Ventilation is a process of supply of external air to the room or the building natural or mechanically. It controls the speed of replacement of room air during a certain span. In certain cases, before air supply to the building it is necessary to remove pollution, using the corresponding systems of filtration. Ventilation plays a crucial role of the infected air and decrease in the general concentration of a virus and, therefore, the virus dose inhaled by the people who are in the building at a distance.
Correctly established ventilation (for example, placement of stitched installations and exhaust channels) provides necessary dilution of air where it is necessary, preventing accumulation of virus pollution. The basic principle consists in replacement of the polluted air by clean. There can sometimes be local barriers interfering this process, for example, of a partition or curtains which are used for creation of conditions for medical procedures. If obstacles such exist, additional or auxiliary measures for achievement of the required efficiency of ventilation can be required.
Effective ways of ventilation of rooms exist in many medical institutions as a part of measures for protection against a drop and contact way of transfer of a disease. Good ventilation also protects the population from an aerosol way of transfer. The possibility of increase in speed of ventilation if necessary can be a little limited to specifications of the producer and their ways of realization.
In many hospitals natural ventilation of chambers, including in some rooms used for an intensive care is used. However, if air flow is blocked (for example, closing of windows and doors), concentration of a pathogen can sharply increase in air that will lead to increase in risk of aerosol transfer and an infection.
Design, operation and maintenance of the rooms ventilated naturally represents difficult process therefore there is a complete guide of the World Health Organization (WHO) devoted to this subject.
The situation with ventilation can be worse in public buildings and other public spaces, such as shops, offices, schools, kindergartens, libraries, restaurants, cruise liners, elevators, conference rooms or public transport where the way of ventilation can vary from specially developed mechanical systems before simple use of open doors and windows. In the majority of these places the speed of ventilation is much lower, than in hospitals for various reasons, including restriction of air flows for economy of energy and expenses. Therefore, in similar places with lower indicators of air exchange the probability that the infected people create risk of spread of an infectious disease is high, allocating a pathogen in air and endangering other people. Various researches of survival of pathogens in aerosols in which the SARS-CoV-2 virus showed stability in aerosol particles with the semi-life period more than one hour so potentially it can get into airways of people were executed, causing an infection and further spread of a disease.
The intensity of ventilation if necessary can be increased by modification of a system. In mechanically ventilated building ventilating air usually is provided with a heating system, ventilation and air conditioning. Sometimes ventilating air moves special fans or an outdoor stitched installation. The strategy of management of heating systems, ventilation and air conditioning can be sometimes changed for the purpose of a certain increase in ventilation in zones of stay of people for risk mitigation of aerosol transmission of infection. In addition to the speed of ventilation it is necessary to consider a set of other requirements, including control of temperature, relative humidity, distribution and the direction of an air flow. Perhaps, it will be in certain cases necessary to provide additional heating in buildings for maintenance of temperature comfort.
Recirculation of air is way of economy of energy, but by means of this mode of ventilation air-borne pollutants (including viruses) from one space can be transported and to extend in other spaces connected to the same system that potentially increases risk of infection with an aerosol way. Proceeding from the available recommendations, during epidemics, including the current pandemic of COVID-19, recirculation of air has to be reduced to a minimum to avoid distribution of virus particles on all room.