How Retardants Work: (2) Chemical action: (a) Reactions in the gas phase: chemical reactions in the flame (i. e. gas phase) can be interrupted by fire retardants. Generally, these retardants are organic halides (haloalkanes) such as Halon and PhostrEx. However, there are situations where the released gas might be more dangerous when this type of retardant is involved. (b) Reaction in the solid phase: some retardants break down polymers so they melt and flow away from the flame. Although this allows some materials to pass certain flammability tests, there is argument over if the fire safety is truly improved by the production of flammable plastic droplets. (c) Char Formation: For carbon-based fuels, solid phase flame retardants cause a layer of carbonaceous char to form on the fuel surface. This char layer is much harder to burn and prevents further burning. (d) Intumescents: These types of retardant materials add chemicals which cause swelling up behind the protective char layer, providing much better insulation behind the protective barrier. In additions to being added to plastics, these are available as paints for protecting wooden buildings or steel structures