̽��ֱ�� of Cambridge - ventilation

No ��safest spot�� to minimise risk of COVID-19 transmission on trains

sc604 — Wed, 22 Jun 2022 04:00:00 +0000

̽��ֱ��researchers, from the ̽��ֱ�� of Cambridge and Imperial College London, developed a mathematical model to help predict the risk of disease transmission in a train carriage, and found that in the absence of effective ventilation systems, the risk is the same along the entire length of the carriage.

̽��ֱ��model, which was validated with a controlled experiment in a real train carriage, also shows that masks are more effective than social distancing at reducing transmission, especially in trains that are not ventilated with fresh air.

̽��ֱ��results, reported in the journal Indoor Air, demonstrate how challenging it is for individuals to calculate absolute risk, and how important it is for train operators to improve their ventilation systems in order to help keep passengers safe.

Since COVID-19 is airborne, ventilation is vital in reducing transmission. And although COVID-19 restrictions have been lifted in the UK, the government continues to highlight the importance of good ventilation in reducing the risk of transmission of COVID-19, as well as other respiratory infections such as influenza.

��In order to improve ventilation systems, it��s important to understand how airborne diseases spread in certain scenarios, but most models are very basic and can��t make good predictions,�� said first author Rick de Kreij, who completed the research while based at Cambridge��s Department of Applied Mathematics and Theoretical Physics. ��Most simple models assume the air is fully mixed, but that��s not how it works in real life.

��There are many different factors which can affect the risk of transmission in a train �C whether the people in the train are vaccinated, whether they��re wearing masks, how crowded it is, and so on. Any of these factors can change the risk level, which is why we look at relative risk, not absolute risk �C it��s a toolbox that we hope will give people an idea of the types of risk for an airborne disease on public transport.��

̽��ֱ��researchers developed a one-dimensional (1D) mathematical model which illustrates how an airborne disease, such as COVID-19, can spread along the length of a train carriage. ̽��ֱ��model is based on a single train carriage with closing doors at either end, although it can be adapted to fit different types of trains, or different types of transport, such as planes or buses.

̽��ֱ��1D model considers the essential physics for transporting airborne contaminants, while still being computationally inexpensive, especially compared to 3D models.

̽��ֱ��model was validated using measurements of controlled carbon dioxide experiments conducted in a full-scale railway carriage, where CO2 levels from participants were measured at several points. ̽��ֱ��evolution of CO2 showed a high degree of overlap with the modelled concentrations.

̽��ֱ��researchers found that air movement is slowest in the middle part of a train carriage. ��If an infectious person is in the middle of the carriage, then they��re more likely to infect people than if they were standing at the end of the carriage,�� said de Kreij. ��However, in a real scenario, people don��t know where an infectious person is, so infection risk is constant no matter where you are in the carriage.��

Many commuter trains in the UK have been manufactured to be as cheap as possible when it comes to passenger comfort �C getting the maximum number of seats per carriage. In addition, most commuter trains recirculate air instead of pulling fresh air in from outside, since fresh air has to be either heated or cooled, which is more expensive.

So, if it��s impossible for passengers to know whether they��re sharing a train carriage with an infectious person, what should they do to keep themselves safe? ��Space out as much as you reasonably can �C physical distancing isn��t the most effective method, but it does work when capacity levels are below 50 percent,�� said de Kreij. ��And wear a high-quality mask, which will not only protect you from COVID-19, but other common respiratory illnesses.��

̽��ֱ��researchers are now looking to extend their 1D-model into a slightly more complex, yet still energy-efficient, zonal model, where cross-sectional flow is characterised in different zones. ̽��ֱ��model could also be extended to include thermal stratification, which would offer a better understanding of the spread of an airborne contaminant.

̽��ֱ��research was funded in part by the Engineering and Physical Sciences Research Council (EPSRC), part of UK Research and Innovation (UKRI).

Reference:
Rick JB de Kreij et al. ��Modelling disease transmission in a train carriage using a simple 1D-model.�� Indoor Air (2022). DOI: 10.1111/ina.13066

Researchers have demonstrated how airborne diseases such as COVID-19 spread along the length of a train carriage and found that there is no ��safest spot�� for passengers to minimise the risk of transmission.

We hope this research will give people an idea of the types of risk for an airborne disease on public transport

Rick de Kreij

Seksan Mongkhonkhamsao via Getty Images

Woman wearing a mask on public transport

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. Images, including our videos, are Copyright ? ̽��ֱ�� of Cambridge and licensors/contributors as identified.? All rights reserved. We make our image and video content available in a number of ways �C as here, on our main website under its Terms and conditions, and on a range of channels including social media that permit your use and sharing of our content under their respective Terms.

Yes

Curbing COVID-19 in schools: Cambridge scientists support CO2 monitor rollout

sc604 — Mon, 17 Jan 2022 12:44:06 +0000

Scientists from Cambridge, Surrey and Imperial College London are supporting the rollout of portable monitors to UK schools as part of project CO-TRACE. ̽��ֱ��researchers behind the collaboration have produced materials to help teachers use the monitors, which have been rolled out to schools nationwide.

̽��ֱ��level of carbon dioxide (CO₂) in a closed space is a good indicator of air quality and can signpost the need for ventilation. As the virus that causes COVID-19 is airborne, ensuring the air is properly refreshed using ventilation is crucial for reducing its spread. ̽��ֱ��device displays levels of CO2 and colour coding to indicate good, normal, or poor ventilation. Well ventilated spaces should have CO2 levels consistently below 800 parts per million (ppm), with readings above 1500ppm indicating poor ventilation or overcrowding.

��CO2 monitors allow teachers to assess the ventilation in their classrooms for the first time,�� said Imperial��s Dr Henry Burridge, co-investigator on the project. ��This is especially important during colder months when ventilation is typically lower due to colder outdoor temperatures, causing COVID-19 and other airborne diseases like the common cold and flu to linger and spread more easily.��

̽��ֱ��monitors mean teachers can see CO2 levels change in real-time as windows are opened and air is refreshed, allowing them to balance ventilation and warmth. Teachers can also use the monitors to know when it is safe to close windows slightly, which could help them keep classrooms more comfortable. As well as being a good ��proxy�� for ventilation, lower CO2 levels have been linked to improved learning outcomes and better cognitive performance.

̽��ֱ��team behind the CO-TRACE project uses experimental modelling, numerical simulations, full-scale observations, and infection risk modelling to understand how the potential for COVID-19 spread changes with indoor air flows, ventilation levels, and the number of people in a space. In 2021, the researchers used monitored CO2 to indicate how much exhaled breath was present within classrooms, and their models found that seasonal variation in classroom ventilation levels could lead to airborne infection risks in winter being roughly double those in summer. This highlights that monitoring excess CO2 could be of significant benefit in mitigating airborne infection risk.

̽��ֱ��portability of the CO2 monitors, supplied by the Department for Education (DfE), means schools can move them around to test different areas, starting with those they suspect may be poorly ventilated.

�� ̽��ֱ��monitors empower teachers to strike a balance between good ventilation and warmth during winter,�� said Professor Paul Linden from Cambridge��s Department of Applied Mathematics and Theoretical Physics, co-investigator on the programme. ��We are pleased that the Government is taking evidence-based action to address air quality and COVID-19 spread in schools.��

̽��ֱ��monitors are accompanied by advice from the project which guides appropriate actions from teacher based on the CO2 readings in classrooms. Recommendations include opening higher windows before lower ones, and closing windows slowly when ventilation is good.

Schools with areas that are consistently low in air quality despite ventilation should consider using air cleaners. For such schools, the DfE is distributing between 7,000 and 8,000 air cleaning units.

When the project was announced in 2021, then-Education Secretary Gavin Williamson said: ��Providing all schools with CO2 monitors will help them make sure they have the right balance of measures in place, minimising any potential disruption to education and allowing them to focus on world-class lessons and catch up for the children who need it. By keeping up simple measures such as ventilation and testing, young people can now enjoy more freedom at school and college.��

̽��ֱ��project is funded by the EPSRC, part of UK Research and Innovation (UKRI).

Adapted from an Imperial College story.

UK schools have received more than 300,000 CO2 monitors as part of a government initiative to reduce COVID-19 spread in classrooms.

̽��ֱ��monitors empower teachers to strike a balance between good ventilation and warmth during winter

Paul Linden

Olivier Le Moal

CO2 monitor

Yes

Interactive tool helps you decide how to protect yourself and others from COVID-19

sc604 — Thu, 02 Dec 2021 00:08:47 +0000

A new interactive graphic developed by UK researchers and published by ̽��ֱ��BMJ will help people decide what to do in everyday situations to protect themselves, and others, from COVID-19.

Based on estimates provided by 26 international experts, it shows the different pathways that may be taken by the virus that causes COVID-19 when it transfers between two people.

It is designed to help illustrate the risks of catching COVID-19 in different scenarios - and what can be done to reduce those risks - based on the available evidence.

As well as the areas of scientific consensus, it also conveys the uncertainties and the disagreement that exists between experts about how the virus behaves, how it is transmitted, and how we can best reduce the likelihood of transmission through personal and social measures.

̽��ֱ��researchers say the tool should support decision-makers and the public to make informed decisions about how to reduce virus transmission in different contexts, such as how to make a workplace or a public area as safe as it can be while still being open and functional.

To create the tool, the researchers, led by the ̽��ֱ�� of Cambridge, consulted 26 experts from a range of disciplines and countries, asking them for every value needed to underpin the graphic.

These included the importance of different virus transmission routes (eg. small and large airborne droplets, contact with contaminated surfaces) during a range of activities (eg. talking, coughing, exercising, eating) in different environments (eg. outdoors or indoors in different sized rooms, with or without ventilation).

They also gathered estimates on the importance of different protective measures, such as face coverings and screens, physical distancing, hand hygiene, surface cleaning, in reducing transmission.

Analysis of all the values showed that airborne transmission routes were most important in almost all situations, while face coverings, especially when worn by an infected person as a form of source control, were the most important mitigation measure.

But importantly, all routes were considered to play a part in transmission, and simple measures such as physical distancing, hand washing, and respiratory hygiene all made a useful contribution.

̽��ֱ��researchers found important evidence gaps and differences in opinion among experts around several variables, including the role of aerosol transmission; the effects of different kinds of masks on inhaled aerosols; and the effects of face coverings on transfer from hand to eyes, nose, and mouth.

��Everyone has been keen to know how much difference each possible action we��ve been told about makes, and finally we have been able to gather together enough knowledge from experts from around the world and in a range of fields to answer those questions,�� said co-lead author Dr Alexandra Freeman from Cambridge��s Winton Centre for Risk & Evidence Communication.

She added: �� ̽��ֱ��tool is interactive, so that you can explore the scenarios that are most relevant to you, whether it��s because you sing in a choir, or want to know about the risks of eating in a small restaurant. How much difference would it make if you opened the windows, or cleaned the surfaces? Have a look and find out.��

��It is all too easy to focus on just a single route of spread for COVID and forget about all the others,�� said co-author Harry Rutter from the ̽��ֱ�� of Bath. ��One of the ways a tool like this can help is by making it clear that all the transmission routes matter, in different proportions in different contexts. ̽��ֱ��fact that one of those routes - airborne transmission - is the main one in most situations doesn��t mean that we can ignore the others.��

̽��ֱ��authors acknowledge some study limitations and say generating robust evidence on the complex and highly contingent routes of COVID-19 virus transmission is not straightforward. But they say they hope their approach will prove helpful to those faced with the challenge of communicating complex, imprecise, and uncertain evidence in the future.

̽��ֱ��research was supported by the PROTECT COVID-19 National Core Study on transmission and environment (managed by the Health and Safety Executive on behalf of HM Government), and the David and Claudia Harding Foundation.?Cambridge co-authors on the paper also included Dr Shaun Fitzgerald from the Department of Engineering and Professor David Spiegelhalter from the Winton Centre for Risk and Evidence Communication.

Reference:
Alexandra LJ Freeman et al. ��Expert elicitation on the relative importance of possible SARS-CoV-2 transmission routes and the effectiveness of mitigations.�� BMJ Open (2021). DOI: 10.1136/ bmjopen-2021-050869

Harry Rutter et al. ��Visualising SARS-CoV-2 transmission routes and mitigations.�� BMJ (2021). DOI: 10.1136/bmj-2021-065312

Adapted from a BMJ press release.?

Is it risky to sing in a choir? What are the risks of eating in a small restaurant? How much difference does it make to open windows or clean surfaces? New interactive tool helps people make decisions on COVID-19.

Everyone has been keen to know how much difference each possible action we��ve been told about makes, and finally we have been able to gather together enough knowledge from experts from around the world and in a range of fields to answer those questions

Alexandra Freeman

Will Stahl-Timmins, ̽��ֱ��BMJ

COVID-19 risk calculator

Yes

Two-metre COVID-19 rule is ��arbitrary measurement�� of safety

sc604 — Tue, 23 Nov 2021 15:54:09 +0000

A team of engineers from the ̽��ֱ�� of Cambridge used computer modelling to quantify how droplets spread when people cough. They found that in the absence of masks, a person with COVID-19 can infect another person at a two-metre distance, even when outdoors.

̽��ֱ��team also found that individual coughs vary widely, and that the ��safe�� distance could have been set at anywhere between one to three or more metres, depending on the risk tolerance of a given public health authority.

̽��ֱ��results, published in the journal Physics of Fluids, suggest that social distancing is not an effective mitigation measure on its own, and underline the continued importance of vaccination, ventilation and masks as we head into the winter months in the northern hemisphere.

Despite the focus on hand-washing and surface cleaning in the early days of the pandemic, it��s been clear for nearly two years that COVID-19 spreads through airborne transmission. Infected people can spread the virus through coughing, speaking or even breathing, when they expel larger droplets that eventually settle or smaller aerosols that may float in the air.

��I remember hearing lots about how COVID-19 was spreading via door handles in early 2020, and I thought to myself if that were the case, then the virus must leave an infected person and land on the surface or disperse in the air through fluid mechanical processes,�� said Professor Epaminondas Mastorakos from Cambridge��s Department of Engineering, who led the research.

Mastorakos is an expert in fluid mechanics: the way that fluids, including exhaled breath, behave in different environments. Over the course of the pandemic, he and his colleagues have developed various models for how COVID-19 spreads.

��One part of the way that this disease spreads is virology: how much virus you have in your body, how many viral particles you expel when you speak or cough,�� said first author Dr Shrey Trivedi, also from the Department of Engineering. ��But another part of it is fluid mechanics: what happens to the droplets once they��re expelled, which is where we come in. As fluid mechanics specialists, we��re like the bridge from virology of the emitter to the virology of the receiver and we can help with risk assessment.��

In the current study, the Cambridge researchers set out to ��measure�� this bridge through a series of simulations. For example, if a person coughed and emitted a thousand droplets, how many would reach another person in the same room, and how large would these droplets be, as a function of time and space?

̽��ֱ��simulations used refined computational models solving the equations for turbulent flow, together with detailed descriptions of droplet motion and evaporation.

̽��ֱ��researchers found that there isn��t a sharp cut-off once the droplets spread beyond two metres. When a person coughs and isn��t wearing a mask, most of the larger droplets will fall on nearby surfaces. However, smaller droplets, suspended in the air, can quickly and easily spread well beyond two metres. How far and how quickly these aerosols spread will depend on the quality of ventilation in the room.

In addition to the variables surrounding mask-wearing and ventilation, there is also a high degree of variability in individual coughs. ��Each time we cough, we may emit a different amount of liquid, so if a person is infected with COVID-19, they could be emitting lots of virus particles or very few, and because of the turbulence they spread differently for every cough,�� said Trivedi.

��Even if I expel the same number of droplets every time I cough, because the flow is turbulent, there are fluctuations,�� said Mastorakos. ��If I��m coughing, fluctuations in velocity, temperature and humidity mean that the amount someone gets at the two-metre mark can be very different each time.��

̽��ֱ��researchers say that while the two-metre rule is an effective and easy-to-remember message for the public, it isn��t a mark of safety, given the large number of variables associated with an airborne virus. Vaccination, ventilation and masks �C while not 100% effective �C are vital for containing the virus.

��We��re all desperate to see the back of this pandemic, but we strongly recommend that people keep wearing masks in indoor spaces such as offices, classrooms and shops,�� said Mastorakos. ��There��s no good reason to expose yourself to this risk as long as the virus is with us.��

̽��ֱ��research team are continuing this research with similar simulations for spaces such as lecture rooms that can help assess the risk as people spend more time indoors.

Mastorakos is a Fellow of Fitzwilliam College, Cambridge. ̽��ֱ��research was supported in part by the Engineering and Physical Sciences Research Council (EPSRC), part of UK Research and Innovation (UKRI).

Reference:
Shrey Trivedi et al. ��Estimates of the stochasticity of droplet dispersion by a cough.�� Physics of Fluids (2021). DOI: 10.1063/5.0070528

A new study has shown that the airborne transmission of COVID-19 is highly random and suggests that the two-metre rule was a number chosen from a risk ��continuum��, rather than any concrete measurement of safety.

We strongly recommend that people keep wearing masks in indoor spaces - there��s no good reason to expose yourself to this risk as long as the virus is with us

Epaminondas Mastorakos

How droplets spread in a cough

Pedro de Oliveira

Visualisation of droplets from a cough

Yes

Scientists develop model to assess COVID-19 infection risk in offices and schools

sc604 — Wed, 06 Oct 2021 10:56:27 +0000

̽��ֱ��model �C developed by researchers at the ̽��ֱ�� of Cambridge, Imperial College London?and the ̽��ֱ�� of Leeds �C uses monitored CO2 and occupancy data to predict how many workers are likely to be infected by an asymptomatic but infectious colleague.

Applications of the infection model have demonstrated that most workers in well-ventilated, quiet offices are unlikely to infect each other via airborne particles, but the risk becomes greater if the space is poorly ventilated or if the workers are involved in activities that require more speaking. For instance, the model predicts each infected person could infect two to four others in an adequately ventilated but noisy call centre. Risks are also likely to increase if the infected individual is a ��super spreader��.

̽��ֱ��model also suggests that halving the occupancy of an office could reduce the risk of airborne transmission four-fold. ̽��ֱ��results are reported in the journal Indoor and Built Environment.

In areas with lower ventilation rates and high occupancy, CO2 levels are higher, so monitoring them can provide a warning to building managers to identify areas where the risk of airborne transmission of COVID-19 are higher. Achievable interventions can then be made, for instance, to improve ventilation or change worker attendance patterns to reduce occupancy.

In shared spaces such as offices and classrooms, exposure to infectious airborne matter builds up, and room occupancy may vary. By using carbon dioxide levels as a proxy for exhaled breath, the model can assess the variable exposure risk as people come and go.

��Ventilation is complicated and airflow is invisible, so it��s hard for people to appreciate the effects in the home or workplace,�� said co-author Professor Paul Linden from Cambridge��s Department of Applied Mathematics and Theoretical Physics. ��Commercially available CO2 monitors are being installed in schools and I would recommend their installation in the workplace.��

��Our work emphasises the importance of good ventilation in workplaces and in schools,�� said lead author Dr Henry Burridge, from Imperial College London. �� ̽��ֱ��model demonstrates that by managing the ventilation and occupancy levels of shared spaces we can manage the risk of airborne infection by a virus such as that which causes COVID-19.��

�� ̽��ֱ��appropriate use of tools such as CO2 monitoring can give building managers a much better understanding of their own ventilation systems and how they are performing for each activity undertaken in the space,�� said Professor Andrew Curran, Chief Scientific Adviser at the Health and Safety Executive and lead for the PROTECT study. ��For most businesses, a COVID-19 control strategy will involve a blended combination of measures identified through a risk assessment �C there is no silver bullet.��

̽��ֱ��research was funded by the PROTECT COVID-19 National Core Study and the Engineering and Physical Sciences Research Council (EPSRC, part of UK Research and Innovation).

Reference:
Henry C?Burridge et al. ��Predictive and retrospective modelling of airborne infection risk using monitored carbon dioxide.�� Indoor and Built Environment (2021). DOI: 10.1177/1420326X211043564

Adapted from an HSE press release.

As more UK workers and students return to offices and schools, a new model has been developed to predict the risk of airborne COVID-19 infection in such environments.

Ventilation is complicated and air flow is invisible, so it��s hard for people to appreciate the effects in the home or workplace

Paul Linden

Israel Amdrade via Unsplash

People in office sitting in front of computers

Yes

Free online tool calculates risk of COVID-19 transmission in poorly-ventilated spaces

sc604 — Wed, 20 Jan 2021 00:55:09 +0000

̽��ֱ��results, reported in the journal Proceedings of the Royal Society A, show that social distancing measures alone do not provide adequate protection from the virus, and further emphasise the vital importance of ventilation and face masks in order to slow the spread of COVID-19.

̽��ֱ��researchers, from the ̽��ֱ�� of Cambridge and Imperial College London, used mathematical models to show how SARS-CoV-2 �C the virus which causes COVID-19 �C spreads in different indoor spaces, depending on the size, occupancy, ventilation and whether masks are being worn. These models are also the basis of a free online tool, Airborne.cam, which helps users understand how ventilation and other measures affect the risk of indoor transmission, and how that risk changes over time.

̽��ֱ��researchers found that when two people are in a poorly-ventilated space and neither is wearing a mask, prolonged talking is far more likely to spread the virus than a short cough. When speaking, we exhale smaller droplets, or aerosols, which spread easily around a room, and accumulate if ventilation is not adequate. In contrast, coughing expels more large droplets, which are more likely to settle on surfaces after they are emitted.

It only takes a matter of seconds for aerosols to spread over two metres when masks are not worn, implying that physical distancing in the absence of ventilation is not sufficient to provide safety for long exposure times. When masks of any kind are worn however, they slow the breath��s momentum and filter a portion of the exhaled droplets, in turn reducing the amount of virus in aerosols that can spread through the space.

̽��ֱ��scientific consensus is that the vast majority of COVID-19 cases are spread through indoor transmission �C whether via aerosols or droplets. And as was predicted in the summer and autumn, now that winter has arrived in the northern hemisphere and people are spending more time indoors, there has been a corresponding rise in the number of COVID-19 cases.

��Our knowledge of airborne transmission of SARS-CoV-2 has evolved at an incredible pace, when you consider that it��s been just a year since the virus was identified,�� said Dr Pedro de Oliveira from Cambridge��s Department of Engineering, and the paper��s first author. ��There are different ways to approach this problem. In our work, we consider the wide range of respiratory droplets humans exhale to demonstrate different scenarios of airborne viral transmission �C the first being the quick spread of small infectious droplets over several metres in a matter of a few seconds, which can happen both indoors and outdoors. Then, we show how these small droplets can accumulate in indoor spaces in the long term, and how this can be mitigated with adequate ventilation.��

̽��ֱ��researchers used mathematical models to calculate the amount of virus contained in exhaled particles, and to determine how these evaporate and settle on surfaces. In addition, they used characteristics of the virus, such as its decay rate and viral load in infected individuals, to estimate the risk of transmission in an indoor setting due to normal speech or a short cough by an infectious person. For instance, they show that the infection risk after speaking for one hour in a typical lecture room was high, but the risk could be decreased significantly with adequate ventilation.

Based on their models, the researchers have now built Airborne.cam, a free, open-source tool which can be used by those managing public spaces, such as shops, workplaces and classrooms, in order to determine whether ventilation is adequate. ̽��ֱ��tool is already in use in several academic departments at the ̽��ֱ�� of Cambridge. ̽��ֱ��tool is now a requirement for any higher-risk spaces at the ̽��ֱ��, enabling departments to easily identify hazards and control-measure changes needed to ensure aerosols are not allowed to become a risk to health.

�� ̽��ֱ��tool can help people use fluid mechanics to make better choices, and adapt their day-to-day activities and surroundings in order to suppress risk, both for themselves and for others,�� said co-author Savvas Gkantonas, who led the development of the app with Dr de Oliveira.

��We��re looking at all sides of aerosol and droplet transmission to understand, for example, the fluid mechanics involved in coughing and speaking,�� said senior author Professor Epaminondas Mastorakos, also from the Department of Engineering. �� ̽��ֱ��role of turbulence and how it affects which droplets settle by gravity and which remain afloat in the air is, in particular, not well understood. We hope these and other new results will be implemented as safety factors in the app as we continue to investigate.��

̽��ֱ��continuing development of Airborne.cam, which will soon be available for mobile platforms, is supported in part by Cambridge Enterprise and Churchill College.

Reference:
P?M?de Oliveira et al. ��Evolution of spray and aerosol from respiratory releases: theoretical estimates for insight on viral transmission.�� Proceedings of the Royal Society A (2021). DOI: 10.1098/rspa.2020.0584

̽��ֱ��vital role of ventilation in the spread of COVID-19 has been quantified by researchers, who have found that in poorly-ventilated spaces, the virus can spread further than two metres in seconds, and is far more likely to spread through prolonged talking than through coughing.

̽��ֱ��tool can help people use fluid mechanics to make better choices, and adapt their day-to-day activities and surroundings in order to suppress risk, both for themselves and for others

Savvas Gkantonas

Gauthier DELECROIX - ��

Five senses series - Taste 1/2

Yes

Licence type:

Attribution

Many ventilation systems may increase risk of COVID-19 exposure, study suggests

sc604 — Tue, 29 Sep 2020 16:28:46 +0000

A team from the ̽��ֱ�� of Cambridge found that widely-used ��mixing ventilation�� systems, which are designed to keep conditions uniform in all parts of the room, disperse airborne contaminants evenly throughout the space. These contaminants may include droplets and aerosols, potentially containing viruses.

̽��ֱ��research has highlighted the importance of good ventilation and mask-wearing in keeping the contaminant concentration to a minimum level and mitigating the risk of transmission of SARS-CoV-2, the virus that causes COVID-19.

̽��ֱ��evidence increasingly indicates that the virus is spread primarily through larger droplets and smaller aerosols, which are expelled when we cough, sneeze, laugh, talk or breathe. In addition, the data available so far indicates that indoor transmission is far more common than outdoor transmission, which is likely due to increased exposure times and decreased dispersion rates for droplets and aerosols.

��As winter approaches in the northern hemisphere and people start spending more time inside, understanding the role of ventilation is critical to estimating the risk of contracting the virus and helping slow its spread,�� said Professor Paul Linden from Cambridge��s Department of Applied Mathematics and Theoretical Physics (DAMTP), who led the research. ��While direct monitoring of droplets and aerosols in indoor spaces is difficult, we exhale carbon dioxide that can easily be measured and used as an indicator of the risk of infection. Small respiratory aerosols containing the virus are transported along with the carbon dioxide produced by breathing, and are carried around a room by ventilation flows. Insufficient ventilation can lead to high carbon dioxide concentration, which in turn could increase the risk of exposure to the virus.��

̽��ֱ��team showed that airflow in rooms is complex and depends on the placement of vents, windows and doors, and on convective flows generated by heat emitted by people and equipment in a building. Other variables, such as people moving or talking, doors opening or closing, or changes in outdoor conditions for naturally ventilated buildings, affect these flows and consequently influence the risk of exposure to the virus.

Ventilation, whether driven by wind or heat generated within the building or by mechanical systems, works in one of two main modes. Mixing ventilation is the most common, where vents are placed to keep the air in a space well mixed so that temperature and contaminant concentrations are kept uniform throughout the space.

̽��ֱ��second mode, displacement ventilation, has vents placed at the bottom and the top of a room, creating a cooler lower zone and a warmer upper zone, and warm air is extracted through the top part of the room. As exhaled breath is also warm, most of it accumulates in the upper zone. Provided the interface between the zones is high enough, contaminated air can be extracted by the ventilation system rather than breathed in by someone else. ̽��ֱ��study suggests that when designed properly, displacement ventilation could reduce the risk of mixing and cross-contamination of breath, thereby mitigating the risk of exposure.

As climate change has accelerated since the middle of the last century, buildings have been built with energy efficiency in mind. Along with improved construction standards, this has led to buildings that are more airtight and more comfortable for the occupants. In the past few years however, reducing indoor air pollution levels has become the primary concern for designers of ventilation systems.

��These two concerns are related, but different, and there is tension between them, which has been highlighted during the pandemic,�� said Dr Rajesh Bhagat, also from DAMTP. ��Maximising ventilation, while at the same time keeping temperatures at a comfortable level without excessive energy consumption is a difficult balance to strike.��

In light of this, the Cambridge researchers took some of their earlier work on ventilation for efficiency and reinterpreted it for air quality, in order to determine the effects of ventilation on the distribution of airborne contaminants in a space.

��In order to model how the coronavirus or similar viruses spread indoors, you need to know where people��s breath goes when they exhale, and how that changes depending on ventilation,�� said Linden. ��Using this?data, we can estimate the risk of catching the virus while indoors.��

̽��ֱ��researchers explored a range of different modes of exhalation: nasal breathing, speaking and laughing, each both with and without a mask. By imaging the heat associated with the exhaled breath, they could see how it moves through the space in each case. If the person was moving around the room, the distribution of exhaled breath was markedly different as it became captured in their wake.

��You can see the change in temperature and density when someone breathes out warm air �C it refracts the light and you can measure it,�� said Bhagat. ��When sitting still, humans give off heat, and since hot air rises, when you exhale, the breath rises and accumulates near the ceiling.��

Their results show that room flows are turbulent and can change dramatically depending on the movement of the occupants, the type of ventilation, the opening and closing of doors and, for naturally ventilated spaces, changes in outdoor conditions.

̽��ֱ��researchers found that masks are effective at reducing the spread of exhaled breath, and therefore droplets.

��One thing we could clearly see is that one of the ways that masks work is by stopping the breath��s momentum,�� said Linden. ��While pretty much all masks will have a certain amount of leakage through the top and sides, it doesn��t matter that much, because slowing the momentum of any exhaled contaminants reduces the chance of any direct exchange of aerosols and droplets as the breath remains in the body��s thermal plume and is carried upwards towards the ceiling. Additionally, masks stop larger droplets, and a three-layered mask decreases the amount of those contaminants that are recirculated through the room by ventilation.��

̽��ֱ��researchers found that laughing, in particular, creates a large disturbance, suggesting that if an infected person without a mask was laughing indoors, it would greatly increase the risk of transmission.

��Keep windows open and wear a mask appears to be the best advice,�� said Linden. ��Clearly that��s less of a problem in the summer months, but it��s a cause for concern in the winter months.��

̽��ֱ��team are now working with the Department for Transport looking at the impacts of ventilation on aerosol transport in trains and with the Department for Education to assess risks in schools this coming winter.

Reference
Rajesh K. Bhagat et al. ��Effects of ventilation on the indoor spread of COVID-19.�� Journal of Fluid Mechanics (2020). DOI: 10.1017/jfm.2020.720.

Ventilation systems in many modern office buildings, which are designed to keep temperatures comfortable and increase energy efficiency, may increase the risk of exposure to the coronavirus, particularly during the coming winter, according to research published in the Journal of Fluid Mechanics.

As winter approaches in the northern hemisphere and people start spending more time inside, understanding the role of ventilation is critical to estimating the risk of contracting the virus and helping slow its spread

Paul Linden

stux

Ventilation

Yes

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Public Domain

Coronavirus pandemic: making safer emergency hospitals

lw355 — Tue, 28 Apr 2020 08:50:22 +0000

Simple, low-cost ventilation designs and configuration of wards can reduce the dispersal of airborne virus in emergency COVID-19 hospitals, say Cambridge researchers.