WHO recommendations for COVID-19 risk mitigation

WHO recommendations for COVID-19 risk mitigation

To prevent and mitigate the risk of COVID-19 infection, the World Health Organization (WHO) developed recommendations for ventilation of indoor spaces we work or live in. Below, we will briefly review the existing types and main characteristics of ventilation for different types of rooms. First, it must be mentioned that the term "ventilation" should be understood as the process of supplying outdoor air to and removing indoor air from a space, achieved by natural or mechanical means. In other words, the supply of indoor air can be accomplished by natural means, without using mechanical means, or by using mechanical means. The basic elements of indoor ventilation are:

  • ventilation rate – the volume of outdoor air that is provided into the indoor space (m³/hr, l/s);
  • airflow direction – the overall airflow direction in spaces, which should be from clean zones to potentially or conditionally dirty zones (public spaces);
  • air distribution – the external air should be delivered to each part of the space.

According to WHO, buildings and premises are divided by their functional use, and each type of space has its own requirements. Thus, there are certain requirements for health care, residential and non-residential spaces. We will review the requirements defined for non-residential facilities, such as public and private buildings characterized by a heterogeneous occupancy rate with people in terms of time and space (for instance, schools, offices, workplaces, universities, religious and commercial spaces) in this article. The minimum fresh air requirement for non-residential settings is 10 liters per second per person regardless of whether natural or mechanical ventilation is employed. That is why airflow rate measurements should be performed to define whether your workplace complies with the WHO requirements. If indoor spaces have a mechanical ventilation system or air removal system, the airflow rate should be measured directly in air distributors or air ducts. If such a system is not available, it is required to measure the natural movement of indoor air velocity ensured by natural drafts, open windows, and doors. Following the WHO requirements, calibrated anemometers and air flow meters can be used to measure air velocity and calculate airflow rate. If measurement results are satisfactory, other ventilation characteristics can be tested. But what to do if the results are negative? That means if the overall ventilation rate is less than 10 L/s/working person. The WHO strategy for improving ventilation must be implemented in this case. For mechanical ventilation systems, the adjustment should be conducted using the system instructions. The fan rpm must be increased to achieve the required amount of air exchange. The following steps are recommended for natural ventilation systems:

  • determine window and door opening locations;
  • ensure, if possible, an adequate supply of fresh air through various openings (for example, from windows to doors or vice versa). If it is not possible, air the spaces by opening windows;
  • use a stand-alone fan (for example, a fan placed directly near the window);
  • install an exhaust fan to provide a mechanical draft or special tools to provide sufficient natural draft;
  • decrease the number of occupants in the room;
  • if other options are not possible to perform, use a stand-alone air cleaner with an F8 class filter or higher-class filter.

Airflow direction and uniformity of fresh air distribution in the office space are essential for airflow. That means that dead air spots should be absent; air should be mixed within the interior space, and polluted air should be removed in an effective and efficient manner. To demonstrate airflow direction and air distribution, visualization tools, such as lightweight materials, ribbons, fibers, or professional tools, such as fog generators, may be used. Watching fog move through a facility, information on dead spots and the intensity of fresh air distribution can be obtained. If there are dead spots in a facility, you need to perform the following steps to eliminate these spots (please note that the recommendations indicated below can be applied only if the fresh air supply complies with the requirements):

  • use a ceiling fan or floor fan;
  • use split systems (a domestic wall-mounted air conditioner) in the ventilation mode.

Also, according to the WHO, the supply of fresh air must be ensured by opening all windows in a facility for 15 minutes when entering or leaving the room, or running a mechanical ventilation system for 2 hours. When using mechanical ventilation systems, maintenance, filter replacement, and heat exchanger cleaning schedules must be observed. It is not recommended to use the recirculation mode, better to minimize recirculation. If it is not possible to use the technical means specified above, a stand-alone air cleaner can be considered.

To carry out scheduled operations and unscheduled testing of ventilation systems, you can contact our specialists, which will perform this task quickly and efficiently. 

Our testing laboratory has all the necessary resources to identify and visualize airflows. That is why you can always count on us.

WHO recommendations for improving and ensuring proper indoor ventilation in the context of coronavirus infection.