What is one indicator that a building may become unstable?

An indicator that a building may become unstable is interior collapse. This suggests that the structural integrity of the building is compromised, which can occur due to various factors such as fire damage, deterioration over time, or excessive load. When sections of a building's interior begin to collapse, it signals that the overall stability of the structure is at risk, and further collapse could occur without warning. This critical observation is crucial for safety during fire operations, as it helps firefighters assess the risks involved when operating within or near the building.

In contrast, healthy exterior paint is not related to structural stability, as it primarily serves an aesthetic purpose and may not reflect the underlying condition of the building. A stable foundation, while essential for overall building integrity, does not guarantee that there are no issues within the structure itself. Open windows, on the other hand, might indicate ventilation or cooling but do not directly relate to the stability of the building's structure.