What is spalling in relation to fire exposure?

Spalling refers specifically to the breakage and flaking of a material, particularly seen in concrete surfaces when they are exposed to intense heat. In the context of fire exposure, when concrete is subjected to high temperatures, the water trapped within the concrete can vaporize, leading to increased pressure. This pressure can cause pieces of the concrete to break away or flake off—this is known as spalling. This phenomenon can jeopardize the integrity of structures, making understanding spalling crucial for fire fighters and building safety professionals. The other options do not relate to the specific process that occurs in concrete under fire conditions. Cracking of glass pertains more to thermal stress in glass materials, melting of metal refers to materials reaching their melting point due to heat, and shrinkage of wood is related to moisture loss and not directly a result of fire exposure.