What action should be taken when entering a building with a fire, to mitigate its spread through an open door?

When entering a building involved in a fire, closing the apartment door is crucial for controlling the fire's spread. An open door can act as a pathway for smoke, heat, and flames to propagate through the structure, worsening the situation and endangering lives. By shutting the door, firefighters can create a barrier that helps contain the fire within the room of origin, limiting oxygen supply and reducing the fire's ability to expand to adjacent areas.

This action is a fundamental principle in fire suppression tactics focused on preventing fire growth and protecting occupants and firefighters. It contributes to a safer environment for both civilians still inside and for first responders entering the building.