Fire behaviour of fire retarded EPS insulation products
Like most organic materials, polystyrene foam is combustible. However, in practice, its fire behaviour depends upon the conditions under which it is used, as well as the inherent properties of the material. The inherent properties depend on whether or not the foam is made of fire retarded material or not.
Most EPS insulation products have been made of fire retarded quality for decades. This is achieved by adding a very small quantity (<1%) of a fire retardant agent to the material. The fire retardant is polymerised into the molecular structure and is insoluble in water, which ensures no fire retardant leaches from the material into the environment. Research shows that the fire retardancy remains effective for decades.
The fire behaviour of fire retarded EPS is significantly different from non fire retarded EPS. Exposed to heat, fire retarded EPS shrinks away from the heat source. The probability of ignition of the material is significantly reduced and welding sparks or cigarettes normally will not ignite it. Another effect of the fire retardant is that its decomposition products cause flame quenching: as soon as the heat source is taken away the flame extinguishes. The effect is clearly illustrated by a demonstration in which a hole is burned into a big block of EPS using a torch. As soon as the torch is taken away the fire extinguishes.
The reaction to fire behaviour should be evaluated not on the material or product, but on the building element or construction element level (also called works). A basic design rule with EPS and other insulating materials is never to use the material uncovered. Because EPS never should be the material facing the fire, reaction to fire classification of the material or naked EPS product is only of formal importance.
The layer really determining the reaction to fire behaviour is the surface layer of the construction, which faces the fire and covers the EPS insulation material. Using a combination of EPS insulation and specific cover layers it is always possible to design a construction which fulfils the fire requirements. Correctly applied and installed EPS is not of influence to the occurrence and the development of fire in a building.