What happens during flame rollout in combustion systems?

During flame rollout in combustion systems, the flame indeed burns outward through the secondary air opening. This phenomenon occurs when there is a failure in the combustion process, often due to insufficient combustion air or a blocked venting system. When the flame does not remain contained within the combustion chamber, it escapes through the openings, which can lead to unsafe conditions. This is a critical issue as it poses a risk of fire and can indicate underlying problems with the appliance that requires immediate attention.

In contrast, the other scenarios do not accurately represent what happens during flame rollout. For instance, if the flame remained contained in the combustion chamber, it would imply that the combustion process is functioning correctly, which is not the case during a rollout situation. Furthermore, while appliances can sometimes shut down automatically in response to severe failures, this does not typically occur during flame rollout itself. Additionally, a blockage of the combustion air intake might contribute to a situation leading to flame rollout, but it does not describe the actual event where flames escape from the combustion area.