Assessment of the Preventive Effect of Defusing on Traumatic Kindling

This is a multicenter, parallel-group, open-label controlled study with single blinded assessment. Visit 1: Following a traumatic event (TE), the investigator team will be deployed to the scene (when indicated by the pre hospital emergency service) and will have the opportunity to meet the victims in the first 24h following the event. The investigators are mental health professionnals (nurses, psychologists ans psychiatrists) and all trained in defusing and briefed on the study protocol. One professional will be designated as the investigator leader for the intervention to manage the participants randomization into one of two possible arms: * the control group: First Psychological Aid FPA (i.e., the immediate victim assistance procedure recommended by the WHO, which does not include a specific psychological intervention); or * the experimental group: defusing. For patients in the experimental group, the defusing session conducted by a trained clinician (see above) takes place immediately after randomization. FPA significantly differs from the defusing. This involves ensuring that basic needs are met: hunger, thirst, warmth/protection from cold, basic hygiene, and the ability to return home alone or with assistance. If needed, the caregiver links the victim to the appropriate resource For all study participants, several outcomes are measured at that timing * emotional distress will be measured using a visual analogue scale VAS (from 0 to 10). * PDEQ (Peritraumatic Dissociative Experiences Questionnaire) and PDI (Peritraumatic Distress Inventory) self-report questionnaires. * Demographic and clinical data will be collected: age, gender, family situation, education level, type of TE (natural or industrial disaster, terrorist attack, workplace accident, etc.), and type of exposure to the TE * The included participants will also receive a symptom montoring form to bring back to Visit 2 (V2). Participants will have to perform a daily self-assessment-twice a day (at midday and in the evening before bedtime)-for the 7 days following the TE, concerning the following dimensions: * Intrusive symptoms: assessing the presence of involuntary visual images of the stressful experience (visual flashes; rated from 0-not at all-to 4-extremely). * Rumination episodes: non-visual memories and distressing, involuntary thoughts regarding the stressful experience (Likert scale range 0 to 4). * Emotional distress associated with the TE (VAS from 0 to 10). * Nightmares related to the event occurring the previous night (Likert scale range 0 to 4). Visit 2 : taking place between Day 7 and Day 10 after the TE, in laboratory. It is composed of the following steps : 1. Baseline assessments * Emotional distress associated with the TE (VAS from 0 to 10). * Blood pressure (BP) and heart rate (HR) * Electrodermal activity (EDA) recorded over 5 minutes * Psychometric assessment Impact of Event Scale-Revised (IES-R) ; the Life Events Checklist for DSM-5 (LEC-5). - * While the participant is filling these questionnnaires, EDA will be recorded continuously, BP and HR will be assessed (5 minutes after the start of the scale administration) 2. The narrative : the participant will be have to expose again the traumatic event (TE) that led to their inclusion in the study. Concerning the narrative, the interview with the investigator will be stantardized so that the narrative will last at least 10 minutes and reactivate the memory of the TE as high as possible. * EDA will be recorded continuously * BP and HR will be assessed 5 minutes after the start of the narrative 3. After the narrative, emotional distress (VAS from 0 to 10), BP, HR and EDA (10 minutes supplementary) will be recorder Visit 3: taking place between Day 30 and Day 40 post TE by phone. It is composed of the following assessments : * Emotional distress associated with the TE (VAS from 0 to 10). * Standardized psychometric scales : PCL-5 (PTSD Checklist for DSM-5); SPS-10 (Social Provisions Scale - 10 items).