Who should begin the preservation of a fire scene according to proper procedures?

The preservation of a fire scene is critical to ensure that evidence is not lost or contaminated, which is essential for an accurate investigation. The first due companies are responsible for establishing the initial command at the scene and begin the process of preservation as they’re the first to arrive and have a clear view of the situation. These crews typically have the responsibility to secure the scene, preventing unauthorized access and ensuring that key evidence remains intact for subsequent investigation.

In this context, it's essential to understand that while investigating Fire Marshals would play a significant role in the investigation process itself, they typically arrive after initial teams have secured the scene. The Fire Chief in command would likely oversee operations but may not be involved in the direct preservation activities that first arriving companies are tasked with. Finally, the last unit to leave the scene would not be appropriate for initiating preservation efforts, as their role is more about conclusion rather than the initial handling of a scene. Thus, the first due companies are the most logical and trained personnel to start preserving a fire scene effectively.