While masks do a decent job at keeping the spread of the SARS-CoV-2 virus at bay, if an infected individual is inside a building, it is almost inevitable that some of the virus will escape into the air. Once the virus is inside a building, you ultimately have two options to stop the spread: bring in fresh air and decontaminate the affected area, or remove the virus from the air from inside the building.
As the vast majority of SARS-CoV-2 transmission occurs indoors, most of it stems from the inhalation of airborne particles that contain 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 hard to do when an estimated 40% of cases are asymptomatic and asymptomatic people can still spread the coronavirus to others.
Fresh, outside air
The safest indoor space is one that constantly has lots of outside air replacing the stale air inside. In commercial buildings, outside air is usually pumped in through heating, ventilating and air-conditioning (HVAC) systems. In homes, outside air gets in through open windows and doors, in addition to seeping in through various nooks and crannies.
Simply put, the more fresh, outside air inside a building, the better. Bringing in this air dilutes any contaminant in a building, whether a virus or something else, and reduces the exposure of anyone inside. Environmental engineers like me quantify how much outside air is getting into a building using a measure called the air exchange rate. This number quantifies the number of times the air inside a building gets replaced with air from outside in an hour.
While the exact rate depends on the number of people and size of the room, most experts consider roughly six air changes an hour to be good for a 10-foot-by-10-foot room with three to four people in it. 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 U.S., especially schools, do not meet recommended ventilation rates. Thankfully, it can be pretty easy to get more outside air into a building. Keeping windows and doors open is a good start. Putting a box fan in a window blowing out can greatly increase air exchange too. In buildings that don’t have operable windows, you can change the mechanical ventilation system to increase how much air it is pumping. But in any room, the more people inside, the faster the air should be replaced.
If you are in a room that can’t get enough outside air for dilution, consider an air cleaner, also commonly called air purifiers. These machines remove particles from the air, usually using a filter made of tightly woven fibers. They can capture particles containing bacteria and viruses and can help reduce disease transmission.
The U.S. Environmental Protection Agency says that air cleaners can do this for the coronavirus, but not all air cleaners are equal. Before you go out and buy one, there are few things to keep in mind. If a room doesn’t have good ventilation, an air cleaner or air purifier with a good filter can remove particles that may contain the coronavirus.
The first thing to consider is how effective an air cleaner’s filter 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 bigger the room (or the more people in it) the more air needs to be cleaned. Depending on your room size, you can browse some of our air purifier offerings here.