Which of the following is a common sign of structural collapse?

A common sign of structural collapse is typically indicated by the presence of cracks and sagging roofs. These physical deformations suggest that the integrity of the structure has been compromised, possibly due to factors like fire damage, excessive weight, or deterioration over time. Cracks can appear in walls, beams, and columns, while sagging roofs indicate that the structural supports may no longer be able to bear loads as they were designed to. This visual evidence is crucial for firefighters and emergency responders to assess the situation and mitigate risks associated with potential collapse.

While smoke and fire, high temperatures, and increased foot traffic can signal dangerous situations, they do not specifically indicate imminent structural failure like cracks and sagging do. Smoke and fire primarily indicate active combustion, which may eventually lead to a collapse, but they do not provide direct physical signs of structural issues. High temperatures, similarly, denote a hazardous environment but do not represent failure in the structure itself, and increased foot traffic may indicate an evacuation or rescue situation rather than warning signs of collapse.