Failure to recognise when an aerosol isn't a droplet 26

[LittleInch]

FacEngrPE dropped this in an obscure post and it reads very well.

Basically the whole epidemiological world though various dieses and viruses were spread by "droplets" which landed on surfaces and then infected people or were sneezed at you.

And a lot of times they are probably right.

But there was a magic 5 micron cut off between droplets and aerosols. Why? Read on

https://www.wired.com/story/the-tee...t-helped-covid-kill/?utm_source=pocket-newtab

So is this a disaster - Well you tell me.
But it goes to show that just because a lot of people write something, it doesn't mean that they originally got the wrong end of the stick and then the error repeats itself until it becomes fact.



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[1503-44]

I saw that article a week ago and I'm still thinking about it. Sometimes those things that are simply known as truths, just need to be challenged. After all, where would we be if the Earth was still believed to be flat. And accepted truths die the hardest of all.

The other surprise was that, if you had asked me about some 5 microns being a limiting factor, I would have said, Why? More from being ignorant than anything else. But in any case, I would not have thought that a 5 micron diameter would have any magical properties, other than how any diameter of a particle affects density and drag in a fluid medium under the influence of convention and gravitional forces might have on final trajectory. I would have immediately raised that question. What's so special about the number 5? Newton, Grashoff and Stokes didn't have any such limits. Why do you?

I had to challenge my own beliefs on siphons lately too. Atmospheric pressure enables them, but gravity drives the flow. Once I realised when you stick something up on the ceiling, it takes work to get it down again, it made sense.

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[Fischstabchen]

The sad part is that hospital protocols are driven by this. A lot of medical personal ended up dying due to the administration not will to provide PPE in excess of droplet protection. The changing of it to airborne mandated a different set of protocols. The fact that this was airborne has been hammered to death with particle simulations, restaurant spread forensics, and validating hamster to hamster airborne spread. The only way such denial makes any sense to me is that the powers that be didn't want the world to grind to a halt.

 

[Alistair_Heaton]

Must admit they were spouting a load of stuff to us about filters and how far it spreads etc.

They couldn't answer the question well if a fart can make it from one end of a plane to another why can't a virus? .

The mouth did a fish impression a couple of times then "stop being vulgar" and it wasn't answered.

 

[1503-44]

That's gas molecular dynamics ..... angstroms are definitely below the particle limit. They will get through 3 masks. Besides those under seat level air recycle intakes grabs them at their freshest. And don't have a bit of trouble getting through the air filters.

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[TugboatEng]

It's a good thing I prefer the back of the plane knowing that Alistair's flatulence has such reach.

On that note, fecal virus shedding persists long after the respiratory presence is over. Most studies I have see show 14 days for respiratory with a peak early. Fecal viral shedding peaks at 30 days.

 

[Alistair_Heaton]

Ahh tug the outflow valve is in the rear pressure bulkhead normally

 

[1503-44]

Everyone's is located there.

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I take no responsibility for any damages or injuries of any kind that may result.

 

[Fischstabchen]

Based on my experiences with having the back row seats, that outflow valve is not enough to restrict shit gas to the shitbox.

 

[IRstuff]

The aerosol/droplet question is only part of the equation; the other part is the viability and infectiousness of the virus is also key to whether social distancing works or not.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

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[1503-44]

That is where there appears to be something to the 5 micron figure, but that's a completely different problem from transport.

Statements above are the result of works performed solely by my AI providers.
I take no responsibility for any damages or injuries of any kind that may result.

 

[LittleInch]

True, it is a multi faceted approach so no one thing is 90% responsible for transmission.

The "failure" in engineering terms is that the 5 micron limit was just hard wired into the thinking when it was based on one specific virus and not on the actual mechanics.

Tug believes you get Covid from public toilets and people farting / fecal vapours
The initial main stream CDC / WHO was that it was large droplets from coughing / breathing and washing hands was a major way to reduce the spread
The loss of the 5 micron limit has increasingly led to the public message about ventilation and open windows etc being important to reduce transmission ( or at least here in the UK it has) with aerosols being a key factor.

So in my mind it's probably evenly spread.
If some infected person is either coughing in your face or shouting at you from close range - large drops
Confined spaces with little ventilation - crowded public transport / bars / pubs / nightclubs - aerosols
Fecal "vapours" or similar - Not seen much research but given that they monitor outbreaks from the sewage system then it might be more significant than we think

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Fischstabchen]

LittleInch,

I don't think that much research has gone into it due to sewer gas generally is not a western problem. With Sars, there was an outbreak in an apartment complex that were determined to have been caused by faulty gas traps in the drains and toilets. This has led people to speculate that COVID-19 could spread similarly due to the two viruses being very similar.

 

[Alistair_Heaton]

Fish you are correct

If I drop one in the front I turn the re circ fan off and engine bleeds high...

We know when cabin crew drop one in the rear galley.

 

[1503-44]

Hah! Now that I know what to do, I'd better like my next ride...

Gymnasiums have been the source of a couple of large outbreaks here.

Statements above are the result of works performed solely by my AI providers.
I take no responsibility for any damages or injuries of any kind that may result.

 

[Alistair_Heaton]

The 787 has duct system that takes the air from the bogs to the outflow so doesn't do the all the farts to the rear. The A220 also empties through the front hold via the avionics bay.

Just for info.

Hardly science about airflow and aerosols but if you can smell shite I reckon a virus can go up your hooter

 

[Latexman]

The SARS-CoV-2 virus has been reported to be 20-500 nm (0.02-0.5 microns) in diameter. Ignoring droplets < 5 microns excludes a whole lot of virus.

Good Luck,
Latexman

 

[Alistair_Heaton]

on a tech note

A cabin which is normally at 8k feet is at 0.75 bar so if your coming from 1 bar at sea level. Its dangerous to hold in 0.25 bar in your guts so the only way to get rid of it is to fart. All perfectly normal for you to be breathing in 100 plus peoples farts in the first 30 mins of flight..

 

[IRstuff]

It has widely been reported that SARS-COV2 is relatively fragile, so individual virus particles are supposedly non-viable for infection, and it's speculated that thousands to millions of particles are required to seriously infect someone. Nevertheless, SARS-COV2 is not like measles, where the measles virus stays viable in the air for hours.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

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[Alistair_Heaton]

out of 500 crew in the last year we have had nobody caught it on an aircraft

even when we had charters with 40% of the punters onboard tested positive on arrival.

I have heard of aircraft with 1 measles case onboard land with 17 % of those not vaccinated or immune already getting it in the next 2 weeks. But it very rare they make those sort of figures available to us lot.