What condition occurs when unburned products of combustion accumulate in the ceiling layer to ignition concentration?

The condition in which unburned products of combustion accumulate in the ceiling layer to an ignition concentration is known as flameover or rollover. This phenomenon occurs when the heat from below ignites these accumulated gases, typically creating a more intense fire hazard. During a fire, particularly in large or enclosed spaces, hot gases rise and collect near the ceiling. If the temperature and concentration of these gases reach a certain threshold, they can ignite suddenly, often resulting in a fireball as the accumulated flammable gases ignite all at once.

Understanding flameover is crucial in fire inspections and firefighting, as it highlights the dangers of flammable gases accumulating in the upper layers of a room, which can lead to rapid spread of fire and increased risk to life and property. Firefighters and inspectors must be aware of this phenomenon to ensure safety protocols are in place to prevent such dangerous conditions from developing.