Surviving Asteroid Impacts: Planetary Defense Strategies.
The safety distance from a city killer asteroid, which would destroy a city but not cause mass extinction, depends on the size, speed, and density of the asteroid. The Tunguska event in 1908 flattened 80 million trees over an area of 2,150 square kilometers, and the safe area was probably 10s of kilometers from the epicenter of the impact. The Chelyabinsk event in 2013 released 75 to 60 times less energy than the Tunguska event, and the 1,491 injuries came from shattered windows. If an asteroid is known to be coming toward where you live, it is important to put as much distance between you and it as possible.