Petri nets modelling of systems with redundancy

Petri nets are very appropriate for modelling and analysis of different systems. In this paper, examples of repairable and irreparable systems modelled using Petri nets have been given. Systems with cold and hot redundancy have been analyzed, also. The redundancy is illustrated using the example of the electric power system.

Burnout in master's students: A case study

Burnout is associated with long-term exposure to workplace stress and it comprises exhaustion, cynicism, and the feeling of inadequacy as its dimensions. University students are exposed to a variety of stress-inducing factors during their studies regardless of the fact that they are not employees. The aim of this study is to examine the relations between specific sociodemographic variables and burnout dimensions among students of master academic studies. School Burnout Inventory (SBI-U 9) is used as the research instrument. The obtained results indicate that there is a connection between students' gender and tuition fee status and burnout. Gender is associated with exhaustion and the feeling of inadequacy, while tuition fee status affects all three dimensions.

Forest roads as the key to forest protection against fire

Planning, construction and maintenance of forest roads is extremely important for successful firefighting in a certain area. This study focuses on the current technical infrastructure in the state forests of Serbia. The average openness of forests in Serbia at the end of 2019 was 20.14 m/ha, while 21.89 m/ha was occupied by public roads. In the period from 2011 to 2019, the average openness of state forests with public roads in Serbia decreased by 3.12 m/ha, or by 1.67 m/ha. The openness of forests by forest roads is the largest and optimal in the Vojvodina region (131.5 m/ha) and significantly lower and insufficient in Belgrade regions (0.35 m/ha), Sumadija and Western Serbia (2.8 m/ha), and Southern and Eastern Serbia (1.8 m/ha). Compared to 2011, the openness of forests in 2019 increased in the Vojvodina region and decreased in other regions in Serbia. Forest roads that have asphalt, concrete or cobblestone lanes are the least represented, about 0.27%. The largest representation of forest roads with a base (stone or gravel hard bottom layer) is about 82.7%.

Concentrations and chemical composition of PM10 and PM2.5 in the Town library in Bor, Serbia

This paper presents the PM10 and PM2.5 concentrations and results of chemical analyses of PM samples collected at the public library in Bor town, Serbia. Two sampling campaigns were carried out during six consecutive working days in June 2015 and in March 2016. The results show that PM10 and PM2.5 concentrations in the library were strongly connected with the respective PM concentrations in ambient air. So, most PM particles in the library originate from the outdoor air. High PM2.5/PM10 ratios in both indoor and outdoor environments indicate the considerable influence of anthropogenic air pollution sources, in this case, metallurgical processes in copper smelting plants. Because the new copper smelting plant started operating in 2016, it is necessary to conduct a new measurement campaign to determine whether there are changes in the concentration levels and chemical composition of PM in the indoor air of public and residential buildings in Bor

Safety and mental health of employees during COVID-19 pandemic: Medical and legal aspect

Supporting mental health has nowadays become the main concern of employers since a growing number of employees is facing the problem of anxiety, loneliness, depression and the like. These problems were particularly emphasized with the outbreak of the Covid-19 pandemic. In significantly changed working conditions around the world, employees and employers have faced mental health problems that are related to numerous stressors and factors related to the pandemic. Given the circumstances, the question is how to protect the mental health of employees in order to preserve their productiveness and well-being after the crisis. The legal system has a very important role in this process, especially the regulations concerning occupational safety and health and labor law in general because it sets the framework which enables the subjects of employment to maneuver their rights and obligations during the pandemic. Therefore, this framework is a key element in taking occupational safety measures in order to preserve the mental health of employees.

Analysis and measures of landfill fire prevention

Large quantities of solid municipal waste containing a variety of flammable substances, that are disposed of in sanitary and non-sanitary landfills and even illegal dump sites, usually entail a high risk of fire. The level of risk is increased by the presence of methane which is released by municipal waste decomposition. The number of landfill fires varies depending on the morphological composition of the waste, ignition sources, meteorological conditions, time of year, as well as fire protection measures. The paper describes the impact of flammable waste on landfill fires, as well as causes, frequency and procedures in preventing and extinguishing landfill fires.

Nitrosamines: Carcinogenic chemical 'intruders' in occupational environments

Nitrosamines, or more precisely N-nitrosamines, along with N-nitrosamides, belongs to N-nitroso compounds, a class of organic compounds that have a nitroso (-N=O) group attached directly to a nitrogen atom. Only a few of them occur naturally while the majority is formed by nitrosation of secondary amines in a living and working environment, food, tobacco smoke, etc. These compounds have scarce application in the industry, but they can be formed in situ, so they can be considered as chemical intruders in working environments. Considering their toxicity, especially carcinogenicity, where there is a risk of exposure to N-nitroso compounds, appropriate protection measures should be taken, including process control, work practices, protective clothing, use of respirators, legal regulations.

Teslameter for magnetic field measurement in high voltage facilities

This paper presents a low-cost three-axis teslameter capable of measuring magnetic field intensity in industrial environments and high voltage facilities. It is based on an MFS-3A three-axis magnetic field sensor, and it can measure magnetic flux density up to ±5 mT in all three axes, with accuracy better than ±0.5% and excellent temperature stability. The proposed teslameter was calibrated using a state-of-the-art reference instrument, Helmholtz coil and temperature chamber. The paper describes the development and the calibration of the proposed teslameter. The obtained results are presented as well.

Ergonomic approach to workplace (re)design during loads handling

Manual handling of loads is a set of activities that involve physical strain during work. For this reason, it is necessary to create ergonomically sound workplaces, which will help improve health and safety in the workplace. The paper describes an approach, which includes ergonomic and productivity factors, for choosing the optimal alternative for loads handling using multicriteria analysis. The purpose of this approach is to select the most important criteria to make decisions on how to reorganize the work process, as well as to meet ergonomic performance goals, all with minimal impact on the company's productivity. The objective of this paper is to analyse and select the optimal alternative for manual handling of loads using the Analytic Hierarchy Process method. The results of the research revealed that handling loads is a more optimal solution when performed by a single person, taking into account ergonomics and productivity aspects, compared to working in pairs or using conveying systems as transport AIDS.

An overview of 1998 versus 2020 edition of Guidelines for Limiting Exposure to electromagnetic fields

One of the most important documents defining recommendations for limiting exposure to almost inevitable electromagnetic radiation was released in 1998 by International Commission on Non-Ionizing Radiation Protection (ICNIRP). This document is "Guidelines for Limiting Exposure to Time-varying Electric, Magnetic and Electromagnetic Fields (up to 300 GHz)". However, the growing knowledge about the electromagnetic field (EMF)-tissue interaction and appearance of innovative telecommunication technologies, raised the need for the improvement of these Guidelines. Thus, the ICNIRP published the latest version of its recommendations in 2020. The purpose of this paper is to briefly present some important differences between the ICNIRP 1998 and 2020 Guidelines and to enlighten their reflection on national EMF legislation.