CNN
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The US Centers for Disease Control and Prevention has extensively updated its ventilation guidance to help prevent transmission of the virus that causes covid-19 indoors.
The agency had advised people to ventilate indoor air before, but this is the first time a federal agency has set a goal (five air changes per hour) for the number of rooms and buildings to be ventilated.
Air quality experts cheered the updated recommendations.
“It is a monumental change. We have not had this. We haven’t had health-based ventilation standards,” said Joseph Allen, director of Harvard’s Healthy Buildings Program.
Allen says that while it’s easy to view the guidance just in the context of Covid-19, it will help with many other airborne hazards, such as wildfire smoke, allergens, and other infectious diseases, such as the flu.
The move comes a day after the United States ended its public health emergency over Covid-19. Public health officials have long downplayed the role of airborne spread in infectious disease transmission, and indoor air quality experts lobbied for years for the CDC to recognize the importance of ventilation in controlling of the pandemic.
“I am pleasantly surprised to see the CDC add this guidance. I find it ironic that they finally published ways to end the pandemic at the same time as declaring it over,” said Kimberly Prather, an atmospheric chemist at the University of California San Diego and the Scripps Institution of Oceanography.
In May 2020, Prather and his co-authors published a perspective article in the journal Science, explaining the airborne spread of Covid-19. Later that year, she and more than 200 other scientists wrote a letter to the World Health Organization and other public health authorities asking them to acknowledge and develop guidance to stop airborne spread.
“If they had broadcast and implemented these changes early on, there would never have been a pandemic,” Prather said.
The new CDC guidance was developed in conjunction with a new standard from the American Society of Heating, Refrigerating, and Air-Conditioning Engineers.
The CDC says that better indoor ventilation can reduce the concentration of viral particles in the air, which reduces a person’s risk of breathing them in and getting sick. Improved ventilation can also reduce the amount of virus a person could inhale, which could lower their infectious dose, which could play a role in the severity of their infection.
The new guide offers detailed recommendations on how to make indoor air healthier. Some of the strategies are as simple as opening a window to let in more outside air and using fans to increase the effectiveness of open windows.
In addition to better air circulation, the CDC recommends cleaning indoor air, using MERV-13 air filters in your HVAC system if possible. Air cleaners or purifiers can be helpful if they use High Efficiency Particulate Air (HEPA). The CDC says these are most important in high-risk areas like schools and doctor’s offices. Systems that use ultraviolet light to kill germs can also be helpful.
As for how much ventilation is enough, the CDC suggests at least five air changes per hour to reduce germs. That’s the equivalent of what a portable air filter provides, as long as it’s the right size for the space in which it’s used, the CDC says.
Ventilation and air cleaning strategies together can help achieve the goal.
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