Which of the following is NOT an indicator of a roof collapse?

Smoke exiting a door is not a direct indicator of a roof collapse. While the presence of smoke can suggest that a fire is nearby or that structural integrity may be compromised, it does not specifically indicate that the roof is in danger of collapsing. Other options like visible sagging of roof supports, fire coming out of a vent hole, and signs of structural failure all provide more direct evidence that a roof may be at risk of collapse.

Visible sagging of roof supports suggests that the weight of materials or fire damage has compromised the structural integrity, indicating possible imminent collapse. Similarly, fire coming out of a vent hole can signal intense conditions that may weaken the roof structure and lead to a failure. Structural failure of any portion of the building is a clear warning sign that the integrity of the entire structure, including the roof, could be compromised.

In summary, smoke exiting a door may indicate fire activity but does not serve as a specific warning of a roof collapse, distinguishing it from the other options that more directly signal potential structural failure.