Ventilation has come blinking into the limelight because of the COVID-19 emergency. For so long a ‘Cinderella’ service, it is now a topic of urgent discussion. Building managers are facing detailed questions about how they are improving airflows to help dilute airborne viral loads.
While this has long been a key preoccupation for the ‘behind the scenes’ facilities managers in healthcare properties, they have never had these discussions under such intense scrutiny before.
There is also a renewed focus on relative humidity (RH) because of growing evidence that viruses thrive when the indoor air is drier.
While these issues are concerning FMs in buildings up and down the country, their implications are markedly more important in healthcare settings where many of the occupants have supressed immunity. There is also greater recognition that building engineering professionals are key members of the wider healthcare team – and, therefore, greater significance should be given to them using all the planned maintenance tools at their disposal.
Vulnerable
The importance of turning buildings into ‘safe havens’ that protect vulnerable occupants – particularly those suffering from respiratory illnesses – from rising air pollution outside and other airborne threats to their health and wellbeing that thrive indoors is also a key issue at government level.
Professor Cath Noakes from the University of Leeds is a ventilation specialist and one of only two engineer members of the Scientific Advisory Group for Emergencies (SAGE) that has been helping the government navigate the pandemic.
She is determined that the industry takes advantage of this increased awareness to ensure buildings are protected for the long-term so that after the current crisis has subsided, we don’t slip back into accepting poorly ventilated spaces with high levels of indoor contaminants.
Speaking at a recent webinar hosted by the Building Engineering Services Association (BESA), she said there was still much to learn about how ventilation can protect building occupants from viruses and other airborne threats, but that settling on a ventilation strategy was not straightforward.
“This is a very complex issue, and it will take years to build up the amount of data needed to make sure we can do this better. However, as a rule of thumb we should aim for [air change rates of] 10 litres per second (l/s) per person and CO2 concentrations below 800 parts per million.”
Noakes confirmed that studies had shown the risk was higher indoors when ventilation provided less than 3 l/s per person and that household transmission was a particular concern. She also explained that the virus thrived in cool, dry, and dark conditions – making RH control a priority.
However, this does not just mean turn up the ventilation and let it rip, but it does support the case for investing in some form of controlled mechanical system and maintaining it properly.
“We know ventilation matters and will be critical for health and wellbeing (including mental health) beyond Covid so we must get this right,” Noakes told the BESA webinar. “We can say we have not seen any evidence of high transmission in well-ventilated spaces – so if we are designing and delivering to the standards set in current building standards that will help, but we may need to go beyond that.”
However, she pointed out that many buildings were not even achieving current standards and many “had no proper ventilation at all”. She also expressed particular concern about ‘naturally’ ventilated spaces because they are dependent on wind direction and temperature so cannot guarantee the target air change rates.
Of course, hospital managers have been keenly aware of the risk of possible cross infection caused by airborne contamination for many years. There is now, however, even more of a need to focus on the frequency of air filter maintenance and replacement to improve the effectiveness of systems along with regular ductwork cleaning to reduce the build-up of particulate matter and biological contaminants.
Droplets
More information is also emerging about how air conditioning systems hold in suspension the water droplets that transport the Covid virus. Therefore, SAGE is advising against using air conditioning in places with low levels of ventilation. The improved hand washing and surface hygiene regimes introduced by many healthcare premises along with air cleaning are also not reasons to ventilate less.
Engineering controls should sit above measures that rely on human behaviour such as distancing and wearing face coverings in any “hierarchy of risk control”, according to Noakes. She also recommends that building managers address source control before studying ventilation requirements. This approach would not necessarily lead to increasing ventilation rates, but a more targeted strategy to ensure refreshed air was reaching all parts of the occupied space – and particularly patient recovery areas. Natural ventilation can leave ‘dead spots’ even when part of the room is well ventilated.
Measuring concentrations of CO2 is a relatively straightforward way to establish whether a ventilation strategy is working as it will act as a “canary in a cage” for other contaminants.
To embed the lessons learned in the pandemic, the industry will have to find ways of proving it is delivering the ventilation performance required in buildings and demonstrate its compliance with the standards that will emerge. Part F of the Building Regulations, which is currently under review, could also be used to beef up the IAQ measures likely to be introduced in the forthcoming Environment Bill.
The question of humidity control remains a challenge for FMs, but it is one they must confront to ensure buildings are properly equipped to deal with all future threats to health and wellbeing.
Dr Stephanie Taylor from Harvard Medical School told a BESA meeting that managing the indoor environment was “the best medicine for treatment and prevention”. She said that numerous studies had identified an RH ‘sweet spot’ between 40% and 60%. Air that is too dry will allow viruses to thrive and be more active, she explained.
“We need to start regarding human health as a key measure of success for our buildings. When we speak, we expire droplets out of our airway that are about 100 microns in diameter. When they enter the air in the room, those droplets shrink according to the RH of the ambient air. If humidity is maintained between 40% and 60%, the droplets shrink to a point where the concentration of salts in those droplets inactivates microbes.”
However, if RH is less than 40%, those droplets shrink even further and the salts preserve the microbes, making them more virulent. “One study at a pre-school showed that humidification decreased flu infections. In fact, it showed that dry air causes infections,” said Taylor.
Other research has also shown that in low humidity indoor environments, the human body has difficulties fighting off infections – compounding these problems.
Covid-19 is not the only illness that thrives in our modern air-tight and heated environment. There are also increases in inflammatory disorders, auto-immune disease, and allergies. Taylor emphasised that there can be no doubt that the indoor environment is in the front line in the fight against future pandemics.
“As a physician I’ve come to realise that managing our indoor environment is the most powerful medicine both for treatment and prevention. The corollary of that is that building professionals really, in my opinion, are the physicians of the future.”