Collapse of structures using _________ construction can occur early in the incident without warning.

• A. Heavyweight
• B. Lightweight
• C. Conventional
• D. Steel Frame

Answer: (B)

Lightweight construction is prone to rapid, unexpected failure when exposed to fire because its members and connections are small and rely on lightweight gusset plates and joints that lose strength quickly as heat builds. The lack of thermal mass allows temperatures to rise fast, weakening wood and fasteners so the roof or floor can collapse suddenly with little or no warning. Heavier, conventional, or steel-frame construction have more mass or different failure patterns and tend to show warning signs or take longer to fail, making early, sudden collapse less likely. This scenario describes lightweight construction.