Reopening businesses after COVID-19 

Businesses have been gradually reopening after lockdown, but Coronavirus is still something we are dealing with. We need to be aware of the risks so we can take measures.

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.

Data about the lockdown

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, gyms, malls.

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 something 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 contract the virus when hanging out in crowded indoor spaces.

Know the risks so you can take measures

A single sneeze or cough can contain up to 200 million viral particles. In a short time, those in front 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 reaching every point of the room (**).

All this clearly explains how it can be easy to get infected by the virus in crowded indoor environments with poor ventilation. That might be the case, for instance, of offices, public transportation or restaurant, which do not usually have sophisticated ventilation systems (***). And the fact that we can produce droplets even when speaking, poses a great risk, especially in the case of an asymptomatic positive individual.

The Chinese restaurant case study

Reopening businesses after COVID-19

All this has explained by a recent study titled “Evidence for probable aerosol transmission of SARS-CoV-2 in a poorly ventilated restaurant”. The above-mentioned study shows how an asymptomatic individual positive to SARS-CoV-2, infected nine other people sitting in a restaurant with 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 minimize the possibility of infection for other occupants, is cleaning indoor air through ventilation systems. In fact, these systems can give a great 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 measure.

The importance of ventilations systems

The use of ventilations systems in spaces such as restaurants, bars, shops, offices and gyms, had 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.

But ventilation systems need to be used correctly in order for them to be effective.

Cleaning and maintenance activities

Of course, 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 in indoor environments during the air exchange process, it is important that ventilation systems can adequately filter and clean the outdoor air.

And finally, air-exchange.

There is a close correlation between the ventilation-rate and infection possibility. That means the higher is the ventilation rate per hour in a room, the lower is the possibility of infection for the occupants.

Correlation between ventilation rate infection possibility in a nutshell

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, for instance, were people usually spend from 2 to 4 hours, 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, we need a higher number of ACH.

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.


- (*)“A world in lockdown”,

- (**) “The Risks - Know Them - Avoid Them”,

- (***) “Putting a balance on the aerosolization debate around SARS-CoV-2”,

- “Evidence for probable aerosol transmission of SARS-CoV-2 in a poorly ventilated restaurant” ,

- (****) “Association of infected probability of COVID-19 with ventilation rates in confined spaces: a Wells-Riley equation based investigation”,