Final answer:
A Critical Incident is an event involving extreme stressors such as grave firefighter injuries or death, prompting the ISO to manage crew wellbeing through rotation or removal.
Step-by-step explanation:
An incident that involves unusually gruesome situations, such as serious firefighter injury, firefighter death, or other potential psychological stresses, is termed a Critical Incident. When such an incident occurs, it is the responsibility of the Incident Safety Officer (ISO) to initiate, through the Incident Commander (IC), a process of rotation and/or crew removal. This action is taken to manage the occupation-related stressors and reduce the risk of post-traumatic stress disorder (PTSD) among first responders, who are exposed to high levels of stress during their service.