SARS-CoV-2 Aerosol Transmission Indoors: A Closer Look at Viral Load, Infectivity, the Effectiveness of Preventive Measures and a Simple Approach for Practical Recommendations

There is uncertainty about the viral loads of infectious individuals required to transmit COVID-19 via aerosol. In addition, there is a lack of both quantification of the influencing parameters on airborne transmission and simple-to-use models for assessing the risk of infection in practice, which furthermore quantify the influence of non-medical preventive measures. In this study, a dose–response model was adopted to analyze 25 documented outbreaks at infection rates of 4–100%. We show that infection was only possible if the viral load was higher than 108 viral copies/mL. Based on mathematical simplifications of our approach to predict the probable situational attack rate (PARs) of a group of persons in a room, and valid assumptions, we provide simplified equations to calculate, among others, the maximum possible number of persons and the person-related virus-free air supply flow necessary to keep the number of newly infected persons to less than one. A comparison of different preventive measures revealed that testing contributes the most to the joint protective effect, besides wearing masks and increasing ventilation. In addition, we conclude that absolute volume flow rate or person-related volume flow rate are more intuitive parameters for evaluating ventilation for infection prevention than air exchange rate.

USE OF DIGITALIZATION MEANS IN THE FORMATION OF THE MICROCLIMATE OF ANIMAL PREMISES

The study of information systems and technologies, specialized software products aimed at solving the problems of animal husbandry management and determining the prospects for their use by specialists is relevant. The main factor determining the life of animals is the environment. One of the ways to intensify livestock (pigs, cattle, poultry, etc.) is a comprehensive automation of labor-intensive technological processes, including the formation of the microclimate of livestock facilities, which would have a positive impact on animal health, productivity and product quality. However, animals are also affected by certain methods and methods of feeding, man-made content, zonal climate, heat-shielding properties of enclosing structures, air exchange rate, ventilation efficiency, sewage condition, manure removal and removal methods, lighting. The impact of microclimate on animals consists of a set of environmental factors: temperature, humidity, air velocity, chemical composition, microbial and dust pollution, lighting, etc. The main parameter of the air environment is temperature. This has the greatest impact on animal health and productivity. The hygienic value of temperature is that it affects the thermoregulation of the body, which is divided into the processes of chemical thermoregulation - the reaction of heat generation and the processes of physical thermoregulation - the regulation of heat transfer. The study of the technology of improving the efficiency of microclimate regulation in livestock premises based on the use of an automated control system is promising. Thus, changing the composition and properties of the environment, you can affect the body of animals, achieving high productivity.

Study of the effectiveness of the use of closed-type UV-recirculators for air disinfection in enclosed space

Introduction. The research is devoted to assessing the results of our studies of indoor air concerning microbial contamination during the operation of a UV recirculator with different modes (different UV doses). Also, a theoretical calculation of the influence of the ratio of the capacity of the UV recirculator to the air volume of the treated room on the efficiency of air disinfection has been made. Materials and methods. The study of indoor air in terms of total bacterial count (TBC), including coccal microflora and yeast and mould fungi, were carried out. Air sampling and evaluation were carried out under the requirements of Methodical guidelines MUK 4.2.2942-11 “Methods of sanitary and bacteriological studies of environmental objects, air and sterility control in medical institutions”. The evaluation of the results was carried out following R 3.5.1904-04, "The use of ultraviolet bactericidal radiation for disinfection of indoor air". During the study, agar culture media were used: Sabouraud agar, yolk-salt agar (YSA), meat-peptone agar (MPA), nutrient agar with the addition of 5% sheep blood (blood agar), bismuth sulfite agar, XLD-agar, cetrimide-agar, “Shine” agar, Endo agar. Results. As a result of the studies carried out, it was shown that a dose of UV irradiation of the order of 12-15 mJ/cm2 leads to an insignificant change in the concentration of bacteria (TBC) and fungi in the air (the efficiency was 58% and 69%, respectively). UV doses of the order of 25-30 mJ/cm2 significantly reduce the concentration of bacteria (TBC) and fungi in the air (efficiency was 99.99% and 99.4%, respectively). A theoretical calculation showed that it is practical to use a UV recirculator of such a capacity that provides an air exchange rate in the room of at least 4 (with ventilation operating at a rate of at least 2). Conclusion. To effectively use UV recirculators in enclosed spaces against bacteria and fungi, it is necessary to use models that provide a UV dose of at least 25-30 mJ/cm2. In contrast, their air capacity should provide an air exchange rate of at least 4.

On Issue of Permissible Content of Ammonium Ions in Chemical Additives for Concrete

Nitrogen-containing compounds that enter concrete together with raw materials, in particular with chemical modifiers of concrete mixture and concrete, as well as those present in Portland cement, are capable of forming ammonia as a result of decomposition. The processes of formation and emission of ammonia cause both a deterioration of the atmosphere of residential premises and are the reason for a decrease in the strength and operational safety indicators of reinforced concrete structures. These circumstances necessitate research and development of methods for determining the safe amount of ammoniumcontaining additives in concrete. Most often, nitrogen-containing compounds contain plasticizing additives, antifreeze and complex additives, as well as setting and hardening accelerators. According to Amendment No 2 STB (Standards of the Republic of Belarus) 1112–98 “Additives for Concrete. General Requirements”, the content of ammonium ions in additives should not exceed 100 mg/kg (except for antifreeze). At the same time, some additives, including plasticizers, which have been successfully used for more than one year without identified problems with ammonia emission, do not fit into the established norm. To determine the maximum permissible concentration (MPC) of ammonium salts in concrete, it is necessary to know the dependence of the emission of ammonia from concrete on various factors, in particular, on the mass content of salts in concrete, the surface area from which ammonia is emitted, the mass of concrete structures, temperature, humidity and air exchange rate in the room. To a lesser extent, the ammonia emission will be affected by the characteristics of the concrete and the reaction conditions for the hydrolysis of salts in the concrete. The paper provides formulas for calculating the emission of ammonia from concrete with the introduction of various ammonium-containing additives. It is shown that, in spite оf the above-standard content of ammonium ions in additives C-3, LST and UP-4, the emission of ammonia from concrete in some cases does not exceed the established maximum permissible concentration (MPC). The volume of ammonia emission from concrete is determined not only by the amount of ammonium ions in the additives, but also to a large extent by the structural and technological scheme of the building and the parameters of the concrete loading of the room. With the known MPC in the air of the room, the given parameters of loading the room with concrete, the formula allows you to calculate the maximum concentration of the additive in the concrete mixture, not exceeding which will ensure compliance with the MPC for ammonia in the air of the premises.

Ensuring Safe Working Conditions during the Operation of the Closed Coal Storages

It is noted that the relevance of the presented studies is related to the need in reducing the aerotechnogenic load on the environment, which, when the coal is stored in the open storage, is practically uncontrollable that leads to the dust pollution of the significant territories. It is shown that ensuring safe operation of the closed coal storages, which are an alternative to the open coal storage, is possible if two conditions are met: the concentration of methane released from the coal stack in the air space of the storage does not exceed the permissible values; reduction to the required level of emissions of coal dust generated during loading and unloading technological operations. The reasons for possible release of methane from the stored coal associated with its residual methane content, the value of which is determined both by the initial value, as well as its decrease during the transportation of coal from the place of its production to the closed storage were identified. It is shown that in order to prevent exceeding the permissible value of methane concentration in the closed storage, it is required to use forced ventilation with an air exchange rate of at least two. It is mentioned that the forced ventilation in combination with the significant volumes of coal dust generated during technological operations can result in an increase in its concentration to the values hazardous for the human health. The analysis of methods for normalizing the dust environment during the operation of closed coal storages is given. The scientific novelty of research is associated with a comprehensive study of the regularities of aero-, gas- and dust-dynamic processes that determine safety of operation of the closed coal storages.

Non-respiratory particles emitted by guinea pigs in airborne disease transmission experiments

Animal models are often used to assess the airborne transmissibility of various pathogens, which are typically assumed to be carried by expiratory droplets emitted directly from the respiratory tract of the infected animal. We recently established that influenza virus is also transmissible via “aerosolized fomites,” micron-scale dust particulates released from virus-contaminated surfaces (Asadi et al. in Nat Commun 11(1):4062, 2020). Here we expand on this observation, by counting and characterizing the particles emitted from guinea pig cages using an Aerodynamic Particle Sizer (APS) and an Interferometric Mie Imaging (IMI) system. Of over 9000 airborne particles emitted from guinea pig cages and directly imaged with IMI, none had an interference pattern indicative of a liquid droplet. Separate measurements of the particle count using the APS indicate that particle concentrations spike upwards immediately following animal motion, then decay exponentially with a time constant commensurate with the air exchange rate in the cage. Taken together, the results presented here raise the possibility that a non-negligible fraction of airborne influenza transmission events between guinea pigs occurs via aerosolized fomites rather than respiratory droplets, though the relative frequencies of these two routes have yet to be definitively determined.

Impact of temporal variability of radon concentration in workplaces on the actual radon exposure during working hours

For workplaces where significant diurnal variations in radon concentrations are likely, measurements to evaluate average radon concentration during working hours could be useful for planning an optimized protection of workers according to the 2013/59/Euratom Directive. However, very few studies on this subject, generally limited to periods of few weeks, have been published. Therefore, a study has been conducted to evaluate the actual long-term radon exposure during working hours for a sample of 33 workplaces of four different types (postal offices, shops, restaurants, municipal offices), mainly located at the ground floor, and with expected considerable air exchange rate occurring during working hours due to frequent entrance/exit of persons or mechanical ventilation. The results show that the difference between the average radon level during working hours and that one during the whole day is about 20% on average and ranges from 0 to 50%. These observed differences, generally smaller compared with those found in other similar studies, are nearly the same if the analysis is restricted to workplaces with annual radon level higher than 300 Bq m–3, and therefore natural or mechanical ventilation normally present during working hours of the monitored workplaces cannot be considered an effective mitigation measure. However, the costs and time-response characteristics of the active monitors, as those used for the present study, will probably allow using more frequently a similar measurement strategy in workplaces.

A Parametric Model for Local Air Exchange Rate of Naturally Ventilated Barns

With an increasing number of naturally ventilated dairy barns (NVDBs), the emission of ammonia and greenhouse gases into the surrounding environment is expected to increase as well. It is very challenging to accurately determine the amount of gases released from a NVDB on-farm. Moreover, control options for the micro-climate to increase animal welfare are limited in an NVDB at present. Both issues are due to the complexity of the NVDB micro-environment, which is subject to temporal (such as wind direction and temperature) and spatial (such as openings and animals acting as airflow obstacles) fluctuations. The air exchange rate (AER) is one of the most valuable evaluation entities, since it is directly related to the gas emission rate and animal welfare. In this context, our study determined the general and local AERs of NVDBs of different shapes under diverse airflow conditions. Previous works identified main influencing parameters for the general AER and mathematically linked them together to predict the AER of the barn as a whole. The present research study is a continuation and extension of previous studies about the determination of AER. It provides new insights into the influence of convection flow regimes. In addition, it goes further in precision by determining the local AERs, depending on the position of the considered volume inside the barn. After running several computational fluid dynamics (CFD) simulations, we used the statistical tool of general linear modeling in order to identify quantitative relationships between the AER and the following five influencing parameters, the length/width ratio of the barn, the side opening configuration, the airflow temperature, magnitude and incoming direction. The work succeeded in taking the temperature into account as a further influencing parameter in the model and, thus, for the first time, in analysing the effect of the different types of flow convection in this context. The resulting equations predict the barn AER with an R2 equals 0.98 and the local AER with a mean R2 equals around 0.87. The results go a step further in the precise determination of the AER of NVDB and, therefore, are of fundamental importance for a better and deeper understanding of the interaction between the driving forces of AER in NVDB.

Emission of harmful gases from animal production in Poland

The aim of the study was to present the scale of greenhouse gas emissions from animal production, and to provide test results from different housing systems. In three free stall buildings, two with slurry in deep channels and one with cattle in cubicles staying on shallow litter concentration of ammonia and carbon dioxide were measured in summer season by using dedicated equipment from Industrial Scientific Research. Air exchange was calculated on the base of balance carbon dioxide method. This method was used in order to estimate the air flow rate. Concentrations of ammonia and CO2 were measured as the base for air exchange and ammonia emission rates. Ammonia emissions were product of ammonia concentration and air exchange rate. Temperature and relative humidity were measured to establish microclimate conditions in buildings tested to show the overall microclimatic situation in buildings. Differences between ammonia emission rates were observed in both housing systems. The highest ammonia emission rate was equal to 2.75 g·h−1·LU−1 in well-ventilated cattle barn with the largest herd size.

On Finding the Right Sampling Line Height through a Parametric Study of Gas Dispersion in a NVB

The tracer gas method is one of the common ways to evaluate the air exchange rate in a naturally ventilated barn. One crucial condition for the accuracy of the method is that both considered gases (pollutant and tracer) are perfectly mixed at the points where the measurements are done. In the present study, by means of computational fluids dynamics (CFD), the mixing ratio NH3/CO2 is evaluated inside a barn in order to assess under which flow conditions the common height recommendation guidelines for sampling points (sampling line and sampling net) of the tracer gas method are most valuable. Our CFD model considered a barn with a rectangular layout and four animal-occupied zones modeled as a porous medium representing pressure drop and heat entry from lying and standing cows. We studied three inflow angles and six combinations of air inlet wind speed and temperatures gradients covering the three types of convection, i.e., natural, mixed, and forced. Our results showed that few cases corresponded to a nearly perfect gas mixing ratio at the currently common recommendation of at least a 3 m measurement height, while the best height in fact lied between 1.5 m and 2.5 m for most cases.