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St John’s scientist leads research to reduce airborne Covid-19 spread in emergency hospitals

“Our work aims to highlight simple yet effective solutions that are relatively easy to install, implement, service and maintain.”

Cambridge scientists say low tech changes in makeshift emergency hospitals can reduce the dispersal of airborne Covid-19.

Professor Andrew Woods, Fellow of Mathematics at St John’s and Head of the BP Institute, led a study with Professor Alan Short of the Department of Architecture to find ventilation designs and ward configurations to reduce virus dispersal.

Emergency wards are being converted from large air-conditioned halls which tend to have top-down air-conditioning. This creates turbulent flows that can mix and spread droplets containing the virus very widely. In this setting it may take over 20 minutes to dilute the concentration of smaller droplets produced in a cough to below a tenth of their original density, which is plenty of time for droplets to travel beyond 20 metres. This puts healthcare professionals in particular at risk as they move through them.

Professor Woods and Professor Short have developed a series of practical solutions to reduce the concentration of airborne viruses in buildings converted into makeshift wards.

“Governments, healthcare decision-makers and construction workers are facing an extreme challenge in the urgent need to construct emergency hospitals,” says Woods.

“Our work aims to highlight simple yet effective solutions that are relatively easy to install, implement, service and maintain.”

The designs, released in a video report, involve relatively low-tech adaptations to ventilation systems and ward configuration, and are relevant for use in the UK and overseas.

The team’s recommendations are based on laboratory experiments that tested ventilation systems for two basic arrangements of beds. One involves placing hundreds of beds in an open hall with low-level partitions while the other sees beds within enclosed patient bays.

In the completely open version, ventilation air (yellow in the image) moves down to the ground and spreads out over the patient beds, leading to a highly mixed environment. When a patient coughs (red) or releases aerosols, the flow pattern of the aerosols can extend across the space to other patient beds, even to patients across the corridor.

open wards

open wards cough

The researchers found that in the enclosed bays, the ventilation flow still comes down from the ceiling (green) and moves into the patient bed-spaces and mixes. However, a good proportion of this air is removed through exhaust ducts located behind the beds. When a patient produces aerosols within a bay (orange), the aerosol concentration remains high in the bay and air is drawn out through the exhaust duct, limiting the aerosol transport into the main space.

subdivided ward

subdivided ward cough

“In a large hall, airflows mix up the airborne aerosols all too efficiently and disperse them through the space across patients and perhaps more significantly nurses and healthcare workers,” explains Woods. “A small measure, such as the installation of part-enclosed patient bays with exhaust ducts can help reduce this dispersion.”

“We’ve developed viable low energy ventilation models for converted spaces in many other climate regions from Temperate Northwest to the Mediterranean, from Continental climates in China and central India to the Mid-West of North America, Canada and marine coastal climates globally,” adds Short.

In particular, the Cambridge team is working with Professor L.S. Shashidhara, Dean of Research at Ashoka University, and advisor to the Indian government and architect C.S. Raghuram, to create viable conversions of marriage halls and sheds as emergency COVID-19 hospitals in India.

“Crucially, the measures we suggest are simple to implement as part of a rapid interior remodelling plan,” says Short. “Our research shows that a small number of straightforward modifications would reduce risk in what is already a very risky environment.”

The research, which has not been peer-reviewed, was carried out in collaboration with colleagues at the University of Cambridge's Interdisciplinary Research Centre in Infectious Diseases

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Published: 30/4/2020

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