Final answer:
In case of a significant firefighter injury or fatality, the ISO should use an initial PIA session as a debriefing to listen to firefighters, facilitate discussion, and promote well-being and learning.
Step-by-step explanation:
If a firefighter injury was significant or if a firefighter fatality occurred, the Incident Safety Officer (ISO) should use any initial Post-Incident Analysis (PIA) session as a debriefing to listen to firefighters. This choice, 'B) Debriefing', offers the opportunity for those involved to discuss what occurred, voice their experiences, share their emotions, and start the process of learning from the incident. Debriefings are critically important for ensuring the physical and mental well-being of firefighters after a traumatic event, and they can also serve as a preliminary step towards preventing future incidents.