Which type of mechanical ventilation uses fans to introduce clean air into a structure?

Positive pressure ventilation is the correct choice for the type of mechanical ventilation that uses fans to introduce clean air into a structure. This method involves creating a pressure differential by blowing air into a specific area, which forces out smoke and heat from the structure. The fans are strategically placed, often at entry points like doors or windows, to ensure that fresh air is pushed inside, helping to improve visibility and control the environment during operations, such as firefighting.

This technique is particularly beneficial in situations where there is a significant smoke buildup, as it can rapidly clear the area, allowing for safer and more effective firefighting efforts. Positive pressure ventilation not only facilitates a better atmosphere for personnel working inside but can also help in locating trapped victims by enhancing visibility and air quality.

Other ventilation types, such as negative pressure ventilation, work on a completely different principle by removing air from a space, which is not the focus of this question. Hydraulic and vertical ventilation refer to other techniques that do not primarily rely on fans to introduce air. Understanding the specific function and application of positive pressure ventilation is essential for effective response and safety in emergency situations.