This collapse pattern happens when one outer wall fails while the opposite wall remains intact, creating a triangular void where victims are likely to survive.

• A. V-Shaped Collapse
• B. Pancake Collapse
• C. Cantilever Collapse
• D. Lean-to Collapse

Answer: (D)

Lean-to collapse happens when one exterior wall fails while the opposite wall remains intact, causing the structure to tilt and leave a triangular void next to the standing wall. That wedge of space can trap victims but still provides a pocket where air and a narrow path to escape or be rescued may exist, which is why survivors are more likely in that scenario with a prompt rescue. The triangular void is a hallmark of this pattern, distinguishing it from other collapse shapes: a V-shaped pattern forms when two opposing walls fail and the void resembles a V, a pancake collapse crushes floors downward with little to no triangular void behind a standing wall, and a cantilever collapse involves a section tipping away on a supported edge rather than a single wall on one side remaining intact.