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Recirculation Fan Filters & Infections.  
User currently offlineHAWK21M From India, joined Jan 2001, 31684 posts, RR: 56
Posted (5 years 5 months 2 weeks 4 days 7 hours ago) and read 2933 times:

Considering the Prevailing swine flu at present.Presuming the virus is present in the cabin due to an ill pax,if this contaminated/affected airflow goes through the Recirculation filters & is seperated.

How long will these viruses survive & what are the chances of an infection spreading to an individual changing/cleaning those filters.

regds
MEL.


Think of the brighter side!
20 replies: All unread, jump to last
 
User currently offlineDocLightning From United States of America, joined Nov 2005, 19941 posts, RR: 59
Reply 1, posted (5 years 5 months 2 weeks 4 days 7 hours ago) and read 2928 times:

I don't know how long the virus particle can remain active (not alive; viruses do not qualify as "alive" for a number of reasons) on a filter.

However, filters actually become MORE effective as they get clogged with debris. This is because the pores get partially blocked with debris, which decreases pore size and filters out more particulate.

However, they get less efficient because it takes more energy to force the working fluid through the filter.


User currently offlineFr8Mech From United States of America, joined Sep 2005, 5490 posts, RR: 14
Reply 2, posted (5 years 5 months 2 weeks 4 days 5 hours ago) and read 2915 times:

I also believe it's a question of humidity. How long can this virus (or any other) survive in the open in the arid conditions found in an operating aircraft?


When seconds count...the police are minutes away.
User currently offlineDocLightning From United States of America, joined Nov 2005, 19941 posts, RR: 59
Reply 3, posted (5 years 5 months 2 weeks 4 days ago) and read 2886 times:



Quoting Fr8Mech (Reply 2):
I also believe it's a question of humidity. How long can this virus (or any other) survive in the open in the arid conditions found in an operating aircraft?

Depends on the virus. A study published just in February of this year showed that influenza virus is more transmissible and survives longer in conditions of LOWER absolute humidity. This strikes me as a bit odd, since I would have guessed that higher humidity would stabilize the virus particle better.

The authors didn't come up with a good mechanism to explain this phenomenon, so more experiments will have to be done to clarify this.


User currently offlineHAWK21M From India, joined Jan 2001, 31684 posts, RR: 56
Reply 4, posted (5 years 5 months 2 weeks 4 days ago) and read 2880 times:

High temperatures works well against the virus,unfortunately the Main distrivution manifold does not provide that at all times.
The concern is the exposure of the virus to Mx persons that carry out the cleaning of the filters.
Although I work on Freighters,but i have quite a few good friend who work on Pax Aircraft & is a concern.
regds
MEL.



Think of the brighter side!
User currently offlineTheCommodore From Australia, joined Dec 2007, 2890 posts, RR: 8
Reply 5, posted (5 years 5 months 2 weeks 3 days 15 hours ago) and read 2848 times:

An airplane is a very dirty place to sit, especially on a long haul trip. A lot of people say that if one person has the flu there is a good chance at least 50% of the pax will also get it. The ventilation system on planes could be improved I think, not sure how long the air is kept in the cabin before it is replaced with new air. Maybe someone could shed some light on this.


Flown 905,468 kms or 2.356 times to the moon, 1296 hrs, Longest flight 10,524 kms
User currently offlineZappbrannigan From Australia, joined Oct 2008, 247 posts, RR: 0
Reply 6, posted (5 years 5 months 2 weeks 3 days 15 hours ago) and read 2844 times:



Quoting TheCommodore (Reply 5):
An airplane is a very dirty place to sit, especially on a long haul trip. A lot of people say that if one person has the flu there is a good chance at least 50% of the pax will also get it. The ventilation system on planes could be improved I think, not sure how long the air is kept in the cabin before it is replaced with new air. Maybe someone could shed some light on this.

Happy to be corrected on this, but everyone in the know I've spoken to about this over the years, plus Boeing's official info (take that as biased advertising if you will) says this is merely a commonly perpetuated myth.

That is, an airliner is no worse (apparently better) than sitting in a room, or on a bus/train/whatever, with numerous other people. The surrounding air is replaced far more often in an airliner than in many other spaces where people group, and I'm told the filtration is far better than in any standard aircon system - the chances of infections being spread through the recirc system are next to zero. Any infections/virii are likely to be spread directly from people in close proximity to you, which is unavoidable unless you or they are wearing face masks.

This info is normally spread along with describing the air in the cabin as "recycled" (implying everything everyone breathes out in the cabin is sucked out then pumped back in again through all the vents).

From memory, chatting to someone at QF about this a while ago, the air in the cabin is completely replaced around every 3 minutes, compared to around 20 minutes for the average room. Further to this, the manner in which the air circulates stops airborne particles wandering from the front to the rear of the cabin.

And if all this is correct - I see no reason why the chances of any infection spreading are greater on a long-haul flight than any other, apart from the fact you're likely to come into close contact with more people on a long-haul flight as you move about the cabin.


User currently offlinePilotpip From United States of America, joined Sep 2003, 3150 posts, RR: 11
Reply 7, posted (5 years 5 months 2 weeks 3 days ago) and read 2790 times:

Modern jets get new air every 3-5 minutes as mentioned. The reason for this is certification standards for smoke evacuation. Another important point to mention is that there is constantly air being introduced that is 100% sterile due to the altitude and high heat it's subjected to in the engines.


DMI
User currently offlineNomadd22 From United States of America, joined Feb 2008, 1881 posts, RR: 0
Reply 8, posted (5 years 5 months 2 weeks 2 days 22 hours ago) and read 2776 times:



Quoting DocLightning (Reply 1):
However, filters actually become MORE effective as they get clogged with debris. This is because the pores get partially blocked with debris, which decreases pore size and filters out more particulate.

That's like saying that closing the inlet to the filter makes it more efficient. The particles a filter traps are trapped because they're bigger than the pores, so there's no way they could block particles that are smaller than the filter pores. Reducing airflow through the filter isn't making it more efficient. It's just blocking airflow. That makes it less efficient because it's not getting the air to filter.



Andy Goetsch
User currently offlineFr8Mech From United States of America, joined Sep 2005, 5490 posts, RR: 14
Reply 9, posted (5 years 5 months 2 weeks 2 days 21 hours ago) and read 2772 times:



Quoting Nomadd22 (Reply 8):
That's like saying that closing the inlet to the filter makes it more efficient. The particles a filter traps are trapped because they're bigger than the pores, so there's no way they could block particles that are smaller than the filter pores. Reducing airflow through the filter isn't making it more efficient. It's just blocking airflow. That makes it less efficient because it's not getting the air to filter.

I'm thinking that in this scenario the filter is more effective at stopping a virus particle because it has additional material to adhere to when the filter starts to 'clog'.



When seconds count...the police are minutes away.
User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 10, posted (5 years 5 months 2 weeks 2 days 20 hours ago) and read 2763 times:



Quoting TheCommodore (Reply 5):
A lot of people say that if one person has the flu there is a good chance at least 50% of the pax will also get it.

How would that work? The airflow pattern in most cabins is from roof-to-ceiling, front-to-back. Flu is carried, primarily, by aerosols. I don't see any possible ventilation pattern that is going to connect one seat to half the other seats on the airplane.

Quoting TheCommodore (Reply 5):
The ventilation system on planes could be improved I think, not sure how long the air is kept in the cabin before it is replaced with new air. Maybe someone could shed some light on this.

It's changed far more often, and far cleaner, than any residential, industrial, or commercial building. If you're OK with a movie theater, covered stadium, or a bus then you've got no reason to be worried about aircraft.

Tom.


User currently offlineNomadd22 From United States of America, joined Feb 2008, 1881 posts, RR: 0
Reply 11, posted (5 years 5 months 2 weeks 2 days 20 hours ago) and read 2763 times:

[

Quoting Fr8Mech (Reply 9):
I'm thinking that in this scenario the filter is more effective at stopping a virus particle because it has additional material to adhere to when the filter starts to 'clog'.

The best way to trap anything is to design a filter to do a job. Substances trapped in the filter will be widely varied and unpredictable in their effect. You can't count on that sort of thing to keep the air fresh and sterile.
The only thing that's certain is that a clogged filter will reduce airflow and increase pressure across the element. And the more pressure, the more contaminants will be forced through.



Andy Goetsch
User currently offlineTheCommodore From Australia, joined Dec 2007, 2890 posts, RR: 8
Reply 12, posted (5 years 5 months 2 weeks 2 days 1 hour ago) and read 2702 times:

Ok Guys, Thanks for the info, I stand corrected.

On a slightly different note.

I Heard something on the TV a few weeks ago about air flow being taken in thru the engines and then into the cabin, it's super heated as it passes thru the engine and then cooled before entering the cabin at various different locations.

However this programme mentioned some examples that if there was a small oil leak within the engine itself then contaminated air would be circulated thur the cabin (once super heated engine oil and air are mixed together it forms a toxic vapour). It noted several occasions where FA's and flight deck crew as well as passengers had smelt something strange in the cabin, and after this many felt a feeling of being durnk/slight paralysis.
Further tests were being carried out (without much help from the industry), however the doco said that because it's something within the airline industry itself not many were willing to be cooperative as there would be big fallout if this was proved correct.

What are your thoughts on this, I'm sorry to be so vague in my description but I was only half listening to the programme.



Flown 905,468 kms or 2.356 times to the moon, 1296 hrs, Longest flight 10,524 kms
User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 13, posted (5 years 5 months 2 weeks 1 day 23 hours ago) and read 2689 times:



Quoting Nomadd22 (Reply 11):
The best way to trap anything is to design a filter to do a job.

True, but many types of filters, not just aviation air filters, are designed to use trapped material as part of the filter media. This is hardly a new, or uncommon, idea in filter design. Sand filters almost don't work at all without this principle.

Quoting Nomadd22 (Reply 11):
The only thing that's certain is that a clogged filter will reduce airflow and increase pressure across the element. And the more pressure, the more contaminants will be forced through.

Filtering is, ultimately, a physical phenomenon between the size of the particle and the size of the pore. More pressure can't push a particle through a pore that's smaller than the particle.

Quoting TheCommodore (Reply 12):
However this programme mentioned some examples that if there was a small oil leak within the engine itself then contaminated air would be circulated thur the cabin

That will happen only with oil leaks in very specific places...most of the gas path is downstream of the bleed air takeoff points.

Quoting TheCommodore (Reply 12):
What are your thoughts on this, I'm sorry to be so vague in my description but I was only half listening to the programme.

There's probably something to it, but if you look at all of these reports together you find that the common denominator is the airline, not the aircraft or engine type. That strongly suggests some combination of human error and psychosomatic effects.

Tom.


User currently offlineHAWK21M From India, joined Jan 2001, 31684 posts, RR: 56
Reply 14, posted (5 years 5 months 2 weeks 1 day 16 hours ago) and read 2664 times:

Anyone aware of the Virus & the length of time it would stay active on the filter.
regds
MEL.



Think of the brighter side!
User currently offlineNomadd22 From United States of America, joined Feb 2008, 1881 posts, RR: 0
Reply 15, posted (5 years 5 months 2 weeks 1 day 10 hours ago) and read 2638 times:



Quoting Tdscanuck (Reply 13):
Quoting Nomadd22 (Reply 11):
The only thing that's certain is that a clogged filter will reduce airflow and increase pressure across the element. And the more pressure, the more contaminants will be forced through.

Filtering is, ultimately, a physical phenomenon between the size of the particle and the size of the pore. More pressure can't push a particle through a pore that's smaller than the particle.

Not if you're talking about solid particles and perfect filters, but more pressure tends to make airflow more likely to find a way around the smallest pores. Filters designed to take out gases are can also work less efficiently or even outgas the previously absorbed gasses when the pressure differential is too high.
Filters like sand filters that work best when packed with a finer media aren't something you'd find on a plane. Even in a swimming pool they'd be pre treated with something like diotomaceous earth to get up to speed. It's not that they work better when contaminated. It's that the stuff filling the voids is part of the design.

Back to the original question, I have to admit to not knowing much on how viral filtering works. Those suckers are pretty small, and I'd guess something more like UV sterilization than physical filtering would be best.



Andy Goetsch
User currently offlineDL From France, joined Feb 2008, 18 posts, RR: 0
Reply 16, posted (5 years 5 months 3 days 13 hours ago) and read 2402 times:



Quoting HAWK21M (Reply 14):
Anyone aware of the Virus & the length of time it would stay active on the filter.
regds
MEL.

Sorry MEL, I only found a french article. It says one of the flu virus (H3N2) can survive 2 weeks on a bank note if the virus concentration is high and if there is mucus. The H1N1 virus survives "only" few hours.


http://3francs6sous.com/2008/01/17/l...-semaines-sur-un-billet-de-banque/


Regards,

DL


User currently offlineHAWK21M From India, joined Jan 2001, 31684 posts, RR: 56
Reply 17, posted (5 years 5 months 3 days 11 hours ago) and read 2383 times:



Quoting DL (Reply 16):
The H1N1 virus survives "only" few hours.

Thats very heartening.Especially for us Mx folks.
Thanks.
regds
MEL.



Think of the brighter side!
User currently offlineAA737-823 From United States of America, joined Mar 2000, 5873 posts, RR: 11
Reply 18, posted (5 years 5 months 1 day ago) and read 2283 times:



Quoting HAWK21M (Reply 4):
High temperatures works well against the virus,unfortunately the Main distrivution manifold does not provide that at all times.

Aah, but it's kinda warm during cruise... so maybe that helps a little. But then, my airline flies routes of 1.5 hours in duration maximum, so........ uh oh.

Quoting HAWK21M (Reply 4):
The concern is the exposure of the virus to Mx persons that carry out the cleaning of the filters.

You're exactly right- and I am going to start wearing gloves and face mask when I change the HEPA filters on our 737s from now on! We changed one in January after an aircraft encountered some VERY unpleasant turbulence.... the entire last four rows of the airplane vomited.... and the HEPA filter reeked of vomit. Lesson learned!

Quoting TheCommodore (Reply 5):
An airplane is a very dirty place to sit, especially on a long haul trip.

Not really- I wish this 50-year-old truth would go ahead and die. HEPA filtration.... You got a hepa filter in your nose? Didn't think so.

Quoting Nomadd22 (Reply 8):
That's like saying that closing the inlet to the filter makes it more efficient.

No, it's true, and we find this in all kinds of filters- engine oil, hydro oil, etc. The issue then becomes that the filter won't let adequate fluid pass, and then the bypass activates, and thus we've got no filtration at all.
This is why we use oil on our car K&N air filters- catch and retain more particles than when dry, which in turn help to catch more particles themselves.


User currently offlineBorism From Estonia, joined Oct 2006, 431 posts, RR: 0
Reply 19, posted (5 years 5 months 3 hours ago) and read 2217 times:



Quoting AA737-823 (Reply 18):
You're exactly right- and I am going to start wearing gloves and face mask when I change the HEPA filters on our 737s from now on! We changed one in January after an aircraft encountered some VERY unpleasant turbulence.... the entire last four rows of the airplane vomited.... and the HEPA filter reeked of vomit. Lesson learned!

Now that's disgusting! Eek!


User currently offlineHAWK21M From India, joined Jan 2001, 31684 posts, RR: 56
Reply 20, posted (5 years 4 months 4 weeks 1 day 13 hours ago) and read 2180 times:



Quoting AA737-823 (Reply 18):
I am going to start wearing gloves and face mask when I change the HEPA filters on our 737s from now on!

We use Face masks/gloves on certain Mx works....Cleaning HEPA filters is one.
regds
MEL.



Think of the brighter side!
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