How we’re helping to unlock the UK through safe ventilation

‘As with many SME design consultancies within the construction industry, the COVID-19 pandemic has delivered a ‘stress test’ like no other in recent times. As we entered the first lockdown in March 2020 , we saw the immediate benefit of an earlier policy to encourage mixing of our team across our three offices to avoid  ‘regional silos’ developing, using remote working software such as MS Teams. The transition to home working therefore, had little impact on our operations.

The loss of person-to-person interaction and the risk this posed to our company culture was a concern. Our recruitment strategy focussed on people that fit our culture and core values, which meant we had a team with the right mindset to face the challenges ahead and to appreciate the big picture. This made the leadership decisions much easier as the workload reduced, and we were forced to take advantage of the government furlough scheme. This put some additional stress on the non-furloughed team who had to pick up the work of others. Without question, it is through the efforts of our entire team that we managed to navigate the crisis and the board will forever be grateful for that.

Prior to COVID-19 we had carried out a wholesale review of our company processes including the development of a new Accountability Chart. This involved throwing away the previous organogram and designing the ideal corporate structure to deliver our services in the most efficient manner. Once the structure had been determined, we were individually assessed by the leadership team from the top down to ensure we had the right people in the right seats. This resulted in some personnel changes and shifting of roles, painful at the time but proven to be the right decision. When COVID-19 came along, the clarity of roles and responsibilities enabled us to work through the many issues arising quickly and efficiently.

As part of our company operating system, we hold weekly leadership team ‘pulse’ meetings. We use EOS cloud-based software with a fixed agenda format which includes Segue, Data, To-Do’s, Rocks, and Issues. These meetings had already transformed our business, providing much needed traction for growth. We had not envisaged how important these meetings would be in the light of the pandemic. We were able to manage COVID-19 related issues as any other business issue before. Each issue was logged in the software during the week, and an IDS process applied (Identify Discuss and Solve) and a ‘To-do’ or ‘Rock’ created with clear ownership and timescales applied and progress tracked at subsequent weekly pulse meetings. The pulse meetings ensure our leadership team are always on the same page and aware of companywide issues.

The UK Government published COVID-19 guidance for workplaces and construction sites during early 2020. At that time, the focus was on hand washing and 2m social distancing and face masks were not mandated.  In our role as HVAC design engineers, with knowledge of ventilation systems and its influence on a healthy building, we were familiar with the enhanced ventilation rates required to help reduce risk of all types of virus transmission. We struggled to reconcile the lack of government advice on the risk of COVID-19 transmission via airborne COVID-19 aerosol.

Our priority was to protect our team when carrying out site inspections. The scenario presenting most concern was entering an occupied internal space with little or no ventilation occupied by tradesmen. Self-employed tradesmen had been given little or no support by government in the early stages of the pandemic and we feared this would result in infected workers returning to the workplace.   We researched the best face mask options available for our team and spoke with accredited mask fitting companies which resulted in the engagement of Harrisons of Hull, who within days of our approach, travelled to our Chester office and test fitted masks to our team using a quantitative test method which measures particles passing through the face mask seal. Our team achieved a 100% seal pass rate, which provided the confidence to allow them to visit sites in a controlled manner and subject to all other COVID-19 protection measures being in place.


As we approached the end of the first lockdown, our attention turned to return to work procedures. Information had been published by UK Government in relation to ‘hands, space and face’ and general office COVID-19 hygiene measures. We struggled to find any clear guidance in relation to far-field (>2m) covid-19 transmission by airborne aerosol. This was the start of our research into far-field COVID-19.

From our early research it became apparent that the World Health Organisation and UK Government were not listening to eminent aerosol scientists who were warning about the risk of far-field airborne aerosol transmission. Historic flaws in the WHO understanding of  aerosol particle size and its ability to travel distances greater than 2m were cited by the aerosol scientific community.   On 6 July 2020, two leading aerosol scientists, supported by an international group of 237 related specialisms, published a commentary in the journal Clinical Infectious Diseases that urged the authorities to acknowledge the potential for airborne transmission. On the 7 July, WHO softened its position and acknowledged further research was needed into far field transmission. So, from the 30th of January 2020 until the 7th of July 2020, far field aerosol transmission was not recognised by the World Health Organisation as a significant route of transmission. Since then, the evidence of far-field transmission has steadily grown, and it is now recognised as being a significant cause of infection.

Armed with this knowledge, we developed a COVID-19 ventilation risk assessment. This incorporates latest guidance from UK government and other reputable industry bodies. We found conflict between the various publications in the early days and we set a hierarchy of documents with government guidance at the top of the list. We incorporated a natural ventilation calculator in order we could calculate air flow rates through window openings, and we invested in air flow measurement equipment. We used the risk assessment to assess the ventilation risk within our three offices. This highlighted some shortfalls, some of which were easily dealt with by repositioning of furniture. Some cellular spaces had to be taken out of use due to inadequate ventilation.

Shortly after we were approached by a client who had followed government guidance with respect to return to office measures but was stuck on how to assess the adequacy of their ventilation systems. We offered to deploy our new ventilation risk assessment and after a couple of long days on site, surveying, measuring windows and recording air flow rates in ducts and grilles we were able to present the client with a concise ventilation risk assessment document which after a few minor changes to their building, enabled them to reoccupy in a safe manner. Since then, we have been approached by several clients and we have performed a similar role helping with their return to work.

As a father of two, one in their final GCSE year and the other at University, my focus has shifted to the phased return of pupils to UK schools planned over the coming weeks. There remains a big question as to whether school classrooms are covid-19 ‘super spreader’ environments. Current UK guidance from SAGE and the HSE is to prioritise improvements where room CO₂ levels are greater than 1500ppm and fresh air rates are less than 5 litres/second/person.

Since 1997, School classroom design regulations have required ventilation systems to be capable of supplying eight litres of fresh air per second, per person. Reduced ventilation rates are often encountered during colder weather when windows are closed or automated ventilation systems are turned down to maintain classroom temperature.


The Federation of European Heating, Ventilation & Air Conditioning Associations has published an online calculator for assessing airborne Covid-19 risk for different space types including classrooms. The following table gives results for a typical classroom under varying ventilation rates and other variables, based on one Covid-19 infected occupant.

Points of note from the above results:

  • Reducing pupil duration in the classroom with gaps between to purge classroom air will prevent the build-up of Covid-19. Transmission risk is very low for one-hour long lessons (scenario A compared to B)
  • Well-ventilated classrooms are key to transmission risk reduction (scenario C,D,E)
  • The amount of speech occurring within the classroom has a significant impact on transmission risk (scenario D,F)
  • Multi-layer fabric masks can significantly reduce the quanta of Covid-19 exhaled and transmission risk (scenario E)
  • A combination of factors including poor ventilation, long duration in the classroom, no mask and noisy children will significantly increase transmission risk

Research is ongoing into airborne Covid-19 transmission and the REHVA calculation tool recognises this and is caveated in numerous places. It ignores near-field and contact transmission which would increase the transmission risks stated above.

There are key steps businesses and education settings should be considering, as the UK unlocks, to ensure workplace ventilation systems are operating effectively, reducing the risk of Covid-19 transmission via aerosol particles. This includes understanding the type of system installed, ensuring it is maintained and operating correctly and delivering the required air flow rate.

Written by Richard Lewis, Technical and Quality Director.

For more information, please contact Richard at

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