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Is air travel whilst wearing masks safer than we think? US Government study says it is

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In the last few weeks, a number of studies have been published that attempt to accurately model how easily SARSCoV2 viral particles spread inside aircraft cabins.

Historically, aircraft have had somewhat of a bad reputation for viral transmission. Intuitively, stuffing a narrow tube with passengers shoulder-to-shoulder seems like it would be a hotspot for contagion.

How safe is flying with a mask

The average passenger is unlikely to know that on modern aircraft, the cabin is filled with completely fresh air every 2-3 minutes, or that all recirculated air must pass through a High Efficiency Particulate Air (HEPA) filter that is capable of removing most bacteria and viruses from the air.

I have had numerous conversations with friends and family who were surprised to find this out!

How do we establish aircraft transmission?

In the past months, several studies have been published on the transmission of coronavirus during air travel.

Three studies were published last month looking at three separate flights that resulted in ‘probable’ in flight transmission:

  • A Vietnam Airlines flight from London to Hanoi on 1st March resulted in a cluster of 16 cases
  • A flight from Boston to Hong Kong on 9th March resulted in a cluster of four cases (two crew, two passengers)
  • A flight from Athens to Tel Aviv in February or early March resulted in a cluster of five cases

All studies rely on retracing the likely path of transmission from contagious ‘index’ patients to the subsequently infected by calculating incubation periods, proximity to index patients and in some cases genomic sequencing to verify if the virus in index and infected cases are related.

It is worth noting that the studies are based on cases when masks were not mandatory during flight.

On the other hand, IATA, the International Air Transport Association, published a study recently that identified only 44 cases of potential flight-related transmission:

“The risk of a passenger contracting Covid-19 while on board appears very low, with only 44 identified potential cases of flight-related transmission among 1.2 billion travellers, that’s one case for every 27 million travellers.

“We recognise that this may be an underestimate, but even if 90% of the cases were unreported, it would be one case for every 2.7 million travellers. We think these figures are extremely reassuring.”

Computers good, real life better

Up until now, questions of flight-related Covid-19 exposure have been based on case studies or computational fluid dynamics, with Airbus and Boeing both studying how aerosols behave in a cabin environment.

There is only so far that computational models can go when modelling the dispersion of aerosols and droplets in aircraft cabins. Questions have been raised about “simplistic” models used by aircraft manufacturers:

“It is difficult to determine the potential exposure risk using available computational fluid dynamics models or contact tracing methods, due to the lack of experimental validation of aerosol transport in the aircraft environment and the lack of detailed tracking of human interactions in aircraft.” (United Airlines study)

We now have something better. This week, the US Department of Defense and United Airlines published a landmark study on the safety of commercial air travel based on real-life scenarios in controlled environments.

How safe is flying with a mask

The study used two United aircraft, a Boeing 777 and a Boeing 767, across 38 hours of flight time and 45 hours of ground-based testing.

Over 300 aerosol release tests were performed, with each releasing over 180 million fluorescent aerosol tracers. The aerosol tracers were ‘exhaled’ by a mannequin called Ruth to best simulate the release of the virus by breathing and coughing, both with a mask on and off.

How safe is flying with a mask

Each surrounding seat in the cabin section contained a bio-defense sensor capable of detecting the aerosols in the cabin air, representing the other passengers in the cabin. Sensors were also placed in galleys and the jetbridge during ground testing.

In addition, thermal blankets were used to simulate the body heat of passengers and subsequent heat emission and potential convection currents generated.

United coronavirus transmission study cabin

Results show extremely low rates of transmission

Once all the numbers had been crunched, the study found that only 0.003% of particles actually made their way into another passenger’s breathing zone when seated and wearing masks. To put it another way, this is only one in every 33,000+ particles.

In addition, around 99.99% of all particles were filtered out of the cabin air within six minutes due to air circulation, ventilation and filtration.

Put another way, the test:

“indicates an extremely unlikely aerosol exposure risk for a 12 hour flight when using a 4,000 virion / hour shedding rate and 1,000 virion infectious dose.”

With evidence mounting that aircraft themselves are very safe provided masks are worn, it now seems that other areas of the passenger experience – such as at the airport itself or public transport – are more likely to result in transmission of the SARS-CoV-2 virus.

You can read the full results here.

Comments (83)

This article is closed to new comments. Feel free to ask your question in the HfP forums.

  • Nathan says:

    Another informative study that will count for nought once buried under reported hysteria and individual presuppositions and prejudices.

  • Jon says:

    I wonder how long post-Covid these will continue to be deemed necessary? I’m sure there are some who would like them to become normality forever. They may well significantly reduce transmission when used correctly and it goes without saying that of course we should all be wearing them when required out of respect for other passengers while this terrible virus is rife, even if only to make them seem safer…

    Sadly the fact is that they *are* uncomfortable (not to mention unnatural) over any length of time, leaving many of us feeling we have little option but to avoid all forms of public transport as far as possible until their use is no longer required. I’ve had to pass up some great long-haul offers recently not out of fear but because the masks just kill it for me I’m afraid. On the plus side I’ve saved an absolute fortune on travel this year – enough for a new car and some work on the house I’d never otherwise have been able to afford.

    • meta says:

      Good. I wish everyone like you had the decency not travel if they find masks uncomfortable.

      • Polly says:

        Good point…it’s the least the travelling public could do, if they really have to travel…

      • Riccatti says:

        One extreme to another.

        Disposable masks start to accumulate harmful cultures within 30-40 minutes of use. Depending on humidity and temperature conditions (after re-use, and being touched a number of times — they are Petri dishes).

        Let’s extend this logic and say I wish everyone have decency not to travel with young kids… with increased temperature, … with dirty soils.

        • meta says:

          Putting on a dirty mask is a person’s choice. Touching the mask is again person’s choice. Harmful cultures you mention harm only the wearer. The wearer has a choice to change mask should they wish. The fundamental issue here is that people do not understand that masks are not there to protect you personally, but others from you! And in doing so, it reduces the risk overall.

          • meta says:

            Also people shouldn’t be travelling with increased temperature anyway and even when there was no pandemic airlines can refuse you boarding in case of sickness. Dirty soils don’t spread virus or harm you unless you touch them or walk barefeet on a plane. Healthy young kids do not spread virus either.

    • Riccatti says:

      Point being made that restrictions, once in place, such as scanners, extra scanners, swipes for drug residues — get worse over time, not removed to old normal.

      We have to pay for the overzealous apparatus and those people who yell at you and threaten not let you through airport security if you don’t zip your liquids tightly in plastic bag (typical Heathrow case).

      It was my personal experience with Heathrow that once you make a verbal comment the agent makes it difficult — they invariably respond that they can make it even more difficult, or in fact acting to do so. They expect compliance to the level of: prison guard/prisoner.

      Even if you don’t travel personally, you pay for these overheads because the businesses you purchase goods and services from pay for staff travel.

  • JK says:

    I’d like to know more about how density of seating affects transmission. This is HFP so I can jokingly imagine an article comparing transmission rates between cabins with suites, fully flat beds herringbone layout, premium economy etc.
    The obvious conclusion will be lower density seating is safer. Great for those who turn left, but wonder if airlines will really convince the rest that sardine class is low risk. If anyone is ill on the plane, everyone nearby is going to be exposed, no matter what the mannequins say.

    • Rob says:

      No they’re not, because the air is blown top to bottom (the HEPA filters at at floor level) so the ability to anything you breath out to travel far forward is minimal.

      The SARS report we covered a few months ago covers this in detail.

  • Fio says:

    I think the issue may not be planes themselves but getting on and off. What really bothers me and I cannot understand is why the hell can’t we use air bridges? Most low costs still mandate use of buses while you see dozens air bridges unused. I get the cost but then why really bother at all. It should be in airlines best interests to minimize the cost of transmission as well as the airport authorities. Perhaps wave additional fees for air bridges and then you solve a lot of issues.

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