Which of the following conditions indicates that a roof is unstable or untenable?

A condition that indicates a roof is unstable or untenable is when heavy smoke is being forced from the building under pressure. This scenario suggests that there is a significant amount of heat building up inside the structure, which can lead to structural failure. Pressurized smoke emanating from a building indicates that there is a major fire threat present, which can compromise the integrity of the roof and other structural elements.

This condition reflects the potential for a backdraft or flashover, where conditions may rapidly deteriorate, further endangering firefighters and increasing the risk of collapse. Therefore, the presence of heavy smoke under pressure serves as a critical warning sign that action must be taken to evaluate the situation and ensure the safety of all personnel involved.

Other conditions listed may present hazards or difficulties during firefighting operations, but they do not directly signify an immediate risk to the structural stability of the roof as strongly as the presence of pressurized smoke does.