What is the risk of getting COVID-19 in an elevator?

By Míriam R García, Institute of Marine Research (IIM-CSIC); Antonio Figueras Huerta, Institute of Marine Research (IIM-CSIC) and Jim Grant, Teagasc

Although the virus is known to be transmitted in confined and closed spaces, official recommendations generally do not explain how to minimize the risk of transmission within buildings, and therefore in elevators. However, a case of transmission by this means has already been described in the press, and different experts have recommended preventive measures. These measures are especially relevant in countries like Spain, with the highest number of lifts per inhabitant in the world.

SARS-CoV-2 remains viable and can infect in aerosols for 3 hours with a significant decrease in the viral titer (from 10 3.5 to 10 2.7 TCID50 per liter of air) similar to what happens with other coronaviruses. By talking, sneezing or coughing, we are generating an aerosol with millions of tiny droplets of saliva in which there are, if infected, millions of viruses that can infect anyone who breathes in those droplets. That is why it is necessary to maintain distances, at least one and a half meters, although better if there are two or three.

Compared to its predecessors, this virus remains stable on different surfaces, in a controlled laboratory environment. It can be detected on a copper surface for up to four hours, on cardboard for up to 24 hours, and on plastic and steel for up to 72 hours. No infectious virus could be recovered on either printed paper or tissue paper after a 3 hour incubation, and no infectious virus was detected in wood and fabric treated on day 2.

Neither were infectious viruses detected after four days on glass surfaces and banknotes, nor after seven days on stainless steel and plastic. Surprisingly, the infectious virus was detected in the outer layer of a surgical mask after seven days.

Possible risks of transmission of COVID-19 in elevators

By sharing an elevator, an infected person (either symptomatic or asymptomatic) can infect another by small drops if the safe distance cannot be maintained. But for the transmission it is not even necessary to share the elevator: it is enough to be in contact with a previously contaminated surface. An expert in air quality and ventilation has come to ensure that people could become infected in elevators in just a few seconds without direct contact.

Theoretically, drops and contaminated surfaces can be avoided by allowing only one person per trip and with good hand hygiene. However, if aerosols are confirmed to transmit the disease, a person could become infected despite taking these preventive measures.

Dr. Richard Corsi, an expert in building pollution control, modeled the virus concentration after an infected person traveled to the 10th floor while coughing and the elevator returned to the 1st floor. The person on the first floor is exposed to 25% of the viral load that the previous passenger ejected on his trip. Unfortunately, there is no scientific post on the job – just a discussion on his Twitter account and in his interview in the New York Times.

Corsi's calculations are based on standard mass balance models. For further study, we recommend the work of Brigham et al. (2019) modeling a 3D elevator with fluid dynamics. In this work, there are different recommendations on the design of the elevator to reduce the risk of transmission of airborne diseases.

Limited evidence on the real risk of transmission in elevators

Scientific evidence is limited on the actual risk of Covid-19 transmission during vertical transport within buildings. At the moment, it is mainly focused on public buildings such as hospitals and shopping centers. These studies generally mention the possibility of transmission within the elevators, but without giving details or doing a thorough study.

Previous work on SARS gives us some clues. One of the works analyzes the transmission in a building block and shows that the probability of infection in the upper and middle floors of a block is significantly higher, although it does not explore the effect of the elevator or the stairs. Another study, with a focus on the same outbreak, considers that vertical transmission took place from window to window during home ventilation. Although he also mentions the risk of contagion in the elevators, which were located in the center and were common to the buildings.

What happens to the current pandemic? At the moment the press has already echoed a case of SARS-Cov-2 transmission in an elevator. It is interesting to note that it is suspected that the infection occurred in an adult without a mask who shared the elevator with an infected person, but not in children who did wear masks. With such data, none of the transmission mechanisms can be ruled out, but it raises the suspicion that the use of masks could be an effective protection measure.

However, few technical reports have recommended concrete measures to prevent the transmission of COVID-19 in the elevators. One is the British Columbia Center for Canadian disease control, which recommends a minimum distance between users of 2 meters, and that the permitted number of people should be advertised on a sign on the elevator door. The report even provides infographics to post on elevator doors.

Number of lifts per inhabitant in countries affected by COVID-19

Even if the risk of transmission were high when traveling vertically in buildings, it would only be significant in those cities where this transport is more frequent.

As already mentioned, Spain, followed by Italy, is the country with the most lifts per inhabitant (France is the sixth). Countries like Germany have a high population, but their inhabitants live more dispersed or in low buildings, many of them without lifts.

Another fact that makes one suspect the importance of elevator transport is that New York City is the most affected in the US. USA And it is not by chance that it is nicknamed "vertical city". The two exceptions appear to be Korea and Japan, two of the countries with the lowest COVID-19 death rates. The massive use of masks could justify this difference.

The correlation between official deaths as of April 23, 2020 and the number of lifts for different countries in Europe has been tested with various statistical tests. The correlation is significant, although still insufficient. Especially since it coincides that cities with high population density have more elevators. And that density could be the real cause.

To reach a more solid conclusion it would be interesting to study other factors, such as the average transport time and the type of elevator (cabin volume, ventilation, automatic door closing …). For this, fluid dynamics simulations could be used.

It would also be interesting to carry out the statistical study with more countries and, above all, to try to obtain data on cities with a more homogeneous distribution of inhabitants and lifts than an entire country.

More research is needed

In any case, we consider that the effect of vertical transport on the transmission of the Covid-19 should be urgently studied. Fundamentally to confirm if the transmission is greater in the so-called "vertical cities" like New York or in cities with many lifts like Spain and Italy.

Measures such as the use of masks in these spaces, informative posters with the maximum number of users on each trip or the use of stairs as an alternative to elevators (generally more open spaces) could, therefore, reduce this contagion rate in these vertical cities.

A version of this article has been published on the madri + d Knowledge Foundation blog.

Míriam R García, Researcher in the process engineering group, Institute of Marine Research (IIM-CSIC); Antonio Figueras Huerta, Research Professor at the Higher Council for Scientific Research, Institute of Marine Research (IIM-CSIC) and Jim Grant, Teagasc

This article was originally published in The Conversation. Read the original.