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

Roof collapse indicators are critical for firefighter safety and effective incident management. When assessing a roof's integrity during a fire, the basic indicators typically include visible signs such as sagging, which suggests structural failure. A sudden increase in fire from a vent opening can indicate that the fire has spread unchecked, possibly due to compromised structural elements. High heat readings from a thermal imaging camera also signal potential dangers, revealing areas of excessive heat that could contribute to a collapse.

Vibration, while it can indicate potential structural concerns, is not universally recognized as a primary indicator of imminent roof collapse. Instead, vibrations could occur for various reasons unrelated to the structural integrity of the roof itself, such as external disturbances or vibrations from equipment. This makes it less reliable than the other indicators when assessing the risk of roof failure in a firefighting scenario.