The risks of airborne coronavirus transmission could be a barrier to a return to work for a third of workers, according to a poll.

A survey, carried out by facilities management company Rentokil Initial, suggested that 30% would like to see assurances on their building’s indoor air quality.

The poll, of 2000 representative adults, also indicated that 68% believe businesses and employers should do more to provide clean air in the premises while 62% of respondents supported the idea of making air purification systems mandatory in public buildings and education facilities.

On both findings, the poll revealed slight increases in the number of respondents expressing concern compared to the results of the same poll carried out in November.

Many employers are currently in discussion with staff about a return to work following furlough or a period working from home: on 29 March, the legal obligation to work at home unless circumstance made that impossible was removed.

However, UK government guidance still states that people should ‘continue to work from home where they can’.

The Health and Safety Executive (HSE) has made clear that assessing ventilation requirements is a vital part of the COVID-19 workplace risk assessment that must be carried out prior to resuming workplace operations; risk assessments should be carried out in consultation with workers or their representatives.

Jamie Woodhall, UK technical and innovation manager at Rentokil Initial, said: ‘These survey results show that tackling air quality and preventing the airborne spread of Coronavirus clearly remains an important challenge, alongside the vaccine rollout.

‘CO2 CONCENTRATIONS REGULARLY GREATER THAN 1500 PPM [PARTS PER MILLION] ARE INDICATIVE OF POORLY VENTILATED SPACES AND ATTENTION SHOULD BE GIVEN TO IMPROVING THE OUTSIDE AIR PROVISION’

‘The scientific evidence continues to build and it is very clear how important good ventilation and air purification is within indoor spaces. When it comes to easing of lockdown measures, the expectation from the public is that businesses and employers need to do their bit in helping to ensure that they are providing clean air, so that the risk of catching an airborne virus indoors is reduced.’

Hywel Davies, technical director of the Chartered Institute of Building Services Engineers (CIBSE), said it had received a high number of enquiries on safe ventilation from the university sector and office-based businesses, with CIBSE’s COVID-19 Ventilation Guidance having been downloaded 70,000 times.

In an email to IOSH magazine, he said: ‘The guidance … is also referenced by the HSE as a source of guidance. The concern is of course with those who are not enquiring: what, if anything, are they doing?’

Noting that ‘measuring’ ventilation performance is technically difficult and can only be achieved when the building is occupied, he nevertheless stresses that “assessments” can be done on unoccupied premises by competent FM teams without any special standards or devices.

This involves examining the maintenance history of any air supply or mechanical ventilation systems, and determining whether it relies on an outside air supply or recirculation – the latter posing more of a risk of aerosol transmission.

Davies added: ‘There is, sadly, no substitute for a bit of hands on investigation, by someone in the building. For larger building, the office manager many need to do some investigation.’

The British Council for Offices recently published a research paper, Thoughts on ventilation design and operation post COVID-19, which stresses the importance of adequate ventilation ahead of the return to work.

Derek Clements-Croome, Professor Emeritus at University of Reading and lead author of the report, said: ‘Ensuring a high standard of indoor air quality may be the most important thing we can do to fight COVID-19, combined with social distancing, washing our hands and wearing masks. Yet too many UK offices have inadequate ventilation. Germany is providing finance to upgrade ventilation systems in buildings and the UK government should consider doing this too.’

The CIBSE guidance Davies refers to suggests that non-dispersive infrared (NDIR) sensors that measure the concentrations of CO2 built up inside a room could be a useful tool to assess ventilation levels – and thereby give one indication of the risk of aerosol transmission inside the space.

It says: ‘CO2 concentrations regularly greater than 1500 ppm [parts per million] are indicative of poorly ventilated spaces and attention should be given to improving the outside air provision.’

However, ‘equivalent CO2’ or eCO2 devices that simply estimate CO2 levels based on the presence of Volatile Organic Compounds should not be used, and even NDIR sensors should only be part of a wider ventilation strategy, the guidance says.

As Davies explained: ‘If I take a typical open plan office for six to eight people pre-pandemic, and it’s now being occupied by three people all well-spaced, the CO2 levels are typically below 800ppm. Is that because the space is well ventilated, or because the ventilation only has to cope with 50% occupancy? So care is needed over the use of CO2 sensors.

‘Sensors for monitoring air quality in existing buildings are an emerging area and it’s not that straightforward. It’s also important that people do the simple things to improve ventilation described in the CIBSE guidance before buying extra detectors or spending money in other ways.’

Another option open to facilities teams and health and safety managers is to install ‘germicidal UV’ devices that use light in the UV-C spectrum to kill coronaviruses. According to Rentokil-Initial, these filter air and also pass it through ‘a mesh of chromed nano titanium dioxide tube filters that are polished with activated carbon. The emitted UV light reacts with the mesh, and in a process called ‘photocatalytic oxidation’ produces hydroxyl radicals, which acts as a disinfectant and breaks down the organic molecules’.

Dr Colm Moore, area technical manager for the UK, Ireland and the Baltics at Rentokil Initial says: ‘Unlike traditional air purification systems, the UVC technology provides a photochemical deconstruction of the RNA and DNA of microorganisms, deactivating their reproductive processes so that the Coronavirus, and other viruses, can no longer spread, before the air is released back into the room.’

CIBSE’s guidance notes that controlled experiments do show that GUV air-cleaning devices are effective at deactivating a range of viruses, including SARS-CoV-2.

However, there is little verified best practice guidance available on ‘real world’ factors such as dosage and exposure time, and how these interact with airflow and ventilation rates.

Discussing these devices, Davies said: ‘It can be safely applied to deactivate [coronaviruses] in buildings, but it’s a fairly specialist area and should only be undertaken by competent installers using properly tested and certified equipment. UV can be hazardous to people on exposure, and so safety precautions covering maintenance and operation are essential – there is HSE guidance on that too.

‘Once installed, and then used as the basis for increasing occupancy, it’s essential that there are alarms if it fails – because it’s not now protecting people – and rapid reaction which may involve an evacuation of certain spaces is triggered.’

The survey’s evidence on levels of staff concern on ventilation comes as a paper by the University of Central Florida suggests that ventilation and mask-wearing are the key controls to prevent indoor airborne transmission – a findings that suggest masks should be mandated while social distancing rules can be recalibrated.

Using computer models of ventilated and unventilated university classrooms, a study published in the journal Physics of Fluids – used the Wells-Riley equation to assess the probability of indoor transmission and Computational Fluid Dynamics to understand air movements.

It found that a ventilation system incorporating a good air filter reduced the infection risk by 40-50%. In the ventilated space, the steady current of air directed aerosols into a filter; in the no-ventilation scenario, the aerosols congregated above the people in the room.

The computer modelling also found that masks help to warm exhaled air, allowing any expelled aerosols to rise vertically rather than reaching adjacent students.

Michael Kinzel, an assistant professor at the university, concluded that the results support recent guidance from the US Centre for Disease Control to reduce social distancing in elementary schools from six to three feet where mask use is universal.