Analysis: knowing how and why you need to ventilate your house properly will help stop the spread of Covid-19
Studies suggesting that the coronavirus may remain viable in aerosols for a few hours has led some people to stop opening their windows to prevent the virus from getting inside. But could this simple behavioural change actually be dangerous to our health?
According to the World Health Organisation (WHO), transmission of the coronavirus will mainly be from tiny droplets of water of between 1 and 10 microns which are released when we talk (roughly 10,000 droplets), cough (around 40,000 droplets) or sneeze (travelling at an ejection velocity of up to 100kph). This size of particle tends to stay suspended in the air anywhere from an hour to half a day.
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From Vox, how coronavirus spreads outdoors vs. indoors
The publication of findings like this may have led some people to fear that opening windows could potentially allow the virus to enter their home and make them sick. But when we look at the problem closer, this fear is clearly unfounded. Furthermore, they could actually be increasing their chances of becoming sick and decreasing their immune defences to fight off a potential virus threat.
Not ventilating adequately to reduce the build-up of dangerous indoor air pollutants can lead to a range of potentially serious health problems. The WHO estimated around 3.8 million premature deaths in 2016 were from diseases attributed to poor indoor air quality such as acute lower respiratory infections, COPD, lung cancer, cardiovascular disease and asthma (which also put us a very high risk of severe illness from Covid-19).
It's all about the humidity
What about the perceived risk of the virus coming inside? While studies have shown that coronavirus may live on metal, glass, or plastic for up to nine days, there has been no solid evidence to suggest it can survive in the air outdoors for long enough to enable long-distance transmission. Recent studies have shown that Covid-19 survives better at low Relative Humidity (RH) (less than 50% RH) and that the opposite is true when it increases beyond this level. In Ireland, our outdoor RH rarely drops below 50%, even in summer, so the virus is unlikely to survive long enough in the outdoor air to travel inside.
However, it is much more common to have a RH of around 50% indoors as it is comfortable for us and helps to prevent mould growth. As we progress out of lockdown to a state of "new normal", with more indoor meetings of people from different households taking place, it is more important than ever to ensure that we take adequate steps to protect ourselves from potential infection. This means ventilating properly in addition to increasing our hygiene habits and understanding that increased occupancy also increases ventilation requirements.
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From SciShow, why does humidity make it feel hotter?
How can we reduce our exposure?
Whilst we may have changed our habits to reduce exposure to pathogens by washing our hands more frequently, avoiding airborne infections can be trickier. There are a number of steps we can take to reduce the likelihood of exposure to virus-laden particles in the air from Covid-19, as well as pollen, dust mites, pet dander and other allergens which can affect our health.
In addition to opening the windows more often and for longer, we can reduce the number of airborne particles we are likely to breathe in by wet cloth dusting, vacuuming regularly (using a HEPA filter) or using an adequately sized personal air purifier with good filtration.
The ventilation question
It's no wonder we are confused about ventilation given how the broad sweeping term is used along with other terms like "air change rates" which tell us nothing about the actual air. Recent studies are now calling for greater clarity through use of terms such as Outdoor Air or Supply Air.
While indoor ventilation helps to control airborne infection, it does not control transmission through droplet spread. Since droplets will not remain suspended in the air, airborne transmission and droplet spread must both be considered. Ventilation and temperature control can help with dilution and control of air flow patterns can also help with droplet spread.
Not opening the bathroom window of a person who is symptomatic or testing positive with Covid-19 can help avoid distributing virus-laden air particles around the house. It would be favourable to run an extractor fan (ducted to outside) for as long as possible in the bathroom of the person with Covid-19 symptoms and instead open windows in other parts of the house to direct the flow of any potential droplets or virus-laden particles outside.
Recirculation ventilation is not advisable at this time due to risk of spreading. This type of kitchen ventilation performs around 35% less efficiently than traditional "duct out" extraction and may be totally ineffective at removing the dangerous indoor air pollutants from cooking. Externally ducted extractor fans are still favourable if you are considering a remodel.
In the future, improvements in our heating, ventilation and air-conditioning system performance will hopefully make worries like these a thing of the past. For now, though, opening windows is actually one of the best things you can do to make sure you breathe easy until all of this blows over.
The views expressed here are those of the author and do not represent or reflect the views of RTÉ
