Bjorn’s Corner: Do I get COVID in airline cabins? Part 9. Stay hydrated.

By Bjorn Fehrm

July 3, 2020, ©. Leeham News: In our Corner series about flying during the COVID-19 pandemic, we examine how cabin humidity affects the risks of getting COVID-19.

The extensive research around the seasonality of flu infections gives us tips for our behavior during flights, now and when the pandemic has left us.

Figure 1. The air conditioning system of an airliner. Source: Leeham Co.

The importance of staying hydrated when flying

I have written before about the cabin Environmental Control Systems, ECS, and how it circulates the air in the cabin from top to bottom and then runs it through hospital-grade HEPA filters on the return path to the ECS, Figure 1. It’s mixed 50-50 with outside air coming from the engines in the ECS, then routed back to the cabin.

One aspect of the ECS air is its humidity. The outside air, tapped from the compressors of the engines, is void of moisture. This air mixes with returned cabin air at the ECS. The water content in the cabin air is coming from the passengers. Therefore, the humidity in the cabin is dependent on the cabin load factor, but in general, it stays below 15% and can be as low as 5%.

Virus living in droplets and aerosols are affected by this low humidity. But any such effect is small compared with the 99.9% filtration of the viruses by the HEPA filters in the cabin return path. What we know is, in modern airliners, the air entering from the top of the cabin is virtually void of virus loads that can infect a person, but also very low on humidity.

The dry air entering the cabin might not affect the virus much before it hits the HEPA filters but it affects us. Our human body’s first line of defense against viruses is dependent on an intact layer of mucus in our respiratory tracts. We know dry air taxes our mucus layers, and it’s considered one of the factors the winter is the flu season.

Winters have lower vapor content in the outside air, and when this low vapor air gets heated for our inside environments, the relative humidity tanks. The low humidity air taxes our mucus layers and it makes us more susceptible to respiratory infections.

It’s one of the reasons long-range passengers are encouraged to drink water to stay hydrated during the flight. In virus times, this recommendation shall be extended to all flights, to maximize the effectiveness of our first line of virus defense.

It’s therefore with pleasure I read this tweet from Air Canada yesterday:

What’s in our complimentary onboard Customer Care Kits? For your safety and peace of mind, every passenger receives a complimentary mask, gloves, bottled water, hand sanitizer and disinfectant wipes in a bag you can dispose of.

There is much an airline can do to help our mindset and improve our defense against the virus when we fly. A mask and water bottle to all passengers cost cents for the airline but can make an important difference to the passenger.

Airports, airlines, and authorities need to take inspiration from each other. And we as passengers shall understand why recommendations for our behavior are as they are. Our knowledge of what to do and not to do in this pandemic grows by the day.


The report about boarding and de-boarding we quoted from last week is now published:


10 Comments on “Bjorn’s Corner: Do I get COVID in airline cabins? Part 9. Stay hydrated.

  1. Good shout out for AC and their positive action to help and reassure passengers!

  2. Bjorn, thanks again for all your efforts in bringing us these data. It’s notable that most aircraft models continue to use the 2003 SARS outbreak for calibration, as there is still no data on COVID super-spreader or cluster events from an airliner. Even the 2003 outbreak has only one super-spreader event, along with a few instances of lesser infections, without any precautions,

    As domestic air traffic builds to 35% in July and 50% in August, we should have better statistical data for COVID and air travel. A lot will depend on implementing the procedures well. But I think both airlines and passengers have strong motivations to do this. Airlines want travel to resume and passengers want to maintain their health and travel safely. So things are aligned for a good outcome.

    I’ve seen additional research this week pointing to social “greeting” events as being the common factor in super-spreader outbreaks. These include cruise ships, weddings, funerals, parties, bars, religious gatherings, etc. All activities with frequent close conversation and touching, hugging, handshakes and even kissing, moving from person to person. Involuntary confinement would have a similar effect even without the greeting aspect, as in prisons or aircraft carriers.

    Those activities seem to be tailor-made for COVID. Given Gerrard’s evolutional perspective, and given how social we are as a species, perhaps the virus has taken advantage of our natures. If so, that understanding gives us a tool to change behavior in larger groups, to slow the spread.

    Interesting also, that without countermeasures, the virus would cause our species to evolve into less social behavior. That could occur through diminishing numbers or by favoring less social individuals. But that doesn’t seem to have worked in the past, so probably won’t this time either.

  3. Ideally speaking, travel in commercial aircraft should be relatively safe.
    In the real world, however, the situation is adversely influenced by various factors. For example:

    – People are wearing face masks incorrectly. Undercover observers on Dutch trains — on which face masks are compulsory since June 1 — recently observed that 11% of travelers were only covering their mouths with their masks, and leaving their noses uncovered. Also, people were lowering their masks in order to cough/sneeze (presumably/hopefully into their elbows), rather than leaving the mask in place. In addition, people were lowering masks in order to eat/drink. A chain is only as strong as its weakest link, so sub-optimal behavior like this puts everyone in jeopardy.

    – Although the nominal airflow inside the aircraft cabin may follow the described laminar path from top to bottom, that flow can — and will — be deformed by turbulence effects caused by passenger movement. Remember that people are constantly moving arms (to adjust ventilation/lighting, for example, or to retrieve a personal item from the floor), and are twisting and turning in their seats to get more comfortable…not to speak of passengers walking to the restrooms and cabin crew walking about. To think that this doesn’t cause significant turbulence is naive: note, for example, how your nose can pick up an increased smell of perfume/aftershave (or body odor) from someone when that person makes even a slight movement.

    I’m not afraid to get on a plane — and I don’t doubt that infection risk on a plane is lower than on a train or bus — but there’s still an inherent risk involved. Time will tell how big that risk actually turns out to be.

  4. Bjorn, greetings. It’s been a while. Not to amp up the paranoia, but what is the protocol on switching out these a/c HEPA filters—timeline and disposal procedures? (I’ve gone from Reagan’s “Trust but verify” to near “Trust no one.”)

  5. Continuous UV cabin lighting is the way to kill COVID19 suspended in the air or deposited on surfaces. In most cases it is no more complex than swapping out bulbs or neon tubes for a UV bulb etc. My national carrier Air New Zealand seems reluctant to take even this simple step to protect the health of passengers or even their cabin crew.

  6. FWIW – Not an ex- spurt on UV- but I think the type ( frequency spectrum ) and intensity of UV needed to disinfect is a no no on human skin and eyes. A lot of the hazardous UV from lucky ole sun is filtered by clouds and moisture and ??, thus the small percentage that reaches you on the beach results in a tan or sunburn along with a dose of vitimain D ? …

    UV light is used on stages for lighting effects, but usually actors wear filters or avoid directd observation.

    Need someone who KNOWS to comment ..

    • Yes, the use of UV light to disinfect requires a combination of intensity and exposure time. UV lighting in the cabin would have the exposure time but could not have the needed intensity. UV lighting in the air handling system could have the needed intensity but probably not the exposure time, given the high flow rates.

      The latter case is also why UV has not been widely endorsed for home heating systems. Hospital UV disinfecting systems have been specifically designed to achieve both criteria. It works well if done correctly.

      There is also a range of effectiveness depending on the type of microorganism involved. UV works by degrading genetic material, and there are varying levels of susceptibility for different viruses and bacteria.

  7. All the airlines that moved from 9 abreast to 10 seats abreast on their 777s, introducing “slim line” seats reducing pitch further below 30 inch, removing personal airflow outlets, get smaller lavatories to save weight, add seats, they are scratching their heads. Or they should be.

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