From a sustainable work perspective, the aim of this article is to gain a better understanding of the firefighters’ working situations in France and the challenges associated with their duties. This will make it possible to identify the specific resources they need and constraints they face. The study, carried out in a departmental fire and rescue service (DFRS) in France, analyses firefighters’ activities during three 12 h shifts in three fire stations, based on direct observation and a quantitative and qualitative analysis of firefighters’ work situations. The results highlight the diversity and variability of situations in terms of duration and resources mobilised at the level of shifts, then interventions, and finally first aid interventions.