With the number of new COVID-19 cases continuing to fall in the U.S., health experts are promoting the use of CO2 monitors as a way to keep that trend going in the right direction as the country begins lifting social distancing restrictions.
“Using CO2 monitors I think is a really important piece of the process of reopening restaurants and schools and businesses because it's a relatively cheap, easily used measure of how well the ventilation rate is matched to the number of people in the room,” Alex Huffman, an associate professor of chemistry and biochemistry at the University of Denver, told Yahoo News.
For months, the Centers for Disease Control and Prevention has warned Americans that COVID-19 is spread via respiratory droplets, such as when a person coughs, sneezes or even simply breathes.
“These viruses may be able to infect people who are further than 6 feet away from the person who is infected or after that person has left the space,” the CDC says on its website.
Huffman is among a group of experts currently studying how the CO2 we breathe out can act as a proxy to gauge how much potentially infectious aerosol is in the room. CO2 monitors, in turn, can be utilized to assess the risk of transmission in a given environment, Huffman said, including situations in which people are either not wearing masks or doing so improperly. As a general rule of thumb, when CO2 levels go up, so does the risk of contracting COVID-19.
“After time it builds up, no matter how far you are away. There's no safe distance to breathing that in,” Huffman said.
In an interview with Yahoo News, Huffman explained how CO2 monitors work and why they can help the country keep COVID-19 at bay.
How would monitoring CO2 levels help stop the spread of COVID?
“When you breathe out, you breathe CO2 out, as well as aerosols that come out of your mouth,” said Huffman. “We can't measure the respiratory infectious aerosols in the room very easily. We can measure CO2 really easily and relatively cheaply, so we use this as a proxy. If CO2 is building up, infectious aerosol risk is also building up."
In terms of reopening restaurants, schools and businesses, Huffman said taking mitigation measures to place CO2 monitors around those establishments is “not hard.” Once the CO2 monitors (which cost $200 on average) are in place, “you have some process by which you observe those numbers and then make some decisions and say, 'If the number is too high, we change our protocols a bit,'” he said.
Once CO2 monitors are in place, what’s an ideal range?
An average outdoor reading of CO2 is about 400 parts per million. For indoors, Huffman said you want to keep the CO2 reading as low as possible, and there’s no perfect cutoff line. But he said anything less than around 800 parts per million is good. Anything above 800 parts per million means aerosol is building up, increasing the risk of COVID infection.
What can you do to increase ventilation and bring the CO2 concentration down?
Increasing ventilation is key, Huffman said, which can be accomplished as simply as by opening a window. Cracking a window in a car, for instance, can make a big difference. Huffman was recently driving with four other family members, and the CO2 levels started around 400 parts per million. After about an hour in the car with the windows up, the CO2 concentration skyrocketed to 4,000 parts per million. Huffman opened the windows, and the levels went back down to around 600 parts per million.
3/ #CO2 Example 1: Poorly ventilated minivan
Serendipitous obs of *really* high CO2 (4000+ ppm) w/ 2 adults/3 kids in car. Then one is #carsick & we crack 2 windows ~1”; CO2 drops immediately to ~750!
Interestingly, drive home had a) much lower CO2 & b) freshly cut tree in car! pic.twitter.com/raXdiPd4nC
— Dr. Alex Huffman (@HuffmanLabDU) December 7, 2020
Huffman said that if you’re in your home, you can also turn on exhaust fans, such as in the bathroom or kitchen, that pull air out of the house. He added that while it’s not the same as ventilation, you can clean the air that's in your home. “So you can have a room-portable HEPA filter, or you can pull that air through the ventilation system in your house, as long as you have a good MERV 13 filter,” he said. “That's not going to touch the CO2 at all in the room, but it will clean out the aerosol that's in the room.”
(Huffman also offers some do-it-yourself ways to measure ventilation rates in your home here.)
What other steps help reduce the spread of COVID-19?
Huffman emphasized that while ventilation and room filtration are certainly important pieces of the puzzle to reducing the risk of spreading COVID-19 in any environment, it’s also important to keep up those other mitigation efforts. “Masking is still critical. Distancing away from [people not in your household] is critical. And also reducing the time that you spend in that place is also critical,” he said. “Those three things are going to be critical, no matter what.”
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