The invention refers to a flame-retarding and flame-blocking agent in the form of a liquid suspension that efficiently slows down the progress of fire and at the same time, blocks forest fires, acting as a chemical firebreak and as a fire extinguisher, as well as to a method of making the suspension. The application process comprises spraying the diluted aqueous suspension/solution of the invention on a strip of land, forest, or silviculture, without harming the environment, animals, agricultural products, and humans. The product acts for a long time after application, is stable for storage, effective regardless of the water used for dilution, easily dispersible in water, biodegradable without containing toxic products or releasing highly toxic gases, and free of heavy metals. The product has a synergistic action between its components, and it is intended to save lives, natural resources and heritage.