Dr PJB Scott and Dr Michael Davies
25th December, 2021
Dr PJB Scott, BA, BSc, PhD., trained in biology and oceanography in Canada. Dr Scott has, for many years, studied the effects of organisms, particularly micro-organisms, on structures in underwater and wet environments and has extensive industrial experience in identification and remediation techniques of microbial attack of materials.
Eur Ing, Dr Michael Davies PhD, MSc, MIMMM, CEng, PEng (Ont) originally trained as a metallurgist and has specialised in materials engineering, corrosion, failure analysis and inspection. He has had extensive experience in these fields in chemical process, oil and gas, marine, power and pulp and paper. He has been a member of the KJA team since 2012.
Early in 2021 a scientific review was carried out for KJA on the transmission of the Covid 19 virus and its implications for elevator use.1 (Link to prior posting here) This was followed up by an article on the same topic published in Elevator World.2 Since then, much more has been learned world-wide about this virus and there have been a number of mutations that have affected its spread. This article updates the latest state of knowledge and what effect it may have on the safe use of elevators.
It is now agreed by scientists and researchers that Covid-19 transmission is largely airborne rather than from contact with surfaces. This is probably even truer with Omicron, so methods to prevent the release of airborne particles and to remove them as quickly as possible are now the main defences to keep elevators safe.
This confirms that ventilation is an extremely important factor while behavioural changes of elevator users, such as mask wearing, not talking, social distancing and increased testing are also key defences.
1. Omicron Variant
Omicron, a World Health Organization variant of concern, was first detected by South African scientists in November, 2021. It has since been reported in most countries in the world and is rapidly becoming the dominant variant worldwide. A report from the Imperial College London COVID-19 response team estimates that the risk of reinfection with the Omicron variant is 5.4 times greater than that of the Delta variant. 3 The protection against reinfection by Omicron afforded by past infection may be as low as 19%. Researchers estimated the growth and immune escape of the Omicron variant in England. They used data from the UKHSA and NHS for all PCR-confirmed SARS-CoV-2 cases in England who had taken a COVID test between November 29th and December 11th 2021. Estimated doubling time of the Omicron variant was less than 2.5 days with a reproduction number (R) of 3.
While it is widely accepted that the Omicron variant is more transmissible than the original strains the actual degree of increase is not yet fully understood. A recent Japanese study found that the Omicron strain is 4.2 times more contagious than the Delta strain.4
The reason for this increased transmission may be due in part to the more successful colonization by the virus of the upper respiratory tract. A team at Imperial College London found that the SARS-CoV-2 Omicron variant has increased replicative fitness in primary cells derived from human upper respiratory tract compared to the previously dominant Delta variant. This suggests that at least part of the rapid growth of Omicron observed in UK in the face of a preceding Delta wave is due to high transmissibility of the virus between people resulting from efficient nasal replication. This, acting in combination with evasion of control by pre-existing neutralizing antibodies suggests that Omicron is likely to spread rapidly regardless of prior vaccine or infection status, and will require a combination of nonpharmaceutical intervention measures for effective control in the community.5
The risk of hospitalization is less for those catching the Omicron variant than those catching the Delta variant. The reduction is 20 to 25% decrease in hospital attendance and 40 to 45% for hospital stays of one day or more.6 Because of its increased transmissibility and escape from antibodies generated by vaccination or previous infection, however, the risk remains a threat to hospital resources.
Symptoms experienced by those testing positive for Covid-19 now so closely resemble those of a common cold that the likelihood of people recognizing that they have the virus is greatly reduced. The symptoms of the original Covid 19 virus were a high temperature and a new, continuous cough. There was also likely to be a loss or change of taste or smell. Since then, the ZOE Covid study in the UK has been monitoring symptoms and their current list of top symptoms for people who test positive is:7
- Runny nose
- Sore throat
These symptoms are similar for vaccinated and unvaccinated individuals. Loss of smell and/or taste and fever are less common symptoms in the initial stages of infection by Omicron than they were for Delta. In the UK in late December, 2021, one out of two people with cold-like symptoms tested positive for Covid-19.
How airborne particles behave in elevators
Increased transmissibility of the virus makes it crucial to understand the behaviour of airborne particles in enclosed spaces. A 2021 fluid dynamics study of how particles behave in enclosed elevators has highlighted that particle removal through ventilation is complex. There are many variables in the operation of ventilation systems within elevators, such as placement of inlet and outlet vents, the number of people in the elevator and their position in the cabin. How some of these factors influence movement of particles has been studied by a team of physicists. They experimented with virus particle behaviour in enclosed elevators under various ventilation combinations with and without air purification (Table 1). Although limited in scope to only one occupant, researchers attempted to find which ventilation regime best avoids airborne virus transmission (AVT). 8
TABLE 1. All the applied ventilation scenarios for the operating conditions in Figure 1 below.
Figure 1. Geometry showing the different inlets and outlets (δz = 3 cm opening) defined for the 3D computation domain. A subject is standing in the elevator’s cabin such that his mouth as a coughing source is positioned at x = 0 m, y = 0.41 m, z = 1.6 m. An air purifier (sanitizer) is attached to the wall at about 1.9 m above the ground of the elevator’s cabin. The air purifier has an air intake (outlet 4) and an air exhaust (inlet 4) for air circulation at ≈60 m3/h.
The placement of ventilation inlets and outlets influences the flow circulation and droplet dispersion significantly. The researchers found that a single inlet at the top of the elevator and a single outlet at the bottom produced the best method for removing particles generated by a light cough (Figure 2).
The air purifier reduces the droplet dispersion but will not eliminate it. The air intake integrated inside the purifier equipment induces flow circulation that can add to the transport of contaminated saliva droplets in the cabin. The time required for droplets reaching the floor of the elevator could be larger than the time necessary to deactivate the virus by other means, such as UV radiation. The effect increases when more infected persons enter the elevator. Thus, the air purifier design must be optimal for reducing flow circulation.
Furthermore, a smaller number of people being in an elevator will minimize droplet spread and its impact on each subject. Also, the subject’s position inside the cabin influences the flow circulation and droplet spread.
The overall practical conclusion is that the placement and design of the air purifier and ventilation systems significantly affect the droplet dispersion and AVT. Thus, engineering designs of such systems must take into account the flow dynamics in the confined space the systems will be installed.
Figure 2. For each pictured (A, B, C, D) Top row: front view. Middle row: top view. Bottom row: side view. Contaminated saliva droplets are illustrated in black after being scaled by a factor of about 250 with respect to their actual size. Subject position 1 corresponds to a person who is standing in the elevator’s cabin such that her/his mouth as a coughing source is positioned at x = 0 m, y = 0.41 m, z = 1.6 m.
Conclusions and current recommendations on risk reduction
Increased rapid growth of the Omicron variant in human upper respiratory tracts suggests that ventilation, reduction in elevator capacity and mask wearing are currently the main defences against transmission of Covid-19 in elevators. Although normal cleaning regimes and hand sanitizing are important, the advice remains the same as our earlier paper – ventilation is key and has now been shown to be even more important. This can be achieved by:
- keeping elevator doors open when idle and for longer when in use where this is possible under local codes,
- leaving ventilation system on during idle operation,
- decreasing elevator capacity by encouraging stair use,
- reducing permitted elevator loading
We understand that any of these options will incur extra costs and inconvenience users but resources would be better spent on these options than in copper cladding of surfaces or installing contactless buttons. While air purification systems may help, they cannot be relied upon to prevent airborne transmission.
The position of the air inlets and outlets significantly influences the flow circulation and droplet dispersion and the chance of transmitting an airborne virus infection. Careful attention to design and operation of ventilation systems is important in reducing the time airborne particles remain present.
Behavioural changes of elevator users can also significantly reduce AVT. Office tenants using elevators should be encouraged to take frequent tests to ensure that they are not infected, particularly if they have any cold or flu-like symptoms. Testing, either by the faster but slightly less accurate lateral flow test (LFT), also called the rapid antigen test (RAT), or the more accurate but slower Polymerase Chain Reaction (PCR) test may be an important weapon in avoiding transmission of the virus. Mask wearing and not talking inside the elevator will also reduce particle dispersion.
The above article provides an updated view based on newer and more recent findings and provide updated guidance from our prior article here. If you need more information regarding the topic and would like to know more and how to properly and safely manage your elevators for your tenants, please don’t hesitate to contact us.
List of references and sources:
1 Dr Michael Davies and Dr PJB Scott, “Elevators and COVID transmission: a scientific review” January, 2021, KJA web site, https://www.kja.com/2021/01/19/elevators-and-covid-transmission-a-scientific-review/
2 Dr Michael Davies and Dr PJB Scott, “Keeping Elevators Safe from Infections”. Elevator World, LX1X, 4th,April (2021) pp. 84-90.
3 Neil Ferguson, Azra Ghani, Anne Cori, Alexandra Hogan, Wes Hinsley, Erik Volz, Report 49 – Growth, population distribution and immune escape of Omicron in England Imperial College London Report 49 16 December, 2021. https://www.imperial.ac.uk/mrc-global-infectious-disease-analysis/covid-19/report-49-Omicron/
4 Anon, reported in Bloomberg, “Japan study confirms omicron variant’s high transmissibility: report” https://www.marketwatch.com/story/japan-study-confirms-omicron-variants-high-transmissibility-report-2021-12-09 9th December, 2021.
5 Jonathan Brown, Jie Zhou, Thomas P. Peacock, Wendy S Barclay, Imperial College London: Omicron vs Delta replication 19 December, 2021: The SARS-CoV-2 variant, Omicron, shows enhanced replication in human primary nasal epithelial cells. 23 December, 2021. https://www.gov.uk/government/publications/imperial-college-london-omicron-vs-delta-replication-19-december-2021/imperial-college-london-omicron-vs-delta-replication-19-december-2021
6 Neil Ferguson1, Azra Ghani, Wes Hinsley and Erik Volz, Report 50 – Hospitalisation risk for Omicron cases in England. College London Report 50, 22 December, 2021. https://www.imperial.ac.uk/mrc-global-infectiousdisease-analysis/covid-19/report-50-severity-omicron/
7 Zoe Covid Study Weekly update 22 December, 2021. https://www.youtube.com/watch?v=CIGC310hPoI
8 Talib Dbouk and Dimitris Drikakis, “On airborne virus transmission in elevators and confined spaces,” Phys. Fluids 33, 011905 (2021); doi: 10.1063/5.0038180