key: cord-0872377-jy6w8m5v authors: Kitamura, H.; Ishigaki, Y.; Ohashi, H.; Yokogawa, S. title: Workplace ventilation improvement to address coronavirus disease 2019 cluster occurrence in a manufacturing factory date: 2022-04-05 journal: nan DOI: 10.1101/2022.04.04.22271935 sha: 6ea70c6c3e7b9e0787ffa062748e5bde97bdadc8 doc_id: 872377 cord_uid: jy6w8m5v A coronavirus disease 2019 (COVID-19) cluster emerged in a manufacturing factory in early August 2021. In November 2021, a ventilation survey using tracer gas was performed to reproduce the situation at the time of cluster emergence and verify that ventilation in the office increased the risk of aerosol transmission; verify the effectiveness of measures implemented immediately in August; and verify the effectiveness of additional measures when previously enforced measures proved inadequate. At the time of cluster emergence, the average ventilation rate was 0.73 times/h, less than the 2 times/h recommended by the Ministry of Health, Labour, and Welfare; as such, the factory's situation was deemed to have increased the risk of aerosol transmission. Due to the measures already taken at the time of the survey, the ventilation rate increased to 3.41 times/h on average. It was confirmed that ventilation rate increased to 8.33 times/h on average, when additional measures were taken. To prevent the re-emergence of COVID-19 clusters, it is necessary to continue the measures that have already been implemented. Additionally, introduction of real-time monitoring that visualizes CO2 concentrations, which can be used to determine the timing of ventilation and limit the number of people entering the room, is recommended. is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted April 5, 2022. ; https://doi.org/10.1101/2022.04.04.22271935 doi: medRxiv preprint 2 are inhaled; as such, the Ministry recommends ensuring proper ventilation to combat aerosol transmission. Japan has "public health centers" which are public institutions under the jurisdiction of the MHLW. There are 469 such centers nationwide based on the Community Health Act. These public health centers provide a comprehensive professional and technical base that supports the health of residents by providing consultation on intractable diseases and mental health, implementing infection countermeasures, and conducting monitoring and guidance on pharmaceutical affairs, food hygiene, and environmental hygiene. They also form a base for health crisis management, such as preventing the spread of diseases in the event of a health crisis and disseminating relevant information. Public health centers conduct "active epidemiological investigation" on patients with confirmed COVID-19 detected in Japan following the Act on the Prevention of Infectious Diseases and Medical Care for Patients with Infectious Diseases. In these investigations, the patient is asked about their activities within 14 days prior to the onset of symptoms to estimate the source and route of infection. They are also asked about their activities 2 days prior to the onset of symptoms to identify close contacts. In the office of a manufacturing factory in Fukuoka Prefecture, five confirmed cases of COVID-19 successively emerged within 1 week in early August 2021, and the infections were confirmed to be a cluster (a group of infected people whose infections are linked). The local . CC-BY 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) The copyright holder for this preprint this version posted April 5, 2022. ; https://doi.org/10.1101/2022.04.04.22271935 doi: medRxiv preprint public health center stated that "the infected people were concentrated inside the office, and although there are working electric fans inside, there are no vents through which the virus can escape, resulting in the spread of infection." Within August, the office ventilation equipment was inspected and repaired to improve these issues, electric fans were relocated to the opposite side of the room considering the airflow, and the room door was opened when working inside. However, as mentioned above, the public health center investigation was based on interviews, and the office's ventilation when the cluster emerged was not evaluated. The level of ventilation after improvement measures were taken was not evaluated either. The affected workplace is a factory and performs desk work in the office and intervention on the operation site. It is managed by mixed groups of daytime workers and two groups with . CC-BY 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) The copyright holder for this preprint this version posted April 5, 2022. ; https://doi.org/10.1101/2022.04.04.22271935 doi: medRxiv preprint two shifts. On average, workers spend 70% of their time in the office and 30% in the field out of the 7 hours and 45 minutes of work per day. At the time of the cluster's emergence, 2-3 people were working in the daytime, and 16 people were working in shifts. As a measure against droplet transmission, 1.4m high partitions had been installed between desks. Layout of the workplace was shown in Figure 1 . In early August, 2021, the first patient, indicated as P1 in Figure 2 , was confirmed by polymerase chain reaction 1 , and then PCR-positive individuals emerged in August within the same group (P2 to P5 in Figure 2 in order). Patients were found only in one of the two groups of shift workers. Interviews with workers revealed the following: P1, P2 and P3 had many opportunities to talk to each other in close proximity in the aisles between desks, P4 and P5 had many opportunities to be in close proximity to other patients not only in the office but also outside of the office, and P1 to P5 often worked in close proximity and talked while they all looked at the same monitor. Figure 3 The office's ventilation frequency was measured as follows: . CC-BY 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted April 5, 2022. ; https://doi.org/10.1101/2022.04.04.22271935 doi: medRxiv preprint 1) Eight CO2 sensors, indicated as S1 to S8 in Figure 4 , were installed. One sensor was installed for each section, separated by the infected person's desk and partition. The CO2 sensor measured and recorded the average CO2 concentration every 60 s. A non-dispersive infrared absorption-type CO2 sensor, TR-76Ui (T&D, Matsumoto, Japan), was used for the measurement. The TR-76Ui sensor can detect CO2 concentrations from 0 to 9,999 ppm, with an accuracy of ±50 ppm (±5%). 2) The office's air conditioner and ventilation system were turned off, and all windows and doors were closed. 3) Dry ice was then vaporized to fill the office with CO2, raising the CO2 concentration well above the background atmospheric CO2 concentration (400 ppm). 4) Ventilation equipment, electric fans, windows, and doors were set under experimental condition1 shown in Table 1 , and at the same time, all employees and researchers left the office because they were CO2 sources. The time at this point was considered as the ventilation start time. 5) The CO2 concentration's transition was monitored remotely, and the measurement was completed after confirming that the CO2 concentration had dropped sufficiently. Table 1 , the office's air conditioner and ventilation system were turned off, and all windows and doors were closed. . CC-BY 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted April 5, 2022. ; https://doi.org/10.1101/2022.04.04.22271935 doi: medRxiv preprint 7) Dry ice was then vaporized to fill the office with CO2, raising the CO2 concentration well above the background atmospheric CO2 concentration (400 ppm). 8) Ventilation equipment, electric fans, windows, and doors were set under experimental condition 2, and at the same time, all employees and researchers left the office because they were CO2 sources. The time at this point was considered as the ventilation start time. 9) The CO2 concentration's transition was monitored remotely, and the measurement was completed after confirming that the CO2 concentration had dropped sufficiently. Table 1 , the office's air conditioner and ventilation system were turned off, and all windows and doors were closed. 11) Dry ice was then vaporized to fill the office with CO2, raising the CO2 concentration well above the background atmospheric CO2 concentration (400 ppm). 12) Ventilation equipment, electric fans, windows, and doors were set under experimental condition 3, and at the same time, all employees and researchers left the office because they were CO2 sources. The time at this point was considered as the ventilation start time. 13) The CO2 concentration's transition was monitored remotely, and the measurement was completed after confirming that the CO2 concentration had dropped sufficiently. Based on the data measured by the CO2 sensor, the ventilation frequency was estimated using Seidel's formula 2, 3 : . CC-BY 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. This study was approved (approval number 21005) by the Ethics Committee on Experiments on Human Subjects of the University of Electro-Communications, Chofu, Tokyo, Japan. Table 2 (Table 3) . On the other hand, the effect of the interaction of the ventilation time and the CO2 sensor location was not statistically significant (p=0.35), and there was no obvious difference in the ventilation frequency depending on the sensor location. Since the individual effects of the experimental conditions and the CO2 sensor location, which are random effects, were not . CC-BY 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted April 5, 2022. ; https://doi.org/10.1101/2022.04.04.22271935 doi: medRxiv preprint statistically significant (p>0.05), respectively, it was unlikely that there was an individual effect other than the effects on the ventilation frequency (Table 3) . According to experimental condition 1, the ventilation frequency at the time of cluster emergence was 0.73 times/h on average. Menzies et al. 4 reported that a lack of ventilation is associated with an increased incidence of airborne infections; the higher the ventilation frequency, the higher the efficiency of air dilution, and the lower the risk of airborne infection. They also stated that a ventilation frequency of fewer than 2 times/h is associated with the spread of tuberculosis, an airborne infection. It has also been reported that the ventilation frequency in junior high school classrooms where tuberculosis outbreaks occurred in Japan ranger between 1.6-1.8 times/h. 5 According to the Guide for Outpatient Treatment of COVID-19 by the Japan Medical Association, aerosols containing the SARS-CoV-2 virus from infected people will remain airborne for more than 3 h in an unventilated room. 6 Strictly speaking, there is a difference between airborne transmission and aerosol transmission; however, a ventilation frequency of only 0.73 times/h identified in this study increased the risk of aerosol transmission. The mean ventilation frequency in experimental condition 2 was 3.41 times/h, 4.7 times higher than when the cluster emerged. Under experimental condition 3, the mean ventilation frequency was 8.33 times/h, 11.4 times higher than when the cluster occurred. The MHLW stated that to improve the ventilation of closed rooms with poor . CC-BY 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted April 5, 2022. ; https://doi.org/10.1101/2022.04.04.22271935 doi: medRxiv preprint ventilation, the ventilation frequency should be increased to ≥2 times/h by opening windows without using mechanical ventilation (e.g., air conditioning and mechanical ventilation equipment). 7 Under experimental condition 2, it was confirmed that the minimum ventilation frequency was secured. The standard CO2 concentration according to the Act on Maintenance of Sanitation in Buildings is ≤1,000 ppm, and it is necessary to secure an outside air introduction amount of approximately ≥30 m 3 /h per person to manage a space's CO2 concentration at ≤1,000 ppm. Since the volume of the office examined in this study was about 240 m 3 , in order to manage CO2 concentration in the office at ≤1000 ppm or less at the average ventilation frequency of 0.73 and 3.41 times/h in experimental conditions 1 and experimental condition 2, respectively, it was estimated that the ventilation achieved under experimental condition 1 could cover five people while that of experimental condition 2 can cover 27 people. At the time of the cluster emergence, 18-19 people, including daytime workers and shift workers, were working simultaneously. The ventilation volume was <30% of the required amount, which increased the risk of aerosol transmission. The ventilation volume achieved under experimental condition 2 would allow the original number of employees to work inside the office, and that under experimental condition 3 would allow 66 people to work in the office simultaneously. Of course, the amount of CO2 that humans exhale depends on their level of physical activity. 8 As such, it would be safer to accommodate a smaller number of . CC-BY 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted April 5, 2022. ; https://doi.org/10.1101/2022.04.04.22271935 doi: medRxiv preprint people than the above estimation when heated discussions takes places or when there is heavy activity to simulate the operation of production line. If the door cannot be released to discuss sensitive content, it also would be safer to keep the number of people inside small and the meeting time as short as possible. In our previous investigation of a cluster occurrence, 9 we reported that 1.6-m high vinyl sheet partitions installed between desks facing each other as a measure against droplet transmission blocked the office's airflow, resulting in a section where air stagnated (vinyl sheet cluster). In the office space of this study, there were no differences in ventilation frequency depending on the sensor location, and there seemed no inhibitory effects of inappropriate partitions on ventilation. However, in the office, an electric fan created an airflow, as shown from the lower side to the upper right part of Figure 1 , which considered to help scatter droplets containing the virus released from the first infected person without an outlet for air to escape to the outside. As a result, it was suggested that virus-containing droplets had gradually accumulated in the upper right part of the office shown in Figure 1 . The office's ventilation was extremely poor at <1 time/h, making it possible for a "leeward cluster" to emerge. In order to prevent leeward clusters, when using an electric fan or blower to ensure adequate air circulation in a room, it is necessary to secure an air outlet and create outflow. The following two proposals may be feasible for the operation of the office: First, when . CC-BY 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted April 5, 2022. ; https://doi.org/10.1101/2022.04.04.22271935 doi: medRxiv preprint doing regular work, set experimental condition 2. If more people are required to work inside the office or during long discussions, add the countermeasure plan confirmed in experimental condition 3. Second, maintain experimental condition 2 and limit the number of people entering the room according to the work content. The use of CO2 sensors to control indoor air quality has attracted significant attention. In addition to the measures mentioned above, introduction of real-time monitoring that visualizes CO2 concentrations, which can be used to determine the timing of ventilation and limit the number of people entering the room, is recommended. [10] [11] [12] We believe that CO2 concentration visualization can create an environment that is more flexible and allows workers to work with greater peace of mind. It is essential to improve ventilation in the workplace, considering feasibility and sustainability and measures that can be put into practice without impeding work. The measures proposed in this study are based on workplace improvement activities and could be implemented continuously without difficulty. Of course, there are cases where improvements led by experts and researchers are necessary, but in the long run, the measures taken by workers who use the site daily are considered essential to prevent the recurrence of COVID-19 clusters. The survey of ventilation of the manufacturing factory where a COVID-19 disease cluster emerged revealed that: (1) the average ventilation frequency in the office at the time of cluster . CC-BY 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. Ventilation is just one measure against aerosol transmission. As measures against COVID-19 in the workplace, it is necessary to continue to avoid the three Cs (closed spaces, crowded places, and close-contact settings), ensure thorough hand hygiene, universal mask-wearing, and social distancing. Table 1 were linked to 1 to 11 in Figure 4 . b: Electric fans were placed in different locations in experimental condition 1 and experimental condition 2 and 3, as shown in Figure 4 . Table 3 . Effects of experimental conditions and CO2 sensor location by mixed-effect model . CC-BY 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) The copyright holder for this preprint this version posted April 5, 2022. is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. 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