Should I open the windows? — A bizarre COVID-19 outbreak

After three years of fighting the epidemic, wearing masks, washing hands frequently, and frequent ventilation have become the key words in our minds. However, a recent outrageous case of COVID-19 infection has overturned people's idea of ​​opening windows for ventilation. So, should we open windows during the fight against the epidemic? Let's talk about it today.

01. Bizarre cases of infection

Zhu Moumou stayed at home but often played with his mobile phone in front of the bedroom window, which was close to the China-Vietnam Railway, and as a result he was infected with the new coronavirus.

This case is very special in that the patient did not have direct contact with the COVID-19 positive person, and there was not even any time and space companionship.

Just because there was a China-Vietnam railway ten meters away from the window, I got infected.

02. About aerosols

The above case information has two reminders:

1. There is a large number of infections on the China-Vietnam Railway, or more specifically, on the trains on the China-Vietnam Railway, such as passengers. And the concentration is so high that it would be high if released outdoors.

2. High-concentration aerosols can spread over long distances and infect people.

This is not the first case of aerosol infection. Similar aerosol infections have been reported in many places.

This is slightly different from the droplets.

Aerosol refers to a gaseous dispersion system composed of solid or liquid particles suspended in a gas medium. The density of these solid or liquid particles can differ slightly from that of the gas medium, or it can differ greatly.

Compared to droplets, aerosols spread farther.

03. Is it appropriate to open windows for ventilation in places where buildings are close together?

However, if we extend this content, we will have some thoughts:

Is it appropriate to open windows for ventilation in places where buildings are close together?

The novel coronavirus that spread along the China-Vietnam railway was most likely spread into the air through the ventilation system and then infected people.

This also gives us a deduction, that is, if there is a high-density COVID-19 infection area, it is very likely to release the COVID-19 through window ventilation.

Moreover, the taller the building, the greater the air humidity and the faster the air flow, the more severe the spread is likely to be.

As shown in the picture above, this is the spread of droplets when a person is standing on the ground, but if the person is standing at a higher place, then this diffusion, following a parabola, coupled with wind, may spread very far.

In fact, transmission between buildings is not impossible. Previously, CDC Weekly reported a study on the transmission of COVID-19 between handshake buildings.

Simply put, there was no close contact between the two buildings, but infection occurred.

The research at that time believed that:

Although the two buildings belong to different structures, they have ceilings on top and are close to each other, so a closed space is formed.

They simulated the scenes in the building at that time, including the opening and closing of the air conditioner in Ward 1 (A), the opening and closing of the door of Ward 1 (B), and the opening and closing of the window in Corridor 2 (C).

Then a fake virus model was released in one place to simulate the situation where an ordinary person releases the virus through aerosol breathing, and the released substances in the air were monitored in several other places.

The results are shown in the figure below, which roughly means that the entire aerosol transmission chain has been proven to exist

This aerosol transmission chain is essentially a situation where the virus is in the air and the aerosol spreads due to aerodynamics. After all, the virus does not become inactive immediately in the air, but it will spread over a certain period of time. During this period, if the diffusion dynamics are sufficient, it will spread far enough. And if the concentration is high enough, it may pose a threat to people who breathe it.

For densely populated communities, especially high-rise communities, if there are dense positive cases, then opening windows will, to a certain extent, be like throwing objects from a high altitude, which can easily allow droplets to spread farther and pose a certain risk.

Therefore, it is recommended that:

1. For handshake buildings, densely populated communities, and areas with a large number of positive tests, be cautious when opening windows.

2. Consider the wind direction when opening windows.

The above is just my personal opinion, but it does not mean that opening windows is wrong. It can only be said that in some special circumstances, opening windows should be done with caution.

Or simply summarize: scientific ventilation!