Those most at risk for developing PTSD are the survivors of trauma, of course. The next most vulnerable are the rescue workers and volunteers at disasters, untrained in psychological techniques. They are seeing and smelling and feeling vivid, unimaginable horrors and fearing for their lives working in unstable structures. Firefighters and police officers, doctors, nurses, and EMTs may have more coping skills. However, all need mental health counseling during the recovery phase.
No prevention for PTSD exists, because traumatic events are often unpredictable and random. In some experimental studies, though, certain blood pressure drugs, if given immediately and taken over time, have shown promise in lowering the intensity of the symptoms, if symptoms are going to develop at all. The problem is that health care providers cannot predict who will develop symptoms and who will not.
For more information on PTSD please see WEB MD.