The next day, they ate lunch at a restaurant.

One of them had Covid-19, but didn't feel sick yet.

Within a few days, other members of the family started showing symptoms.

And a few days after that, so did the family who was sitting at the table next to them.

The family at this table also got sick.

And researchers say this first person was the source of all these infections...

Even though some of them were sitting almost 14 feet away.

But the people eating at these tables didn't get sick.

Why?

An air conditioning unit right here kept the air flowing through this section of the restaurant.

It circulated the virus from this person, through the air, to these other families.

This story highlights something about the coronavirus

that most of us are just starting to understand:

Its ability to travel through the air.

And as public spaces open up, that's led to some big questions:

Is it safe to go to the beach?

What about a park?

And is a runner going to get you sick?

If we think about our actions only in terms of safe or risky, there's really only way

to guarantee you won't get sick or spread Covid-19:

Stay home, isolate yourself, and have zero contact with the outside world.

But maintaining that level of caution all the time isn't really possible for most of us.

We need food.

We need supplies.

And sometimes, we just need to take a walk.

So the goal in protecting yourself and others from Covid-19 isn't to eliminate risk completely --

it's to minimize it.

If this side is perpetual quarantine,

and this side is getting coughed on by a bunch of sick people,

it's about pushing yourself as reasonably close to this side as you can.

So let's start with going for a walk.

And with someone who, like me, has also felt weird about it.

Before I started calling up epidemiologists and talking to them about the risks,

I was actually pretty paranoid.

And then when I actually started digging into the research, I realized the risks of getting

Covid-19 from runners or cyclists outside is much lower than I thought.

Everytime we breathe — but especially when we talk,

and especially when we cough or sneeze —

we let out little droplets of water.

Some of them are pretty big and heavy, and fall to the ground quickly,

like little bits of spit.

Others are really small and much lighter, so they float farther through the air.

And these droplets are what's carrying the virus.

If a droplet floats and then evaporates, that leaves the virus out in the air

for some period of time.

And we don't yet know the amount of virus you have to be exposed to to get sick,

but we do know that you lower your risk by exposing yourself to less of the virus.

And Sigal says there's three ways to do that:

The first is distance.

So, are you six feet away from the person?

Duration.

Are you encountering this person for one second as they whiz past you,

or are you around them for an hour?

And ventilation.

Is there a good airflow moving around you that can disperse any viral particles?

Or are you in an enclosed indoor space where they're just going to stick around?

The difference between how air moves inside, versus outside, is huge.

To show that, I used this spray, which glows under a blacklight.

I sprayed my test subject with it both inside and outside, from 3 feet away.

Even though it wasn't windy, far fewer spray particles reached his shirt outside.

The airflow was so much better at dispersing them.

And being outside also has an effect on the virus itself.

A virus has this protective coat of moisture around it.

There's a lot of things acting on it. So, there's sunlight hitting it.

There's wind. There's rain. There's humidity.

And all of that can work to kind of break apart this protective coat of moisture,

and decay the virus.

A study in China looked at 318 different outbreaks of Covid-19 across the country.

Only one of them involved someone catching it outdoors.

That study hasn't been peer-reviewed, but it's consistent with everything else we know:

That being outside can be pretty-low risk.

But your interactions with other people can increase that risk.

If you're talking to a friend at a close distance, your risk goes up.

And that risk climbs the longer your conversation continues.

But if you're both wearing masks to stop some of those larger droplets from spreading,

your risk goes down.

Shopping at an open-air market is less risky than being inside a store.

But you can reduce that risk by getting in and out quickly.

But what about passing a heavy-breathing runner?

So let me take you through what would actually have to happen for a runner or cyclist outside

to infect you as they pass by.

They would have to expel enough viral particles to be able to kickstart an infection.

Those particles would have to travel several feet of distance;

withstand the pressures of wind, rain, humidity...

Then the particles have to actually land in your throat or your upper respiratory tract.

Or on your hands, which you would then use to touch your eyes, your nose or your mouth.

So all of that is a pretty arduous sequence to execute perfectly.

Going to the beach, or to a park, isn't necessarily dangerous or safe.

The risk can go up or down, depending on how we each behave.

Which means everyone has a responsibility to lower that risk for everyone else.

The point here is not to be cavalier when you go outside.

I think we all still want to be cautious, especially as some states are starting reopening.

Changing your behavior to limit exposure to the virus won't reduce your risk to zero.

But it could lower it enough, that you can breathe a little easier.