Chinstrap or ventilation: what technique experts recommend against COVID-19

As we go through the current coronavirus pandemic, we learned that SARS-CoV-2 is a virus that is mainly spread by air, so it is very important to ventilate enclosed spaces.

But one of the fundamental care that we must take and apply in everyday life, not only against the virus that causes the COVID-19 disease, but also for other coronaviruses that cause, for example, the flu, is the use of a mask or mask.

Infectiologists permanently remember, that a person infected with COVID-19 releases aerosols containing the coronavirus when he talks, laughs or simply exhales. If the person does not wear a mask to block those aerosols, they will likely spread the virus into the air that could be inhaled by others nearby. In the open air, viral particles can disperse even in a light wind. But in the interior of a room, where there is no wind, particles tend to concentrate and remain. Good ventilation can help break the concentration of viral particles, but it can not do everything, they point out.

“Ventilation is excellent, but we know that if we are outdoors, the risks are less. Being able to recreate the same amount of airflow you would have with your natural wind patterns alone in a busy confined indoor space is incredibly difficult to do,” explained Krystal Pollitt, professor of epidemiology and chemical and environmental engineering at the Institute of Global Health at Yale University, in the United States.

After two years of living with COVID-19, we now know that the most common and probable transmission of the virus occurs through aerosols. What are aerosols? According to the World Health Organization (WHO) they are viral particles that are suspended in the air. When humans breathe, talk, sing, cough or sneeze, the respiratory droplets emitted mix into the surrounding air and form an aerosol. Because larger droplets fall rapidly to the ground, respiratory sprays are often described as being made up of smaller droplets less than 5 microns, or about one-tenth the width of a human hair.

That is why these infections tend to occur in events of superpropagation, which are defined when a single person infects many others in a short time and in a limited space. Most of the documented superpropagations occur indoors and have involved large groups gathered in poorly ventilated spaces or attendees who did not wear masks or respect social distance. This suggests that the pathogen travels easily through the air, as opposed to the initial belief that close-range encounters and infected surfaces were the main risks.

“Ventilated air has good circulation and is relatively safe. But when ventilation is not as good, the air is not as well mixed and there may be areas within a room with a higher concentration of particles,” said Varghese Mathai, an assistant professor in the Department of Physics at the University of Massachusetts-Amherst, who has conducted studies on how coronavirus spreads in an environment.

“You can't really predict where these areas aren't well mixed in a room. Really, it is a multidimensional problem, and it is not easy to predict in a room not so well mixed how safe it is to stay for a long duration,” added Mathai. And if the transportation system wants maximum efficiency to cool or heat the air in a cabin, it can close the air intake and use what is already inside, explained Aly Tawfik, director of the Fresno State Transportation Institute and associate professor at the Department of Civil Engineering and Geomatics at California State University, Fresno, United States.

In May 2020, Tawfik and his team conducted an experiment to see how a viruses through buses with a typical ventilation system. Using non-toxic colored candles and steam, they simulated how air flowed on a variety of buses. They found that HVAC systems are extremely efficient and keep cold or warm air inside a bus much longer than some might expect. When the team introduced smoke, they saw it spread in seconds and fill the entire cabin. Even when they opened the doors and brought fresh air into the HVAC systems, the smoke lingered for minutes. Researchers believe the virus behaves the way smoke did and could persist even after an infected person has left the bus.

“These were unpleasant findings, because it means that opening doors and windows doesn't help much,” the expert concluded. With another experiment, the team tried to see if they could treat the air to make it safer. They tested the buses with three viruses similar to the coronavirus. Cooling the air mitigated an average of about 80% of viruses, and warming was around 90%. “That doesn't necessarily mean it's safe, because this 10% is still millions of viruses,” Tawfik said. On the one hand, it is not clear how much virus is needed to infect someone. HEPA filters mitigated about 94% of viruses. Ionizers were a little less efficient, but photocatalytic oxidation and UV lights were better. UV lights in the HVAC system eliminated about 99% of viruses.

Traveling by plane without a mask

People can get COVID-19 on airplanes, especially when an infected person does not wear a mask, scientific studies have shown, but the air system of an airplane is much more important than that of a bus or train.

Airplanes use HEPA filters that can capture about 99% of airborne particles. They also have better air circulation when flying. Air usually enters through the top of the cabin, is extracted through the floor vents, fed through those filters, and finally sent back to the cabin.

Airplanes bring air from top to bottom about 20 to 30 times per hour, creating a 50-50 mixture of outdoor and recirculated air and reducing the potential spread of the virus. So, the risk of getting sick is low, experts say. However, people generally spend much more time on airplanes than on the subway or bus, and more time on a crowded plane can increase someone's exposure.

When a plane is parked, it doesn't have that superior circulation. “Aircraft systems are a bit similar to bus systems when they are on the ground. This is why you will notice that the temperature is not so well regulated then, and it is also so when the same amount of fresh air is not circulating. So it's about dealing with the same challenges,” Tawfik concluded.

KEEP READING: