There are three methods for flame retardance: vapor phase inhibition, solid phase char formation, and quench and cool systems.
1) The vapor phase inhibition approach to flame retardants aims to interrupt the radical gas phase of a fire. By disrupting the phase in which flammable gas is released the system is cooled and the supply of flammable gas is reduced or suppressed.
Bromine Flame Retardants (BFRs) are the most prolific flame retardant used for their vapor phase inhibition properties. Bromine in particular is used because as it is heated the compound releases active bromine atoms into the gas phase, before the material reaches its ignition temperature. These atoms quench the chemical reaction occurring within the flame and either extinguish the fire or slow the spread of the fire–such that there is increased escape time or increased time to attempt other means of fire extinction.
2) Solid phase char flame retardants are designed to build up the char layer, once the fire has begun. What is particularly interesting about the formation of char is it can have a two-fold benefit. It hinders the release of combustible gasses while also forming a protective layer that shields the underlying material from the heat of the flame.
Melamine-based flame retardants are commonly used for their solid phase char functions. These flame retardant compounds fall into the category of nitrogen flame retardants. When in the condensed phase the molecule structures transform into cross-linked structures. That is when the transformation process occurs and char is formed.
3) Quench & cool systems utilize hydrated minerals because of the endothermic reaction that occurs when the system is heated. In the presence of fire, the hydrated minerals release water molecules that cool the polymer and interrupt the combustion process. In more simple terms, the release of water is chemically induced and the system is then cooled such that reactive gasses are not released and therefore cannot burn.
Aluminum and magnesium hydroxides are two compounds that interfere with the burning process through the release of inter gases (like water vapor). In this process a protective char layer is formed or energy absorption–the amount of energy available for the spread of fire–is reduced.
