Covid19

[Tom]

On a lighter note I had to go the bank yesterday and do a transaction at the teller window. I drove into the parking lot, stopped and pulled my mask over my face. It occurred to me that in the not so distant past that would have aroused suspicion.

[thollandpe]

What I've read is that every 2 minutes the air in the cabin has been totally replaced by air from the outside which would mean less patogen stagnation ?? But what do I know I read this on twitter and I am not an expert.

Unfollow that twitterer. A two-minute turnover is 30 air changes per hour (ACH). In the US we design operating rooms for 15-20 ACH overall, with 3-4 ACH outdoor air.

[Saab2000]

Unfollow that twitterer. A two-minute turnover is 30 air changes per hour (ACH). In the US we design operating rooms for 15-20 ACH overall, with 3-4 ACH outdoor air.

The airplane I am flying today has a placard on the wall for passengers to read when they board.

It reads:

“This aircraft has been treated with an electrostatic anti-microbial protectant and uses HEPA filters that remove 99.97% of airborne particles. A full exchange of fresh, outdoor air occurs every 2-3 minutes while in flight.”

There are a couple qualifying footnotes but I didn’t see the fine print. Nor can I vouch for accuracy of the numbers or implied protections. But I think they’re trying to do the best possible for the employees and customers.

Just pointing this all out. Everyone needs to make their own decisions based on the best information and their own requirements.

[gregl]

The airplane I am flying today has a placard on the wall for passengers to read when they board.

It reads:

“This aircraft has been treated with an electrostatic anti-microbial protectant and uses HEPA filters that remove 99.97% of airborne particles. A full exchange of fresh, outdoor air occurs every 2-3 minutes while in flight.”

There are a couple qualifying footnotes but I didn’t see the fine print. Nor can I vouch for accuracy of the numbers or implied protections. But I think they’re trying to do the best possible for the employees and customers.

Just pointing this all out. Everyone needs to make their own decisions based on the best information and their own requirements.

I can vouch for the accuracy of this statement (aeronautical engineer, type-rated in multiple aircraft). The older generation of jet airliners (designed before the late-1970s) had essentially 100% continuous air circulation. That is, all cabin air came in through the compressor section of the engines ("bleed air") or a separate turbo-compressor, was cooled to a comfortable temperature by an air cycle machine (similar to a home heat pump) and/or vapor cycle system ("freon air conditioner") and exited the cabin through outflow valves. As a general rule of thumb, all air in the cabin was circulated out of the aircraft in approximately 1 minute. Starting with the Boeing 757/767, air filtration was added to the systems and the cabin air was partially recirculated. This was done to increase fuel efficiency since more of the engine's compressed air was used for propulsion rather than cabin pressurization. This led to the 2-3 minute air recirculation time in most of today's aircraft. The Boeing 787 went to electrically powered compressors for cabin pressurization to do away with bleed air pressurization entirely. I am not aware of the 787's air recirculation rate.

Greg

[bcm119]

What are those studies, and what is the air circulation on planes? There are objective criteria for this (airflow in air changes per hour, ACH, and filtration rating, MERV). And whether the space is flushed pre- or post-occupancy, or if the air is cleaned with UV or bipolar ionization.

There is guidance on this, specifically in regards to the airborne transmission of infectious aerosols from the American Society of Heating, Refrigeration, and Air Conditioning Engineers (ASHRAE), and I’m curious what’s being offered in this application//.

This is the article I was thinking about when I wrote that. Not exactly a rigorous study, but general info about air circulation that reduced my anxiety a bit.
https://medical.mit.edu/covid-19-upd...afe-air-travel

[Lionel]

I came to SFO from MRS about a week ago. One of the most pleasant trip I had in a long time. We had 80 passengers in a 777. I was in first class (social distancing measure), my closest neighbor was 4 rows behind me on the opposite window. In other words I could not really see him at all. Business class was almost empty. Service was outstanding and no masks required at your seat because you are well, alone.

They probably lost a lot of money on that flight.

[Saab2000]

They probably lost a lot of money on that flight.

Maybe. Maybe not as much as one might imagine. It is likely your 777 was laden with a fair amount of freight.

[thollandpe]

The airplane I am flying today has a placard on the wall for passengers to read when they board.

It reads:

“This aircraft has been treated with an electrostatic anti-microbial protectant and uses HEPA filters that remove 99.97% of airborne particles. A full exchange of fresh, outdoor air occurs every 2-3 minutes while in flight.”

There are a couple qualifying footnotes but I didn’t see the fine print. Nor can I vouch for accuracy of the numbers or implied protections. But I think they’re trying to do the best possible for the employees and customers.

Just pointing this all out. Everyone needs to make their own decisions based on the best information and their own requirements.

I can vouch for the accuracy of this statement (aeronautical engineer, type-rated in multiple aircraft). The older generation of jet airliners (designed before the late-1970s) had essentially 100% continuous air circulation. That is, all cabin air came in through the compressor section of the engines ("bleed air") or a separate turbo-compressor, was cooled to a comfortable temperature by an air cycle machine (similar to a home heat pump) and/or vapor cycle system ("freon air conditioner") and exited the cabin through outflow valves. As a general rule of thumb, all air in the cabin was circulated out of the aircraft in approximately 1 minute. Starting with the Boeing 757/767, air filtration was added to the systems and the cabin air was partially recirculated. This was done to increase fuel efficiency since more of the engine's compressed air was used for propulsion rather than cabin pressurization. This led to the 2-3 minute air recirculation time in most of today's aircraft. The Boeing 787 went to electrically powered compressors for cabin pressurization to do away with bleed air pressurization entirely. I am not aware of the 787's air recirculation rate.

Greg

This is the article I was thinking about when I wrote that. Not exactly a rigorous study, but general info about air circulation that reduced my anxiety a bit.
https://medical.mit.edu/covid-19-upd...afe-air-travel

Thanks for the replies. From that article, "For starters, the air quality on a commercial airliner is actually quite high, with the air volume in the cabin being completely refreshed every two to four minutes." That's a tad misleading because that's total airflow, which is only 40% to 50% outdoor air. So Jim's placard that reads "A full exchange of fresh, outdoor air occurs every 2-3 minutes while in flight" sounds suspicious to me. As does the tweet Thomas read.

The FAA mandates that outdoor air is supplied at a rate of 7.4 to 10.0 cubic feet per minute (cfm) per passenger, based on cabin pressure. The ASHRAE handbook (HVAC Applications, Chapter 13 - Aircraft https://www.ashrae.org/file%20librar...i_a19_ch13.pdf) says recirculation is about 10 cfm per passenger. That works out to 11-15 air changes per hour (ACH) of fresh outdoor air, and 20-30 ACH of total airflow.

HEPA filtration is great, that's for the recirculated air. Another good thing about recirculating air is that it keeps the humidity higher. Boeing says the 787 can hold 14% relative humidity (RH) during cruise, whereas other planes can be in the single digits. That's not good, see below.

Good news that the ventilation scheme for planes is pretty good, supplied overhead and returned at the floor. That's better than in most offices. Also nice that it's partitioned front-to-back.


Opinion: the middle seat sucks. Always has, always will.

So what does ASHRAE recommend for ground-bound applications to prevent the transmission of infectious aerosols?

Ventilation. The closest I see to an airplane cabin is a lecture hall, and code ventilation for outdoor air works out to ~8 cfm per person. Planes are 7.5 to 10 cfm per person. Lecture hall default occupancy is 150 people per 1000 sq.ft. and I think planes may be more densely packed. And just like in lecture halls, if every other seat is empty, the effective ventilation rate has doubled. Same ventilation, fewer people. Like Lionel's flight.

Filtration. ASHRAE recommends MERV-13 filters, and HEPA is like MERV-17. So the planes have that covered.

Humidity control, stay between 40% and 65% RH. This ain't happening on an airplane. You don't want to condense moisture on the inside of the cold fuselage. But in low humidity droplets can travel a greater distance, many viruses and bacteria have increased viability, and we humans are more susceptible to those bugs. So wear your damn mask. Not only to keep the bugs out, but also to create your own microclimate with humidity in the target range!

Edit: another recommendation is a pre-occupancy flush period for 3 ACH outdoor air. So if I were a crew member or passenger I'd ask for the plane to have the ventilation on for at least 20 minutes before I step aboard.

[vertical_doug]

Thanks for the replies. From that article, "For starters, the air quality on a commercial airliner is actually quite high, with the air volume in the cabin being completely refreshed every two to four minutes." That's a tad misleading because that's total airflow, which is only 40% to 50% outdoor air. So Jim's placard that reads "A full exchange of fresh, outdoor air occurs every 2-3 minutes while in flight" sounds suspicious to me. As does the tweet Thomas read.

The FAA mandates that outdoor air is supplied at a rate of 7.4 to 10.0 cubic feet per minute (cfm) per passenger, based on cabin pressure. The ASHRAE handbook (HVAC Applications, Chapter 13 - Aircraft https://www.ashrae.org/file%20librar...i_a19_ch13.pdf) says recirculation is about 10 cfm per passenger. That works out to 11-15 air changes per hour (ACH) of fresh outdoor air, and 20-30 ACH of total airflow.

HEPA filtration is great, that's for the recirculated air. Another good thing about recirculating air is that it keeps the humidity higher. Boeing says the 787 can hold 14% relative humidity (RH) during cruise, whereas other planes can be in the single digits. That's not good, see below.

Good news that the ventilation scheme for planes is pretty good, supplied overhead and returned at the floor. That's better than in most offices. Also nice that it's partitioned front-to-back.


Opinion: the middle seat sucks. Always has, always will.

So what does ASHRAE recommend for ground-bound applications to prevent the transmission of infectious aerosols?

Ventilation. The closest I see to an airplane cabin is a lecture hall, and code ventilation for outdoor air works out to ~8 cfm per person. Planes are 7.5 to 10 cfm per person. Lecture hall default occupancy is 150 people per 1000 sq.ft. and I think planes may be more densely packed. And just like in lecture halls, if every other seat is empty, the effective ventilation rate has doubled. Same ventilation, fewer people. Like Lionel's flight.

Filtration. ASHRAE recommends MERV-13 filters, and HEPA is like MERV-17. So the planes have that covered.

Humidity control, stay between 40% and 65% RH. This ain't happening on an airplane. You don't want to condense moisture on the inside of the cold fuselage. But in low humidity droplets can travel a greater distance, many viruses and bacteria have increased viability, and we humans are more susceptible to those bugs. So wear your damn mask. Not only to keep the bugs out, but also to create your own microclimate with humidity in the target range!

Edit: another recommendation is a pre-occupancy flush period for 3 ACH outdoor air. So if I were a crew member or passenger I'd ask for the plane to have the ventilation on for at least 20 minutes before I step aboard.

I want a window seat and ultraviolet light by my feet

[ZenNMotion]

I dunno, I have zero technical knowledge of air quality in flying tubes. But my nose and respiratory system may know something the engineers don't, and that is my asthma kicks my ass on any flight longer than a couple hours, my nose runs and my lungs get wheezy- long runs across the US or to Europe are bad and longer runs such as to Africa or Asia take at least a day for my respiratory system to recover. And it's not just simply because the air is dry, I have lived in very dry climates. The air inside aircrafts was crap even before covid and flying now terrifies me despite what any sticker by the entry port says.

[bcm119]

I dunno, I have zero technical knowledge of air quality in flying tubes. But my nose and respiratory system may know something the engineers don't, and that is my asthma kicks my ass on any flight longer than a couple hours, my nose runs and my lungs get wheezy- long runs across the US or to Europe are bad and longer runs such as to Africa or Asia take at least a day for my respiratory system to recover. And it's not just simply because the air is dry, I have lived in very dry climates. The air inside aircrafts was crap even before covid and flying now terrifies me despite what any sticker by the entry port says.

I wouldn't rule out dryness of the air. Air at 37k feet is way drier than at the surface, even in dry climates. Dew points at that altitude are well below zero, drier than the highest deserts. I'd guess that irritates the resp. tract.

[Sbti]

First reported Sturgis related Covid death.
https://www.mprnews.org/story/2020/0...-covid19-in-mn

[Chik]

I dunno, I have zero technical knowledge of air quality in flying tubes. But my nose and respiratory system may know something the engineers don't, and that is my asthma kicks my ass on any flight longer than a couple hours, my nose runs and my lungs get wheezy- long runs across the US or to Europe are bad and longer runs such as to Africa or Asia take at least a day for my respiratory system to recover. And it's not just simply because the air is dry, I have lived in very dry climates. The air inside aircrafts was crap even before covid and flying now terrifies me despite what any sticker by the entry port says.

OT, and I'm not asthmatic, but after an intercontinental flight, it takes me 24-36 hours to get the cabin air smell out of my breath. It seems to linger in my lungs...

[ldamelio]

OT, and I'm not asthmatic, but after an intercontinental flight, it takes me 24-36 hours to get the cabin air smell out of my breath. It seems to linger in my lungs...

No offense, but this makes no sense physiologically. Probably a combination of dehydration and some depressurization effect.

[deano]

I wouldn't rule out dryness of the air. Air at 37k feet is way drier than at the surface, even in dry climates. Dew points at that altitude are well below zero, drier than the highest deserts. I'd guess that irritates the resp. tract.

I was going to chime in with something like that - not even the Gobi or the Atacama approach the dryness on board an aircraft. Last year, my wife and I flew American from Chicago to Barcelona for our tenth anniversary (well the trip to BCN was for the anniversary, not the American flight itself, but I digress...). American only operates the Dreamliner out of Chicago for international flights, or did at the time, so we were guaranteed to be on one. Those can withstand much greater humidity in the cabin and I have to say it did not disappoint; not hype at all! I felt like a human being after disembarking.

[Chik]

No offense, but this makes no sense physiologically. Probably a combination of dehydration and some depressurization effect.

No offence taken, and you're prolly right. The "cabin air smell" was not intended to literally mean that my breath smells like the cabin but the fact that it smells a certain, odd way after a long flight and only after a long flight.

[vertical_doug]

No offence taken, and you're prolly right. The "cabin air smell" was not intended to literally mean that my breath smells like the cabin but the fact that it smells a certain, odd way after a long flight and only after a long flight.

I think it was meal served with mystery meat or pasta sauce not the air. Or maybe it is a the cheap wine leading to wino smell....
Lots of stuff on a plane to mess with the system.

[deano]

I think it was meal served with mystery meat or pasta sauce not the air. Or maybe it is a the cheap wine leading to wino smell....
Lots of stuff on a plane to mess with the system.

That is true, plus the body is weird. I once had dengue fever and ate InNOut Burger upon my return to the states. Tasted a weird version of it for a month. Still taste it if I try to remember.

[htwoopup]

I dunno, I have zero technical knowledge of air quality in flying tubes. But my nose and respiratory system may know something the engineers don't, and that is my asthma kicks my ass on any flight longer than a couple hours, my nose runs and my lungs get wheezy- long runs across the US or to Europe are bad and longer runs such as to Africa or Asia take at least a day for my respiratory system to recover. And it's not just simply because the air is dry, I have lived in very dry climates. The air inside aircrafts was crap even before covid and flying now terrifies me despite what any sticker by the entry port says.

Not to pile on, and this may not be the answer to the problem...

When I was commuting from NY to Seoul in preparation for televising the 88 Olympics, the commute was on a non-stop flight. It was so long that an extra crew flew on the plane to take over after so many hours.

That crew always slept until it was their turn. They always put a moist handkerchief over their nose and mouth while they were in the cabin and sleeping.

I don't know how that would work or be in lieu of in the mask world but perhaps it would fix your issue.

[Chik]

I think it was meal served with mystery meat or pasta sauce not the air. Or maybe it is a the cheap wine leading to wino smell....
Lots of stuff on a plane to mess with the system.

Certainly a worthy hypothesis! However, not in my case because I usually don't eat on flights except for the packet of nuts or whatever at the beginning of the flight.