What is a 'positive-pressure ventilation' (PPV) and how does it relate to vertical ventilation?

• A. PPV is a method of exhausting air from a structure using a fan
• B. PPV uses a fan to push air into a structure; it can be used before or after vertical ventilation to help establish a favorable airflow pattern
• C. PPV involves opening all windows only
• D. PPV uses only natural draft to ventilate

Answer: (B)

Positive-pressure ventilation is the technique of using a powered fan to push fresh air into a burning building, creating interior pressure higher than outside. That inflow drives the room air, heat, and smoke toward available exhaust openings, establishing a defined airflow path. In vertical ventilation, opening a roof or other vertical exit provides a clear route for the hot gases to escape. Using PPV in conjunction with that vertical exhaust is common because it helps set and maintain the favorable airflow: pushing air in at an entry encourages the smoke and heat to move toward the vertical shaft and out through the roof vent. PPV can be applied before vertical ventilation to start moving air toward the exhaust, or after to sustain the flow as the vertical opening is established. The key idea is that PPV creates a controlled, forced inflow that, together with the vertical exhaust, directs smoke and heat upward and out rather than letting them spread laterally.