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Controlling the spread of COVID-19 has become a priority worldwide. After case reports in December 2019, social distancing has been widely adopted as a containment strategy. Therefore, it is essential to control the risks and ensure safety in educational, public, and workplaces.

To reduce the risk of COVID-19 transmission, measures against all three routes of infection (contact, droplet, and aerosol) and to reduce the probability of infection through multiple defenses, social distance, mask, vaccine, etc., are required.

However, compared to contact and droplet transmission, which can be prevented by social distancing and the use of masks, aerosol transmission is difficult to visually recognize, and the effectiveness of respective countermeasures has not been confirmed. Accordingly, mass transmissions of COVID-19 have been reported in poorly ventilated areas.

The inappropriate use of plastic sheeting for preventing droplet infection has caused clusters of infectious diseases and threatened workplace safety.

The use of carbon dioxide (CO 2) sensors to control indoor air quality has attracted significant attention. The measurement of indoor CO 2 concentration (referring to exhaled air) is considered an effective method for indirect risk management to ensure that exhaled aerosol particles containing SARS-CoV-2 do not remain indoors.

Therefore, these devices have been widely installed as a safety measure in places where people gather, such as restaurants, stores, classrooms, and offices. The guideline for its operation considers a provisional control value of 800-1000 ppm set by government agencies of each countries as the maximum CO 2 concentration. Under pandemic conditions, the Centers for Disease Control and Prevention has indicated that the CO 2 concentration should be maintained below 800 ppm, which has been considered a good safety indicator.

However, as CO 2 concentration is not a direct risk indicator and there is no direct epidemiological relationship between CO 2 concentration and COVID-19 transmission.

In a new study, researchers used a CO 2 sensor network and conducted a tracer gas experiment to evaluate the complex ventilation conditions in a business site in Japan, where a cluster of COVID-19 infections occurred. In 2021, 14 infections occurred among 30 workers who spent a short time in a large work preparation room. The room was divided by four partitions, and only a small number of entrances and exits served as ventilation routes.

The objectives of this research were to 1) demonstrate a method for evaluating and determining the state of air quality management in an office with a complex geometry using a CO2 sensor network, and 2) verify the effectiveness of ventilation improvement measures.

The Researchers concluded that for aerosol infection control, which should be conducted in parallel with measures against contact and droplet transmission, the maximum height of partitions should be strictly controlled, and they should be installed at a height and orientation that do not interfere with ventilation. Measurement using sensor networks is effective in detecting such a ventilation bias.

Ventilation bias caused by ventilation pathways and inappropriate use of plastic sheeting can be detected by a CO 2 sensor network and time series data analysis. Estimated ventilation rate will be a good index to suppress the formation of the COVID-19 cluster.