What can the hospital do to prevent my friend from killing himself?

The best thing that the hospital can do to prevent imminent suicide is to put your friend on constant watch, first in the emergency room and then on the hospital psychiatry ward. The surest way to prevent someone from killing herself is for someone else to be there to prevent it. The nurses and the technicians have experience in keeping depressed people from harming themselves, and they’ll be following explicit hospital guidelines on what to do in a suicide emergency.

In addition to staying with and watching your friend, the hospital can provide an environment free of deadly objects, treat her depression, and offer sedation if she is panicky or afraid.