Which time range is associated with catastrophic failure in lightweight construction?

• A. 5-7 minutes
• B. 7-9 minutes
• C. 10-12 minutes
• D. 15-20 minutes

Answer: (A)

The key idea is that lightweight construction can reach a sudden, total loss of strength very quickly when exposed to fire. These systems have little mass to absorb heat, so temperatures rise through timber and fasteners fast. As heat weakens connections and reduces the cross-section of members, a single critical member or joint failing can trigger a rapid, cascading collapse. That rapid progression typically falls into a short window, around five to seven minutes, making the catastrophic failure time range the five-to-seven-minute mark.

The other options imply longer times before collapse, which doesn’t match how quickly lightweight assemblies can lose their load-carrying capacity under fire conditions.