The 15-minute rule, and other covid recommendations

Keeping an eye on my watch while conversing.

Since writing the previous blog entry (“What is my risk?”) I have encountered additional information to refine the risk calculation I outlined.  I found a reference that provides a better value for the relative intensity of aerosol generation between the activities of talking and passive breathing: approximately 10X (compared to my placeholder value of 2).  When this weighting is applied to the social interaction duration histogram, the critical exposure is reduced from four person-intensity-hours to three.  

This does not seem like a large impact on critical exposure but the intensity level associated with talking now requires that all of those short interactions become shorter.  If the critical exposure is 3 hours at level 1 (silent breathing in the same room), and talking is 10 times more intense, then an exposure of 0.3 hours (18 minutes) in conversation with an infectious person will deliver the critical dose of virus-laden aerosols.  This suggests a limit of 15 minutes in any interaction with a stranger: the 15-minute rule.

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What is my risk?

Taking a calculated risk at a favorite restaurant’s outdoor patio

Ever since the covid19 stay-at-home orders were relaxed for my state, I have been struggling to find some rules to guide me as we try to safely host small gatherings with qualified friends (today’s rules: outdoors, safe-distancing, maximum of two guests–who have also been in semi-quarantine).

I’d like to know “what is my risk?” after encountering N people in a day and spending a certain amount of time with each.  In particular, if I interact with store clerks for a few minutes each, walk or bicycle past maybe a hundred people, or sit in a (sparse) movie theater with a few dozen others for two hours, what risks am I taking?  I want to put it in relative terms with the risk I willingly accept when I drive a few miles for an everyday errand.

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Swedish Candelabras

A modest Swedish house in Skalo, Poldi’s ancestral home. Nearly all the houses are in this traditional red color with white trim.
A close up shows the candelabras in the windows, a wintertime custom here.

While in Sweden over the Christmas season, we noticed the popularity of candelabras placed in the windows of people’s homes.  In these northern latitudes where the darkness of the winter night dominates the few hours of daylight, the distinctive chevron of lights provided a cheery greeting from the windows of the traditional-styled Swedish houses.  

I thought it would be a nice accent to our own home with its not-so-traditional windows cut into a mansard roof.  Surely Ikea would have such an item, with some suitable unpronounceable name, but I was disappointed.  Perhaps I needed to shop the Ikea stores in Sweden rather than our Americanized versions of them.

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Retirement Inauguration

The logo for a project called Mongoose, an early system that was able to compute and send images to color copiers and printers.

Today was my last day of employment, and I will now be exchanging the two major foci of my creative time. 

My interests in photography and astronomy and art was always secondary to my full-time work as a color scientist, an occupation that has provided a long and fulfilling career. 

But this particular outcome was something of a fluke; the education I pursued was a hodge-podge of art, science, and engineering, and my early career was filled with jobs at not-quite-successful entrepreneurial startups that caused my dad to inquire where I was working next, because he wanted to avoid investing there!

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Career’s End

From my gun collection: an electron gun, extracted from a cathode ray tube

After years of fearing the consequences of corporate RIFs (“reduction in force”), aka layoffs, and having survived a dozen or more of them, I had finally reached the point where losing my job would have a lesser consequence.  I had built up my savings in anticipation of some future retirement and was now working for the sheer pleasure of it.  

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