waterreactive

Waterreactive materials are substances that react with water to form heat, hydrogen gas, or other products. These reactions can be rapid or even explosive under certain conditions, especially when water is present as a liquid and the material is finely divided. The term is used in chemical safety to indicate the need for moisture control during handling, storage, and transport.

Common examples include alkali metals (lithium, sodium, potassium) and alkaline earth metals (calcium). They rapidly form hydroxides and hydrogen on contact with water. Metal hydrides such as sodium hydride NaH and calcium hydride CaH2 release hydrogen when hydrolyzed. Calcium carbide CaC2 reacts with water to yield acetylene and calcium hydroxide. Some reactive hydrides and organometallics, like lithium aluminium hydride LiAlH4, can react violently with water, producing heat and hydrogen.

Hazards associated with water reactivity include heat buildup, ignition of released hydrogen, pressure buildup, splashing, and formation of corrosive or toxic byproducts. Materials may ignite spontaneously in air after reacting. Storage and handling require dry, moisture-free environments, exclusion of water and humid air, and segregation from acids and oxidizers. Labels, safety data sheets, and risk assessments should specify water reactivity and appropriate controls.

Safety measures include using inert atmospheres or sealed, dry containers; handling in a glovebox or fume hood; and having compatible, non-water-based quenching or extinguishing options for emergencies. In the event of contact with water or moisture, remove ignition sources and follow emergency procedures.