At 100% seating capacity transmission model calculations with a 4,000 viruses/hour shedding rate and 1,000 virus infectious dose show no inflight aerosol transmission for 12 hour flights.US Department Of Defense Study
Prior to today, the problem with most covid-19 studies examining flight risks for passengers, is that they’ve been based on assumptions which dilute the true ability to come up with real data based conclusions. Enter: the US Department of Defense and United Airlines, using real live passenger jets and sophisticated air sensors used by the military to detect biological and viral threats in the air, with real time tracking of all particles.
The Department of Defense sponsored the study but used United Airlines jets to take a look at how particles of virus from covid-19 would spread in flight at altitude, but also while parked at a gate without engines running; across different aircraft types. Beyond the main message of low transmission risk, the conclusions on where to sit and what works to mitigate spread were fascinating.
They basically turned a Boeing 767 and Boeing 777 into flying government laboratories equipped with the most sensitive detection gear on the planet, and a mere 54 trillion fluorescent aerosol markers to track how virus spreads.
The purpose of the study conducted by the DOD using United planes was to examine the safe movement of US troops via air travel, so results should not show any bias or hope for positive outcomes, but rather scientific reasoning and data to support any conclusions.
What the study found was effectively zero spread of covid-19 from airborne aerosol transmission across a variety of 12 hour flights with masks on. Researchers believe this is mostly thanks to the robust air filtration systems which technically make planes 10-15x safer than homes and other indoor breathing environments, at least as far as air flow goes. Only 1 in 33,000 particles made it anywhere near another passenger breathing zone.
Airplane Air Flow
You may have seen an airline CEO on television recently discussing their HEPA air filtration systems and how they make a difference. You may have also been skeptical about those claims. But that’s misplaced. Airline air systems filter at least 99.7% of harmful particles out of the air within 60-120 seconds of release.
Using the CDC airborne contaminant removal table, and our experimental data, the 767 and 777 both removed particulate 15 times faster than a home, and 5 to 6 times faster than recommended design specifications for modern hospital operating or patient isolation roomsUS Department of Defense Study
Experts estimate covid-19 transmission risk as a factor of the viral dose combined with exposure time, and this makes a massive leap in curbing both factors.
Testing Airplane Flow And Aerosol Transmission
United Airlines and the US Department of Defense spent 38 hours in the air and 45 hours on the ground using real life scenarios and actual 767, 777 cabins, with the same air systems used on passenger jets, and the exact air conditions used on the ground parked at a gate.
They filled the cabin to 100% capacity with highly sophisticated bio-defense sensors in the place of passengers, which are used to protect presidents, troops, subways and airports around the globe, capable of sensing a threat with the smallest of aerosol or droplets. The study placed the sophisticated bio sensors on each seat and simulated things in the forward cabin, as well as front, middle and rear of the economy cabin.
To be ultra clear the “cough” and breathing style tests, of which more than 300 were conducted, released over 180 million fluorescent aerosol tracers with each one, which were designed to be covid-19 virus. That’s just 54 trillion fluorescent aerosol particles released in this study, no big deal.
Adding to the real life scenarios which aim to eliminate the chance of variables being overlooked, body heat was added via thermal blankets to each seat, to simulate how temperature and body may effect air flow currents on board.
The result: “extremely unlikely aerosol exposure risk for a 12 hour flight when using a 4,000 virion / hour shedding rate and 1,000 virion infectious dose.” The important thing to remember is that aerosols aren’t everything. Passengers must use personal hygiene to minimize droplet risk on surfaces too.
Here’s What The Study Concluded
The study concluded that there’s an infinitesimally small chance of catching covid-19 on planes, and makes the separate IATA airline study, which suggests one in 27 million as a probability, seem somewhat likely to be realistic. Here’s the big headline…
For the 777 and 767, at 100% seating capacity transmission model calculations with a 4,000 viruses/hour shedding rate and 1,000 virus infectious dose show no inflight aerosol transmission for 12 hour flights.
The data presented herein couples well with existing modeling and epidemiologic studies of commercial airframe transmission. No secondary cases were traced on a 350-person 15-hour flight from Guangzhou to Toronto, which included symptomatic (coughing), PCR-positive patient, and his wife, who tested positive a day after landing (Schwartz, et al. 2020). Similarly, surface contamination, via the aerosol route is minimized by the rapid removal of contaminants before settling can occur.US Department of Defense
But the extremely low chance of aerosol transmission isn’t the only thing worth noting from the landmark airline study. In fact, many gems of information are offered in the document, including a few helpful tips for airlines and passengers to stay safe from droplets too. Here’s a few bits direct from the study…
- Arm rests and table tops closest to the release location are consistently the highest level of contamination for each release location
- Keeping air supply and recirculation mode (HEPA-Filtration) operating is critical. Ground supply and APU behave similarly, but there is likely more uncertainty with variations in ground supply flow rates and suppliers, since the test team was only able to test the single provided system
- Loading passengers in smaller groups and allowing distance on the jetway is likely beneficial to maintaining social distancing guidelines, but simulated infected personnel within these jetways was not tested.
- The highest collected aerosol concentration is always located closest to the release point of that DNA tagged bead, with lower risks forward of a release than aft of the release.
- Contamination of surfaces via non-aerosol routes (large droplets or fecal contamination) is more likely in lavatories and other common areas.
- Overhead gasper (air nozzle) supply (on or off) does not make a significant impact on aerosol risk and could continue to be used primarily for traveler comfort.
Basically, wipe down your seat surfaces regularly with disinfecting wipes during flight, avoid touching surfaces around the lavatories as much as possible, and wipe down afterward and in general, perhaps avoid the rear of the plane.
The chances of in-flight transmission are increasingly concluded as low, but the steps taken before and after flight to mitigate covid-19 risks matter.
Choosing safe airport transportation and practicing regular hygiene measures before and after arrival at the airport can make all the difference, as can all social distancing. Travel is safer than you think, but only if practical measures being touted by health authorities are followed.