non-combustible visor made of fire-resistant materials and installed above the opening leading to a parking lot. Given the results of the work, a set of necessary fire-figh­ting actions are proposed to ensure the possibility of arranging open parking lots in residential apartment buildings.

Conclusions. It is shown that the fire safety of residential apartment buildings that have open single-level parking lots is achievable in case of the use of fire-resistant bearing and enclosing building structures, non-combustible materials for cladding, finishing the facade of a building, as well as in the case of making a canopy, a balcony or a gallery above the opening that leads to the parking lot.

88-98 412
Abstract

Introduction. An important engineering task, to be solved in the process of designing buildings and structures for hazardous industrial facilities, is to determine values of loads caused by outdoor explosions of the fuel-air mixture. Nowadays software packages, that use the computational fluid dynamics (CFD) approach, are widely applied in the design practice to assess various effects on building structures. In this regard, it is necessary to develop a load calculation method, that employs numerical simulation, and verify it in comparison with the experimental data.

Goals and objectives. The purpose of this work is to use the method of computational fluid dynamics to analyze external sympathetic detonation loads on various types of buildings and structures.

The body of the article. The article addresses the “compressed balloon” method used to analyze loads, caused by outdoor explosions of gas. Dependencies, proposed in the article, are needed to set the input data and make numerical calculations using the computational fluid dynamics (CFD) technique. The numerical modeling of various experiments in the ANSYS Fluent software package was conducted. The authors compared the results of numerical modeling and standard engineering methods with various experiments to assess the accuracy of the “compressed balloon” method used to analyze an outdoor detonation explosion.

Conclusions. The authors have proven the qualitative and quantitative convergence of the numerical model of blast wave propagation and the experimental data. This calculation method allows to accurately apply the pressure profile to any surface of a building or structure in the course of an outdoor detonation explosion and estimate the bearing capacity of building structures. The proposed method can be used in the design of buildings or structures that feature various configurations.

QUESTION - ANSWER

99-104 269
Abstract

The author addresses various types of contact joints and methods of preventing the emergence of large transient resistances on them. The article has guidelines governing regular preventive repair works aimed at the maintenance of contact points. The analysis of various technical solutions for the protection of power grids from high transient resistances has been conducted. The author demonstrates methods used to control and monitor the condition of potentially dangerous contact sections of a power grid. The author makes recommendations on the joint application of management actions and technical facilities to address fire safety issues of electrical installations of buildings.



ISSN 0869-7493 (Print)
ISSN 2587-6201 (Online)