What is "spalling" in relation to fire investigation?

In the context of fire investigation, spalling refers specifically to the phenomenon where concrete or masonry materials blow apart or flake off as a result of exposure to extreme heat during a fire. This occurs because the intense heat can break down the structural integrity of these materials, leading to cracking and, ultimately, fragments being ejected or dislodged. Such evidence can be crucial in fire investigations as it helps to determine the severity of the fire and the conditions under which it burned.

Identifying spalling can aid investigators in assessing how long the materials were exposed to high temperatures and the nature of the fire itself. This physical evidence can provide insights into the fire's intensity, duration, and the effectiveness of fire suppression efforts, all of which are key factors in understanding the dynamics of the fire event. The other options do not accurately represent the phenomenon of spalling in relation to fire investigation.