Introduction. The absence of the burning parameters of forest combustible materials does not allow a reliable calculation of the heat flux from a forest fire affecting the energy facilities of Vietnam. Therefore, the study of the combustion of samples of Vietnamese trees krone is an urgent scientific and practical problem.

Goals and objectives. The purpose of the article is to substantiate the source data for mathematical modeling of the parameters and thermal effects of high forest fires on the objects of power industry in Vietnam. To achieve it, experimental studies of the burning of trees krone samples of the most common deciduous and coniferous trees of Vietnam were carried out.

Methods. An experimental method is used to study the burning of trees krone samples in a small-sized experi­mental installation. The analysis of the results is made.

Results. Experimental dependences of the specific mass speed of gasification and specific coefficient of release of carbon monoxide on the time of testing of trees krone samples of five most common deciduous and coniferous trees of Vietnam were obtained. The average values of the above mentioned parameters were compared with the values obtained during the burning of tree trunk samples and given in the literary sources. It is shown that time-­average experimental values of specific mass speed of gasification of all samples of tree krone are 2.7–5.7 times less than corresponding values, which were determined during tree trunks burning. At the same time experimental average values of specific coefficient of release of carbon monoxide at burning of tree krone are 2.5–10.9 times more than corresponding values in case of burning of wood mass of tree trunks.

Conclusion. An experimental study of the burning of trees krone samples of the most common deciduous and coniferous trees of Vietnam allows to substantiate the choice of specific coefficient of release of carbon monoxide and specific mass speed of gasification required for mathematical modeling of parameters and thermal effects of high forest fires on Vietnamese energy facilities.

Introduction. The data presented in the article indicate that the problem of improving fire safety of vehicles is very topical. The aim of the article is to develop a scientifically based method for studying a copper conductor with signs of local current overload in order to establish the cause of its damage during a fire-technical examination.

Materials and methods. The studies were carried out with a JSM-6390LV scanning electron microscope with an add-on device for energy dispersive microanalysis. The fracture surfaces of the copper conductor were analyzed without preliminary sample preparation.

Theoretical foundations (theory and calculations). An updated model of ultimate stress-strain state of inelastic pure bending of a copper rod of circular cross section has been developed. The solution has been reduced to simple rating formulas that allow us to evaluate the bearing capacity of flexible single copper conductors. The applicability of the developed mathematical model during the fire-technical examination is shown by a specific example.

Results and discussion. Examples of vehicle fires caused by critical bending of the wiring harness are given in the article. Experimental data confirmed that the copper conductor under current overload melts in the critical bend area. The need to clarify the wording of the term “local current overload” is justified.

Conclusion. A method for determining the critical bending of a copper conductor at which its melting can occur under electric current has been proposed. The data presented in the article can be used by experts in an expert study of copper conductors from fire sites to establish the mechanism of their damage and, ultimately, the cause of a vehicle fire.

Introduction. A normative document Set of Rules 2.13130.2012 (item 5.4.3) states that if an required fire resistance limit of structures is equal to R15 (RE15, REI15) an application of non-protected steel structures is possible. But an actual fire resistance limit depends both on a reduced thickness of the structure and a temperature regime of a fire (for example “cellulose” or hydrocarbon regime). This study is aimed on a numerical evaluation of the actual fire resistance limit of the non-protected steel structures for the standard “cellulose” and hydrocarbon temperature regimes of fires at various reduced thickness of the structures.

Methodology and results. A numerical modeling of a heating of the structures was carried out using the software FDS 6. The non-protected steel structures having the reduced thickness δ_cr from 3 to 60 mm were considered. The fire resistance limits were determined as a time interval from a beginning of the fire to the time moment when the temperature of the structure reaches a value of 500 °C. Dependences of the actual fire resistance limits on δ_cr were obtained. These limits for the hydrocarbon fire were substantially lower than for “cellulose” one. A dependence of a ratio of the fire resistance limits for the hydrocarbon and “cellulose” fires on the reduced thickness of the structure was found.

Conclusion. The results of this study confirm the requirement of the normative document Set of Rules 2.13130.2012 (item 5.4.3) concerning a possibility of the application of the non-protected steel structures in the case when the required fire resistance limit is equal to R15 (RE15, REI15), but only for the “cellulose” fire. But this requirement is not valid for the hydrocarbon fire.

Introduction. The relevance of this work is due to the frequent occurrences of various chemical substances affecting ropes in sport and in the industry of high-altitude works, as well as due to the lack of open-access information on changes in the rope tensile strength under effect of chemicals.

Aims and purposes. The aim of this work is to improve the safety practices in the usage of ropes both in sport and in industry by assessing the effect of acid solutions on the rope tensile strength, and by providing recommendations for pre-usage visual inspection procedures so that to detect ropes exposed to acids.

Methods. We study the influence of sulfuric acid, hydrochloric acid, and phosphoric acid, as substances widespread in sport and industry, on static polyamide rope, the type of rope used commonly as personal protective equipment. The methods used involve measuring the breaking strength of the ropes after either 30 sec and 1 hr of exposure to different concentrations of these acids. In addition, photographs of ruptures are provided, so that safety specialists be able to detect future causes of rope failures.

Results. The results of the tests conducted show the main markers of the effects of acids on the samples to be the following: increase in the stiffness of the rope in relation to parts not exposed to the acid; increase in the hardness in the areas of exposure, as a result of sintering of individual fibers; sticky surface of the sheath, in the cases when partial dissolution of the sheath takes place.

Conclusion. Though all acid solutions tested have negative impact on rope strength, not all are easy to detect. Particularly deceiving can be ropes with polyether sheath, in which the latter, being less sensitive to acids, may camouflage the damage to inner fibers, while after 30 sec of exposure to 45 % H₂SO₄ such damage leads to decrease in the tensile strength down to 46,8 % of its original strength. Thus, we conclude that the only reliable way to protect oneself from a rope failure is to know the history of the rope in an entire manner.

Introduction. When studying fire safety laws and regulations, including foreign ones, one can draw a conclusion that protecting people during evacuation is mainly ensured by dividing the building into fire compartments, specifying geometric properties of escape routes and exits, and by equipping buildings with automated fire prevention systems. However, in order to assess the actual possibility of evacuating people, their number, physical condition, and degree of mobility must be known, as well as the number of patients who will need to be moved on stretchers or in wheel-chairs.

Main (analytical) part. This paper provides schedules for occupancy rates of medical departments in different units of a health care facility, namely, in the internal medicine and inpatient surgical units. Obtained empirical values presented in this publication are part of daily operating process and are included in the workflow: each day head nurses collect data on rates of patient occupancy in medical departments. The total number of processed empirical data was 297,000 values.

Conclusions. The studies that have been carried out demonstrate which geometrical properties must be ensured for refuge areas and that buildings of the inpatient surgical type are the most relevant location where they can be designed. Areas of refuge must be provided for surgery and intensive care departments where people can wait for rescue. Some categories of patients in intensive care units, as well as in the surgical department, are not subject to evacuation, because it is not possible to interrupt surgeries after reaching a certain stage.

Introduction. Ensuring the necessary level of fire safety of objects of different classes is achieved by the use of automatic fire extinguishing installations — drencher, sprinkler, etc. Such installations, feeding extinguishing agents (eg, water) with the required intensity, are designed to localize and eliminate the fire. But there is a significant class of objects for which it is required not to extinguish the fire, but to contain its spread until the arrival of fire departments. This is due to both the features of the structural and functional purpose of the protected objects, and restrictions on the use of extinguishing agents (water). Such facilities are equipped with automatic fire containment installations.

Problem. If the known automatic fire extinguishing systems set out the requirements according to intensity of extinguishing substances in a protected area with one sprinkler and other parameters for silent automatic fire containment installations such requirements are formulated in General terms. This complicates the design and subsequent operation of automatic fire containment systems.

Ways to solve this problem are: a) establishment of a list of premises and buildings that are appropriate to equip automatic fire containment installations; b) determination of the working intensity of the supply of extinguishing agents to contain the fire; c) assessment of the required operating time of the automatic fire containment installation; d) assessment of the pass of extinguishing agents. In this regard, the article provides relevant theoretical expressions and examples of quantitative estimation of activation time system, a flow rate of extinguishing agents to suppress fire, stock fire-extinguishing agents. Also information on classification of automatic fire extinguishing installations and the approximate list of the objects which are subject to protection by automatic fire containment installations is given.

Conclusions. Thus, on the basis of the above material can be formulated the basic requirements for the design of automatic fire containment systems, for which it is advisable to develop a special regulatory document.

Introduction. The article presents the regularities of particles distribution of fire extinguishing powder fractions in the cross sections of the simulated unregulated non-stationary gas stream. The distance from the fire extinguisher cut which the stream is most stable in terms of the content of fire extinguishing powder particles is determined. There are works in which the physical and chemical properties of fire-extinguishing powders are considered, the movement of powder particles in the stream is modeled, the influence of the fractional composition of the powder on its fire-extinguishing capacity is determined. At the same time distribution of powder fractions during its movement in gas-powder stream is not considered. The purpose of the present work is to find ways to improve the efficiency of powder extinguishers by controlling the distribution of powder fractions in a non-stationary gas stream.

Materials and methods. Experimental study installation consists of coordinate table oriented perpendicular to gas-powder stream direction. The table is equipped with collectors that allow to collect powder samples at control points of flow cross-section. Food sodium chloride (further — salt) was used in the experiment. Its characteristics correspond to GOST R 53280.4–2009 and allow to apply it as a model. The coordinate table was installed sequentially at a distance of 500, 750, 1000 and 1250 mm from the fire extinguisher cut. Next, a shot of salt with a known fractional composition was supplied with a fire extinguisher model to a coordinate table and the retained powder samples were taken. The mass and fractional composition of the samples collected by each collector were then determined. Stability of the particle distribution in the gas stream by statistical analysis (by Fischer’s criterion) was measured for their content.

Conclusions. Regularities of different fire extinguishing powder fractions distribution in cross section of non-regulated non-stationary gas stream are established and analytically described. These regularities can be used in finding ways to regulate fire extinguishing powder fractions during fire extinguishing. The most representative and stable in accuracy (correctness and precision) results of powder fractions content in the section of non-stationary gas stream at a distance of 1000 mm from the fire extinguisher cut. This should be taken into account in further research.

Analysis of existing technical solutions for lightning protection of buildings and structures is made. The requirements of regulatory documents on lightning protection of objects are considered. The features of the use of various systems of lightning rods to protect objects from direct lightning strikes are indicated. Methods of ensuring the safety of buildings and structures from secondary manifestations of lightning are presented. The inappropriateness of using active lightning rods (ESE terminals) instead of existing classical solutions of lightning protection is shown.