How Can the Flu Spread Inside an Airplane?

In just the third week of 2017, the influenza virus in the United States managed to reach epidemic proportions according to the Centers for Disease Control and Prevention. As the flu season rages on, the number of cases continue to rise, and with it, so does the death toll.

The flu is a contagious respiratory illness that is spread through the air. Each year, the virus infects tens of millions of individuals in the United States and accounts for upwards of 56,000 deaths. The best means of protection against this virus is to receive the recommended doses of the seasonal flu vaccine; however, that does not guarantee 100% protection. Therefore, researchers around the world are constantly seeking better ways to control the spread of the virus. To this end, researchers are turning to simulation technology to understand how the flu spreads in confined spaces, such as airplanes.

According to a news article on Popular Science, airplanes are not only one of the most efficient modes of transportation for humans, but also “one of the most efficient modes of travel for pathogens.” Because so many individuals are cramped into one confined space for a prolonged period of time, it only takes one sick individual for the flu to quickly spread.

Since the severe acute respiratory syndrome (SARS) outbreak in 2002, the Federal Aviation Administration (FAA) has been dedicated to understanding just how pathogens in the air spread on airplanes. In the article, Robert Harwood, PhD, aerospace and defense industry director for ANSYS, a global leader in engineering simulation, spoke about the connection between SARS and airplanes. He explained, “There were outbreaks all over the world, in Asia, Africa, and Europe. The reason it happened so quickly was because people got on airplanes and spread the pathogen.”

After the SARS outbreak occurred, the FAA sought to “ensure the safety and health of airplane occupants.” To do so, they created the Centers for Excellence and Airliner Cabin Environment Research, a program that focused on the utilizations of different technologies—such as cabin sensor systems and contamination mitigation technology—to better track harmful pathogens. Simulation technology developed by ANSYS also entered the playing field.

When speaking on using simulation technology to potentially track pathogens, Dr. Harwood said, “With traditional engineering, you come up with an idea, build a model or prototype, test it, and modify it until you get the product you want. The business we’re in, before you cut metal, you use computers to simulate the physical behavior of that product to cut down on modifications.”

In addition to what ANSYS simulation software is typically used for—such as “engineering, physics, structural mechanics, elastics, fragmentation”—it is also capable of modeling the “aerodynamics of fluids.” Because of this capability, the software is perfect for tracking how the influenza virus spreads in a contained space, such as pressurized cabins. This is why the FAA’s Center for Excellence at Purdue University has been analyzing ANSYS simulations for a number of years.

According to the article, “the air [in airplanes] is constantly being pumped in from inlets in the ceiling and recycled out through vents at the passengers’ feet, making airflow models quite complicated to create.” In order to overcome this issue, Purdue researchers focused on any variable that might influence the “velocity and direction of the flow of air,” such as the positioning of the vents, or the “currents” created by flight attendants as they walk down the aisles. Identifying these variables helped the researchers develop “hundreds of scenarios” on how different germs can spread in pressurized cabins.

The researchers utilized the simulation technology to create a video simulation which shows a view inside of a crowded airplane. In the simulated airplane environment, one individual sneezed, creating a plethora of multicolored particles that are released into the air, essentially creating a storm cloud of germs over all of the passengers. The particles within the cloud scattered all over the cabin, but there were a few unlucky passengers who were hardest hit; the seats with the highest risk of infection were the ones that were directly adjacent to the sneezing passenger. According to ANSYS, “Flu particle movement depends on air flow in the cabin. Air circulates from overhead fans to lower vents. Flu particles disperse through plane with cabin air flow.”

“The particles are colored to show you where the stuff goes. Those droplets get picked up by the airflow and get transplanted all over the cabin. They actually spread quite far,” stated Dr. Harwood in the article.

The scenario depicted in the video is just one way in which these germs can spread.

By analyzing these different scenarios, researchers then advise the FAA with different recommendations on how to make airplanes safer for their passengers. In addition, the technology also allows airlines to make cost-efficient improvements to their airplanes. How? According to the article, “By simulating how new air conditioning systems will affect airflow, airlines can figure out which systems reduce germ travel for the lowest cost.”

When speaking of the implications of this technology, Dr. Harwood said, “[Airlines] want the cheapest flight but also for their passengers to be healthy. Our technology is useful because they can see how they can achieve that and improve performance without sacrificing cost.”