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.
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. https://aircanada.com/cleancareplus
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: https://www.mdpi.com/2071-1050/12/13/5329