May 8, 2020, ©. Leeham News: In our Corner series, we now dig into this important subject: Is my probability of getting infected with the COVID-19 virus higher in an airliner cabin than in other places?
We look at simulations of how the virus travels when we breathe/cough and how the virus load propagates in an airliner cabin. Then we talk about infection probabilities compared with other environments.
The scientists are sure the main infection path is when inhaling droplets coming from exhaled breathing air from an infected person.
Recent simulations by Florida Atlantic University using a simulated aerosol with the smaller and more dangerous droplets (10 to 20 microns in size) show the finer droplets travel up to 3m (10 feet) after a cough, and these can hover in the air for a minute after the cough. Figure 1’s upper part shows the beginning of this process (the stripes in the cloud are from laser lighting effects).
The Florida Atlantic University video with different cough simulations is here.
We got the right to show the simulations and asked Professor Dharak to make a simulation with a face mask. The difference is dramatic, Figure 1 lower part.
The virus can also survive a day or more on a non-porous surface (to not dry out so fast) like a metal handle or our mobile phones. To be infected, the virus must then be brought to our nose, mouth, or eyes by our hands, and there enter our tissues.
This is why regular handwashing is so important and why handwashing or rinsing hands with alcoholic gel after touching public surfaces are recommended.
The probability of getting the virus to the lungs where they can cause a dangerous infection is much higher through the aerosol path than the touch path. There is still no clear evidence of a touch path infected patient, according to the experts.
When flying on an airliner post-COVID, both paths are in focus.
The danger of inhaling infectious droplets/aerosol depends on how far it travels from the infected person and how long it stays airborne. In areas without a directional airstream displacing the droplets/aerosol from our breathing level, the risk is higher. Figure 1 is such a case.
Examples thereof are any indoor confinements like shops, stations, trains, buses, work areas, and airport check-in or waiting areas.
Airliner cabins do not count to this category. The Environmental Control System preparing the air we breathe in aircraft builds on a directional airflow from top to bottom. The flow, which is substantial (the air is exchanged in the cabin every other minute), enters at the roof level and travels down to the floor area, where it exits through air vents in the outer walls besides our shoes.
As the air goes back to the air conditioning system in the belly of the aircraft, it passes HEPA (High-Efficiency Particulate Air) filters that catch the rather large COVID-19 viruses. The air is then mixed with new air from the aircraft engine compressors and enters the cabin at the roof level to retake its journey downwards to the outlets sitting at the bottom of the cabin walls.
This orderly airflow will be disturbed by movements in the cabin, and this is why probably the highest risk of contamination is during boarding and deplaning the cabin. The risk during flight is lower, supported by examples given by IATA in the week (see below).
As seen in Figure 1, the mask minimizes the risk of an infected person propagating virus droplets to neighbors in the cabin. Once past the floor outlets, HEPA filters catch the virus. The mask born by neighbor passengers adds additional protection from inhaling any residue aerosol from an infected co-passenger.
Wearing masks has been part of Asian culture for decades. When I first saw it during travel in Japan, I thought, “people are nervous about getting infected here.” I was wrong. It’s not the persons fearing an infection that wears the mask; it’s the infected person. Asians with flu put on a mask of courtesy to other people.
This is a habit we should adopt, not only in COVID times.
“And we should stop the stupid hand-shake,” says the chief US immunologist Dr. Fauchi. “It has no place in modern society, not now and not after the Pandemic.” This leads us to the touch path.
While scientists are clear over the aerosol path, the touch path is intellectually plausible but with a lower probability of infection. How low is not clear as there has been no cases or studies that have proven such an infection chain.
The chain is possible, and the use of an alcoholic gel after touching common areas such as lavatory handles and doorknobs, etc. shall minimize this risk path. The mask, in addition, makes inadvertent touching the sensitive nose and mouth tissues more difficult.
IATA (the association of the world’s airlines) issued recommendations in the week ahead of a re-starting of flying. Masks for passengers and crew are imperative, and we understand why.
IATA also points to none of the known flights, where post-flight confirmed COVID-19 infected passengers traveled, resulting in infected co-passengers. There were three cases of a passenger to crew infections however, as here, the communication is face to face. Once again, mask-wearing makes sense (this was before crews and passengers wore masks).
We have asked Airbus and Boeing to support us in explaining the in-cabin airflow better, and we will dig deeper into this in the next Corner.