Ventilation and “clean” air are essential to prevent COVID-19 – why is it so difficult to implement?

Since the start of the pandemic, it has been known that the transmission of the new coronavirus is through the secretions that are expelled through the mouth and nose when talking, sneezing or coughing from infected people, which can remain in the air for hours.

From where the main preventive measures in restaurants, bars, shops, schools and other public places aim to improve the ventilation of environments, the installation of filters or carbon dioxide sensors to monitor air quality Rather than rigorously disinfecting surfaces, which is considered to be ineffective in preventing disease.

“We’ve spent billions and billions of dollars disinfecting, which is no use, but things like having a $ 50 filter in every classroom, we didn’t. For the aerosol scientist at the University of Colorado at Boulder, José Luis Jiménez, “Touching a contaminated surface has a 1 in 10,000 chance of causing infectionAccording to the United States Centers for Disease Control and Prevention, therefore, hand washing and standard cleaning practices are probably sufficient to remove any coronavirus that lands on surfaces or in hands. “

A large body of data now suggests that COVID-19 is spread mainly by inhaling fine aerosol particles that can remain in the air for hoursthe researchers argued in separate publications in BMJ Yes The Lancet.

Ten lines of scientific evidence support airborne transmission, while little data supports the theory of droplet contagion or contact with contaminated surfaces as the primary means of spread of the virus. On April 30, the World Health Organization (WHO) updated its transmission information to recognize aerosols as the source of spread.

So things, learning how to clean the air from potentially virus-laden aerosols could have long-term health benefits and keep businesses and schools open during future outbreaks, including other illnesses. Clean air strategies can help stop the resurgence of COVID-19 after vaccination campaigns achieve long-awaited herd immunity, as well as prevent flu, colds and many other respiratory illnesses, including potential future pandemics.

Researchers believe that “Removing respiratory viruses from the circulation would improve not only health, but also profitability”. In the United States alone, annual economic losses from influenza are $ 11.2 billion, and other respiratory viruses cost an estimated $ 40 billion. Global monthly damage from COVID-19 is estimated at $ 1 trillion.

“There has to be a change in the perception that we cannot afford the cost of control, because the economic costs of infections can be huge and can exceed the initial costs of the infrastructure to contain them,” the scientists wrote.

Ventilation and filtration, the keys to a virus-free environment?

Air cleaning is first and foremost a matter of adequate ventilation and filtration. ANDThe equipment to do these things has been around for decades.

“We have the tools, we have the knowledge,” said Charles Haas, an environmental engineer at Drexel University in Philadelphia.

Ventilation replaces stale indoor air with fresh outdoor air, diluting the concentration of any viruses present. Simply circulating air with fans is not enough. “If all you’re doing is moving around in dirty air, the net effect won’t be beneficial,” Haas said.

Most experts recommend completely replacing all the air in a room six times an hour. That’s about the average for many schools, offices and retirement homes, said Nora Wang Esram, senior research director for the American Council for an Energy Efficient Economy, a Washington-based nonprofit. DC. Hospitals often exceed this level of ventilation. Homes are among the least ventilated places people spend their time, some exchanging air only once every two hours, he says.

Getting adequate ventilation can be as simple as opening a window or turning on the fan on a heating and air conditioning unit. But there are tradeoffs in rising energy costsEsram warned. “Usually we say increase the ventilation, which means your fan has to run faster. Open the hatch and bring in more fresh air. Put a filter. But there is a limit and a balance. It’s not like you can maximize everything at once, ”he explained.

In many places, including office buildings, hotels and shops, windows do not open. There, the heating and cooling system is the only option to remove stale air and bring in fresh outdoor air.

What happens in a room makes a big difference in how much virus is removed from the air, reported Martin Bazant, a physicist and chemical engineer at MIT, and MIT colleague John Bush, an applied mathematician. “An interesting part of the science that has developed over the past year … is the heavy reliance on vocalization [para] the generation of aerosols ”, argued Bazant. For example, wheezing during exercise does not generate as many extra drops. It really comes from your vocal cords. ” Talking or singing generates more aerosol particles, and the louder the sound, the more aerosols are generated. So a choir room would need more ventilation than a school library, where people sit quietly.

Another aspect to consider is that increasing ventilation in a room can carry infectious viruses into rooms connected by HVAC vents. If a person with COVID-19 were in a room and the CVC system was turned off, infectious virus particles would remain in that room, he says. “As soon as you start adding airflow to the space, you move the virus from the infected room to the uninfected room. [conectada]”said Timothy Salsbury, a mechanical engineer at the Pacific Northwest National Laboratory in Richland, Washington.

And that’s where the leak comes in. Experts recommend filtering the air through materials that can trap airborne particles containing the virus. These devices include HEPA filters or heating and air conditioning filters with a minimum efficiency ratio, or MERV, value of 13 (MERV values ​​range from 1 to 16. The higher the number, the better the filter can. effectively capture small particles). Increasing filtration to remove coronavirus from the air may be a good substitute for increasing ventilation, Jiménez said.

HEPA filters effectively remove viruses, pollen, dust, bacteria and other particles from the air. Some units can be expensive and they tend to move air slowly, effectively reducing the number of air changes per hour. Some large rooms or rooms where many people congregate, such as classrooms, may require multiple units.

A study in the Netherlands found that HEPA units removed air from bubbles that replaced coronavirus-carrying aerosols better than open windows and doors.

Filters will remove viruses from the air in the long term, but unless there is a filter between two people, it will not stop the transmission of the virus in the short term. Bazant analyzed. That’s why masks are important, because if both people use masks, “it’s like having two filters.”

Restaurants and bars have an added challenge in the filtration department as customers do not wear masks when eating and drinking. “And lingering over dinner can create a cloud of particles that other diners can breathe in,” added Kimberly Prather, aerosol researcher at the Scripps Institution of Oceanography in La Jolla, Calif., For whom “the more people go. the time in potentially laden air with viruses, the greater the risk of infection ”.

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