Which construction type is most prone to rapid collapse and requires a defensive exterior approach?

• A. Steel-frame construction.
• B. Wood-frame (light-frame) construction.
• C. Concrete tilt-up.
• D. Masonry bearing-wall.

Answer: (B)

Lightweight wood-frame construction is highly vulnerable to rapid structural failure when exposed to fire. The framing uses thin studs, joists, and roof trusses with lightweight connections and often concealed voids. As heat and flames attack these members, they can lose strength and fail quickly, sometimes with little warning, causing a fast collapse. That fragility makes interior entry extremely risky, so a defensive exterior approach is favored—focus on controlling and extinguishing the fire from outside and protecting exposures rather than committing personnel inside.

In contrast, heavier construction types like steel-frame, concrete tilt-up, and masonry bearing-walls have more inherent mass and redundancy, which generally means they resist fire longer and don’t collapse as quickly, allowing for different tactical decisions. The core idea is that the rapid-collapse risk and the need to fight from the exterior are most pronounced with lightweight wood-frame construction.