What term describes the spread of fire from one floor to another through exterior windows?

• A. Vertical fire extension
• B. Horizontal spread
• C. Lateral fire growth
• D. Upward flame propagation

Answer: (A)

Vertical fire extension describes the spread of fire from one floor to another through openings in the building’s exterior, such as windows. When heat and flames from a lower level vent through a window, they can ignite the contents on an upper floor, allowing the fire to climb to higher levels. This differs from horizontal spread, which stays on the same floor, and from interior vertical spread via stairs or shafts, which follows internal pathways. Recognizing this path is crucial for anticipating rapid escalation and for strategies that limit window openings or seal them to slow the vertical reach of the fire.