After how many minutes of exposure to fire will unprotected lightweight steel and wooden trusses fail?

Unprotected lightweight steel and wooden trusses are particularly vulnerable to fire due to their construction and materials. When exposed to high temperatures, lightweight steel can lose its structural integrity quickly, often within a matter of minutes.

The correct choice indicates that unprotected trusses can begin to fail in the critical timeframe of 1 to 5 minutes under fire exposure. This is significant for firefighters to know, as it underscores the urgency of providing immediate protection to these structural elements during firefighting operations. The rapid failure of such trusses can lead to catastrophic structural collapse, posing a serious risk to both firefighters and occupants inside the building.

Understanding this timeframe helps firefighters to develop strategies for tackling fires where these types of trusses are present, ensuring they can protect themselves and others by addressing the fire quickly to prevent structural failure.