Science News has this extensive review of the current viral transmission research for coronavirus.
What’s actually safe is unknown. It may depend on many factors, including whether people are inside or outdoors, how loudly people are speaking, whether they are wearing masks, how well-ventilated a room is, and how far the virus can really fly.
One should still wear a mask in public. This will help protect you and others no matter what the safe distance is for any particular situation.