Is Six Feet Enough To Fly Safely Again? Most Studies Still Say No
Is Six Feet Enough To Fly Safely Again? Most Studies Still Say No
Every industry in the world right now is trying to retool itself to operate everything 6’ apart, from customers to staff, to check out lines to bathrooms (are we closing every other urinal yet?).
For some companies this is a relatively easy, if costly, fix. Even though meatpacking plants are under the microscope, for instance, due to recent coronavirus hotspots, work stations can be re-spaced 6’ apart and separated by plexiglass or plastic in addition to requiring workers to utilize supplemental PPE. The same fast audible applies to many manufacturing and assembly plants where workers have their own space on the line and don’t interact frequently with one another.
But traders on the stock exchange floor? Restaurants and bars? Sports and concerts? Real estate and construction? Airlines and hotels? When your business is predicted on the premise of close interpersonal contact and constant face-to-face collaboration, maintaining 6’ of social distancing and communicating through masks become vastly more complicated.
So with so much riding on 6-feet, what’s the science behind it? And is 6’ enough space between people to make getting on a plane, waiting 4-hours in line at TSA, staying at a hotel, grabbing an Uber, or going to the beach this summer safe in the first place?
Several recent studies suggest, “No”.
Ever since COVID-19 sprung loose, social distancing recommendations and requirements have been based on the 6’ mantra.
6’ makes sense as a rule of thumb. It emotionally feels like a conservative personal safe zone during a pandemic, and since we generally measure ourselves relative to other people from the 6’ reference point, it’s a distance most people can eyeball quickly and know when others are infringing on their space.
The science behind 6’ dates back to a 1930s’ disease model developed by William F. Wells who was researching tuberculosis transmission at the time.
Prior to Wells’ research, conventional wisdom established by Carl Flügge in the late 19th century presumed that respiratory pathogens traveled predominantly through large “droplet transmission”, which settled around an infected individual (think Pig Pen from Charlie Brown) when he or she coughed or sneezed, and subsequently could infect someone close to them through direct contact while the droplet was still in its fluid phase. Flügge wasn’t incorrect. His thesis was just incomplete.
Wells’ was the first research to divide respiratory pathogens in two potential transmission categories: “large” or “small” droplets, or more specifically, “droplets” versus “aerosols”. He discovered two important things vis a vis COVID-19 today. First, “large” droplets can only travel as far as their size, weight, and “ballistic ejection” force will carry them, at which distance they settle and quickly evaporate. That distance was rougly 6’, or 2 meters.
The second thing Wells discovered was that “small” droplets, by contrast, hang in the air longer in plume cloud exhalations which gives them time to evaporate into a “droplet nuclei”, or “aerosol”, phase, at which point they can continue to drift virtually weightlessly like viral plankton for hours or even days in the air stream.
Since Wells’ work, infectious disease control strategies—like quarantines, mask requirements, social distancing, and disinfection protocols previously employed to stem Zeka and Ebola—all have been based fundamentally on whether a virus is transmitted from human-to-human through large or small droplets, or both. Hence, the Wells’ 6-foot rule.
The basic gist of the MIT study is that when it comes to the 6-foot rule not all viruses travel the same. Respiratory viruses in particular spread in specific ways at different speeds over varying distances and even under uniquely accelerating conditions. Some, for instance, look like garden hoses on full spray-mode where the water quickly descends and soaks into the ground. Others look like Febreeze in the sunlight in a hot, moist room, “turbulent gas clouds”, as the study calls them, that can carry the virus in seconds up to 27’ in the air, before drifting away for hours on the wind, or getting sucked up into building ventilation systems, as a recent 2020 Chinese study confirmed about how COVID-19 can spread.
What virologists still don’t know yet is exactly how coronavirus moves undetected (large vs. small droplets), nor how long the pathogen can remain airborne under different temperature and humidity conditions. So the CDC, the White House, and most states and municipalities in their guidance and requirements so far have defaulted back to Wells’ original 1930s’ guidance: 6’ is a good rule of thumb.
But what if it isn’t? When is 6’ not enough? What if I’m at the beach versus inside a slaughterhouse? Is 3’ OK if I’m a 22-year old triathlete? Or should I err on the other side of caution at 12’ if I’m 63 with an underlying pulmonary condition? And what if coronavirus can, in fact, hang in the air for hours in an aerosol phase?
MIT’s study suggested that context is everything. Breathing at rest is relatively benign, compared to coughing which is an explosion. Sneezes are like viral canons. One’s immediate surroundings, a person’s own physiology and predispositions, and PPE equipment also are critical to determining if 6’ actually is a safe distance to reduce the risk of airborne transmission.
On the World Health Organization’s general guidance for 3’ social distancing and the U.S. Centers For Disease Control’s recommendation for 6’, the MIT paper was blunt.
“Given the turbulent puff cloud dynamic model,” wrote the author, Lydia Bourouiba, PhD. “Recommendations for separations of 3 to 6 feet (1-2 m) may underestimate the distance, timescale, and persistence over which the cloud and its pathogenic payload travel, thus generating an underappreciated potential exposure range. For these and other reasons, wearing of appropriate personal protection equipment is vitally important for health care workers caring for patients who may be infected, even if they are farther than 6 feet away from a patient.”
The 6’ debate got more complicated three weeks later, when a Belgium/Dutch study led by Bert Blocken went viral on Medium postulating that sophisticated computational fluid dynamic (CFD) models showed people exercising outdoors need far more room than 6’ between themselves and others to avoid spreading the virus.
Runners and bikers breathe harder and faster over more distance than a subject at rest, the study demonstrated in a now famous simulation. Their exhalations, as a result, follow them like viral contrails, sucked behind in the wind eddies of their own bodies, and engulfing them in a swirling mass of pathogenic particles which, on a crowded bike or running path, adds up to a collective, horizontal COVID-19 plume cloud.
The study, while not yet peer reviewed or published, generated immediate vitriol from the outdoor industry, but its methods and conclusions were proven to be sound. Ultimately, they concluded that people walking should stay 13’ away from others, joggers 30’, and cyclists 65’ to minimize the risk of airborne, aerosol-based virus transmission.
So if recent data suggest that 27’-30’ is the actual distance coronavirus can travel under real world conditions, ergo people walking and jogging outside, running to catch a train, or fumingly hyperventilating in the gate waiting area after being bumped from their flight, why are we reopening beaches, bars, airline routes, and summer travel before we even know how to mitigate the virus’s spread in the first place? What if 6’ has been all wrong all along?
Part of that answer is: “It’s the economy stupid”. The other side of the calculus is uncertainty. Without definitive science, quick decisions generally get made on rules of thumb, conservative judgement, and sound situational awareness.
“Everything is about probability,” Dr. Harvey Fineberg recently told the New York Times. Fineberg is the head of the Standing Committee on Emerging Infectious Diseases and 21st Century Health Threats at the National Academies of Sciences, Engineering and Medicine. “Three feet is better than nothing. Six feet is better than three feet. At that point, the larger drops have pretty much fallen down. Maybe if you’re out of spitting range, that could be even safer, but six feet is a pretty good number.”
When it comes to reopening the global economy, however, many public health and infectious disease experts still don’t sound confident that 6’ is enough room for error. When it comes to resuming long-haul and international travel specifically, like getting on to 8-hour economy trans-Atlantic flight, or boarding a train across town or a bus across a state line, grabbing an Uber, cab, or a rental car, they express even less optimism that 6’ and masks can mitigate a second potential wave of infections if states re-open too soon and unfettered travel resumes too quickly.
“The virus is so small, it can hitch a ride even on tiny, tiny particles,” said Dr. Fineberg. “But how important is each size and how well they can transmit disease is still not fully understood.”
When it comes to the airlines, the road back will be tough. Right now the primary focus is sanitization and decontamination, before boarding, onboard, and on arrival, including misting luggage and, in some airports, passengers themselves. Other seating re-alignments and distancing concepts also are in the works.
But pre-sanitized surfaces and less people per flight only go so far after the pilot closes the doors, people start breathing and coughing in a closed vacuum, and 15 passengers have to use the same lavatory. Though filtered, every airline’s air is constantly recirculated so whether you’re 6’ or 60’ apart you’re inevitably breathing in the exhalations of every other person on the plane.
Which is precisely the question Bourouiba’s and Brocken’s research brings to light. Where does the 6’ rule actually make sense and protect you from airborne infection? And when is it a source of false confidence to give businesses uniform guidance to implement and get the economy up and running again?
As a broad consensus, most U.S. and international health experts still don’t think it’s safe to open up hair salons in most cities, let alone reboot airlines or unrestricted interstate travel, until there is widespread testing and contact tracing available, evidence of community immunity and anti-bodies, as well as progress made towards a vaccine. No one in the airline industry, meanwhile, believes that it’s financially viable long-term to seat passengers 6’ apart, nor agrees that the industry has the ability just take a break, gut their planes, and start the new normal from scratch.
Whatever the airlines decide to do in the immediate future to get planes back in the air, the science so far looks certain to undermine the industry’s guidance and recommendations as more studies emerge about how coronavirus travels and how long it persists particularly in artificial air environments.
In the shorter-term, the same logic holds for trains, buses, subways, trolleys, and any public transit operation. Is 6’ enough? And do you have the right to ask for more if it’s not?
Beaches in some Spanish coastal towns this are re-opening this summer, spacing chairs in demarcated plots 2 meters apart paid for through a contactless app, which seems more plausible since everyone’s siloed and tanning themselves at rest. But what if a spontaneous game of futbol breaks out and the plumes start swirling?
Ultimately, short-term travel especially internationally is going to come down to risk tolerance. As more data emerge on how coronavirus is transmitted and where and for how long it can spread, planning to minimize exposure and maximize social distancing based on conditions will be travel’s new survival skill.
What you can and can’t do this summer and where you can travel also will be determined by how local and state health officials interpret the constant incoming data, quantify what safe social-distancing should be in the first place, and what they allow you to do.
It’s just going to get more interesting as Memorial Day gets closer.