Fire Danger and Polystyrene

Polystyrene does not support a fire. The authorities controlling polystyrene’s usefulness as a product regulate that polystyrene is not to burn on its own. Polystyrene used in construction is treated with a fire retardant to sufficient levels so that once the heat source is removed the polystyrene cannot continue burning and self extinguishs.

The process of combustion is when solid fuel (coal, wood etc) is heated to such an extent that gases eminate from the fuel. These gases combust with oxygen and produce more heat which in certain circumstances lead to the spread of the fire. Polystyrene is no different so fire retardants were added by regulatory authorities to such a level to ensure the combustion process ceased if polystyrene, on its own, was on fire. Check this by lighting the polystyrene with a cigarette lighter – it will burn until the lighter is removed.

It is a pity that timber framing is not treated with the same material (Boric treatment, many years ago, actually resisted the spread of flame in wood).

Fuels are designated with a calorific value (i.e. the amount, of heat given off during combustion). In basic terms, and by ignoring the efficiency of fuel, a fuel’s weight is a close approximation to its calorific value. An average house clad with Hitex contains 6 cubic metres of polystyrene or 100 kg of fuel. An average house contains 6000 kg of wood based products – 60 times more fuel – none of which is protected with fire retarders. The belief that polystyrene will burn down the house is a myth.

Please Note: Polystyrene is essentially used for cladding and therefore installed on the outside of the building so any vapours or combustion byproducts vent directly into the air – not inside where the occupants are.

The Australian Fire Protection Authority produced the following table showing “expected time to death” of some common household materials when exposed to combustion gases. Polystyrene, is in fact one of the more safer products.

Data taken from the Australian Fire Protection Authority as published in their monthly bulletin No. 245 – March 1983 describing toxicity of gases produced by heating some common materials.

Material

Wool
Cotton
Wood
Cooking Oil
Flour
Polyurethane Foam
Polystyrne Foam

Time to Death (mins)

7.6 +/-1.3
13.1 +/-2.1
14.0 +/-1.5
17.4 +/-0.3
19.5 +/-2.3
20.0 +/-1.7
28.6 +/-0.5

There have been two fires out of 2500 homes in 17 years incorporating the Hitex Cladding.

In one case a rubbish bin placed against the Hitex and directly under an underfloor vent, caught fire. The piling structure was significantly destroyed but the floor above escaped. The Hitex melted up the wall creating an air gap, which meant the fire could not break through to the framing. Therefore the house was saved.

In the other case a neighbour’s house was significantly destroyed. The Hitex clad house, which was very close to the boundary suffered polystyrene melt. Because Hitex has its mesh fastened back to the framing, the plaster remains intact and will not fall off, thus providing separation to the framing. For the studs to catch fire an intense heat would be required for the plaster to glow red and radiate sufficient heat for the wood to ignite. This did not happen.

As the designer and supplier of the Hitex Cladding system, Hitex believes the fact that the polystyrene initially melts is a significant design feature in a fire situation. A vacuum is created between the plaster and the framing because the mesh is over nailed. This helps in “extinguishing” the fire by reducing the amount of oxygen.

Hitex has been tested under both flame spread and cone calorimeter. When specifying fire resistant walls, specify Hitex FRR plaster.

	“Polystyrene burning” makes a good news story.
	Fire fighters responses are sensationalised by the media.
	The apparent frailness of polystyrene together with the fact that it burns in a fire means that some peoples perspective makes headlines.