Which method is not the most reliable for determining whether there is hidden fire?

• A. Direct inspection
• B. Thermal imaging
• C. Odor of smoke
• D. Atmospheric monitoring

Answer: (B)

Thermal imaging isn’t the most reliable on its own because it only shows surface heat and depends on heat transferring to what the camera can see. A hidden fire can burn inside voids, behind walls, or within insulation where little heat reaches the exterior, so no hot spot may appear even though embers are active. It can also be misled by other heat sources, reflections, or ambient temperatures, giving readings that don’t reflect the true fire condition. While thermal imaging is a valuable tool to guide where to probe, it should be used alongside direct inspection and other indicators like odor and atmospheric measurements to confirm hidden fire. Direct inspection provides firsthand evidence of embers or smoldering material, and atmospheric monitoring can reveal combustion products that indicate ongoing fire, making those methods more reliable overall when confirming hidden fire.