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WHO Changes 'Social Distancing' to 'Physical Distancing'

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Re: WHO Changes 'Social Distancing' to 'Physical Distancing'

#61

Post by badfrog »

lawlessone wrote: post #44
nabla9 wrote: post #39

Earlier quoted context omitted.

Here: 1) Exposure to influenza virus aerosols during routine patient care. https://academic.oup.com/jid/article/207/7/1037/2192312 >HCPs within 1.829 m of patients with influenza could be exposed to infectious doses of influenza virus, primarily in small-particle aerosols. 2) Short-range airborne transmission of expiratory droplets between two people. https://www.ncbi.nlm.nih.gov/pubmed/27287598 >The threshold distan…

>The goal is to get as small dose viruses at once as possible. Immune system can usually fight off small exposure. This is interesting, i had always thought it was binary, either you get infected or you don't

> This is interesting, i had always thought it was binary, either you get infected or you don't

IIRC, some vaccines work by exposing the person to a tiny amount of virus so that their immune system can "learn" how to fight that particular type of virus.

Re: WHO Changes 'Social Distancing' to 'Physical Distancing'

#62

Post by badfrog »

robocat wrote: post #2

I am hoping we have good science behind the “1.5 metre” distance rule... Does anyone have links to videos that show how breath swirls around, especially in outdoor areas? I guess I could get some pollen and try and model it myself!

This is kind of interesting. Check figure C.2. The behavior of droplets depends on size, but they all either evaporate or fall to the ground within 4.5 seconds. Knowing this has made me feel better about better about walking a dozen feet behind somebody outside.

https://www.ncbi.nlm.nih.gov/books/NBK143281/

Re: WHO Changes 'Social Distancing' to 'Physical Distancing'

#63

Post by robocat »

badfrog wrote: post #62
robocat wrote: post #2

I am hoping we have good science behind the “1.5 metre” distance rule... Does anyone have links to videos that show how breath swirls around, especially in outdoor areas? I guess I could get some pollen and try and model it myself!

This is kind of interesting. Check figure C.2. The behavior of droplets depends on size, but they all either evaporate or fall to the ground within 4.5 seconds. Knowing this has made me feel better about better about walking a dozen feet behind somebody outside. https://www.ncbi.nlm.nih.gov/books/NBK143281/

Figure C2: https://www.ncbi.nlm.nih.gov/books/NBK143281/figure/annexc.f...

If evaporation matters, then transmission rates should depend strongly upon humidity. However, there are studies saying transmission rates decrease with relative humidity. Maybe drying is irrelevant, or maybe there is another factor, or maybe the studies are wrong.

Re: WHO Changes 'Social Distancing' to 'Physical Distancing'

#64

Post by robocat »

nabla9 wrote: post #39
robocat wrote: post #2

I am hoping we have good science behind the “1.5 metre” distance rule... Does anyone have links to videos that show how breath swirls around, especially in outdoor areas? I guess I could get some pollen and try and model it myself!

Here: 1) Exposure to influenza virus aerosols during routine patient care. https://academic.oup.com/jid/article/207/7/1037/2192312 >HCPs within 1.829 m of patients with influenza could be exposed to infectious doses of influenza virus, primarily in small-particle aerosols. 2) Short-range airborne transmission of expiratory droplets between two people. https://www.ncbi.nlm.nih.gov/pubmed/27287598 >The threshold distan…

> 1) Exposure to influenza virus aerosols during routine patient care. https://academic.oup.com/jid/article/207/7/1037/2192312

A relevant graph is https://academic.oup.com/view-large/figure/90149845/jis77302...

This shows that large droplets don’t travel, but that small (Issue 1: drop off rates look to rude approximation to be r^2. The were measuring a point source. If you are standing in a line of people, you need to integrate along the line, and inter-person distance needs to be increased. A field of people (supermarket) needs something different...

Issue 2: large droplets should travel further if outdoors? (turbulent air)

Issue 3: cigarette smoke is a familiar visual indicator: “cigarette smoke particle mainly distributed in the size range 0.1 to 1.0 micron”. Think about how the smoke exhaled by someone travels (ignore how smoke travels from end of cigarette due to heated air).

Re: WHO Changes 'Social Distancing' to 'Physical Distancing'

#65

Post by badfrog »

robocat wrote: post #63
badfrog wrote: post #62

Earlier quoted context omitted.

This is kind of interesting. Check figure C.2. The behavior of droplets depends on size, but they all either evaporate or fall to the ground within 4.5 seconds. Knowing this has made me feel better about better about walking a dozen feet behind somebody outside. https://www.ncbi.nlm.nih.gov/books/NBK143281/

Figure C2: https://www.ncbi.nlm.nih.gov/books/NBK143281/figure/annexc.f... If evaporation matters, then transmission rates should depend strongly upon humidity. However, there are studies saying transmission rates decrease with relative humidity. Maybe drying is irrelevant, or maybe there is another factor, or maybe the studies are wrong.

I actually can't tell whether evaporation is good or bad. If a droplet evaporates, does the virus die or does it float freely through the air?

Re: WHO Changes 'Social Distancing' to 'Physical Distancing'

#66

Post by robocat »

londons_explore wrote: post #19
nitrogen wrote: post #11

Earlier quoted context omitted.

You might need to use small droplets rather than pollen to get relevant results. The Ars Technica summary of COVID-19 might have a reference for that distance figure; IIRC it was based on the distance that most droplets travel before falling. * https://arstechnica.com/science/2020/03/dont-panic-the-compr...

Behaviour dramatically depends on droplet size. Fog can last many hours and blow many miles before dissipating.

“Cloud, fog and mist droplets are very small. Their mean diameter is typically only 10-15 micron (1 micron = 1/1000 mm) but in any one cloud the individual drops range greatly in size from 1 to 100 micron dia.“

Fog also has very high humidity (otherwise it would evaporate), so any study that shows lower transmission of the virus in high relative humidity environments has relevance to anyone that assumes droplet evaporation matters? https://www.accuweather.com/en/health-wellness/new-study-say...

So fog is very relevant, thanks.

Re: WHO Changes 'Social Distancing' to 'Physical Distancing'

#67

Post by hanche »

robocat wrote: post #63
badfrog wrote: post #62

Earlier quoted context omitted.

This is kind of interesting. Check figure C.2. The behavior of droplets depends on size, but they all either evaporate or fall to the ground within 4.5 seconds. Knowing this has made me feel better about better about walking a dozen feet behind somebody outside. https://www.ncbi.nlm.nih.gov/books/NBK143281/

Figure C2: https://www.ncbi.nlm.nih.gov/books/NBK143281/figure/annexc.f... If evaporation matters, then transmission rates should depend strongly upon humidity. However, there are studies saying transmission rates decrease with relative humidity. Maybe drying is irrelevant, or maybe there is another factor, or maybe the studies are wrong.

I distinctly remember reading recently that it's absolute, not relative, humidity that counts. The article did not give a reason, nor can I remember the source (sorry).

Re: WHO Changes 'Social Distancing' to 'Physical Distancing'

#68

Post by cameldrv »

xxpor wrote: post #47
fyp wrote: post #46

In china, a lot the spread isn't from stranger to stranger but family to family: https://www.bloomberg.com/news/articles/2020-02-28/coronavir... https://youtu.be/e3gCbkeARbY?t=37 How do you do physical distancing within your home? Eat meals alone? Don't share cups/plates? Wear gloves for doorknobs? I feel like there's currently no solution for this.

You can't avoid a lot of that, given the physical constraints within a home. This just means it's even more critical for people who live with others to do physical distancing so they don't bring it home.

Wuhan avoided it with a centralized quarantine. If you were positive, you weren't allowed to go back home and infect your family.

Re: WHO Changes 'Social Distancing' to 'Physical Distancing'

#69

Post by robocat »

ken wrote: post #36
robocat wrote: post #2

I am hoping we have good science behind the “1.5 metre” distance rule... Does anyone have links to videos that show how breath swirls around, especially in outdoor areas? I guess I could get some pollen and try and model it myself!

Like https://vimeo.com/399120258 ?

Interesting, although that is tracking heat?

If we assume the same volume of air is expelled in the examples, then that video just looks sciency, and really doesn’t show us anything actionable (apart from don’t sneeze directly at people, duhhh!).

Also, why cough onto the back of the hand? What cultures is that normal?

Re: WHO Changes 'Social Distancing' to 'Physical Distancing'

#70

Post by spaceprison »

comicjk wrote: post #54

What about a more visual description, like "safety circle"? When I was a Boy Scout learning to use an axe, they called the danger zone within reach of the axe the "blood circle". A bit overwrought, but it certainly stuck in my mind. I think they say "safety circle" now.

I have been thinking "blood circle" this whole time!
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