Inside, Landon said, part of the concern is proper ventilation. Outside, there’s an unlimited amount of fresh air so the virus can’t become trapped. Indoors, without the introduction of new air, there may be an increased risk. In hospitals, ventilation systems exchange air at least six times in an hour. In regular buildings, like restaurants or libraries, there may be fewer air exchanges. Plus, turning up the heat or AC can make it difficult for common ventilation systems to filter air. Landon said indoors, both proper distance and wearing a mask are imperative.