As required by the Approved Documents for the Fire Safety Clauses of the New Zealand Building Code, Polystyrene must be protected in certain situations from direct exposure to a potential fire by surface coatings, claddings and linings, and concrete slabs.

The performance of Expanded Polystyrene in a fire situation depends on the temperature that the product is exposed to. above 500 degrees C, the combustible gas formed when EPS melts will self ignite (i.e does not require piloted ignition). Between approximately 350-500 degrees C, an ignition flame is required to ignite the combustible gas mixture. Below 350 degrees C, although a combustible gas is present above 200 degrees C, burning will cease when the ignition source is removed. At lower temperatures EPS will shrink and retreat from a heat source and will not ignite. 

A CSIRO report on toxicity of combustion products from cellular plastics concluded as follows:- ".... the potential toxic hazard appears to be no greater than for wood. Carbon monoxide is the principal toxic gas evolved and the toxicity due to any other gas is believed to be insignificant. Relatively little carbon monoxide is produced unless the polystyrene is flaming and, since it retracts from the flame, the likelyhood of high concentrations must be considered small in most fire situations...". For further informaion please contact Plastics NZ