Virus Infection Risk : How Close is Too Close? How Far is Safe Enough?

 

Executive Summary :

(a)  Six feet is good, more distance is better, and less rapidly becomes much worse.  Risk is a factor not just of distance but also of time, and is worse indoors than outdoors.  We should not reduce the 6′ guideline.

(b)  Risk is also a function of time.  The longer we are in a risky environment, the more our chance of catching the virus.  Minimize your risk-time exposure.

(a)  Distance Issues

Currently the hot topic of discussion is whether we should be relaxing or holding firm with our social distancing restrictions – indeed, there are even some people thinking we need more social distancing controls.

But, so far, there’s been one aspect of social distancing that has gone strangely unchallenged (by just about everyone except the airlines) and that’s the requirement to keep six feet apart from other people.

This is very strange, because there is nothing magic about 6′.  It is not like a light-switch.  There is not really any difference in safety/risk between being 5’11” apart and being 6’1″ apart, and even if you widen the range to 5’6″ or 6’6″, the risk level remains reasonably similar.

Furthermore, the 6′ distance was originally recommended back when little was known about the ability of the virus to spread via aerosolized clouds of virus particles.  It was thought the primary spreading mechanisms were either transferring by touching something contaminated, or by being “directly hit” by larger heavier droplets of virus after someone coughed or sneezed at you.

It is worth noting that the touch method of infection is now thought to be less prominent, and of course has nothing to do with distance because the virus can last on surfaces for some/many hours.

And the sneeze/cough method can shoot droplets at astonishing speed, and for much longer distances than six feet.  There are studies showing sprays of droplets going 12, 18, 24 feet, even rarely to 36 or further feet.

The key thing about these sorts of larger sized droplets is they relatively quickly fall to the floor.

Now there is an increasing realization that much of the spreading is probably also via much smaller droplets, aerosolized droplets.  These smaller droplets are so light they hang suspended in the air for many minutes before gradually dissipating.  Simply breathing or speaking is enough for the aerosolized droplets to be expelled (and if you are shouting or singing, you are expelling many more than if you are speaking quietly or silently breathing).  A person could be three or six or ten or twenty feet away from you, and breathe out a cloud of virus droplets, then you walk through that cloud two or three minutes later, with almost all the particles still in the air and waiting to be breathed in again.  Staying 6′ away makes no difference if you’re following each other through an aisle in a store.

As a side comment, there is an irony in the trend towards making aisles one-way rather than two-way.  This increases our risk of this type of infection, because instead of quickly passing a person in the opposite direction, we’re instead trailing behind the person in front and getting to breathe in whatever they have just breathed out a few seconds earlier.

So, the six foot rule.  If you consider these three forms of infection, it has no relevance for touching, definitely helps and reduces but doesn’t eliminate the risk for people coughing/sneezing, and doesn’t help so much for aerosolized droplets just hanging in the air.

Why was it decided to set the distance at 6′?  Why not more?  Why not less?  Clearly, it is nothing more than a round number that is easy to visualize and easy to explain.

The airlines have tried to distort this and have risibly suggested that if 6′ is the necessary distance, then anything less than 6′ is a fail, and there’s no difference then as between 5 feet and 5 inches.  Some airlines have used this to justify why they are not blocking out middle seats, and allowing passengers to be boxed in, with people in front and behind (typically with about 2’6″ spacing) and passengers on either side (typically with about 1’6″ spacing).

This is totally incorrect.  Six feet is not a magic distance, but the closer you are, the more your risk increases.  Three feet is more risky than six feet – especially for an extended period of proximity such as on a flight, but it is still very much better than 1 1/2 feet, which is what the airlines are trying to now tell us is perfectly fine.

This also raises another point.  The risk of infection is a combination of both distance and time.  A brief close encounter when passing someone in the opposite direction on a narrow sidewalk (especially if outside) is much less risky than being seated next to someone on a plane, at “danger close” distance, for many hours.

It is also not just being seated next to one other person.  With three people in the row ahead, two alongside you in your row, and three more in the row behind, that is eight people who are all way too close, plus more in the rows on the other side of the aisle and the rows two ahead and two behind.

But, back to the six foot rule again.  Here’s an article now questioning the six foot rule (or, as it is in metric countries, 2 metres which is actually 6’7″), from the perspective of wondering if it is unnecessarily too much distance.

It is very foreseeable that businesses who are currently being inconvenienced by the six foot rule would be happy to see it dropped to something smaller.  And it is also true that wearing a decent mask – one that actually works, rather than one that looks good – can compensate for some of the increased risk with closer distancing, but we think particularly in environments where we are eating and drinking, at least 6′ should remain the absolute minimum.

In a restaurant or bar, we of course can’t wear a mask while eating and drinking, and we have a terrible combination of proximity, extended time while close to other people, a larger number of other people passing close to us (meaning more risk that at least one of them might be infected), people speaking louder than normal (and expelling more virus particles as a result) and an entirely new way of becoming infected – virus droplets can land on our food or in our drink and be ingested that way.  That’s a whole bunch of reasons to be very much more cautious.

Distance is important, and while six feet doesn’t guarantee our safety, it is very much better than three feet or any other lesser distance.  This is admitted to in the article, although only when/if you read down to the bottom.  It then reveals that some experts equate just a few seconds of interaction at 3 ft (1m) as being the same as an hour or two at 6 ft (2m).

Let’s be sure to insist on, and observe ourselves, six feet of distancing, and discourage any attempts to reduce that down.

(b)  Time Issues

A good way of thinking of the risk of catching the virus is to think of the virus like radiation.

Many of us are familiar, from movies or real time, Geiger counters and how radiation risk is a function of both the strength of the radiation and how long we’re exposed to it.  It is almost exactly the same with the virus.

The preceding section was all about the “strength” of the virus.  The other part of understanding your risk is the time you’re exposed to it.

This doesn’t require a lot more explanation.  Simply stated, any time you’re in a place of elevated risk, try and spend as little time there as possible.  Be quick when you go shopping.  If you need to converse with someone else, as well as keeping your distance, be brief.  And so on.

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David.

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