It is also common for coaches to have swimmers practice starts from the blocks. This is safe when the lane space in front of the blocks is clear of other swimmers and the water depth is adequate.

Practicing starts when there are other swimmers in the same lane coming into the blocks is not safe. Some swimmers may not be able to consistently place their dives to assure that they enter the water at the required side of the lane. And the potential injury is much greater than when two swimmers collide while swimming past each other in the same lane. The additional momentum of the diving action increases the likelihood of serious injury when there is a collision.