6 Feet May Never Be Enough for Covid-19
Keeping Your Distance While Going the Distance
Social Distancing is hard enough to practice as is. But new research shows that many people aren’t staying back nearly far enough.
This is especially true for outdoor exercise enthusiasts, a category that seems to include more people every day.
The World Health Organization has long advised keeping a minimum of 3 feet, while the CDC has championed a distance of at least 6 feet. But, one study suggests you need more space even in windless indoor settings where no one is gasping mid-workout.
Don’t Stand So Close To Me
A study in Wuhan, China looked at airborne and surface transmission for Covid-19 in 2 Hospital wards — it’s currently available on early release on the CDC’s website.
While the paper is not yet finalized, it found that the virus could spread through the air up to a distance of 13 feet. Yes, this was in a highly contaminated environment. But it was also an environment where almost everyone was wearing masks and other protective gear.
As concerning, the study found that the floor universally tested positive for the presence of the virus. In fact, staff shoes seemed to be functioning as carriers.
In addition, as medical staff walk around the ward, the virus can be tracked all over the floor, as indicated by the 100% rate of positivity from the floor in the pharmacy, where there were no patients.
-Guo Z-D, Wang Z-Y, Zhang S-F, Li X, Li L, Li C, et al. Aerosol and surface distribution of severe acute respiratory syndrome coronavirus 2 in hospital wards, Wuhan, China, 2020. Emerg Infect Dis. 2020 Jul [04/15/2020]. https://doi.org/10.3201/eid2607.200885
This is obviously a greater danger in an area where the virus is widespread. But one meaningful takeaway is the importance of washing your hands thoroughly after putting on or removing your shoes.
Hello From the Other Side (of the Road)
That’s not the only problem facing us though, my fellow outdoor athletes. Nor even the biggest one.
Our real problem is aerodynamics.
Social Distancing and the Aerodynamics of Motion
Enter another research paper currently available on early release, this one found on urbanphysics.net: Towards aerodynamically equivalent COVID19 1.5 m social distancing for walking and running.
The idea at the heart of it is summed up in a few sentences from the abstract.
…countries world-wide have declared — sometimes by law — a “social distance” of about 1.5 m to be kept between individuals. … However, this social distance has been defined for persons that are standing still. It does not take into account the potential aerodynamic effects introduced by person movement…
In short, even assuming 6 feet is enough, we need to take into account wind and air movement caused by our own speed.
In my experience running the sidewalks and bike paths of an active community, that’s not happening. Heck, I’m lucky to get 6 feet from even half of the people I pass out there!
Back to the findings of this paper:
When you’re running, cycling, walking, or just standing in a strong breeze, the movement of the air around you creates a slipstream. This stream of air and particles trails behind you in the direction you came from (or the direction the wind is blowing).
This phenomenon is well known and used by experienced athletes. After all, it’s much easier to maintain speed in someone else’s wind shadow. If you’re not familiar with the concept, it’s why you see so many cyclists moving in straight lines one after another.
You’re letting the person in front do the harder work of breaking the wind. Meanwhile, you reap the benefit of spending less energy to match their speed.
Unfortunately, that “wind shadow” also transmits the Covid-19 droplets MUCH farther than 6 feet. The slipstream flows in a more or less straight line, and this paper suggests you need to avoid it almost completely.
How far back exactly do you need to be? That depends on the lead athlete’s speed (or the speed of the wind). Let’s use an example from the paper to illustrate:
Analyzing the results of all the simulations, the main conclusion is that substantial droplet exposure occurs when the trailing runner is positioned in the slipstream of the leading runner, up to a distance between both that depends on the traveling speed.
For walking at 4 km/h a distance of about 5 m leads to no droplets reaching the upper torso of the trailing runner.
For running at 14.4 km/h this distance is about 10 m.
I’ll translate for my fellow Americans. The authors are saying that if a person in your path is walking at a mere 2.5 miles per hour (roughly a 25–30-minute mile), you must maintain a distance of at least 17 feet to ensure no droplets land higher than your torso.
If the person is running full out at 9 miles per hour (roughly a 6:40 pace, pretty aggressive for the typical mid-afternoon road runner), the slipstream carries droplets even farther. Behind a runner, stay at least 33 feet back to keep your droplet exposure to a minimum.
Cyclists were not addressed in this study. But one could reasonably assume virus-laden droplets travel yet farther in the wake of a speedy athlete on a bike.
So much for 6 feet.
My Friends, Never Stand Downwind
Fortunately, the paper includes ways to avoid or minimize the chances of additional spread via slipstream. In fact, we can take our cues from nature.
The Flying V is a common sight among migrating birds — if you’re still looking to run, walk, or bike with friends, you’d be well-served to adopt a staggered formation like this.
Avoiding the Covid-19 Slipstream
You can dodge this issue if you maintain standard social distancing by running side-by-side (at a distance of 3–6 feet). It’s easy to hold a conversation at this distance, and you’ll stay out of each other’s slipstreams with almost no effort.
That said, remember that it’s not all about the motion of you and your fellow athletes. Pay attention to local wind conditions too.
If the wind is shifting, or coming crosswise to your path, you’re better off staggering your formation. Trailing runners should stay to either side of the moving athlete in front. This keeps you out of the potentially dangerous flow of droplets.
Seriously, just look at the birds!
You say, “Goodbye”, I say, “Hello”
This is all well and good. If you’re reading this, you’re already concerned about keeping yourself healthy and limiting the spread of the novel coronavirus.
Unfortunately, when you go out you’re bound to find many people who seem not to have heard about the importance of social distancing.
What’s a safety-conscious runner to do?
Sidewalk Etiquette for Social Distancing
The most important thing is to protect your own health (and the health of anyone you care for) first.
So while it often grates on us as Americans to step aside for anyone, I suggest re-framing that attitude.
Rule 1: Take charge of maintaining distance, and don’t wait for the other person to move.
When I go out, I’m not stepping off the bike path to make room for someone else. I’m “challenging myself with technical running terrain” and “taking my health into my own hands.”
In other words, be the role model for social distancing. You don’t want to play chicken with Covid-19.
It may sound a bit silly, but if you rely on other people to meet you halfway on social distancing, you’re bound to come up short. On the other hand, if people see you going to lengths to keep at least 6 feet distant, it may make them more aware of their own bad behavior.
Rule 2: Earn cooperation through kindness.
There may be some scenarios where this is difficult though. Narrow wooded paths or sidewalks with a busy street on one side and unbroken buildings on the other can both present problems.
If you find yourself crossing paths with someone else and in need of their cooperation to maintain a safe distance, we’re right back to role model territory.
After all, how would you respond if someone angrily shouted at you to move over?
Here’s what I do: Keep your eyes up to watch for oncoming trail-users. When you see someone, slow down, wave and call out to them from a distance of 20–30 feet.
With a smile and a friendly tone, say something like “I’ll take this side, and you take that one.”
If you’re overtaking another athlete who may not have seen or heard you, it’s common courtesy to let them know — and even more important now. In the US, the standard is usually “Passing on your left!”
I suggest everyone use the same, adjusting the side for whatever is customary where you live. The important thing though is to keep things friendly. Convey through your face, tone, and body language that you’re doing this out of concern for everyone’s health, including theirs.
And if you absolutely HAVE to pass inside a 6-foot range? Turn your face away and use your shirt to cover your mouth and nose until you’re past.
Under normal circumstances, this might be considered rude, but today’s circumstances are anything but normal.
Rule 3: Don’t put yourself in needless danger.
Finally, try to avoid these situations when possible. Do you really have to take that route, or is there a safer (if less convenient) option that doesn’t put your health at risk?
Now is the time to explore alternate routes, or switch up your training times if possible. Experiment, and see how few people you can encounter on your runs. Make a game of it!
If it’s not going to drive you insane, you can always keep your training entirely at home. Now’s the time to get your money’s worth out of that treadmill, stationary bike, or rowing machine that you had to have.
While I’m not suggesting we all follow the example of the Virginia man who ran a marathon in his driveway, his actions do illustrate that there’s a lot we can do at home.
Ultimately, your own actions are all you can control in this situation. I hope you join me in attempting to be a positive role model on our paths and trails in these strange times. If nothing else, stay home and stay safe.
