According to the material, rollover occurs when which condition exists?

• A. There is spontaneous ignition
• B. Everything in a confined area ignites at almost the same time
• C. Unburned smoke is heated in the absence of oxygen
• D. Pressurized smoke rises to the ceiling and then begins to rapidly bank down

Answer: (A)

Rollover occurs when the hot, unburned fuel gases that have collected near the ceiling reach their ignition temperature and ignite on their own. In a compartment fire, heat causes fuel-rich smoke to stratify at the ceiling; when that layer autoignites, flames sweep along the ceiling, which is the rollover phenomenon. This is different from flashover, where the entire room ignites almost simultaneously, or from heating the smoke without ignition. The ignition of the ceiling-layer gases — spontaneous ignition of the upper gas layer — is what defines rollover.