An airplane is a confined space with all the associated risks and concerns about the spread of infectious agents such as viruses or microbes.
This is a topic that some people normally worry about and it becomes a general concern when everyone has COVID-19 in mind.
Where does the air we breathe on a plane come from?
Modern aircraft operate at very high altitudes, at levels where the pressure is much lower than on the ground and the oxygen content of the air much lower. In other words, it is impossible for us to breathe at these altitudes, hence the presence of oxygen masks that are triggered in case of cabin depressurization (but that’s another subject so we’ll talk about it another time).
The pressurization of the cabin provides passengers with breathable air, which is a factor of comfort but above all of safety. To do this, the aircraft must be perfectly sealed to resist the pressure difference between the inside and the outside, otherwise one of the possible consequences is an explosion.
An airtight system means no outside air supply, which is unthinkable if you don’t want to see the occupants of the aircraft suffocating one after the other.
A mechanism thus allows the contribution of external air in order to renew the air which one breathes on board. It remains to be seen if it allows us to breathe healthy air.
How is an aircraft supplied with air?
The air is logically taken from outside. But at this altitude, remember, it is cold. A modern airliner flying between 9500 and 12 200m of altitude, the outside temperature oscillates between -44 and -64° (-50° at 10 000m which is the “standard” altitude). Unbreathable. In addition, at this altitude it is very low in oxygen and does not provide the human body and brain with the oxygen it needs.
The air is therefore captured at the level of the engines (rest assured that it does not pass through the engines and is therefore never in contact with the kerosene or combustion gases). It undergoes a strong rise in temperature (an airplane engine has a temperature of about 800° while cruising) which makes it possible to destroy all the potential microbes and micro-organisms if they have survived the -50°.
But at this moment the air becomes too hot and is still low in oxygen. It is cooled, humidified and compressed before being sent into the cabin.
But this only concerns half of the air in the cabin at any given time! The other half is recycled interior air. So if there is a risk, maybe it comes from there.
Air recycling in aircraft
The air taken from outside the aircraft is therefore mixed with an equal amount of interior air which is recycled. The air you see coming out of the nozzles is therefore composed of 50% fresh air and 50% recycled air.
The recycled air passes through filters called HEPA filters (High-Efficiency Particulate Air). They allow to filter in one passage, at least 99,97 % of the particles of diameter superior or equal to 0,3 µm (micrometers or 10-6 or “millionth of meter).
It doesn’t mean anything to us, simple passengers, but you should know that this level of filtering is used in only a few types of places:
- Operating rooms and operating theatres
- Microbiological safety station
- “Clean room” housing state-of-the-art computer or microelectronic installations
- Homes of people vulnerable to air pollution.
The EASA (European Aviation Safety Agency) published in 2017 two studies on air quality in airplanes commissioned to independent organizations that will enlighten you on the subject if you want to go deeper.
The WHO itself recognizes that the risk of transmission by air is very low, at least through the air.
So if the outside air and the recycled air are free of any suspicion we can fly in peace? Not yet! Finally, it is necessary to ensure the speed of air renewal in the cabin. Filtering is good, but if you do it every 3 hours, the passengers have time to be contaminated by all the miasmas present in the cabin.
Air is renewed every 2 to 3 minutes
In old planes like a B747 the cabin air is completely renewed every 4 minutes, in recent planes like the A350 the air is renewed every 2 to 3 minutes or between 20 and 30 times per hour.
So to put it plainly you are less likely to be contaminated by the air you breathe on an airplane than if you are at home (even with the windows open), on a train, in an office or even in a hospital (unless you are in an operating room).
The only reproach we can make about the air we breathe in the airplane is that it is dry, very dry, even if this is improving very slightly in the new generations of aircraft.
But you can still catch diseases on a plane
However, we should not be too optimistic. As with any means of mass transportation, there is no such thing as zero risk. Shelves, toilets and chairs can be nests of germs in airplanes as well as in trains or any means of transportation. But here what comes into play is more the attention that the airlines pay to cleaning than the means of transport itself.
Take a look at how Emirates disinfects its cabins in response to COVID-19.
And of course, in extreme situations like that of a virus like COVID-19, we can say that an additional security can be reassuring and that if in addition to the way the air is treated, a minimum of distance is kept between the passengers. If some people talk about one meter for the most common viruses, for SARS a study of 2003 had evaluated them at 6 feet (1,80m) but on the ground, not in a plane. Since a virus cannot spread through ventilation, it is only too close that can be dangerous, so it is best to take precautions.
Image : virus in plane by EugeneEdge via Shutterstock
