Which statement best distinguishes flashover from a backdraft and lists two indicators for each?

• A. Flashover is the rapid involvement of all combustibles; indicators include a sudden heat rise and rollover flames at the ceiling; backdraft is ignition of accumulated gases with air entry; indicators include dense layered smoke and a sudden ignition when a door or window is opened.
• B. Flashover occurs only from the floor to ceiling and backdraft is caused by wind inside the structure.
• C. Flashover is slower than backdraft and shows smoke stratification.
• D. Backdraft occurs only outdoors and has no indicators.

Answer: (A)

Understanding the difference between flashover and backdraft comes down to how heat, fuel, and air interact inside a burning compartment. Flashover is the rapid involvement of all combustibles in the space as the temperature climbs to the point where all contents ignite almost simultaneously. The telltale signs are a sudden heat surge and the appearance of rollover flames at the ceiling as superheated gases ignite in sequence.

Backdraft, on the other hand, results from the buildup of flammable gases produced by pyrolysis in a oxygen-poor environment; when air is suddenly introduced, those gases ignite explosively. Its indicators include dense, layered smoke and a dramatic, often rapid ignition when a door or window is opened and air rushes in.

The other statements don’t fit because they misstate how these phenomena occur or their indicators—for example, flashover isn’t a floor-to-ceiling progression, backdraft isn’t caused by internal wind, and the notions of slower progression or smoke stratification don’t accurately describe the two events.