Flame retardant (FR) characterizes the fire behavior of materials. Flame retardant materials prevent the spread of fire or are sufficiently resistant to fire. Corresponding materials, which must not contain asbestos or halogens such as fluorine, chlorine or bromine, are used in cables, printed circuit boards and other electronic components and systems.
The resistance of the base materials in terms of their flame retardancy is defined in FR classes. For printed circuit boards, there are four FR classes that differ in their resistance to fire. For example, FR class 2 has phenol as the reactive resin and hard paper as the reinforcing material. FR-3 is based on epoxy resin, FR-4 and FR-5 have a glass fabric composite as the reinforcing material, with FR-5 being designed for higher temperatures.
Unlike printed circuit boards, cables, especially indoor FO cables, are concerned with Flame Retardant non Corrosive( FRNC), which are used to specify fire behavior, reduce fire load and smoke emission. The flame retardancy of cables is specified in IEC 60332-1.