What is the primary concern regarding trusses and joists when exposed to fire?

When evaluating the primary concern regarding trusses and joists when exposed to fire, the focus is on their propensity for structural collapse. Trusses and joists are designed to be lightweight and are often constructed from materials that, while engineered for strength, can be significantly weakened when subjected to high temperatures from a fire.

During a fire, the heat can cause the steel or wood within these frameworks to lose their structural integrity, leading to a potential failure of the entire system. This means that firefighters need to be particularly cautious when working in structures that utilize trusses and joists, as the risk of sudden collapse poses a serious threat to safety.

The other options do not reflect the critical issues associated with fire exposure. For example, while trusses and joists may include some non-combustible components, they generally are not categorized in this manner overall. Additionally, although some materials can resist higher temperatures, this resistance diminishes significantly in the context of ongoing exposure to extreme heat, which makes them prone to collapsing rather than being stable under such conditions. Lastly, improved firefighting capabilities are not a characteristic of trusses and joists under fire conditions; instead, the focus should be on the hazards they present.