What is the value of peer support groups for emergency rescue workers (police officers, EMTs, and firefighters)?

Evidence suggests that first responders, such as police officers, EMTs, and firefighters, are under a great deal of stress. For example, the national suicide rate of police officers is two to three times that of other people in the population (see the link below for more information).
One of the ways that first responders are increasingly dealing with stress is critical incident stress management (CISM), a peer-led way to help first responders to deal with trauma and stress. This process was developed to help first responders by leveraging the knowledge of their peers and by recognizing that first responders already know how to cope with traumatic and stressful events. However, some critical incidents are so stressful that first responders' coping strategies can't handle them. As a result, they have thoughts and feelings that are troubling but normal and that should be recognized as natural outcomes of the events. 
CISM teams receive supervision from mental health professionals, but they aren't therapeutic in nature. Instead, their goal is to provide advice and education, such as recognizing the signs of stress. The focus is on practical advice, and first responders are much more likely to accept advice if it comes from a peer rather than an outsider. Peers speak the same language as the first responders, and the first responders know that peers understand their concerns. People in cultures such as the police are resistant at times to getting help from the outside, as they don't feel that outsiders understand their culture. If they speak with peers, they can process critical events in a safe way and process what they went through without feeling judged. First responders, particularly police officers, do not want to be referred to a mental health professional, as that kind of professional has to impose consequences, such as taking away their gun. Instead, while processing an event with peers, first responders can talk about the event, including how it might have affected them at home, and learn practical strategies for dealing with stress, such as exercise and balanced meals.