Otis Worldwide Corporation, a leading company for elevator and escalator manufacturing, installation and service, recently released the results of a three-month academic study that investigates how elevator airflow affects potential exposure to the Covid-19 virus and a science-based approach for how to mitigate that exposure in elevators.
The findings show the significant amount of air exchange present in most elevators combined with simple mitigation strategies – including all riders properly wearing a surgical-style mask1 and the installation of a common type of air purification system2 – puts an elevator ride on the lower end of the exposure spectrum.
The study concludes that a short elevator ride represents a relatively low risk of exposure compared to several everyday activities – less than outdoor dining and comparable to a trip to the supermarket – when simple mitigation is in place, according to Otis.
With science continuing to point to respiratory droplets and aerosols as a principal means of transmission, the study focused on airflow and the impact of ventilation rates and types, purification technologies (specifically needlepoint bipolar ionisation - NPBI) and the proper use of masks, says the leading elevator manufacturer.
The study was led by Dr Qingyan (Yan) Chen, the James G Dwyer Professor of Mechanical Engineering at Purdue University in the US, who is widely recognised for his research into the spread of infectious disease through indoor air systems – and how to prevent it.
Dr Chen uses sophisticated computational fluid dynamic (CFD) modelling in his research, which has focused on indoor environments, aircraft cabins and building design and analysis. He has published three books and over 470 journal and conference papers.
Dr Chen and team looked at likely exposure to the virus, which can be quantified by the frequency, duration and intensity of exposure. The duration of a typical elevator ride is short – usually less than a minute. Multiple scenarios of two-minute elevator rides were modelled to assess relative risk, says Otis.
Intensity of exposure is impacted by the level of air exchange or ventilation. Elevators have significant air exchange by design, compared to many other indoor spaces, and are required by code to have openings for ventilation. Many elevators also have fans to increase ventilation.
“Air exchange is important. Our findings concluded that the higher ventilation in an elevator, relative to the compared activities, results in lower exposure opportunity. If all passengers properly wear masks, the relative exposure risk drops 50 per cent. Air purification, called NPBI, can reduce this by an additional 20-30 per cent,” says Dr Chen. “We compared the relative exposure risk of elevators to other common activities in a typical workday, including an hour-long bus ride and eight hours in an office environment. Riding an elevator was a lower exposure risk activity, given the short duration of an elevator ride.”
Qualitative comparisons place riding an elevator with all passengers wearing masks in a low exposure risk category, with a relative risk similar to that of shopping in a supermarket, Otis adds.
“Elevators are an essential part of everyday life for many, often the first leg in your journey and the last on your route home. We know many passengers have questions about exposure risks associated with riding an elevator, and we want to provide answers verified by science,” says Robin Fiala, Vice President, Marketing and Sales. “We’re sharing the study results broadly in advance of publication to keep riders well-informed and limit misconceptions.”
More details of the elevator airflow study, including a technical whitepaper, are available on otis.com. The full technical report, authored by the Purdue University research team, is available by request and expected to be published in a peer-reviewed academic journal later this year.
1. All riders properly wearing (nose and mouth covered) surgical-style masks as recommended by the World Health Organization as compared to no riders wearing masks.
2. Air purification called needle point bipolar ionization (NPBI) as compared to elevators without NPBI air purification.