Certified Fire Protection Specialist (CFPS)

What accounts for a major part of natural air movement in buildings under normal conditions?

1. Ventilation systems

2. Stack effect

3. Occupant movement

4. Equipment operation

The correct answer is: Stack effect

The stack effect plays a significant role in natural air movement within buildings under normal conditions. This phenomenon occurs due to the temperature differences between the indoor and outdoor environments. Warm air tends to rise because it is less dense than cooler air. As it rises, it creates a lower pressure area at the base of the building, pulling in cooler air from outside through openings or lower levels. This effect is particularly pronounced in taller structures, where the height enhances the pressure differences that drive the upward movement of air. Ventilation systems, while important for managing indoor air quality, rely on mechanical means to move air rather than natural forces. Occupant movement contributes to airflow but is typically localized and less predictable than the consistent and systemic influence of the stack effect. Similarly, equipment operation can cause air movement but is dependent on specific appliances running and varies by situation. In contrast, the stack effect remains a fundamental and ongoing source of natural ventilation under various weather conditions, making it a major contributor to the overall air movement in buildings.