What is a common sign of prolonged fire exposure in buildings?

The occurrence of dark smoke from truss roofs or floors is a significant indicator of prolonged fire exposure in buildings. When fire burns for an extended period, it produces dense, dark smoke, which is often laden with soot and other particulates. This dark smoke can indicate that the fire is consuming building materials like wood or synthetics, which are more likely to emit dark smoke when they are burning.

In the context of truss roofs or floors, the presence of dark smoke suggests that the structural integrity of these components may be compromised. Prolonged exposure to fire can lead to charring and weakening of trusses, which are critical for support within the structure. Firefighters and first responders can use this information to assess the fire's impact and make informed decisions about tactics for extinguishment and structural stability during their operations.

The other options do not serve as direct indicators of prolonged fire exposure. Smoke alarms going off can happen at the onset of fire exposure. Rapid water application is a tactical response to ongoing fire conditions rather than a sign of prolonged exposure. Increased lighting conditions are not relevant to fire exposure and do not indicate changes in fire behavior or structural risks. Thus, dark smoke is a key sign that indicates a higher risk associated with fires that have