Working principle of flame retardants

Usually, flame retardants prevent a fire by physically blocking it or triggering chemical reactions, thereby reducing the flammability of the material.
Body movements
There are several methods that can delay the combustion process through physical actions:
By cooling: Some chemical reactions actually cool the material.
By forming a protective layer to prevent the underlying material from catching fire.
By dilution: Some flame retardants release water and/or carbon dioxide during combustion. This may dilute the free radicals in the flame enough to extinguish them.
Commonly used flame retardant additives include a mixture of magnesite and magnesite, aluminum hydroxide, and magnesium hydroxide. When heated, aluminum hydroxide dehydrates to form alumina (alumina, Al2O3), during which water vapor is released. This reaction absorbs a large amount of heat and cools the material it binds to. In addition, alumina residues form a protective layer on the surface of the material. A mixture of calcium magnesium carbonate and water magnesite works in a similar way. They absorb heat and decompose, releasing water and carbon dioxide, endowing the material they are in with flame retardancy.
Chemical action
Gas phase reaction: Chemical reactions in flames (i.e. gas phase) can be interrupted by flame retardants. Usually, these flame retardants are organic halides (haloalkanes), such as Halon and PhostrEx. The chemicals used in these types of flame retardants are usually toxic.
Solid phase reaction: Some flame retardants decompose polymers, causing them to melt and flow away from the flame. Although this allows some materials to pass certain flammability tests, it is not yet clear whether the generation of flammable plastic droplets truly improves fire safety.
Carbonization: For carbon based fuels, solid phase flame retardants can cause the formation of a layer of carbon carbon on the fuel surface. This carbon layer is more difficult to burn and prevents further combustion.
Intumescent materials: These types of flame retardant materials contain chemicals that cause expansion behind the protective carbonization layer, providing better insulation. They can be used as plastic additives and as paints to protect wooden or steel structures.