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What precautions should be taken in the workplace to limit airborne transmission of the virus?

Text updated on 2020-11-23

If you work in an office environment, open windows and check air conditioning filters and features before returning to work. In order to avoid the risk of airborne contamination, wearing a mask, ventilating all rooms (office, cafeteria, sanitary facilities) and maintaining a distance between people and scheduling time between people for small office rooms are recommended.

Airborne contamination

The transmission of SARS-COV-2 is largely by air, especially during interactions in confined spaces. See the question Is the SARS-CoV-2 coronavirus transmitted by aerosols? In addition, studies have shown that the coronavirus can remain airborne for several hours (it remains detectable but it is not yet known whether it is still infectious). Therefore, what precautions should be taken in the office to minimize the risk of airborne contamination?

The influence of aeration and filtration quality

Ideally, the windows should be open, so that the air in the room is continuously renewed. If this is not possible, for air conditioning systems, the most important thing is to deactivate or reduce the air recirculation and to renew the air with high-flow outside air. Important values to consider are: the time taken to completely renew the air, the frequency with which the air is renewed.

HEPA filters are devices that filter out fine particles (at least 99.98% of particles with a diameter of 0.1-0.2 µm according to current standards). These HEPA filters are capable of filtering a large part of the airborne viral particles. These filters are not necessary if the air comes from outside. They are only useful if indoor air is recirculated. They should be changed regularly and the temperature and humidity conditions should be checked.

In cases of recirculating air, the quality of room air filtration can greatly reduce the likelihood of infection. Thus, the situation will not be the same in the case of a room equipped with high-efficiency HEPA filters, and in rooms that do not have this type of device.

What are the right distancing measures to take in the office according to the type of ventilation?

Research conducted by a team from Harvard University has modelled the probabilities of airborne contamination in a shared workspace, depending on the type of ventilation. In order to minimise the risk of aerosol contamination below 1%, this work leads to the following recommendations:

1 - It is strongly advised to keep your mask on in offices, so as to minimize the risk of air and surface contamination.

2 - Refresh the air in rooms regularly with outside air.

3 - If it is impossible to renew the air in the rooms with outside air :

In rooms equipped with high-efficiency air filters of the HEPA type, several people can work in the same room, provided that they are at least 5 meters apart and that their workstations are positioned in such a way that they are seated in separate ventilation streams (i.e., in air corridors that do not mix between the outlet and inlet of the ventilation system). Another possibility is to use plexiglass walls to modify the air flows. In offices that are not equipped with HEPA filters, it is recommended that only one person occupies a room at any one time, with a waiting time between two occupants. A waiting time of 3-4.5 hours is recommended for a ventilation system that renews the air every half hour to eliminate the majority of viral particles that could be suspended in the air. However, it is possible that a shorter time may be sufficient, as it is not yet known how much coronavirus is sufficient to infect a person.

... Prefer to telework when possible!

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Recommendations on distancing measures to be taken at work depending on the air filtration mode in the offices.

Augenbraun, B., Lasner, Z., Mitra, D., Prabhu, S., Raval, S., Sawaoka, H., and Doyle, J. (2020), Assessment and Mitigation of Aerosol Airborne SARS-CoV-2 Transmission in Laboratory and Office Environments. Harvard University.

Airborne transmission of the virus is important.

L. Brosseau (2020), Commentary: COVID-19 transmission messages should hinge on science, Center for Infectious Disease Research and Policy.

A regularly updated Google document, written by more than a dozen American experts, containing general and practical information on the transmission of SARS-CoV-2 by aerosols.

FAQs on Protecting Yourself from COVID-19 Aerosol Transmission.

Airborne transmission of the virus is made possible by extensive replication of the virus in the throat. The study published by the Charity groups in Germany shows that the virus is present in the mucus of the nose and sputum from the onset of symptoms and remains in the sputum long after symptoms have ended.

Wölfel, R., Corman, V.M., Guggemos, W. et al. Virological assessment of hospitalized patients with COVID-2019. Nature 581, 465-469 (2020).

Identification of the virus within a 4-meter radius of COVID-19 patients in hospitals in China.

Guo ZD, Wang ZY, Zhang SF, Li X, Li L, Li C, Cui Y, Fu RB, Dong YZ, Chi XY, Zhang MY, Liu K, Cao C, Liu B, Zhang K, Gao YW, Lu B, Chen W. Aerosol and Surface Distribution of Severe Acute Respiratory Syndrome Coronavirus 2 in Hospital Wards, Wuhan, China, 2020. Emerging Infect. Dis. 2020 Apr 10;26(7)

This review mentions that airborne transmission of the SARS-CoV-2 coronavirus is most likely caused by droplets and aerosols.

Cascella M, Rajnik M, Cuomo A, et al. Features, Evaluation and Treatment Coronavirus (COVID-19) [Updated 2020 Apr 6]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2020 Jan-.

This article raises the fact that transmission of the SARS-CoV-2 coronavirus could be caused by aerosols.

Wang, J., & Du, G. (2020). COVID-19 may transmit through aerosol. Irish journal of medical science, 1-2. Advance online publication.

Theoretical calculations estimate that coronavirus in a 5 um droplet can stay in the air for 9 minutes, while coronavirus in a 2 um droplet can stay for 1 hour. These theoretical estimates suggest that the distance recommended by the WHO (1 meter) or the CDC (~ 2 meters) may not always be sufficient depending on draught or ventilation conditions.

Singh, N, Kaur, M. On the airborne aspect of COVID-19 coronavirus. arXiv:2004.10082 [physics.pop-ph] PREPRINT

Experimental measurements show that the SARS-CoV-2 coronavirus can be present in an air suspension for several hours and remains infectious when tested on cultured cells 2 hours after aerosolization.

van Doremalen, N., Bushmaker, T., Morris, D.H., Holbrook, M.G., Gamble, A., Williamson, B.N., .... Munster, V. J. (2020). Aerosol and Surface Stability of SARS-CoV-2 as Compared with SARS-CoV-1. New England Journal of Medicine, 382(16), 1564-1567. doi:10.1056/NEJMc2004973

The efficiency of HEPA filters is 99.994% for particles of 50 nm, and greater than 99.996% for particles of 0.5 μm and more.

Zhang, Z., Yi, Y., Zhao, M., Wang, W., & Qi, J. (2014). A blunt sampling probe developed for an in situ leak test of HEPA filters in high-level biosafety laboratory. HVAC&R Research, 20(2), 221-229. doi:10.1080/10789669.2013.855070

The efficiency of HEPA filters is 99.96% for aerosols containing DNA, mimicking coronavirus-containing aerosols.

Morono, Y., Hoshino, T., Terada, T., Suzuki, T., Sato, T., Yuasa, H., Kubota, Y., & Inagaki, F. (2018). Assessment of Capacity to Capture DNA Aerosols by Clean Filters for Molecular Biology Experiments. Microbes and environments, 33(2), 222-226. https://doi.org/10.1264/jsme2.ME18012

Further reading

Do I have to wear a mask if I don't have any symptoms?

Can a mask be "worse than nothing"?

How can teleworking be improved?

How to organize a meeting of less than 50 people indoors?

Is the SARS-CoV-2 coronavirus transmitted by aerosols?

What is the recommended distance between two people?