Flame rollout occurs when:

Flame rollout occurs when the combustion air zone (CAZ) pressure is lower than the burner compartment pressure. This condition leads to a situation where the flame is not contained within the combustion chamber and instead escapes into the surrounding area, creating a dangerous scenario.

When the pressure in the CAZ is lower than that in the burner compartment, it disrupts the proper flow of combustion gases. As a result, the combustion process does not function as designed, leading to the potential for flames to roll out of the appliance and into the living space. This phenomenon can pose a significant risk of fire and exposure to harmful combustion gases.

Understanding the dynamics between CAZ pressure and burner compartment pressure is critical in assessing the safety of combustion appliances and ensuring they are functioning correctly. Proper installation and sufficient airflow also play vital roles in preventing issues like flame rollout, but the specific relationship indicated in this correct answer is the primary cause.