EPS Fire behaviour
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Improving the Fire Performance of Polystyrene Insulated Panel in New Zealand
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Effect of Heat on EPS
As EPS is heated it softens, and at about 150ºC it begins to shrink. This continues until it is reduced to its original density prior to expansion. Continued heating will melt it to liquid and then a combustible gas will form above 200ºC. This gas can be ignited at temperatures between 360ºC and 380ºC, and will self ignite around 500ºC. When burning, it produces 40 - 45 MJ/Kg of heat. Temperatures of this magnitude usually occur only in well developed fires.
Flammability
As with many construction and packaging materials, EPS must be considered combustible. Its fire behaviour depends on the type of material and its application conditions. It is important to distinguish between the two commonly used grades of EPS.
All EPS used in construction products in New Zealand contains a flame retardant conforming to AS 1366, part 3 - 1992.
The flame retardant reduces the flammability and spread of flame on the surface of EPS products, to such an extent that it is classified as "flame retardant" according to the European Standard DIN 4102. If ignited with a flame the EPS extinguishes itself as soon as the ignition flame is removed.
The flammability of EPS construction products is reduced with surface coatings, such as plaster, and metal cladding as in sandwich panels. Non flame retardant EPS, typically used in packaging, will sustain combustion and the resultant fire spread at a rate of about 3cm per minute over the surface. This is comparable to other combustible solid materials. EPS does not catch fire spontaneously, and small sources of ignition will not ignite it.
Smoke and Dangerous Gas Emissions
The burning of EPS is less harmful than burning timber and many other commonly used building materials. Gases released during combustion are predominantly carbon dioxide and carbon monoxide. Tests carried out in accordance with European Standard DIN 53436 show that the levels of dangerous gases are considerably less than those occurring when burning timber.
Early Fire Hazard Properties
Testing in accordance with AS 1530.3-1982 to determine early fire hazard properties shows that EPS compares favourably with many timbers in most categories.
Comparative Testing of some Materials to AS 1530.3 - 1982
'Test for early fire hazard properties of materials.' |
| Material |
Ignitability
Index
(0-20) |
Spread of
Flame Index
(0-10) |
Heat Evolved
Index
(0-10) |
Smoke Developed
Index
(0-10) |
| EPS(i) |
12 |
0 |
3 |
5 |
| Softboard (ii) |
16 |
9 |
7 |
3 |
| Oregon (ii) |
13 |
6 |
5 |
3 |
| Bluegum (ii) |
11 |
0 |
3 |
2 |
| Radiata Pine (iii) |
14 |
8 |
9 |
3 |
| Hardboard (iii) |
14 |
7 |
9 |
5 |
Experience in Fire Situations - Case Studies
Tiffany Food Factory, Christchurch (1989)
A small fire damaged the contents of the electrical control room, constructed of EPS sandwich panel. The flame retardant EPS was contained within the steel faces of the insulated sandwich panel and thus EPS did not fuel the fire.
Fletcher Moana Fisheries, Auckland (1991)
A significant fire caused extensive damage with losses estimated in excess of $1.5 million. The cool store and processing areas were both constructed of insulated sandwich panel, and metal clad EPS insulation was installed around pipe work at high level. 
Approximately 50% of the EPS pipe insulation melted, but being metal clad it was contained by the cladding and the EPS did not contribute to the fire. Similarly the flame retardant EPS in the sandwich panels melted, but was contained and this EPS did not contribute to the fire. The steel facing on the panel and the bolts holding the ceiling panels in place all performed satisfactorily in the fire.
House Fire in Howick, Auckland (1996)
This house fire caused one fatality and led to considerable, media comment about the flammability of EPS building materials, in this case EPS EIFS (Exterior Insulation Finishing System) cladding.
Detailed investigation by engineering consultant MacDonald Barnett Partners Ltd concluded that the EPS did not spread the fire. Only 5% of the EPS actually burnt and it added less than 1% to the total gases produced by the fire. The small amount of EPS which did burn only did so after the fire was well developed and the interior would have become untenable to occupants.
The New Zealand Fire Service stated that "The principal fuel for the fire in its early stages had been normal furnishings, drapes and household appliances."
