Air of authority: interview with Professor Catherine Noakes

Professor Catherine Noakes’ knowledge of ventilation and infection transmission has made her one of the government’s key scientific advisers on Covid-19. In recognition of her work, she was made an OBE last month. Alex Smith talks to her about the challenge of winter and the impact of infection control going mainstream

Professor Catherine Noakes

Professor Catherine Noakes has been an expert in airborne infection transmission for 18 years, but it was only when the Covid-19 pandemic took hold in spring that people really took notice.

‘It was seen as a curiosity,’ says Noakes, professor of environmental engineering for buildings at the University of Leeds. ‘They didn’t see it being important, as they didn’t see transmission happening. It suddenly matters now.’

Noakes’ knowledge of ventilation and its impact on air quality has put her at the forefront of the UK’s struggle to minimise the spread of Covid-19. Her contribution was recognised last month when she was made an OBE for ‘services to the Covid-19 response’.

She sits on the Scientific Advisory Group for Emergencies (SAGE), advising the government on its response to the pandemic. She also convened and chairs the Environment and Modelling Group (EMG), a cross-disciplinary sub-group of engineers, architects, clinicians, modellers, microbiologists, behavioural scientists and public health specialists. It provides advice to the government on the physics of Covid-19 spread and the risks of exposure in buildings, and puts forward mitigation strategies to keep people safe.

Sir Patrick Vallance, the UK government’s chief scientific adviser, said that, under Noakes’ leadership, the ‘EMG work has had widespread and significant impact, not just on the government’s response to Covid-19 – where it has informed policy across a range of departments – but also on public advice that is supporting the safe reopening of businesses and public services’.

Noakes also supported CIBSE in producing guidance on ventilation for Covid-19 and she has contributed to the World Health Organization (WHO) guidelines on ventilation for control of the virus. She was one of 36 experts in airborne infection who called on the WHO to accept that Covid-19 could be transmitted through aerosol routes.

Her work has also been recognised by The President’s Special Award for Pandemic Service by the Royal Academy of Engineering.

At Leeds University Noakes has helped devise a strategy for keeping staff and students safe during the pandemic. This involves keeping well ventilated and keeping interactions to as small a social circle as possible. ‘If you do interact, interact outside,’ she advises.

Active on Twitter, Noakes (@cathnoakes) takes time to answer questions from the public, and offer the latest advice and research on Covid-19 – as well as humorous snapshots of everyday life in Yorkshire.

Noakes says she never over-simplifies the science, even with politicians who want yes or no answers. ‘We wrestled with this for quite some time, but we can’t make it less complex,’ she says. ‘It is what it is. It’s physics.

‘One of the real challenges we are finding with ventilation is that people want a simple rule – but there isn’t one. It’s a specialist area and we need to recognise it in that way.’

One of the challenges with ventilation is that people want a simple rule – but there isn’t one. It’s a specialist area and we need to recognise it in that way”

Even now, Noakes says it’s difficult to say categorically that airborne transmission of Covid-19 is definitive because of the complex multiple routes of transmission, but an increasing body of evidence points to the airborne route being a major transmission factor.

‘When it’s poorly ventilated, and where people are generating large amounts of aerosol through activities such as singing and loud speech, that is when transmission is most likely,’ says Noakes.

She highlights the infamous choir practice in Washington State, where a superspreader infected 52 people over 2.5 hours; and a case in South Korea in August, when 27 people were infected in an air conditioned Starbucks with recirculating indoor air.

With Covid-19 infections rising sharply across the UK, Noakes is now focusing on keeping building occupants safe over the coming winter.

‘Winter adds risk factors together,’ she says. ‘People want to socialise indoors, and we know that the virus survives in colder and dryer conditions. We also know it’s susceptible to the UV in sunlight and, in winter, we don’t have sufficient UV to kill the virus so effectively. We are also generally more susceptible to viruses in the winter.’

Using ventilation in the winter is more difficult because drawing in too much outdoor air – either through natural or mechanical ventilation – will cause thermal discomfort. Rather than having windows open all the time, Noakes suggests having them open slightly to maintain baseload, before opening them more fully to air a space.

‘If you combine the airing period with when people leave a room, you can effectively flush the room and reset it to zero for the next occupancy period,’ she says. ‘That’s one way that we could try to manage comfort and energy, and the need for ventilation.’

Noakes says maintaining humidity above 40% and temperature above 18-20°C is important. The likely cause of large clusters of infections among food-factory workers was the recirculation of chilled air in the processing plant, she says.

Ultraviolet germicidal irradiation (UVGI) and Hepa filters may be solutions in poorly ventilated spaces where there is limited opportunity to bring in outdoor air. However, Noakes says people have to consider the unintended consequences.

Some air purifier technologies can produce ozone. For example, when oxygen particles are broken apart by high-energy UV-C light, the atoms combine again with other oxygen atoms to form ozone.

‘Ozone is a respiratory irritant,’ says Noakes. ‘You need to think “are people going to be exposed to air chemistry that may be detrimental to their health?”’

She also warns that chemicals from UVGI may degrade materials, while decontaminates from foggers [equipment producing fine spray] may be harmful to occupants if not handled properly. ‘If people are decontaminating space using foggers, they need to think about the chemical being used. Is there off-gassing involved, and how long before you can go safely back into the space?’

Noakes says suppliers often don’t say what the ‘fog’ contains, and she believes there is an important role for engineering professionals to advise those responsible for making buildings Covid-19 secure, such as school principals.

‘The headteacher makes sure the boiler is running, but it’s not their role to maintain and set the boiler,’ she says. ‘It’s the same with ventilation. It’s their responsibility to make sure it’s running smoothly, but it’s up to someone else to set it up and make sure it’s working correctly.’

Career highlights

Professor Catherine Noakes completed a degree in mechanical engineering at the University of Leeds, where she has spent almost all her career. She studied fluid dynamics for her PhD, modelling photographic film coatings, and then worked on industrial drying, which piqued her interest in ventilation. 

It was while doing post-doctoral research on using UV disinfection for tuberculosis that Noakes first appreciated the connection between fluid dynamics and people’s health, which took her into the field of infection transmission.

Other senior positions she has held at Leeds include deputy director at the Institute for Fluid Dynamics and director of research for the School of Engineering. Through the Athena Swan Charter, she also leads on promoting gender equality at the Faculty of Engineering.

Noakes is currently heading up a study of new computational models to understand disease transmission in healthcare and is involved with a major new University of Leeds project, supported by government, to understand Covid-19 spread on public transport.

CO2 monitors can be used as an indicator of poor air quality, but Noakes warns that they are not necessarily an indicator of good air quality. ‘CO2 has some benefits, particularly for multiple occupant spaces. If it’s more than 1,500ppm, then you need to do something. If you have higher aerosol generation in a space then the threshold should be closer to 800,’ she says

‘But you can’t say that a low CO2 means a space is safe. In a large area, for example, CO2 will build up very slowly. It may appear to have a low CO2 value, but there may be areas where it’s higher.’

Noakes believes the Covid-19 pandemic will force people to take ventilation seriously and help safeguard buildings against the risk of infections.

‘There are a lot of people working on energy and air quality, but there are very few people working on infection transmission,’ she says. ‘With the right heat-recovery systems, which ensure good ventilation that is energy efficient, there’s no disadvantage. The long-term payback is improved health and productivity, and lower energy use.’

Noakes accepts that, in the short term, many will have to live with existing systems, but, with investment, we will all benefit. ‘It’s taken a pandemic to get people looking at ventilation,’ she says, ‘but if we do invest as a nation, there’s a potential big win.’