Which of the following is NOT associated with rollover characteristics?

Rollover is a phenomenon in which unburned combustible gases accumulate in a space, and when they reach a sufficient concentration, they ignite and create a flame front that rolls across the ceiling towards the ventilation openings. The correct choice indicates that involving unburned contents is not characteristic of rollover. In rollover, it is specifically the combustion of gases that have accumulated and led to ignition.

During the growth stage of a fire, rollover is likely to occur, as the fire develops and heat creates ideal conditions for unburned gases to accumulate. The involvement of fire gases is central to rollover, as it is these gases that can reach a flammable range and ignite. Therefore, the ignition of gases reaching a flammable range is a critical component of rollover. In contrast, the notion of unburned contents suggests physical materials that have yet to be ignited, which does not align with the behavior of rollover involving primarily the ignition of gases.