Written 8 June 2020
The COVID-19 emergency has had a huge impact on our society and the way we all live our lives. The restrictive measures on social and economic activities imposed by governments across the world to slow down the spread of the SARS-CoV-2 virus, have literally stopped our economies.
Since the outbreak of Coronavirus, nearly the entire global population has been affected by some form of containment measures. About 4.2 billion people or 54% of the global population, representing almost 60% of global GDP, have been subject to complete or partial lockdowns due to the COVID-19 emergency.
During these days, though, many countries – although with different timing – have been switching to a new phase, gradually resuming their economic activity, even reopening shops, restaurants and gyms.
Of course, this is great news. But while this is an important step for the recovery of the world economies, it is vital to be aware of the fact that Coronavirus is still an issue we are dealing with.
More specifically, while businesses such as restaurants, bars, gyms, and many others, are going to reopen to the public, it is important that both business owners and customers know that there is still a risk for people to get infected when congregating in indoor spaces.
A single sneeze or cough can contain up to 200 million viral particles. In a short time, those close by can receive a thousand virions, which is enough to lead to an infection. The viral load of an infected person can vary. The largest and heaviest drops fall almost immediately to the ground, while the others can remain suspended in the air, spreading more easily in indoor environments and potentially reaching every point of the room.
All this clearly explains how it can be easy to become infected by the virus in crowded indoor environments with poor ventilation; generally the case, for instance, in offices, public transport and even restaurants – which do not usually have sophisticated ventilation systems. And the fact that we can produce droplets even just speaking, poses a great risk, especially in the case of an asymptomatic positive individual.
Ventilation as a preventative measure
This is exactly what has been shown by a recent study entitled “Evidence for probable aerosol transmission of SARS-CoV-2 in a poorly ventilated restaurant”; which shows how an asymptomatic individual positive to SARS-CoV-2, infected nine other people sitting in a restaurant with a very low ventilation rate. In fact, the Chinese restaurant case study, shows that the ventilation rate in the restaurant was between 2.7 and 3.7 m³/h per person – 10 to 15 times lower the ventilation rate advised by most authorities and professional associations.
The study points out how ventilation systems and adequate air-exchange rate can be an important resource to clean indoor environments from contaminants – including viruses – in a space like a restaurant thanks to the extraction of the indoor air and the introduction of filtered air from the outdoor environment. This is important because, once a SARS-CoV-2 positive individual enters a building, the only way to minimise the possibility of infection for other occupants, is cleaning indoor air through ventilation systems, which contribute in reducing the concentration of SARS-CoV-2 in the air, and therefore the risk of transmission between people.
In conclusion, we need to be aware of the risks related to spending time in crowded indoor environments, but that should not prevent us from living our lives, since we will probably have to live with the virus until a vaccine will be available. This means we should know the risks in order to be able to avoid them through preventive measures.
The use of ventilation systems in spaces such as restaurants, bars, shops, offices and gyms, has been demonstrated to be an effective solution to protect people from the spread of SARS-CoV-2 during this pandemic. Then, business owners should consider ventilation as a preventive measure to protect both their business and their customers.
Also, it is important to understand that ventilation systems need to be used correctly in order for them to be effective.
So, to get the most out of the use of your ventilation system, it is important to carry out proper maintenance activities. It is therefore necessary to proceed with normal cleaning and maintenance activities to ensure correct operation.
Another important aspect, then, is related to the level of filtration of the outdoor air that the systems can guarantee. Since we do not want to introduce outdoor contaminants into indoor environments during the air exchange process, it is important that ventilation systems can adequately filter and clean the outdoor air.
The importance of air-exchange
There is a close correlation between the ventilation-rate and infection possibility. That means the higher the ventilation rate per hour in a room, the lower the possibility of infection for the occupants.
That has been clearly explained in the study “Association of infected probability of COVID-19 with ventilation rates in confined spaces: A Wells-Riley equation-based investigation”, which indicates that, once an asymptomatic infector who has not been identified as confirmed COVID-19 patient enters a public confined space, there is a 2% probability of infection at the common ventilation rate (500-2500 m3 /h). If we consider the case of a restaurant were people usually spend from 2 to 4 hours, for instance, we know that to keep the probability of infection between occupants at 1%, we need 2.4 ACH (/h) (air change per hour) if occupants are not wearing masks, while 0.6 ACH (/h) is enough if occupants are wearing masks. Of course, to keep the probability of infection even lower, a higher number of ACH is needed.
So, once an asymptomatic infector enters a public confined space, the risk of infection for other occupants is quite high if there is not proper ventilation in the building, or there is no ventilation at all. Therefore, it is fundamental to make sure that the ventilation system is properly sized and can provide the right exchange rate per hour.