What is the only construction material that does not yield heat when burned in pure oxygen?

Gypsum is a unique construction material in that it consists primarily of water in its chemical composition. When subjected to high temperatures, particularly in the presence of pure oxygen, gypsum does not contribute heat to the combustion process. Instead, it undergoes a physical change known as dehydration, which releases water vapor and helps to suppress flames and resist further burning. This property makes gypsum a crucial material in fire-rated assemblies and walls, as it can help contain fires and provide critical time for evacuation or intervention.

In contrast, materials like wood, steel, and concrete behave differently under fire conditions. Wood, being an organic material, combusts easily, producing substantial heat and flames. Steel, although not combustible, can lose its structural integrity at high temperatures, potentially leading to failure. Concrete, while more fire-resistant than wood, can still conduct heat and, under extreme conditions, may experience spalling or cracking. Thus, understanding the non-combustible nature of gypsum under these conditions highlights its essential role in fire safety in building construction.