We still hear every day how important it is to keep a minimum distance of 1.5 meters on the terrace, in the restaurant and in the store. Don’t forget to wear your (homemade!) Face mask on public transport, that’s the motto, because you might not always be able to keep that distance there. It is of the utmost importance to protect your own health and that of the people in your immediate environment.

Dutch governmental institute RIVM, which plays a decisive role in Dutch government policy, initially believed that a mask would add very little extra protection against Coronavirus. It was even opposed to its use because that might give “a false sense of security”. This advice was later on reversed, but the use of medical grade masks is still discouraged due to potential shortages for health professionals. And so our government now advises the use of simple, possibly homemade mouth masks, eg a piece of textile. The added value of this for the protection is, to say the least, questionable, it can at most help to contain the spread of larger drops when coughing/sneezing.

The aviation industry has long been known for its exceptionally powerful lobby. This was once again confirmed in this Corona era: suddenly it was declared (also by the same RIVM) to be safe to travel by plane, even with all seats occupied. At the same time, coaches, cinemas and restaurants were only allowed to use up to about 25% of their capacity in order to guarantee the 1.5 meter distance (this latter limitation has since been mitigated).

The argument for this “exemption” for the aviation industry is the supposed supreme quality of air exchange on board. Almost all major airlines also use their advertising campaigns to applaud the air quality on board. The air in the cabin is said to be as clean as in an operating room. “All air on board is completely refreshed every 3 minutes with fresh air from outside,” they say. In addition, “the HEPA filters used successfully filter all contamination (including bacteria and viruses) from the air”. And finally “the air flows through the cabin from top to bottom almost at every row of seats, so it is not transported from front to back (or vice versa)”. Therefore chances of a virus infection would be minimal (especially in combination with such a homemade mouth mask) …

Unfortunately, reality is a lot less flourishing: the quality of the air in an airplane cannot be compared to that in an operating room at all. The main differences:

  1. In an operating room, all air is taken fresh from the outside and filtered with high-quality HEPA filters before it is let in. The air is supplied at a relatively low speed over a large area. The fresh air then displaces the air present almost without mixing (laminar flow), this makes the refresh very effective. The air is also not reused, but is always completely replaced by clean air from the outside. This process guarantees a very high air quality.
  2. Because all air entering an aircraft cabin comes directly and unfiltered from the engine, this air is always contaminated with various toxins, including Organophosphates. The air is supplied via a considerably smaller surface area and a higher flow rate. This creates much more vortex and mixing of fresh and existing air, which reduces the effectiveness of the exchange. After that, about 50% of the air is reused, and only this already used air is cleaned by a HEPA filter before being remixed with the “fresh” air from the engine. This recirculation is used to save costs (fuel), but is of course at the expense of air quality!
  3. The number of people per cubic meter of space in an airplane is many times greater than in an operating room. The number of liters of fresh air per person is therefore much lower in an airplane than in an operating room. Moreover, by moving (walking back and forth) and heat production, this greater “human density” causes an additional increase in swirl and mixing of fresh and used air.
  4. During boarding and alighting, the so-called APU (Auxiliary Power Unit) supplies the required air (and also electricity) on board. This APU is often the cause of contaminated cabin air. However, the APU may not be used (or only to a very limited extent) at an increasing number of airports due to increasingly strict environmental and noise regulations. In that case, a mobile air conditioning unit under the aircraft is used, or an installation that is, for example, permanently installed on the platform or in the gate. Unfortunately the use of such an installation implies that the “own” air conditioning on board, and with it the much praised HEPA filters, are not in operation! And all that a a time when everyone is sitting/standing extra closely together, and is moving a lot (storing luggage, etc.), so maximum risk of infection!

Prof. Dr. Dieter Scholz, professor of aircraft systems at the University of Hamburg, discusses the problems with air exchange in aircraft in this report of the TV program Nano (German spoken, English subtitles available).

All in all, you can say that people in an airplane are close together (often for a long period of time), with a moderate quality of air exchange. The probability of infection with the Coronavirus (or any other contagious disease) is certainly not imaginary, as has been shown in the past (read this article in the Daily Mail of September 2020 about  the infection of several passengers with the Covid19 virus, where these passengers had not even been seated close to one another, and this article form the Center of Disease Control of March 2021 about multiple infections on a flight from Dubai to Auckland NZ). A similar “super spreading event” on board of an aircraft  was also demonstrated earlier, with the SARS virus.

Stichting Fly Aware therefore advises to always wear a good quality face mask when flying, eg the Cambridge Sky Mask. This offers a much better protection than a homemade mask, it protects you against both virus and bacterial infections and against the many other toxins that are present in the air on board.

One side note is in order here: the Cambridge Mask offers the user good protection with its FFP3 quality filter. However, this protection only works when breathing in, so to protect the user. The mask is equipped with a so-called outflow valve, a valve that opens when you exhale. This is done to increase wearing comfort because the mask offers less resistance when exhaling. But it does not protect the environment from the user’s exhaled air. However, due to Corona measures, this may currently be required in public transport (and airplanes). There are two ways to overcome this:

  1. The outflow valve of the Sky Mask can simply be taped so that it does not open. This can be done, for example by placing a small sticker on the inside of the valve. You will notice that it takes a little more energy to exhale, but it does not disturb the filter effect.
  2. You can of course also wear a simple homemade mask (of textile) over the Sky Mask to comply with the rules. The wearing comfort is then better preserved, because the breathing resistance increases less and excessive moisture is prevented in the mask.

With these simple measures you can ensure yourself a much better protection (and definitely not only against viruses!