Fire-retardant

A fire retardant is a substance that reduces flammability of fuels or delays their combustion. This includes chemical agents, but may also include substances that work by physical action, such as cooling the fuels, such as fire-fighting foams and fire-retardant gels. Fire retardants may also be coatings applied to an object, such as a spray retardant to prevent Christmas trees from burning. Fire retardants are commonly used in fire fighting.

Home fires damage about 400,000 homes, and cause approximately 7 billion US dollars in direct damage annually in the United States. Because of the importance of prevention, fire retardation has become a very notable industry.

In general, fire retardants reduce the flammability of materials by either blocking the fire physically or by initiating a chemical reaction that stops the fire.

There are several ways in which the combustion process can be retarded by physical action:

Commonly used fire retardant additives include mixtures of huntite and hydromagnesite, aluminium hydroxide, and magnesium hydroxide. When heated, aluminium hydroxide dehydrates to form aluminum oxide (alumina, Al₂O₃), releasing water vapor in the process. This reaction absorbs a great deal of heat, cooling the material into which it is incorporated. Additionally, the residue of alumina forms a protective layer on the material's surface. Mixtures of huntite and hydromagnesite work in a similar manner. They endothermically decompose releasing both water and carbon dioxide, giving fire retardant properties to the materials in which they are incorporated.

...
Wikipedia