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This story originally appeared in The Conversation
From Shelly Miller, University of Colorado Boulder
The vast majority of SARS-CoV-2 transmission occurs indoors, mainly through inhalation of particles in the air that contain the coronavirus.
The best way to prevent the virus from spreading around a home or business is to simply keep infected people away. However, this is difficult to do when an estimated 40% of cases are asymptomatic and asymptomatic people can still transmit the coronavirus to others.
Face masks adequately prevent the virus from spreading into the environment. However, when an infected person is in a building, it is inevitable that a virus will leak into the air.
I’m a professor of mechanical engineering at the University of Colorado Boulder. Much of my work has focused on how to control indoor infectious disease transmission indoors, and my own university, my children’s schools, and even Alaska state law have asked me for advice on how to make them indoors safe during this pandemic period.
Once the virus gets into the air inside a building, you have two options: bring in fresh air from outside or remove the virus from the air inside the building.
Fresh air from outside
The safest indoor space has enough outside air to replace stale indoor air.
In commercial buildings, outside air is typically pumped through heating, ventilation and air conditioning systems. In private households, outside air enters through open windows and doors and seeps through various nooks and crannies.
Put simply: the fresher the outside air in a building, the better. Bringing this air in will dilute any pollutant in a building, be it a virus or something else, and decrease the exposure of people inside. Environmental engineers like me quantify the amount of outside air entering a building using a measure called the air exchange rate. This number indicates how often the air in a building is replaced by outside air in one hour.
While the exact rate will depend on the number of people and the size of the room, most experts think about six air changes per hour is good for a 10-foot by 10-foot room of 3 or 4 people. . In a pandemic this should be higher. A 2016 study suggests that an exchange rate of nine times an hour will reduce the spread of SARS, MERS, and H1N1 in a Hong Kong hospital.
Many buildings in the United States, especially schools, do not meet recommended ventilation rates. Fortunately, it can be quite easy to get more outside air into a building. Keeping doors and windows open is a good start. Attaching a case fan to a blower window can also greatly improve air exchange. In buildings with no windows that open, you can change the mechanical ventilation system to increase the amount of air it pumps. But in every room, the more people are in the room, the faster the air needs to be exchanged.
Using CO2 to measure air flow
So how do you know if the room you’re in has enough ventilation? It’s actually quite a difficult number to calculate. However, there is an easy to measure indicator that can help. Every time you exhale, you release CO2 or carbon dioxide into the air. Since the coronavirus is most commonly transmitted through breathing, coughing, or speaking, you can use the CO2 levels to determine whether the room is filling with potentially infectious exhalations. You can use the level of this component to estimate whether there is enough fresh air flowing in from the outside.
In the open air, the CO2 content is slightly more than 400 particles per million (ppm). A well-ventilated room contains around 800 ppm carbon dioxide. Slightly higher than that and it’s a sign that the room may need more ventilation.
Last year, Taiwanese researchers at Taipei University reported on the effects of ventilation on a tuberculosis outbreak. Many of the classrooms were under-ventilated and had CO2 levels above 3,000 ppm. When engineers improved air circulation and got CO2 levels below 600ppm, the outbreak stopped completely. According to the research, the increase in ventilation accounted for 97% of the decrease in transmission.
Since the coronavirus spreads in the air, higher levels of CO2 in a room likely means that there is a greater chance of transmission if an infected person is indoors. Based on the previous study, I recommend keeping CO2 levels below 600 ppm. You can buy good CO2 meters online for around $ 100. Just make sure they are accurate to 50ppm.
If you find yourself in a room where you don’t get enough outside air to dilute it, consider an air filter, also known as an air purifier. These machines remove particles from the air, usually using a filter made of tightly woven fibers. They can trap particles that contain bacteria and viruses and reduce the transmission of diseases.
The United States Environmental Protection Agency says air filters can do this for coronavirus, but not all air filters are created equal. There are a few things to consider before buying one.
The first thing to consider is how effective an air purifier filter is. Your best option is a cleaner that uses a HEPA (High Efficiency Particulate Air) filter as it removes more than 99.97% of all particle sizes.
The second thing to consider is how strong the cleaner is. The larger the room or the more people there are, the more air needs to be cleaned. I worked with a few colleagues at Harvard to develop a tool that would allow teachers and schools to determine how well performing the air filter you need for different class sizes.
The last thing to consider is the validity of the information provided by the company that manufactures the air filter.
Air filters are certified by the American Appliance Manufacturers Association, so the AHAM Verified Seal is a good place to start. Additionally, the California Air Resources Board has a list of air purifiers that are certified as safe and effective, although not all use HEPA filters.
Keep the air fresh or get out
Both the World Health Organization (WHO) and the U.S. Centers for Disease Control and Prevention say poor ventilation increases the risk of coronavirus transmission.
When you are in control of the indoor climate, make sure there is enough fresh outside air flowing into the building. A CO2 monitor can help you give an indication of whether there is adequate ventilation and whether CO2 levels are starting to rise. Open some windows and take a break outside.
If you can’t get enough fresh air into a room, an air filter might be a good idea. When you receive an air filter, remember that it does not remove CO2. Although the air is safer, the level of CO2 in the room can still be high.
If you walk into a building and it feels hot, clogged, and overcrowded, there is probably not enough ventilation. Turn around and go.
By paying attention to air circulation and filtration, improving them where you can, and staying away from places where you can’t, you can add another powerful tool to your coronavirus toolkit.
This article was translated by El Financiero. This article is republished by The Conversation under a Creative Commons license. Read the original article.