Negative pressure fans are particularly useful when:

The correct choice highlights the effectiveness of negative pressure fans in scenarios where victims are present in interior rooms with closed doors. In such cases, these fans help create a negative pressure gradient within the structure, which can aid in drawing smoke, heat, and toxic gases out of the enclosed space. This is particularly crucial when it comes to improving air quality for any victims trapped inside, potentially increasing their chances of survival while also facilitating rescue efforts by allowing responders to work in a safer environment with reduced impediments from smoke or hazardous fumes.

In situations like wildfires or general outdoor environments, the advantages of negative pressure fans may not be applicable because the outdoor airflow dynamics are very different from indoor environments. Additionally, when victims are absent from the scene or during evacuations, the focus shifts primarily on clearance rather than controlling the internal atmosphere, making the use of negative pressure fans less critical. The primary mission of negative pressure fans is to enhance safety for individuals who might still be inside a building, especially when they are compromised by closed doors that can isolate them from potential rescue and clean air.