Some New Science on Virus Transmission on Airplanes

[GordMay]

Originally Posted by NedX

... Do you happen to know the minimum size of particles for which that filtration system is effective? e.g. 10 microns, 5 microns, < 5 microns? A few months ago, when people thought SARS-CoV-2 was transmitted when relatively large droplets got in your eyes, nose, or mouth, a lot of modern systems, which are effective for particles as small as 5-10 microns, were considered safe.
Given what we know now about aerosol spread of SARS-CoV-2, really effective filtration is something that can handle SARS-CoV-2 particles that can be as small as 1 micron....

Originally Posted by Dockhead

I believe HEPA filters, in order to be called HEPA filters, have to filter down to 0.3 microns.
See: https://en.wikipedia.org/wiki/HEPA

Yes DH, but it gets better ...

The “SARS-CoV-2" COVID-19 particle is about 0.125 microns (125 nanometers) in diameter, but it is always bonded to something larger (small droplets and particles).
It falls squarely within the particle-size range, that HEPA filters capture with extraordinary efficiency, 0.01 micron (10 nanometers) and above. This NASA study [1] of HEPA filtration is quite technical, but the graph on page 7 and the preceding paragraph do a good job of explaining why HEPA filters are actually most efficient—almost 100% at 0.01 micron—at capturing ultrafine particles below the 0.3-micron HEPA test standard.
This means HEPA purifiers would efficiently capture viruses (and any aerosolized droplets of saliva and mucus that contain them) that are drawn into their filters.
[1] “Submicron and Nanoparticulate Matter Removal by HEPA-Rated Media Filters and Packed Beds of Granular Materials” ~ by J.L. Perry, J.H. Agui & R. Vijayakumar
➥ https://ntrs.nasa.gov/api/citations/...0170005166.pdf

[mountaindweller]

Originally Posted by NedX

Thanks, Captain. I definitely appreciate your comments. And I am seconding Dockhead's appreciation for what you do.

Do you happen to know the minimum size of particles for which that filtration system is effective? e.g. 10 microns, 5 microns, < 5 microns? A few months ago, when people thought SARS-CoV-2 was transmitted when relatively large droplets got in your eyes, nose, or mouth, a lot of modern systems, which are effective for particles as small as 5-10 microns, were considered safe.

Given what we know now about aerosol spread of SARS-CoV-2, really effective filtration is something that can handle SARS-CoV-2 particles that can be as small as 1 micron.

Of course, if passengers didn't take off their masks to eat, and people didn't sit close to each other, what you have in place would be enough. But I don't think that happens on a transcontinental flight...

Our guidance doesn't state actual HEPA micron size but states that system removes bacteria and virus clusters with an efficiency of greater than 99.99% and all cabin air is exchanged every 3-5 minutes.

[Dockhead]

Originally Posted by Singularity

Travel by airline is just not sitting in a seat; the entire constellation of exposures 'door to door' must be considered (assuming avoiding illness is the concern, and not just illness obtained on an airplane is the concern).

Certainly. Of course.

Originally Posted by Singularity

-------------------------------------------
A survey of 700 epidemiologists:
https://www.nytimes.com/2020/12/04/u...s-survey-.html

Review Article: Influenza Transmission on Aircraft
...overall secondary attack rate among traced passengers of 7.5%. Of these secondary cases, 68 (42%) were seated within two rows of the index case.

Behaviors, movements, and transmission of droplet-mediated respiratory diseases during transcontinental airline flights

For the infectious passengers, we use the conservatively high transmission rate of 0.018 per minute of contact, which is four times the transmission rate we estimate (16), which describes an incident in 1977 in which 38 of 54 passengers and crew became infected with influenza-like illness after waiting in an airplane on an airport tarmac for 4.5 h with no air circulation.

Behaviors, movements, and transmission of droplet-mediated respiratory diseases during transcontinental airline flights

40% of the transmission occurred outside of the two-row zone, suggesting that movement may be an important factor in disease transmission

Transmission of infectious diseases during commercial air travel

One 3-hour flight carrying 120 passengers travelling from Hong Kong to Beijing on March 15, 2003,31 began a superspreading event accounting for 22 of the 37 people who contracted SARS after air travel.

And how is any of this relevant?

All these accounts of infection on planes concerns full planes with unmasked, unscreened passengers -- as the good Captain mentioned upthread. Flying on planes with HEPA filters with other passengers who have been screened and wear masks, on places which are scrubbed down between every flight, where middle seats (and most often, alternate rows) are empty, is a different ball game. I was infected with COVID myself on an airplane (Saigon-Singapore); it was a totally different experience (plane jam-packed with coughing Chinese) from flying today.

The survey of 900 epidemiologists is just about their own personal lives, and air travel doesn't particularly stand out.

Different people have different lifestyles, and make different personal judgements about risk vs. other considerations. Some people are perfectly happy to stay at home; for many people air travel is a perfectly dispensible part of life.

For others, less so. For me, personally, air travel and different kinds of public life are not optional. I take probably 10 international flights per month, on average. My interests, both personal and professional, require it -- I live in the air between several different countries. I can't live without social life and I can't live without culture -- life without theatre, concerts is simply life not worth living in my book; I will take any risk not to give that up. Fortunately I am living in a part of the world where many are like me -- I was in a concert day before yesterday (Gidon Kremer in Tallinn; fabulous); I've been in the theatre a few times since the pandemic started, and in the cinema more than I can count. I would simply shoot myself if I were locked up in a part of the world where all this was just shut down.

Reminds me of an old Russian joke [loosely translated]:

Guy goes to the doctor. Asks, nervously -- doctor, doctor -- how long do I have left to live? [сколько мне еще жить?]

Doctor: Well, I can't say unless you answer a few questions.

Guy: Go on.

Doctor: So, how many packs of cigarettes do you smoke a day? Two? Three?

Guy: None! I have never smoked, would never smoke.

Doc: OK. So -- tell me, how much vodka do you drink a week? Two bottles? Three?

Guy: None! I've been a teetotaler my whole life; never touch the stuff.

Doc: OK. So tell me -- how often do you have sex? Four times a week? Five?

Guy: None! I'm not married and don't have a girlfriend.

Doc: [Thinking] Now tell me this -- I just don't understand -- why do you even CARE how long you have left to live?

Rather philosophical, like most old Soviet jokes. And absolutely relevant to this discussion. Life is not valuable just in itself. Life is only valuable when you consider for what. For different people, the answer to "for what" may be very different.

[NedX]

Originally Posted by mountaindweller

Our guidance doesn't state actual HEPA micron size but states that system removes bacteria and virus clusters with an efficiency of greater than 99.99% and all cabin air is exchanged every 3-5 minutes.

I'm sold.

Came to this forum this morning with a solid sense of public health best practices and the epidemiology of SARS-CoV-2; leaving it with a better grip on HEPA filtration than I had.

God Bless the Cruisers Forum.

[Dockhead]

Originally Posted by mountaindweller

Our guidance doesn't state actual HEPA micron size but states that system removes bacteria and virus clusters with an efficiency of greater than 99.99% and all cabin air is exchanged every 3-5 minutes.

My guess is that this plus masking plus empty rows and middle seats just about eliminates airborne transmission in the aircraft.



Of course a hole appears in this if people take off their masks to eat or drink. I solve this by not eating or drinking and not taking my N95 mask off at all.

[Dockhead]

Originally Posted by NedX

I'm sold.

Came to this forum this morning with a solid sense of public health best practices and the epidemiology of SARS-CoV-2; leaving it with a better grip on HEPA filtration than I had.

God Bless the Cruisers Forum.

[Auspicious]

Originally Posted by Dockhead

I have been flying a LOT since borders reopened in May -- average couple of times a week I guess. I have not felt unsafe -- everyone is masked, and I've never seen a person with a cough on board. Planes are not full so I'm usually able to sit fairly well separated from other passengers.

I flew two weeks ago for the first time since February. I’ve been doing one-way car rentals to get to and from deliveries. STT, CLT, and BWI were crowded. The two planes I was on were crowded. Lots of noses hanging out, some chin bras, and a surprising number of mask necklaces. Very disturbing.

Originally Posted by mountaindweller

flight attendants monitor mask compliance (yes, anti-maskers can be a problem).

People who don’t wear masks or wear them properly know they are cheating. You can tell because they fix their masks when they see a flight attendant coming. I suggest a bounty (FF miles) to passengers who identify noncompliance.

Originally Posted by Dockhead

Of course a hole appears in this if people take off their masks to eat or drink. I solve this by not eating or drinking and not taking my N95 mask off at all.

Me too. I can skip two or three meals. Drinking is harder. Hydration is important.

[CAVOK]

HEPA filters only filter air that has been recirculated in a pressurised jet aircraft. Yes, the airflow generally flows from above the cabin to the floor outlets to be drawn back into the Recirc Fans and the HEPA filters before being redistributed. A significant amount of the airflow exits through leaky seals and/or the outflow valves which control the cabin pressure. This air generally drifts back through the cabin in a single aisle aircraft before exiting, so in that case HEPA Filters have no effect. Larger aircraft may have dual outflow valves but there is still cabin drift.
Definitely wear the best mask you have on an aircraft and socially distance as best you can.. In and outside the aircraft

[Mick of 42]

The input ducts still need to create flow to get the air to the filters... where that flow goes would take a supercomputer to work out.

[Old fella]

Originally Posted by Dockhead

Well, I think your second paragraph contradicts the first.

Of course you want to prevent death, but you won't do that efficiently if you just reactively vaccinate the last people in the chain and let the epidemic rage among those who are causing community spread. It's not old people in nursing homes who are out spreading the virus. You've got to protect people, but if you're not proactively stopping the epidemic by going after the spreaders, you're going to prolong the pandemic and you will be killing people no matter what. The priority should be stopping the epidemic.



The actual policy will be to vaccinate "essential workers" first -- that is, grocery store and shop clerks, restaurant waiters, bus drivers, cleaners, workers in meat factories, all kinds of people who can't work from home and who have a lot of social contacts. These are people disproportionately hard hit and also people who are spreading the virus. This is good policy.



Really? There is no shortage of N95 masks here. There are stacks of boxes of N95 masks on tables in every pharmacy in the Nordic region. I buy them one box at a time in order to minimize impact on the supply chain, but I have had no problems buying them. People aren't hoarding them. And they're not that expensive; about €15 for a box of 10 which is pretty much the pre-pandemic price.

Surgical masks (which I wouldn't use) are given away free in a lot of places -- boxes set out for people to take as they like. I'm right now in a hotel in Riga in Latvia and there is a box of surgical masks, and a box of gloves, sitting out in the elevator lobby of every floor.

It's not like that in the U.S.?

You are dead right. It’s a hell of a decision to have to make eh, saving some while condemning others. But what you say makes perfect sense, but I wouldn’t want to be calling the shots for who to start with.

[Moana Bella]

It is important to bear in mind that the corona virus is droplet based. Therefore, the droplets fall fairly close around where someone is coughing - say a metre or two.
Plenty close enough to infect people in the close confines of a plane.
But then you see mass spread throughout the cabin. Alan Joyce may be right about airflow and filtration on the planes, but that does not account for the main method of spread for droplets. That is the surfaces we touch, after someone has coughed or even just breathed out virus-laden droplets. The virus can live for some hours on surfaces. Studies have found that humans commonly touch their faces an astounding 2-3000 times per day. And the virus is transmitted from the surface we touch, into our bodies through eyes, noses and mouths when we touch our face. I bet that infected person went to the bathroom, the bar, and walked up and down at some stage. That would be enough to leave droplets on traytops, seats, coffee cups etc. Gross thought I know but thats how it happens.
So, when I finally get on a plane in Australia I will be wearing a mask to stop myself touching my mouth and nose, and eyeglasses to remind me not to touch my eyes.
Hand wipes, sanitiser and frequent had washing are also key.
Its hard, but remember - DON'T TOUCH YOUR FACE!

[NedX]

Originally Posted by Moana Bella

It is important to bear in mind that the corona virus is droplet based. Therefore, the droplets fall fairly close around where someone is coughing - say a metre or two.
Plenty close enough to infect people in the close confines of a plane.
But then you see mass spread throughout the cabin. Alan Joyce may be right about airflow and filtration on the planes, but that does not account for the main method of spread for droplets. That is the surfaces we touch, after someone has coughed or even just breathed out virus-laden droplets. The virus can live for some hours on surfaces. Studies have found that humans commonly touch their faces an astounding 2-3000 times per day. And the virus is transmitted from the surface we touch, into our bodies through eyes, noses and mouths when we touch our face. I bet that infected person went to the bathroom, the bar, and walked up and down at some stage. That would be enough to leave droplets on traytops, seats, coffee cups etc. Gross thought I know but thats how it happens.
So, when I finally get on a plane in Australia I will be wearing a mask to stop myself touching my mouth and nose, and eyeglasses to remind me not to touch my eyes.
Hand wipes, sanitiser and frequent had washing are also key.
Its hard, but remember - DON'T TOUCH YOUR FACE!

Unfortunately, it's been a few months now that scientists have been coming around to the conclusion that aerosolized transmission (i.e., transmission via those microscopic aerosol particles we've been discussing in this thread) is a big reason for the unchecked community spread of SARS-CoV-2 that we're seeing in this country and anywhere people continue to meet in large groups or avoid masks.

Not sneezing on each other and wiping your hands and surfaces with antimicrobial substances are great precautions, because large droplets naturally do contain the virus, too, but those precautions alone will not stop the spread of SARS-CoV-2, because aerosol particles can travel farther than six feet and can linger in the air, and you only need to speak or breathe or laugh or whatever to release them.

[Nor does a temperature reading, since many/most (?) people are presymptomatic when they transmit the virus, and some never realize they are infected. Nor do you need to have a high fever to show symptoms of COVID-19]

[I work with public health experts and epidemiologists, so I'll be a pedant and add that SARS-CoV-2, the coronavirus that causes COVID-19, is one of 7 coronaviruses known to affect humans. Other coronaviruses include the ones that caused SARS and MERS (both deadly respiratory diseases essentially eliminated as a worldwide threat thanks to excellent coordination by world infectious disease agencies, in which the US played a large role), as well as the one that causes the common cold, to which we have largely adapted.]

[Singularity]

Originally Posted by Mick of 42

The input ducts still need to create flow to get the air to the filters... where that flow goes would take a supercomputer to work out.

You're practically not kidding.

Back in the late 2000s I spent a little time working on a couple projects at NASA (not related to this subject, but I saw the research). Basically there was a shuttle mission to service Hubble (STS-125) which had some technical challenges whereby it was determined that a backup shuttle (STS-400) needed to be on standby to fly and return the STS 125 crew if needed.

If 400 flew, it would have had to return 11 people while Boeing/Rockwell had lost the original flow calcs to determine if the cabin air circulation (not O2/CO2 levels, but circulation) would be problematic with 11 up. They had to crap out some new flows pattern...crazy expensive, while 400 never flew.

I'd suggest in important to recognize that 0.1 microns are captured by a mask only rated down to 0.3 microns (Gord and Chotu have posted about Brownian motion recently) where turbulence is good at slamming aerosols into structures (e.g. bulkhead, seat rest, atop one's hand) such that all the contents of the cabin, to some degree (requiring a supercomputer to delineate %) people act like a big N95 in front of, protecting, the HEPA filter.

All in, HEPA filters as stipulated up-thread are part of the overall risk mitigation picture, particularly where compliance/complacency are issues.

[Moana Bella]

Thanks Ned X for sending through this link. Highlights what a tricky organism it is.
I have been watching this because I train people on infectious waste, and I have heard talk of it being aerosol, but seems there is still no concrete proof.
If true, it makes it much more dangerous, and would call for much more serious permanent restrictions than we have had anywhere.
In countries with significant numbers of infections it would be impossible to pin down. Even with the DNA testing they now seem to be doing to identify strains.
But Australia makes for an interesting case study due to relatively few cases, so easier to analyse. In the 5 states and territories with fewer than 1000 cases, there have been zero cases where the transmission point cannot be identified. Most are returning travellers from overseas, but all cases acquired locally have been traced to a close contact. This would suggest that aerosol transmission is rare or none.
But of course we can't rely on that either, because Australia has locked things down pretty tight. Overseas entries are all quarantined, and there have been only 2 instances of the virus escaping quarantine via a quarantine hotel worker. Our recent outbreak in SA saw every case traced to close contact, except 1 that was surface acquired at a known (and very infamous) pizza shop.
This could mean that aerosol spread is too rare to show up in small populations, or that it has mutated in some countries, after places like Australia shut down.
Either way, the same personal precautions apply - wash your hands, don't touch your face, and wear a mask. Can't hurt - should help.
Hopefully enough vaccinations for all are not far off now.

[Nineteen]

Originally Posted by Wotname

Interesting. Alan Joyce (QANTAS CEO) was on the media the other day sprouting on about how aircraft travel was more Covid safe than other travel. Of course, he might be biassed [emoji2].

IIRC, the thrust of his argument was having the air vent open above each passenger directs the air flow downwards over each passenger and then the air is exhausted from near floor level. The volume of clean air introduced from outside has been increased on QANTAS aircraft.

I dunno the truth of this but he seemed convinced!

He is also on record for saying the all QANTAS international passengers would need to vaccinated if/when a vaccine becomes widely available.

As an engineer working on these aircraft - the first thing 90% of passengers do is close the gasper vents - I don't get it as it is the freshest air.....