Why do ventilation controlled fires tend to burn more intensely?

Ventilation controlled fires tend to burn more intensely primarily because they experience increased oxygen access. In fire dynamics, oxygen is a critical element that supports combustion. When a fire is ventilation controlled, it typically means that the availability of oxygen is limited by the environment. However, when ventilation is introduced into the area, such as through openings like windows or doors, the amount of oxygen available to the fire increases significantly.

This surge in oxygen allows the fire to burn more rapidly and at a higher intensity, as it can now sustain and amplify the combustion process. With more oxygen available, the flames can grow larger, and the heat production can escalate. Consequently, the fire can transition to a more vigorous burning phase, leading to potential flashover conditions if enough oxygen is introduced quickly.

In contrast, a lack of sufficient airflow would not provide the fire with the necessary oxygen, leading to a slower and potentially smoldering combustion process. Therefore, the correct choice highlights the importance of oxygen in fire behavior specifically in ventilation controlled situations.