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Simple, low-cost ventilation designs and configuration of wards can reduce the dispersal of airborne virus in emergency COVID-19 hospitals converted from large open spaces, say researchers at the University of Cambridge.
However, large air-conditioned halls tend to have top-down air-conditioning, which creates turbulent flows that can mix and spread droplets containing the virus very widely. At six full changes of the air in the hall in an hour, 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. This, say the researchers, is plenty of time for droplets to travel beyond 20m, putting healthcare professionals in particular at risk as they move about through “a slowly refreshing miasma”.
Professor Andrew Woods FRS of Cambridge’s BP Institute (BPI) and Professor Alan Short of the Department of Architecture have developed a series of practical solutions to reduce the concentration of airborne virus experienced by patients and healthcare workers in buildings converted into makeshift wards.
The designs, released today 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 recommends subdividing the large floorplate of a typical hall into enclosed patient zones, a minimum of 16 metre square, with some 10-20 beds separated by solid partitions up to 3 metre height, and lighter clear polythene sheeting above taped up to prevent air leaking in or out. Air is drawn through the back of the patient bays by an outflow ventilation duct, removing dirty air from the space and providing a clean corridor space for healthcare workers.
“Effective ventilation is critically important in helping to suppress cross-infection, and nowhere more so than in an infectious diseases ward,” says Short. “Patients coughing or being ventilated will project droplets, some containing the virus, as an aerosol. They are so small that they may take tens of minutes to fall to the floor as the droplet evaporates in still air.”
“Governments, healthcare decision-makers and construction workers are facing an extreme challenge in the urgent need to construct emergency hospitals,” adds Woods, Director of the interdisciplinary BPI. “Our work aims to highlight simple yet effective solutions that are relatively easy to install, implement, service and maintain.”
The team’s recommendations are based on physical laboratory experiments to test ventilation systems for two basic arrangements of beds: what is becoming a standard approach of placing hundreds of beds in an open hall with low level partitions, compared with arranging beds within enclosed patient bays so that, as far as possible, the exhaust air does not permeate the rest of the hall.
In the completely open version, ventilation air moves down to the ground and spreads out over the patient beds, leading to a highly mixed environment. When a patient coughs or releases aerosols, the flow pattern of the aerosols can extend across the space to other patient beds, even to patients across the corridor.
In the version subdivided into patient bays, the ventilation flow still comes down from the ceiling and moves into the patient bed-spaces and mixes, but a good proportion of this air is removed through exhaust ducts located behind the beds. When a patient produces aerosols within a bay, the aerosol concentration remains high in the bay and as air is drawn out through the exhaust duct this limits the aerosol transport into the main space.
“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.”
“The strategies will work in many different climates,” adds Short. “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.”
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.”
Because of the urgent need to share information relating to the pandemic, the researchers have released their preliminary report now, ahead of submitting to a peer-review journal. However, the designs are based on decades of research by Woods and Short on how particles like viruses are transported in mechanically ventilated spaces. Two key publications:
- Mingotti, N. and Woods, A.W. (2015) On the transport of heavy particles through an upward displacement-ventilated space. J. Fluid Mechanics 772: 478-507
- Short, C.A. (2017) The Recovery of Natural Environments in Architecture: Air, Comfort and Climate. Routledge, Abingdon, UK, [ISBN 978 1 138 65146 3]
The research was carried out in collaboration with colleagues at the Interdisciplinary Research Centre in Infectious Diseases, University of Cambridge.
ENDS
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About the University of Cambridge
The mission of the University of Cambridge is to contribute to society through the pursuit of education, learning and research at the highest international levels of excellence. To date, 109 affiliates of the University have won the Nobel Prize.
Founded in 1209, the University comprises 31 autonomous Colleges, which admit undergraduates and provide small-group tuition, and 150 departments, faculties and institutions. Cambridge is a global university. Its 19,000 student body includes 3,700 international students from 120 countries. Cambridge researchers collaborate with colleagues worldwide, and the University has established larger-scale partnerships in Asia, Africa and America.
The University sits at the heart of the ‘Cambridge cluster’, which employs 60,000 people and has in excess of £12 billion in turnover generated annually by the 4,700 knowledge-intensive firms in and around the city. The city publishes 341 patents per 100,000 residents.
Original post https://alertarticles.info
