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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.”

How safe is flying with a mask

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)

  • Littlefish says:

    Good article. Yes, that latest study is very helpful.
    For me the key result is the 0.087% on page 21. The 777 seat 47D results graphic.
    So … waaaay higher than 0.003%.
    Neighbours are getting far the highest dose, but the drop-off further from the infectee is pretty quick (which confirms previous consensus).
    So it boils down to, am I able to avoid a seatmate?
    Things are brighter on short-haul and where Airlines are mandating masks, as the doses will be much less.
    Interesting results graphics though as spread does go a row or two back in some situations.

  • Olly says:

    Does it say what happened when the mannequin took off her mask to eat lunch? Or walked around the cabin with the mask not fully over their face?

    • Andrew says:

      This is the problem with masks. Theoretically they should work. In reality they’ve had little to no impact everywhere they’ve been introduced. People just don’t use them properly.

      • Chris says:

        Apart from say Taiwan and large parts of SE Asia

      • mr_jetlag says:

        They work when used properly, and when people follow scientific advice.

      • Littlefish says:

        Masks work very well. Sure they would work better if of better quality / better fit / higher take up, etc etc. But at best they are reducing virus levels from 100% to 40%-75%. Which is huge and fine, its just not a 100% reduction.
        Same with distancing, same with hands washing. Neither are 100% effective.
        Hence why time in exposure to the virus is a large factor and indoors is so much riskier.
        By & large, households and social settings (parties, pubs, places of worship) show up at the top of the charts for transmission across europe from contact tracing data. Each are settings where mask wearing will be low and time indoors in close proximity is high.
        In these situations trying to mitigate with masks would seem too onerous and unlikely (in the West); so its simply a case of adopting different measures in those settings …. which is currently just not happening. It needs to!

      • @mkcol says:

        If you’re going to make sweeping statements such as this then you need to evidence the source, unless this is just your opinion.
        Otherwise your statement becomes pointless.

    • TripRep says:

      Or visiting the toilet, ewww

  • Andrew says:

    The thought of keeping a mask on for a 12 hour flight and trying to sleep whilst wearing it is reason enough not to fly. I’ll be sticking to Qatar business class where you’re free to take off your mask after boarding and leave off for the entire flight (economy have to keep it on with a visor too).

    • Barry cutters says:

      No airline I’ve been on in the last few weeks is really enforcing that you have to keep the mask on;
      BA- long shorthaul, Ryanair , and lot long/short haul

      I flew to Athens yesterday on a 787-8 in club , took the mask off once seated – put it back on for 5 mins to go to the loo abs grab a beer . But apart from that was off most the journey . Most others the same- or the very least had the nose exposed .

      I’m not supporting or condemning – just sharing my observations and highlighting that if your worry is wearing a mask for 12h , I would worry too much . Cabin crew seem to take a pragmatic approach and treat us like adults .

      • Susan says:

        I wear a mask to protect others in case I’m contagious but asymptomatic. If the airlines aren’t requiring this basic courtesy then they’re not getting my cash.

      • AJA says:

        Your real world evidence of the lack of compliance with mask wearing rather negates the benefits that the studies try to prove.

        If the majority on board do not wear their masks all of the time then that is what the studies should simulate.

        I remain unconvinced by the claims of the benefits of HEPA filters.. The trouble is replacing air every 3 minutes is not often enough but I understand why the airlines do it because of fuel savings.

        Also if HEPA filters were as effective as claimed then there would be no need to wear masks at all. Plainly that’s not true or there would be close to zero cases of covid transmission on board.

        I think these studies are important and if they convince some people to travel that’s great for the airlines.

        • Iain miller says:

          I suspect the results of the simulated without the masks would be broadly similar.

          And they can’t have people thinking masks are of little bene8can they?

      • elt says:

        BA flights to sicily 2 weeks ago , both out and back, had several announcements during flight reminding people to wear masks.

    • simpletastes says:

      At least since late August, Qatar also has required Business Class passengers to wear masks throughout the flight unless eating or drinking. The difference is that Economy Class passengers also have to wear visors throughout the flight unless eating or drinking.

  • David Walker says:

    What it does also not say is the touch situation of hat racks ,tables seat fabrics and cabin crew giving out forms and collecting them, loaning pens and passengers passing them around and I dare not even think what happens in a toilet.
    Now we KNOW that the virus stays on surface for 14 days ..

    And can I just remind you there is no such thing as FRESH AIR on an aeroplane.
    You are getting the exhaust fumes intake of warm, pressurised air On ALL aircraft except the 787 which uses an ioniser to recirculate the same Cooler, filtered air for the duration of your flight.
    Look up up TOXIC AIR SYNDROME .. Boeing have started paying people now compensation for KNOWING this was poisoning passengers and crew to terrible illness and slow death.

    • Polly says:

      Bring your own wipes and wear disposable gloves too….and keep the mask on as much as possible, if it’s necessary to fly somewhere…

    • Kevin says:

      I suggest you google aircraft air conditioning systems, and learn the source of the air that ends up inside the cabin – I’ll give you a clue though, it’s not from the exhaust section as you suggest.

  • The Savage Squirrel says:

    As your article says: real life better than simulation
    In Vitro studies like the one the article is based on can give you a basic understanding of one of the dynamics at play and nothing more. Basically where to focus efforts on transmission. The cannot and should not be used to draw conclusions about real world risk levels in complex and dynamic environments (such as hundreds of humans interacting in an aircraft).
    To give a simple example why – 99.99% of particles may not reach other people directly via aerosol – however a greater number will deposit on the person themselves (they’re closer to their own mouth than anyone else, right?). If they then touch stuff or get up and walk around – or pass objects to others – or other people nearby do (so 100% probability of this) the situational dynamics and risk levels change completely.

    You’re obviously trying to make the point that perceived risk or aircraft transmission is greater than actual risk, which is true and well accepted (see the 2005 Lancet paper on infectious disease and commercial air travel) – but your final sentence that the airport and public transport are more likely locations for spread than aircraft are entirely unsupported by any of the material in the article (leaving aside the fact that aircraft ARE public transport). That conclusion drawn from that body of evidence would be a fail mark in a school level science write-up; and would be laughable at research level.

    Ultimately the only thing that can give you a basis for real world risk is measurement of the real world with all its complexity. As you rightly recognise, current studies are limited and flawed (although again, given your graduate journalist team, quoting the IATA “study” and describing it as such, when it is merely a non-peer-reviewed opinion peice by a body with an obvious and massive bias motive – isn’t great). The studies we have are – like all real world restrospective studies – flawed and compromised, but they are, and will remain, the best we have for assessing real world risk; and as they grow in number they should gain some accuracy and reliability.
    Welcome to science – it’s flawed, imperfect, and gives equivocal and uncertain answers. But it’s the best we’ve got.

  • Chris Heyes says:

    Another perspective would be allow planes to fly but ban airports and public transport

  • sayling says:

    1.2 billion passengers is a helluva lot of people that have been flying 😳

    • Tariq says:

      How many people do you think are on the planet? 🤣

      Likewise when people talk about thousands or millions of infections or deaths. In the grand scheme of things, the numbers are insignificantly low.

  • Ian says:

    It is not when seated on the aircraft that concerns me providing face masks are being worn that concerns me but the scramble which exists on disembarkation when every passenger seems to stand up, retrieve their hand baggage and attempts to be the first of the plane (which happened to me last week on an EasyJet flight from Stanstead to Edinburgh!)

    • Littlefish says:

      Yep! And this I am able to counter-act somewhat with my own behaviour.
      I move up to my highest filtration mask for boarding (if a scrum) and from the bing-bong on arriving at the Gate. It is uncomfortable to use for more than 20 minutes or so, so I switch from my in flight fact attire.
      Its also handy for any long or poorly organised immigration queue.

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