…[A] single lightning flash could kill over 50 people with one strike. It has happened in both China and India where people tend to crowd together during thunderstorms. There is definitely not safety in numbers when lightning is involved.
via Lightning could kill dozens at a sports venue: the importance of prevention.
The old rule used to be 30-30. Now the first 30 has been dropped. The rule is when the thunder roars, go indoors. If you can hear thunder at all, you are close enough for lightning to strike.