Federal Minister of Health Karl Lauterbach (SPD) had to explain at the moment, why what he really wanted, namely the FFP2 masks on board flights from October, is now not required after all. He said at a press conference (09/06/22): Wearing masks on buses and trains makes sense and is necessary. The situation is slightly different in airplanes – partly because there is more air circulation on board thanks to filter systems.
In an interview with NDR-Info (09/07/22, 7:58 am), he added that the difference in the ventilation of trains and planes is due to physical factors. The risk of infection in rooms with high ceilings would be lower. Airplanes (as opposed to trains) would have such high ceilings. Furthermore, a mask requirement on the plane is not enforceable. There would be no point in passing a law if it was not enforced.
What knowledge is available on the subject? Infection can occur in a plane by a sick person sitting next to you, on the same bench, in the same row of seats or a few rows away (WHO 2009). If the sick person breathes or even coughs or sneezes, people sitting next to you can become infected because the virus spreads with the smallest droplets (aerosols). The closer someone sits to a sick person and the longer the flight, the greater the likelihood of infection. It is a well-known fact that we sit very close together on a plane and on long-haul routes we sit together for a long time. Studies have shown that no person on board is safe from infection when a sick person is on board (Olsen 2003). Masks help, but are no guarantee against infection. FFP2 masks are better than surgical masks.
An airplane is not a closed system like a submarine. The aircraft is ventilated with air from the outside. This is especially important to remove the CO2 produced when breathing out of the cabin. The outside air must be brought from the low outside pressure to the higher cabinet pressure. It costs energy. The heat generated by the many passengers must also be dissipated. More air must be used for this. In order not to have to compress even more air from the outside, air is circulated (recirculated). So that the plane does not become a virus loop, and viruses from the front row do not spread to the back row via the air conditioning system, there are recirculation the air HEPA filter (Heavy dust filter), which can even filter out viruses quite reliably. Half of the air entering the cabin is outside air, the other half is recirculated air. Only the outside air ensures a sufficiently low CO2 concentration, because the HEPA filters cannot filter CO2. Outdoor air and recirculated air together give a value of Virus concentration in the cabinthat only half as high is as it would be with outside air ventilation alone (Figure 1).
So: The HEPA filters reduce the virus concentration, but cannot remove the virus from the cabin, because the viruses are introduced directly into the cabin and only then enter the filters. For a possible infection on the plane, it is decisive whether there are one or more sick people nearby. The effect of the HEPA filter is secondary. Unlike the possibly sick seat neighbor, the HEPA filter is far away in the cargo hold. However, the masks are between the passengers as a barrier (picture 2).
The volume flow of fresh air per person is crucial for ventilation. The approval rules (CS 25,831) prescribe a volume flow of at least 5 liters per second per passengers (18 cubic meters per hour). What this means becomes clear in relation to an apartment. My apartment e.g. B. is equipped with a ventilation system. mine examination 25 liters per second (90 cubic meters per hour) – i.e. per person 5 times as much air as one person in an airplane.
Let’s assume that there are 2 cubic meters of air available per person in the plane, then the air in the plane is theoretically exchanged 18/2 = 9 times per hour. The number of theoretical air changes per hour is air exchange rate called. A theoretical air change in the plane then takes 1/9 hour or 6.7 minutes. In my study, which is 36 square meters and has a ceiling height of 2.5 meters (volume: 90 cubic meters), the air is theoretically only replaced once an hour. The air exchange rate in an airplane is 9 times higher. Nevertheless, the ventilation in my studio is significantly better than the ventilation in an airplane (picture 3).
A hill ceiling height (as cited by Lauterbach) leads to a large volume, which the air exchange rate (which is irrelevant) reduce would The air volume flow per passenger is important.
Conclusion: An error has been made using the air change rate, which has impressively high values for the aircraft (9), but is irrelevant. A small quantity per person (as in an airplane) results in a high air exchange. The air volume flow per passage is and remains decisive.
The air exchange rate is important in dynamic processes, if e.g. B. is about getting a spontaneously occurring cloud of smoke out of the plane quickly. But this is about quasi-steady states during an entire flight. It is therefore not the case that viruses left the plane in 6.7 minutes. If a sick person is on the plane, then viruses are always present, because a sick person transmits viruses continuously – not just on boarding.
The comparison between plane and train: The ventilation with a volume flow of air per passenger is comparable in the train to that in the plane. The filter type is not primarily important. There is no significant difference in ceiling height between planes and trains. It is less cramped to sit on the train in average traffic conditions. In the best case, distances can therefore be better maintained on the train than on the plane. More volume per passenger is available on the train. This means that only the parameter for the insignificant(!) air exchange is worse than in the plane. Many parameters must be used to compare ventilation between planes and trains. The values are very similar, differences even out. On this basis a radical decision to wear masks (here yes, there no) cannot be physically justified.
In the current situation, the mood was once again made with the inappropriate “aircourse” parameter.to tilt the mask requirement on planes. The effectiveness of the HEPA filter was also misjudged. We already had the argument in 2020.
In the current situation, there is no mention of it a mask requirement on the plane protects the health of the cabin crew would mean which has extremely close contact with the passengers when it comes to service. Passenger masks are more important than crew masks. Without a mask requirement on flights, flight attendants must be allowed to decide for themselves whether or not they want to wear a mask at work.
It is incomprehensible why a mask requirement should be easy to enforce on the train, but very difficult on the plane. It is also strange not to legislate on the basis of obviousness, but on the basis of expected resistance. This would mean that the population would be able to abolish or prevent unwanted laws and regulations (e.g. a speed limit) by systematically breaking the rules. The difference is that the obligation to wear masks on planes is not about simple rebellious citizens making representations, but about an influential area of the German economy that is well and assertively organized by associations. Significant in this Lufthansa, which has a competitive advantage (comfort advantage) compared to the railways, whose masks are only dispensed with in the plane. In the end, it’s always about the money.
“Ventilation of airplane cabins in the Corona pandemic – legend and truth”
“Theory of ventilation of aircraft cabins”
Regarding the flight attendants’ situation:
“COVID-19 in the Aviation Industry: The Good, the Bad and the Necessary” (U.S. Perspective)
Andreas Scheuer, Aviation Summit 23 July 2020, fresh air quota and climate curtain