Which one of the following chemicals is used in foam fire extinguishers?

Aluminium sulphate is a key chemical component used in chemical foam fire extinguishers. In these systems, aluminium sulphate reacts with sodium bicarbonate (baking soda) to produce carbon dioxide gas [t3][t7]. This reaction occurs in the presence of a foam stabilizer, which helps trap the generated carbon dioxide to create a thick, stable foam capable of smothering fires, particularly liquid pool fires [t2][t7]. The resulting gelatinous precipitate of aluminium hydroxide further aids in the firefighting process [t1]. While modern firefighting often uses Aqueous Film Forming Foams (AFFF) or fluorinated foams, the traditional chemical foam extinguisher specifically relies on the reaction between aluminium sulphate and sodium bicarbonate [t3][t4]. Other sulphates like copper, cobalt, or nickel sulphate are not used for this purpose in standard fire protection equipment.

Sources

1. [1] https://www.science.gov/topicpages/f/fire+fighting+foam