How can you use ventilation and air filtration to prevent the spread of coronavirus inside?

The vast majority of SARS-CoV-2 transmission comes in, mostly from inhaling airborne particles containing the coronavirus. The best way to prevent the virus from spreading in a home or business would be to simply keep infected people away. But this is difficult to do as an estimated 40% of cases are asymptomatic and asymptomatic people can still spread the coronavirus to others.

Masks do a decent job of spreading the virus in the environment, but if an infected person is sitting in a building, some virus will inadvertently escape into the air.

I’m a professor of mechanical engineering at the University of Colorado Boulder. Much of my work has focused me on controlling the transmission of invasive diseases into the air indoors, and I have been asked by my own university, my children’s schools and even the Alaska State Legislature for advice on how to can make indoor spaces safe during this pandemic.

Once the virus escapes into the air in a building, you have two options: bring in fresh air from outside or remove the virus from the air inside the building.

It’s all about fresh, outdoor air

The safest indoor space is one that constantly has a lot of outdoor air that replaces the stomach air inside.

In commercial buildings, outdoor air is mostly pumped through heating, ventilation and air-conditioning (HVAC) systems. In homes, outside air enters through open windows and doors, in addition to being sucked in through various nooks and crannies.

Simply put, the fresher, outdoor air in a building, the better. Insertion into this air dilutes any contaminant in a building, or a virus or anything else, and reduces the exposure of everyone inside. Environmental engineers like me quantify how much outdoor air enters a building with a measure called the exchange rate for air. This number quantifies the number of times the air in a building is replaced with outside air in an hour.

Although the exact rate depends on the number of people and the size of the room, most experts consider roughly six air changes per hour to be good for a room of 10 meters by 10 meters with three to four people there. In a pandemic, this should be higher, with one study from 2016 suggesting that an exchange rate of nine times per hour reduced the spread of SARS, MERS and H1N1 in a Hong Kong hospital.

Many buildings in the US, especially schools, do not meet recommended ventilation rates. Fortunately, it can be pretty easy to get more outdoor air into a building. Keeping windows and doors open is a good start. Placing a box of in a window that blows out can also greatly increase air exchange. In buildings that do not have operating windows, you can change the mechanical ventilation system to increase the amount of air it pumps. But in every room, the more people inside, the faster the air needs to be replaced.

By measuring CO2 for air measurements

So how do you know if the room you are in has enough air exchange? It’s actually a pretty hard number to calculate. But there is an easy to measure proxy that can help. Every time you exhale, you release CO2 into the air. Since the coronavirus is often spread by breathing, coughing or talking, you can use CO2 levels to see if the room is full of potentially infected exhaustion. The CO2 level lets you estimate when enough fresh air is entering.

Outside, CO2 levels are just above 400 parts per million (ppm). A well-ventilated room will have about 800 ppm CO2. Any higher than that and it’s a sign that the room needs more ventilation.

Last year, researchers in Taiwan reported on the effect of ventilation on a tuberculosis outbreak at the University of Taipei. Many of the rooms in the school were underventilated and had CO2 levels above 3,000 ppm. When engineers improved circulation and got CO2 levels below 600 ppm, the outbreak stopped completely. According to the study, the increase in ventilation was responsible for 97% of the decrease in transmission.

Since the coronavirus is spread through the air, higher CO2 levels in a room probably mean that there is a higher chance of transmission if an infected person is inside. Based on the study above, I recommend trying to keep the CO2 levels below 600 ppm. You can buy good CO2 meters for about $ 100 online; just make sure they are within 50 ppm exactly.

Air purifiers

If you are in a room that cannot get enough outside air for dilution, consider an air purifier, also called air purifier. These machines remove particles from the air, normally using a filter made of tightly woven fibers. They may contain particles that contain bacteria and viruses and may help reduce disease transmission.

The U.S. Environmental Protection Agency says air purifiers can do this for the coronavirus, but not all air purifiers are the same. Before you go out and buy one, there are a few things you need to remember.

The first thing to consider is how effective a filter for air purifier is. Your best option is a cleaner that uses a high-efficiency particulate air (HEPA) filter, as these remove more than 99.97% of all particle sizes.

The second thing to consider is how powerful the cleaner is. The larger the room – as the more people in it – the more air needs to be cleaned. I’ve partnered with some Harvard colleagues to put in place a tool to help teachers and schools determine how powerful an air purifier you have for different classrooms.

The last thing to consider is the validity of the claims made by the company that produces the air purifier.

The association of household appliance manufacturers certifies air purifiers, so the AHAM-verified seal is a good place to start. In addition, 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 air fresh when coming outside

Both the World Health Organization and US Centers for Disease Control and Prevention say that poor ventilation increases the risk of coronavirus transmission.

If you have control over your indoor environment, make sure you get enough fresh air from outside circulating inside the building. A CO2 monitor can help give you an indication if there is enough ventilation, and if CO2 levels start to go up, open some windows and take a break outside. If you can not get enough fresh air in a room, an air purifier may be a good idea. When you get an air purifier, you need to make sure that they do not remove CO2, so although the air may be safer, CO2 levels could still be high in the room.

If you enter a building and it feels hot, stuffy and full, chances are there is not enough ventilation. Turn around and leave.

By paying attention to air circulation and filtering, improving them where you can, and staying away from places where you can’t, you can add another powerful tool to your anti-coronavirus toolkit.

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