Does it or does it not, fly — A COVID-19 story

Amit Mishra, Asit Mishra

A well-balanced diet of fear is crucial for survival! We have seen both extremes of this in the last few months. When the pandemic created mass hysteria we saw how the civilized world went crazy and started hoarding toilet papers! The other extreme is the German Chancellor Angela Merkel’s statement in February that 60% of us would get infected by this virus. That statement, at that time, felt a bit too pessimistic (even though it was based on scientific evidence). Now we have seen how that fact-based, well-guarded, fear made Germany one of the most successful countries to control the virus (with minimal infringement of human rights).

Now that many countries have started to relax lockdown (even when cases are spiking for some nations (like India and South Africa)) we believe that agencies, companies and facilities are turning a blind eye towards a big concern: “is Covid-19 air transmissible?”. A major reason for this relaxed attitude is the presence of two opposite stands in research communities (some saying it is air-transmissible and some saying it is not). These opposing view points are often presented in media in a simplified manner, without the nuances, further muddying up the water. Such media behaviour often leads people to turn a blind eye.

We shall quickly discuss if the virus “flies” or not!

Few facts.

1. The virus can not fly!
2. Trapped in mucous droplets that one exhales the virus can go as far as these droplets can go.
3. Best ways to avoid these droplets are A) be far from people; B) wear mask; and C) (often ignored) have as much ventilation as possible.
4. You need to be exposed to a decent amount of virus to get infected. (It is difficult to say as of now, what is the exact meaning of “decent amount”.)

“Barriers” affect spread of virus laden drops

Respiratory viruses like the one causing Covid-19 are supposed to have three main modes of transmission — close contact (droplets), fomites (touch surfaces), and airborne. From the beginning of this crisis, WHO has highlighted the first two modes, completely excluding the third one. That does seem like a contradiction right? For this kind of situation, you would prefer to be safe rather than sorry.

You may be thinking why is there so much uncertainty around something seemingly trivial? Partly, the answer lies (as often) in the physics of the phenomenon and partly, it is about rigid nomenclature.

Broadly speaking, there are two types of fluid particles we emit, viz. droplets and aerosols. Droplets are bigger and heavier whereas aerosols are tinier and lighter. For an excellent pedantic review one can read this blog.

However, there is lack of a clear distinction as to what size (diameter) differentiates the two. Different sources, especially from different fields of investigation, have different demarcations, starting from 5 to 100 micrometers. This is where the problem with nomenclature crops up. But let us not get confused by things that can lead you down the rabbit hole of technical jargon.

Coming to the physics part of the issue, the behaviour of the tiny vs larger fluid particles, once emitted from our nose or mouth, can change immensely depending on how they were expelled, how fast they were coming out, if there is a breeze or not, how humid is your environment etc. For example, normally, one would expect larger drops to quickly fall to the ground but with a breeze, they can travel farther, talking loudly spreads them wider than a normal voice and sneezing even further; in low humidity conditions, the drops can quickly lose water mass and larger drops can become smaller before they hit ground; even wearing masks, by barring normal flow, affect the spread of droplets and aerosols.

What we know for sure is this:

Viruses can travel in drops of moisture and mucous infected individuals exhale.

Technically, airborne transmission is related to spread via aerosols (smaller droplets). But, the virus does not understand our technical definitions. Airborne or not, the virus certainly travels via air — it is, after all, a respiratory infection.

In spite of this, it took a long time for WHO to recommend mask wearing as a preventive measure. Even now, both WHO and CDC recommend use of masks but still do not consider the airborne route of transmission as a viable mode. It is expected that allowing for airborne transmission may generate panic in public, but it could very well be a healthy dose of panic.

Once we change the way we see these phenomena, a lot will change automatically. Let us think of other examples of particles/particulates moving through air and try to see what we can conclude.

1. A classic example of such spread is how we can smell a cologne across the hall! Yes, it can travel that far!
2. It is difficult to smell the cologne in a park or on a beach (unless you are seating really, really close).
3. In a room with AC on, we smell that cologne for a much longer duration. And sometimes we can smell cologne from another room served by the same AC!
4. In another example, let us visualise a hall with a fan and a person wearing cologne is seating near it. If you are in the way of the fan’s head then you get a good, strong smell of the cologne!

One extremely important (and often ignored) factor is ventilation, or its lack and the role of AC systems. Studies show how crucial it is to make sure that ACs in facilities/restaurants/malls are not spreading the virus. For a more detailed discussion please have a look at one of our previous blogs. In confined spaces, it comes down to ventilation by outdoor air, directions of movements of air streams, and strength of the air streams when trying to predict the path virus laden particles will take.

The chances of catching the virus from outside is quite low because the atmosphere is essentially huge and can quickly dilute exhalations.

So, there are two main take homes.

1. First, viruses can spread through tiny drops of moisture exhaled by an infected person — even if they do not show symptoms.
2. Secondly, in confined spaces the authorities and indoor air engineers need to be very, very careful in making sure that they are not turning their facility into a petri dish.

Informed and balanced diet of fear is good. Let us know the enemy and the enemy’s plan of “motion” and act accordingly.