There are two EPS types prevalent in the building industry, of standard quality and flame-retardant or FR grade. The FR grades are modified to make the expanded material much more difficult to ignite and considerably reduce the rate of flame spread.
It is why the Expanded Polystyrene Association of Southern Africa (EPSASA) recommends FR grade EPS, although both types are extensively used for insulation, depending on the predetermined material behaviours, building conditions and fire conditions assessments.
Extensive EPSASA testing shows that the use of fire-retardant additives for EPS improves the behaviour of EPS in fire conditions. EPS-FR grade contains a small quantity of fire-retardant agent that is a self- extinguishing grade, environmentally friendly, and contains no additives such as toluene, dimethylbenzene, ethylbenzene, and does not contain prohibited substances (HBCD).
When exposed to a fire source, the FR grade foam will shrink rapidly and distance itself from the heat source to reduce the likelihood of ignition, its primary benefit. The additive will further decompose and cause a reduction of flames, limiting flame spread. Note that the FR grade EPS will stop burning if the ignition source is completely removed.
Expanded Polystyrene (EPS) manufactured by the Isowall Group is fast becoming recognized as the insulation material of choice by specifiers of “Bills of Quantities”. This comes largely as a result of our technical knowledge backed up by years of experience in the building and construction industry.
Heat release and gas toxicity
Expanded polystyrene foam is organic, and all EPS will eventually burn, including the FR grades. However, there are significant notable differences to be made between standard quality EPS and FR grade EPS, specifically considering heat release and ignition points.
For starters, fire ignition proves to be more difficult and delayed for EPS treated with a fire-retardant additive, especially for usual smaller heat fluxes less than 50 kW/m2. Also, no flaming ignition was observed at a heat flux of up to 20kW/m2.
The overall heat content of materials also influences fire severity in terms of fire growth. The rate of release of heat content is of major importance, and it is dependent on combustion conditions and ventilation. For higher heat fluxes above 50 kW/m2, the rate and peak of heat release were deemed lower for FR grades than for standard grades.
Heat release from expanded polystyrene materials is more rapid compared with other organic products such as timber, but of shorter duration. This is important and happens because of the unique chemical composition and lower density of expanded polystyrene foam, with only a 2% styrene mass and 98% air compared to other materials.
The calorific volume by volume of EPS material is also smaller compared to other cellulosic products, such as fibre insulating board or timber, although EPS materials have a higher calorific value than the more dense timber, for example (40 MJ/kg versus 18.6 MJ/kg).
Burning EPS will release smoke and gases. In both EPS grades, the toxicity of the released smoke fumes is considerably less than those of other commonly used materials. However, with FR grade EPS, the amount of gases such as carbon monoxide and monostyrene will be considerably less than standard quality EPS for higher temperatures (300°C – 500°C). Also, there is no negative effect on smoke development from the fire retardants in FR grades.
Isowall Group manufactures and distributes the Isolite range of EPS products to users of thermal insulation, packaging, semi-rigid cushioning, and specialised shape-moulded products. Our Isolite EPS sheets are FR Grade.
View here more properties of our Isolite EPS range.