BART has put up a diagram that allows riders to see how they are circulating air through BART cars. The cars are filled with supply air, circulated air, and fresh air. It takes approximately 70 seconds to replace all the air inside the car. Riders inside the cars have 75% filtered air and 25% fresh air, you can get more information about BART's airflow here.
BART cars filter & replace inside air about every 70 seconds. This was the case before COVID-19 and is still now. Air is filtered more effectively than in an office or grocery store. We've also begun new pilot tests for better filtration.
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