What is spalling?

Spalling refers to the process in which concrete (or other materials) breaks away or separates in chunks, often as a result of exposure to high temperatures in a fire. When concrete is subjected to extreme heat, it can develop internal stresses due to the expansion of trapped moisture or the breakdown of its structural integrity. This can lead to explosive spalling, where pieces of the concrete suddenly break loose. This phenomenon is a critical consideration for fire investigators, as it can indicate the severity of the fire and the performance of building materials during the event.

The other options describe different phenomena that are not relevant to spalling. For instance, the complete burning of wood refers to a combustion process, while the residue left on surfaces after a fire pertains to soot or ash deposition. Cooling hot metal after exposure to water is unrelated to spalling, as it describes thermal shock, not the breakdown of a material like concrete during a fire. Understanding the exact nature of spalling is vital in assessing fire damage and material performance.