I'm afraid I have a different opinion regarding CISD (and probably regarding many other forms of "Psychiatric First Aid")

Critical Incident Stress Debriefing (CISD) is often used in in an attempt to prevent or minimize adverse outcomes of traumatic exposure. There are relatively few controlled studies on CISD, and among trauma researchers (not necessarily those who train and "sell" CISD to agencies) there is IMHO no consensus that CISD is actually helpful. Some studies have shown it can be harmful, others have not.

"The intervention has generated controversy, perhaps in part due to its widespread use in the absence of solid empirical evidence from randomized clinical trials to demonstrate its effectiveness. Now a new study by VA and DoD investigators provides the first such evidence—and the results are disappointing. "

Participants in carefully done CISD probably DO feel that the intervention was helpful. This perception (among participants) that it was helpful and not harmful suggests that it will continue to be used... if only for the social and emotional comfort it initially provides. It probably reduces immediate distress and improves group cohesion among first-responders and military units.

However, aside from this there is little evidence of meaningful effect in preventing or reducing any of the serious psychological consequences seen among trauma survivors (such as ASD or PTSD). Neither the presence or absence of CISD has an effect on these problems.

According to The National Center for PTSD
"recent research indicates that psychological debriefing is not always an appropriate mental-health intervention. Available evidence shows that, in some instances, it may increase traumatic stress or complicate recovery. Psychological debriefing is also inappropriate for acutely bereaved individuals. While operational debriefing [this is NOT really CISD..sic] is nearly always helpful (it involves clarifying events and providing education about normal responses and coping mechanisms), care must be taken before delivering more emotionally focused interventions.

A recent review of eight debriefing studies, all of which met rigorous criteria for being well-controlled, revealed no evidence that debriefing reduces the risk of PTSD, depression, or anxiety; nor were there any reductions in psychiatric symptoms across studies. Additionally, in two studies, one of which included long-term follow-up, some negative effects of CISD-type debriefings were reported relating to PTSD and other trauma-related symptoms (1).

Therefore, debriefings as currently employed may be useful for low magnitude stress exposure and symptoms or for emergency care providers. However, the best studies suggest that for individuals with more severe exposure to trauma, and for those who are experiencing more severe reactions such as PTSD, debriefing is ineffective and possibly harmful. "