Blowing Bubbles - don't get sick!

I've been thinking about airflow a lot lately because the best way to avoid catching SARS CoV-2 is don't breathe in the virus.  Yeah, you can get it by touching stuff and then sticking you finger in your eye, but that's ain't what's driving this thing.  It's breathing.  It's a respiratory virus, after all. https://www.cdc.gov/coronavirus/2019-ncov/prevent-getting-sick/how-covid-spreads.html

(also interesting...not all fomites are created equally. It's hard to get virus on your hands from cloth https://aem.asm.org/content/79/18/5728)

Not all breathing is created equal.  A breath can spew 50-3000 particles.  A cough, 3000, and a sneeze, 30,000.  A person breathes about 15 times a minute.  So, for round numbers' sake, lets just say that minute of breathing equals one cough, and 10 minutes of breathing equals one sneeze.  So, while you don't want to be around sneezing and coughing people, it's not great to be around plain old breathing for long periods of time.  It's the sneaky way the asymptomatic are getting the job done!

So, people breathe, cough and sneeze and then you breathe in the same air space.  You can only get infected if you breathe in enough.  So, how much is "enough"?   It seems, no less than 1000 virus particles to maybe 10 times that is a minimum infectious dose.  That's the range - based on how its kissing cousins behaved (SARS and MERS)  If you get less than the minimum dose, your body just throws the bugs out with the rest of the trash.  More than than, it can get overwhelmed and you're infected.

So people spew out particles.  Wouldn't it be nice if they could just blow away before you could breathe too many of them in?  It happens.  It can depend where you are.  Big volume, big air flow will move and dilute the droplets.  Small volume, little flow - not so much.

Airflow is a complicated thing.  Engineers try to grasp it working backwards from tests, generating all sorts of equations fitted empirically to test results.  Scientists try to grasp it from the physics, working from the fundamentals toward predictions that can be tested.  There's a lot going on in a mixed gas like air.  Atoms vibrating and banging into each other depending on temperature and pressure.  There's a big gap between science and engineering with air flow.  What you are trying to find out and what you need the results for will determine what approach you take.  There is no "one size fits all" approach for air flow.

Commercial buildings often have rather sophisticated HVAC ventilations systems.  Much of the air is recirculated.  It has to be.  It's the only practical way to deliver enough heat or cooling without installing enormous, prohibitively expensive systems.  Still, most are designed to exhaust some air and introduce some outside, make-up air.  A typical system will replace about 99% of the air in the building in about an hour (ACH = 4 means roughly 2/3 of the air is changed every 15 minutes.  1/3 ^ 4 = 0.01)

Airplanes have high air change rates, zoned airflow and very good filtration. Some specifics here https://www.erinbromage.com/post/flying-in-the-age-of-covid-19

Cars have "flow through" ventilation.  They used to use this as a selling feature in the 1970s.  Now , all cars have it.  Air comes in the cowl, exits by vents in the back of the passenger compartment.  So, as long as you have the recirculation off and the fan blowing, you have good airflow through the car.  It's about 10x the ventilation of a building.

Much less airflow in your car if you have this turn on.

Homes are a mixed bag.  The HVAC systems are 100% recirculating.  The air change rate depends on how often you open and close doors and windows and leaky your home is, in general. Nice, tight new replacement windows?  Not leaky.  Old, draftly wood double hung?  Leaky.


This nasty virus is really a wimp, unlike the norovirus, which is a tough bugger.  Coronaviruses fall apart under all sorts of circumstances.  The fat covering dissolves almost immediately with soap, alcohol and other disinfectants.  The protein spikes denature with light, heat, rough surfaces.  The RNA inside gets blown up by UV light.  The virus is most happy when it's floating around protected in a drop of water and that's exactly what our respiratory systems do - blow out drops of water.  Very small, to be sure, but drops none-the-less.

Many of these drops are 100 micron range and pretty much fall straight down to the floor when you exhale, but most are around 1 micron and float around for a bit.  Some also evaporate and leave the "solid" content - virus and some salt and some other bodily goo, floating around on their own for a quite a while.   The longer a person is in a place, the more breathes are being breathed and the more of these droplets are hanging around in the air. They can accumulate until a steady state is reached where the amount dropping to the floor, sticking to the walls and exiting the building is equal to the rate new ones are being breathed out.  The smaller the space and the lower the air change rate and the more people are in the space, the greater the steady state density of breath droplets.

How long does a "naked" virus remain effective floating in the air?  I can't find a good answer.  The trouble is, it's hard to test.  Those "it lasts three hours" articles you read are the result of testing for fragments of the RNA.  The virus has long lost it's fat coat, spikes and probably intact set of RNA.  It's like asking how long cars can last and pointed to a Ford Model A in a junkyard.  Yeah, it looks like the husk of a car.  It's still made of steel.  But I hasn't been able to run in 70 years.

So, maybe a viable virus can hang around in the air, naked, for several minutes?  Plus, there are all those viruses still hitching a ride in very tiny water droplets?  I needed a good way to visualize what's happening.  I thought of soap bubbles. You know, the kind kids play with or are modern day substitutes for throwing rice at weddings.  You blow them, they move on the air currents until the water evaporates and the bubble "pops".

Perhaps a good way to think of your risk is to think about everyone around you blowing soap bubbles.  Every breathe blows out bubbles.  They are carried by the airflow.  Your goal is not to have many soap bubble land on you.  One or two, not so bad.  Dozens and dozens, not good.

So if you are outside and there's a breeze going, with air swirling all over the place, it's gonna be really hard to get any bubbles on you.  The very turbulent air flow pushes them up, down, left and right and they have all the open space to flow into.   If you're inside, with a lot of people, and the air flow is very low and recirculating, you have lots and lots of bubbles, barely moving at all, with no place to go.  Just hanging around - hard to keep them off you!

The longer you hang around the bubble blowers and the closer you get to them, the more they're gonna get on you!  So, avoid the bubbles!  Stay healthy!



Some really excellent reading in links below.  All of these are footnoted with links to studies used in their blog.  My blog post here is really a "meta-post" leveraged from these.


https://www.erinbromage.com/post/the-risks-know-them-avoid-them?fbclid=IwAR37zdJrhlCadX28hrt9S4QwXiS5HWIZKWLI5ViSivz5_-sjUgWUecI7ecQ


https://www.facebook.com/jenniferkastenmd/posts/119907962995484

https://www.facebook.com/jenniferkastenmd/posts/120574959595451?__tn__=K-R

Corona Times

Well, a lot has happened since March 13th. 

The "wash your hands and cover your cough" and do some mild social distancing campaign was too little too late.  Heavy social distancing followed by shelter in place became the rule in a lot of places as the race was on to keep COVID-19 cases from overwhelming hospitals.  Some place managed to get ahead of the curve and kept cases to a minimum, mashing the curve down - notably San Francisco  and California. Some places get going too late and got swamped - notably Albany GA and NYC.  The Atlanta area was in the middle.  The metro counties got going a couple weeks ahead of the state and managed to keep the local hospitals afloat and use of the emergency overflow spaces to a minimum (so far...)

Watching all this play out so fast was horrific.  Knowing how much worse it could have been was not much consolation.  Hearing about the pain that places in the world that got going late, notably Italy,  were going through was sobering enough to not think twice about obeying the shelter in place rules.

Helping my wife's 80+ y.o. parents, we doubled down on our social distancing, doing curbside for groceries and generally staying out of any buildings except our house.   We still do takeout and delivery of restaurant food, trying to help keep economy going.  Our grown kids, who live in the area, have done the same.  They are helping our chances, and consequently, the in-laws chances of "keeping clean".  I have to say, even doing that is stressful, remembering to wear a mask and wiping down stuff.  Really, though, compared to what a lot of people are going through, that stress is really a "first world problem."

Anecdotal stories and statistics filled our news feeds and were handed down through friends and relatives.  A lot of it was like waiting on a Tsunami, not knowing how high the wave would be. 

Consuming so much news was confusing and stressful.  There is so much not known that getting a clear picture of what to do, how to do it and what will happen was very difficult.  "The virus can 'live' 72 hours on surfaces".  "The virus was found on a cruise ship two weeks after everyone was off."  "There is plenty of testing." Friends with symptoms can't get tested.  It's only airborne droplets that are contagious.  Aerosols can travel 30 feet.  It could be on you shoes. This person has it.  That person died.  Only older people with co-morbidity get the severe form of the disease.  A young, healthy person died.  Lots of kids get it and are asymptomatic.  Are they "carriers" or not?  Drug treatments are being tried.  They help!  They are worthless!  They aren't being tried the right way!


Usually, more information is better and reliable information is the best.  With this thing, so much is unknown, or known imperfectly, that speculation, conspiracies and misinformation fill the void at a great rate.  It felt like this: https://www.instagram.com/tv/B_PrvZdhMiR/?igshid=yumazu0pfnn5

Using Twitter news feeds is normally helpful, but there is just too much and whole day of it will sink your psyche, so I've tried, mostly unsuccessfully, to limit my Twitter time. 

One source of information I've found most useful and enlightening is a woman who blogs on Facebook. Her "about": ".... a pathologist with degrees in infectious disease epidemiology, mathematical modeling of epidemics, and fieldwork in epidemic control." In other words, she's a subject matter expert.  Here's a link https://www.facebook.com/jenniferkastenmd/  

So, after the first couple weeks, we've kind of settled into a new routine.  What does that look like?  What's surprising, interesting, annoying?  What's keeping us busy?

That'll be the next blog posts. 

Hub and Spoke. Be a hero to someone you don't know.

Is this an blog on hub and spoke vs. lane transportation operating philosophies?  No.  This is about everyone's favorite topic, Coronavirus, and the problem with it. 

The problem, generally,  isn't that it's so deadly or horrible to survive for most people.  So, why not just let everyone get it and get over it and be done with it?  The problem is how fast the infection spreads and what that means for our health care system and patients who need it.  If we just let things happen, the 10% or so that need hospitalization for a while will swamp our "right sized" healthcare industry.  We don't have enough beds, doctors and ventilators to cover even a fraction of what would be needed if we did that.  That means a lot of folks would die unnecessarily.  What to do, then?  In general, we need to "flatten the curve".

https://www.statnews.com/2020/03/11/flattening-curve-coronavirus/

For the more "math-y" https://medium.com/@tomaspueyo/coronavirus-act-today-or-people-will-die-f4d3d9cd99ca

How to flatten the curve?  Have fewer spokes.  Make your spokes skinny.

If you think of yourself as a hub that is connected to the other people you come in contact with as spoke, and draw that picture out with each person you are connected to as having a spoke with each person THEY are connected to and so on, you can see that if each person has a lot of spokes, then you don't have to go out too far until you come to someone who has coronavirus.  Fewer spokes, you have to go out more "levels" until you reach and infected person.

If you then think about each spoke as a conduit for likely transmission, then you can draw that spoke as a fat pipe if it's close contact and skinny if it's a less likely path for transmission.   Somebody you sit next to at work - fat pipe.  The person who stocked those black beans you bought at Kroger this morning - skinny pipe.  So, the goal is to have less spokes and make each spoke as skinny as possible.

If you think about indoor places with hard surfaces that have lots of traffic - airports, mass transit vehicles, grocery stores - and you know that the virus can stay viable on hard surfaces for a couple of days - you then have lots and lots of skinny spokes to lots and lots of people who have touched that surface or item or coughed on it in the past couple days. 

If you think of each day as its own diagram, then overlay each day on top of the other, you can see that repeated contact with the same people is not as risky as contact with different people each day.

Right now, each infected person is infecting over two other people.  That's what causes the geometric growth of cases.  If you want the number cases to stop growing, you have to get that transmission number under one.  You do that by cutting the number and width of the spokes between each of us.

The problem isn't whether you or I will have a rough time with the disease.  Odds are, we won't.  But, out "sized for normal circumstances" health care industry can't handle a sure the size of what this virus did to China and now Italy.  Places that have "flattened the curve" have death rates of 1% or less because it doesn't overwhelm their health care system  Places that are overwhelmed have much higher death rates.

And, each of us trying to cut or shrink our spokes to others we contact doesn't just affect us, but everyone they have spokes to, and those people, and on down the line. 

How do you reduce and shrink your spokes?  Tons of ideas here: https://www.cdc.gov/coronavirus/2019-ncov/community/index.html

But, remember this doesn't mean you have to lock yourself in a closet!  There are lots of low risk, skinny spoke things you can do.  Go for a drive.  Go for a hike.  Go bicycling.  Gardening.  Go camping.  Play tennis and golf.  Play cards with your friends.  Go to the botanical gardens.  Go railfanning. (of course!).  Get back into your hobbies and crafts.  Go to the beach.  Get to those procrastinated house projects.  Make a photobook of your last trip.  Go shopping - on Amazon.  Plan your next trip (this problem IS going to be solved - it's just how much pain we have to go through...and how long it will take)   Learn a new language or calculus (huh?)

So, it's not about us.  It's about all of us.  Pay attention to your spokes!  The life you save may be your friend's co-workers son's mother-in-law.