Chlorine trifluoride is an interhalogen compound with the formula ClF3. This colorless, poisonous, corrosive, and extremely reactive gas condenses to a pale-greenish yellow liquid, the form in which it is most often sold (pressurized at room temperature). Despite being famous for its extreme oxidation properties and igniting many things, chlorine trifluoride is not combustible itself. The compound is primarily of interest in plasmaless cleaning and etching operations in the semiconductor industry, in nuclear reactor fuel processing, historically as a component in rocket fuels, and various other industrial operations owing to its corrosive nature.

This oxidizing power, surpassing that of oxygen, causes ClF3 to react vigorously with many other materials often thought of as incombustible and refractory.

It is known to ignite sand, asbestos, glass, and even ashes of substances that have already burned in oxygen. In one particular industrial accident, a spill of 900 kg of ClF3 burned through 30 cm of concrete and 90 cm of gravel beneath.

There is exactly one known fire control/suppression method capable of dealing with ClF3—flooding the fire with nitrogen or noble gases such as argon. Barring that, the area must simply be kept cool until the reaction ceases. The compound reacts with water-based suppressors and CO2, rendering them counterproductive.

Exposure to larger amounts of ClF3, as a liquid or as a gas, ignites living tissue, resulting in severe chemical and thermal burns. ClF3 reacts violently with water and exposure to the reaction also results in burns. The products of hydrolysis are mainly hydrofluoric acid and hydrochloric acid, which are usually released as steam or vapor due to the highly exothermic nature of the reaction.