Which is a sign that a structure is susceptible to collapse?

A structure showing doors stuck in shifted frames indicates that there has been a significant shift in the structural integrity of the building. This condition often suggests that the load-bearing elements of the structure may have become compromised due to factors such as fire damage, water saturation, or other structural failures. When frames shift, it can mean that the foundation or walls are no longer providing adequate support, increasing the risk of collapse. Identifying doors that are difficult to open due to a change in frame alignment serves as a crucial warning sign for firefighters, alerting them to potential hazards when operating within or near the structure.

In contrast, discoloured drywall at floor level can indicate moisture intrusion, while inverted fire patterns indicate a fire was possibly more intense at the floor and is not a definitive sign of structural failure. Delaminated plywood typically relates to water damage or poor material quality but does not necessarily signal an immediate risk of collapse. Thus, the mechanism behind how each condition can relate to structural integrity helps to underscore why shifts in door frames are particularly critical in assessing the safety of a building during firefighting operations.