During a fire, what happens during the calcination process?

During the calcination process, chemically bound water is driven out of gypsum, leading to its transformation into a powder called calcium sulfate hemihydrate, commonly known as plaster of Paris. This process is significant in fire investigations because it helps identify materials that were present during the fire and can offer insights into the conditions of the fire.

When gypsum is exposed to high temperatures, the water that is chemically bonded within its structure is expelled. This is critical to understand when analyzing fire damage, as it provides information about the temperatures reached during the fire and the materials involved.

The other options address different phenomena that may occur during a fire, but they do not specifically relate to the calcination of gypsum. Water evaporation from wood and conversion of fuels into gas concern different aspects of combustion and material change, while a temperature increase simply indicates a general condition without specifying a particular chemical process like calcination.