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Suggested Citation:"4 COVID-19 Risk and Mitigation in Airports." National Academies of Sciences, Engineering, and Medicine. 2022. Flying in the COVID-19 Era: Science-based Risk Assessments and Mitigation Strategies on the Ground and in the Air: Proceedings of a Workshop. Washington, DC: The National Academies Press. doi: 10.17226/26426.
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4

COVID-19 Risk and Mitigation in Airports

Generally speaking, the risk of COVID-19 transmission in airports is more difficult to study that the risk on planes because instead of being a small, enclosed space with people sitting in assigned seats, airports are large, open structures with large, chaotic flows of people that make it essentially impossible to determine if and when a transmission might have occurred. Nonetheless, some efforts to model and understand the transmission risks in airports have been made, and several workshop speakers mentioned those.

As for risk mitigation in airports, many of the measures that are effective in airplanes—mask wearing, improved air ventilation and filtration, disinfection of surfaces, and so on—are also effective in airports. For example, when Joseph Allen, an associate professor at Harvard University’s T.H. Chan School of Public Health, described the findings from a 2013 National Academies of Sciences, Engineering, and Medicine report, Infectious Disease Mitigation in Airports and Airplanes,1 he described a “healthy buildings strategy” that included a recommendation on maintaining heating, ventilation, and air conditioning (HVAC) systems in such a way that they ensured healthy air. In particular, Allen said, one can decrease the risk of COVID-19 transmission in airports by increasing the ventilation rate and maximizing outdoor air ventilation, increasing filter efficiency by upgrading to filters with a MERV13 rating or higher, and supplementing this with portable air cleaners. These actions are particularly important in areas where masking cannot be done, such as in airport restaurants and bars.

But while airports have many similarities to airplanes in terms of which risk reduction measures are most likely to be effective, they also have their own unique characteristics that require different approaches. Three speakers in particular described COVID-19 risk and mitigation in airports. Saskia Popescu, an assistant professor in the biodefense program at George Mason University’s Schar School of Policy and Government, offered an overview of infection prevention in general and how it can be applied to air travel, particularly in airports. David Kipp, the vice president of technology services at Burns Engineering, which provides and manages technologies for airport operations, discussed different methods that airports have used to reduce the risk of COVID-19 transmission and explained which have been successful and which have not. Jack Spengler, a professor at Harvard University’s T.H. Chan School of Public Health described some modeling studies designed to better understand the factors that influence risk in airports and what changes can be made to reduce those risks.

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1 National Academies of Sciences, Engineering, and Medicine (NASEM), 2013, Infectious Disease Mitigation in Airports and Airplanes, Washington, DC: The National Academies Press, https://doi.org/10.17226/22512.

Suggested Citation:"4 COVID-19 Risk and Mitigation in Airports." National Academies of Sciences, Engineering, and Medicine. 2022. Flying in the COVID-19 Era: Science-based Risk Assessments and Mitigation Strategies on the Ground and in the Air: Proceedings of a Workshop. Washington, DC: The National Academies Press. doi: 10.17226/26426.
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AN OVERVIEW OF INFECTION PREVENTION AS APPLIED TO AIR TRAVEL

Infection prevention and control is “pretty much what it sounds like,” Popescu said—stopping and preventing the spread of infectious diseases. Originally practiced mainly by health care workers to prevent health care–associated infections in patients, health care workers, and visitors, it has become much broader in scope. Showing a figure that displayed infection prevention in terms of stack of “Swiss cheese slices” (Figure 4.1), she explained that today’s infection prevention takes a holistic approach to preventing infectious disease prevention, which includes such steps as disease surveillance, cleaning and disinfection, improved ventilation, masks and other personal protective equipment, social distancing and quarantines, contact tracing, risk assessments, and communication. It’s not just one piece, she said. It’s all of these things.

So, Popescu continued, how is that applied to air travel? What makes air travel a unique environment, she said, is the combination of things it entails—not just the airplane, but the airport, baggage claim, buses and other forms of transportation, and so on. “Unfortunately, when we talk about air travel in the context of COVID, it’s so much focused on the airplane,” she said. That is understandable to an extent, but the other pieces are also important, she said, and she worries that they get neglected when people talk about infection prevention in air travel. For instance, she has observed that people in airports may be very cautious about the restaurants and bars, but then they get their food to go. “So people don’t necessarily crowd at restaurants,” she said, “but if you go to the gates, everybody’s got their food to go there—their drinks, their snacks—and everybody is sitting there eating, masks off, and only distanced by one seat.”

Similarly, she said, there has been so much focus on masking and social distance when people are checking in at the gate and then on the airplane, but when people get to the baggage claim they feel as if they’ve already done what they need to do. The result is often a baggage claim area with people squeezing together, even taking their masks off.

Yet another example, Popescu said, can be found on terminal buses. A great deal of attention is paid to proper ventilation in the airports and airplanes, but the buses are poorly ventilated spaces where people are clumped together. “And more than one time, I’ve seen people just take off their masks because they’re frustrated.” This is why it is important to approach infection prevention holistically and look at all of the pieces together, not just some of them.

Turning to specific recommendations, Popescu said she worries about variability in mask compliance. “We focus a lot on the airplane, but how many times has somebody actually gone up to an individual and asked them, please bring the mask over your nose?” She has noticed that masking requirements are not necessarily enforced at various places around the airport, and she has even observed airport staff not wearing their masks correctly.

Image
FIGURE 4.1 The Swiss cheese model of infection prevention. SOURCE: Saskia Popescu, George Mason University, presentation to the workshop, adapted from Ian M. Mackay and James T. Reason, illustration courtesy of Rose Wong.
Suggested Citation:"4 COVID-19 Risk and Mitigation in Airports." National Academies of Sciences, Engineering, and Medicine. 2022. Flying in the COVID-19 Era: Science-based Risk Assessments and Mitigation Strategies on the Ground and in the Air: Proceedings of a Workshop. Washington, DC: The National Academies Press. doi: 10.17226/26426.
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“Little things like that are signals to the travelers that that’s okay to do.” She observed that scientific studies of disease transmission often assume that people are wearing their masks perfectly 100 percent of the time. It is never that simple, she said. So it is important to consider the human dimension, but it is not obvious how that could be modeled in a transmission study.

Moving to cleaning and disinfection, she said, “It’s never as simple as a spray or hand sanitizer.” With sprays, it is important that they be on the Environmental Protection Agency’s List N of substances that are effective against the COVID-19 virus, but more is needed. Each disinfection requires proper application, which means that there must be the appropriate contact time—2 minutes, or 5 or even 10, depending on the product. But most people applying them don’t read the instructions and simply spray, wipe, and walk away. This is probably one of the biggest failures in cleaning and disinfection, she said, that when workers are trying to get surfaces done quickly, they do not pay attention to the contact time.

There is a different set of issues for disinfection with ultraviolet (UV) radiation. UV-C can be a very effective germicidal, Popescu said, but there is little data on the duration, dose, and wavelengths that are necessary to kill the COVID-19 virus. Furthermore, UV-C does not penetrate biofilms, and it does not replace manual cleaning and disinfection—which is part of the problem in the way that some of the other speakers mentioned. Finally, there is variability in the many UV-C products being sold to use against COVID-19, she said, and there are no performance standards in non-medical settings. “So essentially, UV-C companies can pretty much say whatever they want, and it can be entirely non-effective.”

A larger issue, Popescu said, is that people tend to focus on one or two things to reduce risk, but risk reduction is additive, so it is important to combine a variety of approaches. “If we’re going to be focusing on cleaning and disinfection and air quality and ventilation, we can’t forget about proper mask usage,” she said, and if people are told that one particular activity is high-risk, it can push them toward other choices that could also be risky—like eating their food at the gate to avoid eating it in a restaurant. “I want to make sure that we’re not focusing so much on one intervention strategy, but investing in all of them.”

Popescu suggested that one question must regularly be asked when assessing risk—“What are we focused on, and what are we ignoring?” Too often, efforts to solve one problem end up creating another. For example, in their efforts to keep things sanitized, airlines will pass out bags with a snack, water bottle, and hand sanitizer to the passengers on a plane, but what happens? Row by row, as people get their bags, they take off their masks and eat and drink and have a short breather. “Yes, there’s great ventilation and air exchanges and filtration,” Popescu said. “That’s helpful. But if everybody around you is unmasked, eating and drinking, there’s only so much the ventilation is really going to help with.” So perhaps, she suggested, airlines could ask people to look around them and, if others nearby are eating and drinking, wait a few minutes to take their turn.

Similarly, a focus on passengers on airplanes can lead to neglect of the transmission risks in airports to waiting passengers or ground crew or other staff. Popescu said she is very concerned about those non-aircraft environments, such as the gate, because she sees some of the worst air travel behavior there. And if transmission does occur in the airport as opposed to the airplane, it is very difficult to pinpoint exactly where it occurred.

Popescu closed by asking what it will take to establish sustainable infection prevention efforts. “We’re doing a lot right now,” she said, “but the goal is to keep this going so we don’t fall back into a pre-pandemic mindset.” Human factors assessment will likely play a role, as well an all-hazard approach. And one of the bigger challenges that has arisen with the pandemic is how best to communicate guidance. “We’ve said, ‘Mask up or 6 feet apart,’ so people really think that there is this invisible wall at 6 feet and suddenly that microbe won’t be able to go past it. But we want people to think critically.” It will depend on being able to communicate complex infectious disease nuances. Part of that will be explaining to people that the recommendations might change as more is learned, and that this is okay because it means that the recommendations are getting better.

Sustainable efforts will be helped by the involvement of multi-disciplinary groups, including experts in such areas as infection prevention, epidemiology, virology, aerosol science, science communication, and more. “You need everybody to come to the table to have these conversations and help guide a multi-disciplinary, holistic approach,” she said.

“My goal,” Popescu concluded, “is to drive cultural change that includes infection prevention as a facet of air travel during COVID, but beyond COVID.” Hopefully, she said, some of these efforts will become a normal part

Suggested Citation:"4 COVID-19 Risk and Mitigation in Airports." National Academies of Sciences, Engineering, and Medicine. 2022. Flying in the COVID-19 Era: Science-based Risk Assessments and Mitigation Strategies on the Ground and in the Air: Proceedings of a Workshop. Washington, DC: The National Academies Press. doi: 10.17226/26426.
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of air travel going forward, such as cleaning and disinfection, distancing, and not traveling when sick or wearing a mask on the airplane when not feeling well. “All of these things are things that I think we are hoping to infuse ultimately into air travel.”

AIRPORTS’ RESPONSE TO THE COVID-19 PANDEMIC

Kipp described some of the ways that airports worked to adapt to the COVID-19 pandemic. In particular, he said, the responses of airports to the pandemic mostly fell into three broad categories—disinfection and health, consumer confidence, and trial and error.

Concerning disinfection and health, Kipp said that when confronted with the growing COVID-19 pandemic, airlines got busy cleaning—and often in ways that were different from anything they had tried before. As an example, he showed a picture of an autonomous self-driving, ultraviolet (UV) light-disinfecting vehicle that resembled the machine used to resurface ice in ice rinks. It was introduced at the Pittsburgh airport in collaboration with Carnegie-Mellon University. Overall, he said, disinfecting with UV light, UV-C in particular, has proved to be very effective, and it is now being used in a number of airports.

A second example he offered was touchless travel, in particular the use of a smart phone to check in at a kiosk. That is also being used in many different airports, he said, to check in, get baggage tags printed, and even to pay for things along the way.

The second broad category of airport responses was to pay more attention to consumer confidence. Kipp said he found that particularly interesting because increasing consumer confidence “has not traditionally been a skill set that the airport industry has had.” Instead, airports have traditionally focused on service quality and passenger satisfaction and very little on consumer confidence. But airports have been paying more attention; for example, of the sorts of confidence-related factors that airports should pay attention to, he showed some data from Gensler, a major airport planning and design company, which showed a major difference between infrequent travelers and heavy travelers in which parts of the travel journey they find most concerning. While 75 percent of the infrequent travelers named the flight itself as most concerning, only 25 percent of the heavy users did, as they were more concerned with what goes on in the commute, the gate area, or the baggage check.

The third category of response by airports to the pandemic, Kipp said, has been trial and error. Airports have tried many different things to become safer in the face of the pandemic (Figure 4.2). Some have been quite simple, such as stickers on the floor to direct travelers, and some have been quite advanced, such as passengers prearranging their scheduled time slots for the TSA checkpoint. “Some of these things will become part of the permanent environment, and many of them will not,” he said.

Kipp then offered a few specific examples of the types of things that airports have tried over the years. A number have installed thermographic screening systems, often known as fever detection or fever screening, for detecting elevated body temperatures. Some have used facial analysis and facial recognition to facilitate travel—in essence, a type of touchless technology to identify passengers without having to handle identification. On-site rapid testing for COVID-19 is also getting a great deal of attention. There are pop-up health facilities in probably 20 or 25 airports around the country now, and they can be used in particular for international travelers who may be required to have proof of a negative test in order to travel. And one technology that has not yet caught on in the United States but that is in use in the Hong Kong airport is a disinfection booth that passengers enter in order to be disinfected.

Some of the trials have been successful, and the technologies behind them are likely to be adopted by more airports, Kipp said. Touchless technology is one example. The public has adapted easily to touchless technologies and even to having their faces matched to their driver’s license or their passport as a way to move through the airport. New cleaning technologies have also proved very successful, and airports have had success with using digital channels to get information to the public to help them understand what is going on in their airport. “You’d be amazed at how many different channels there are for people to receive information,” he said.

On the other hand, some technologies have not worked so well. Airport passengers do not like invasive processes that involve swabbing or spraying, for instance. Tracking passengers through the airport using facial recognition has also proved too invasive. Some airports have experimented with it, Kipp said, originally for security purposes and later for contract tracing, if it proved necessary, but it “begins to get heavy on the creepy scale for

Suggested Citation:"4 COVID-19 Risk and Mitigation in Airports." National Academies of Sciences, Engineering, and Medicine. 2022. Flying in the COVID-19 Era: Science-based Risk Assessments and Mitigation Strategies on the Ground and in the Air: Proceedings of a Workshop. Washington, DC: The National Academies Press. doi: 10.17226/26426.
×
Image
FIGURE 4.2 Various methods utilized by airports to prevent viral spread during the pandemic. SOURCE: David Kipp, Burns Engineering, presentation to the workshop, from T. Osbaugh, 2020, “Airports Are Facing a New Reality,” Gensler dialogBLOG, March 31, https://www.gensler.com/blog; courtesy of Gensler.

a lot of people.” Thermographic screening, while it is not invasive, also does not offer much useful information. Airports have found that most people with a fever do not come to the airport in the first place, so few people are caught with this sort of screening. And physical reconfiguration of the airport—for example, trying to increase social distancing by building bigger walls and bigger spaces—is just too expensive for most airports.

In closing, Kipp said that the success or failure of certain technologies or processes depends as much as human psychology as the functionality of the technology. For instance, when touchless kiosks were installed in the Los Angeles airport so that people could use their phones to check in, “what happened was half of the people looked at the kiosk and looked at the typical check-in desk where there was no line and went there because it was easier for them. So human behavior is a big part of what we’d love to know.”

RISK CONSIDERATIONS FOR AIRPORTS

Unlike commercial airliners, which have similar functions and very similar designs, airports have very different designs, Spengler said. Even though they have similar functions, the layouts and processes can differ dramatically from airport to airport.

The United States has about 450 primary commercial airports, which serve more than 10,000 passengers a year, Spengler said. They range from small, regional airports to large hubs, the largest of which is Atlanta’s airport, which before the COVID-19 pandemic was handling 50 million passengers a year.

In one sense, Spengler said, airports have a major advantage over many other indoor spaces when it comes to dealing with the transmission of a respiratory virus such as COVID-19, because they are composed of connected spaces with very large volumes and plenty of air flow through the spaces. Showing a photo of a wide open airport space, he said, “It’s almost like being outdoors in terms of the amount of air that is available to ventilate that space.” However, he added that is not always the case in airports. Some areas, such as security checkpoints,

Suggested Citation:"4 COVID-19 Risk and Mitigation in Airports." National Academies of Sciences, Engineering, and Medicine. 2022. Flying in the COVID-19 Era: Science-based Risk Assessments and Mitigation Strategies on the Ground and in the Air: Proceedings of a Workshop. Washington, DC: The National Academies Press. doi: 10.17226/26426.
×

passport control, and luggage areas, are generally much more enclosed and often have low ceilings in order to hold security cameras. These are the more challenging parts of airports in which to mitigate the transmission of a virus.

Generally speaking, he said, mitigation activities to slow the spread of the virus involve reducing or removing the source, increasing dilution of the virus in the air, managing the density of people in a given space, and limiting the amount of time they spend in spaces where might come in close contact with other people. One thing they discovered from speaking with those running the airports was just how much confusion there was in the beginning of the pandemic about how to respond and how little guidance they received from the federal government. So they had to get onto a very rapid learning curve, he said.

The response was impressive, Spengler said. The staffs at the various airports that his group spoke with implemented a number of programs in response to COVID-19—social distancing, enhanced cleaning and disinfection services, touchless systems, and the like—and some of the larger airports even had people dedicated to innovation and doing pilot projects. The result was a great deal of innovation in areas such as plastic barriers, touchless technologies, and even the use of UV light to clean the hand grips on escalators.

In the future, once passengers return to airports, Spengler said, it will present a challenge, particularly with the localized congestion areas that are inevitable in certain parts of airports. To understand the issue in general terms—since there are so many different airports with so many different designs—the group decided to develop some generic models to study the issue. Working with the typical physical dimensions of such spaces and their ventilation characteristics, they created a model in which they could modify certain parameters to understand the effects that different factors had on transmission risk. if ceilings are higher, for instance, or the air exchange rate is increased or if people chose to eat at the gate and took the masks off. What was happening in the small areas around people was crucial, he said—it doesn’t matter how good the overall air exchange rate is; what is important is what is happening right where an individual person is exhaling and inhaling.

They did these simulations for boarding gates, security areas (for both passengers and security personnel), and break rooms. And the point of the effort, Spengler said, was to lay out a method that airport operators could use on their own to assess the various strategies they have on at hand to mitigate transmission. They did not end up recommending any specific model, but they pointed out models that are in the public domain that airport operators could easily adapt for their own purposes. This allows operators to examine those situations where the passenger densities are unavoidably higher than desirable and see what the effects of different control strategies will be. Would portable air cleaners help? How about upper-room UV?

The group also carried out some simulations of what passengers experience at airport. A person would walk through the airport at different times, board a shuttle bus and ride it for a while, and would take measurements of the level of carbon dioxide at the different places and in different situations. Because people exhale carbon dioxide, its level is an indication of overall risk of virus exposure if infected people are nearby—the higher the level, the less quickly the air from a space is being replaced with outside air. One thing the group found was that after they boarded a shuttle and a number of others did as well, the carbon dioxide levels went up noticeably. “So we decided to pay particular attention to this issue,” Spengler said.

To study it further, the groups worked with colleagues from the University of Maryland to build some sophisticated computational fluid dynamic models of a bus, a shuttle bus, and a terminal train in order to determine how risk of transmission is dependent on various factors. The bottom line, Spengler said, is that risk is decreased by maximizing airflow, maintaining good filtration, keeping passenger density low, and keeping the time passengers spend in such enclosed spaces to a minimum.

In closing, Spengler described a simulation the group did of how the use of Plexiglas barriers to separate the various segments of a long, snaking line affected transmission risk among those in the line. The use of these barriers created what he called “Plexiglas canyons,” and the simulation showed that their use had an unanticipated effect. In the configuration of that particular airport, the ventilation was such that when there were no Plexiglas barriers, a person’s exhaled breath—and, potentially, virus particles—was quickly pulled into the return register so that the surrounding people had little exposure to it. But with the barriers, the canyon effect kept the exhalations trapped nearby so that people following an infected person could potentially be breathing in viral particles the entire time they were in line. The moral, Spengler said, is not that the Plexiglas barriers should not be used but rather that they should be used with careful consideration of exactly what effect they might have.

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Suggested Citation:"4 COVID-19 Risk and Mitigation in Airports." National Academies of Sciences, Engineering, and Medicine. 2022. Flying in the COVID-19 Era: Science-based Risk Assessments and Mitigation Strategies on the Ground and in the Air: Proceedings of a Workshop. Washington, DC: The National Academies Press. doi: 10.17226/26426.
×
Page 29
Suggested Citation:"4 COVID-19 Risk and Mitigation in Airports." National Academies of Sciences, Engineering, and Medicine. 2022. Flying in the COVID-19 Era: Science-based Risk Assessments and Mitigation Strategies on the Ground and in the Air: Proceedings of a Workshop. Washington, DC: The National Academies Press. doi: 10.17226/26426.
×
Page 30
Suggested Citation:"4 COVID-19 Risk and Mitigation in Airports." National Academies of Sciences, Engineering, and Medicine. 2022. Flying in the COVID-19 Era: Science-based Risk Assessments and Mitigation Strategies on the Ground and in the Air: Proceedings of a Workshop. Washington, DC: The National Academies Press. doi: 10.17226/26426.
×
Page 31
Suggested Citation:"4 COVID-19 Risk and Mitigation in Airports." National Academies of Sciences, Engineering, and Medicine. 2022. Flying in the COVID-19 Era: Science-based Risk Assessments and Mitigation Strategies on the Ground and in the Air: Proceedings of a Workshop. Washington, DC: The National Academies Press. doi: 10.17226/26426.
×
Page 32
Suggested Citation:"4 COVID-19 Risk and Mitigation in Airports." National Academies of Sciences, Engineering, and Medicine. 2022. Flying in the COVID-19 Era: Science-based Risk Assessments and Mitigation Strategies on the Ground and in the Air: Proceedings of a Workshop. Washington, DC: The National Academies Press. doi: 10.17226/26426.
×
Page 33
Suggested Citation:"4 COVID-19 Risk and Mitigation in Airports." National Academies of Sciences, Engineering, and Medicine. 2022. Flying in the COVID-19 Era: Science-based Risk Assessments and Mitigation Strategies on the Ground and in the Air: Proceedings of a Workshop. Washington, DC: The National Academies Press. doi: 10.17226/26426.
×
Page 34
Next: 5 The Aviation Industry's Response to the COVID-19 Pandemic »
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The National Academies of Sciences, Engineering, and Medicine convened a workshop on February 4th and 5th, 2021 to review the issues related to safety of passengers and employees in commercial air transportation, for domestic and international travel, during the COVID-19 pandemic. The workshop explored best practices to assess and mitigate COVID-19 transmission risks experienced during the travel chain, from the departure airport entrance to the destination airport exit. The workshop also identified areas where more research is needed to address gaps in understanding. This publication documents the presentations and discussions held during the workshop, and is presented as a synthesis of the workshop.

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