When studying fire behavior, the fire “triangle” and now “tetrahedron” come up. For this discussion, I’ll stick to the triangle which indicates the requirements for a fire. They are: Fuel, Oxygen and Heat. With an open door or window, Oxygen is readily available and thus will allow the fire to continue to grow. Often with all doors and windows closed, the fire will become oxygen starved and could potentially go out. Ever notice when the fire department enters the building, the fire seems to take off? More oxygen, more fire.
We have lost many buildings because the occupants leave the door open when they leave the building. If they had closed the door after them, the fire would have spread more slowly and could have resulted in less damage.
The bottom line: Close all doors when leaving.