Last edited 13 Nov 2017

Fire behaviour of expanded polystyrene


[edit] Introduction

EPS has many benefits to offer the construction industry including its super lightweight composition, sustainability credentials and of course its excellent thermal performance. These unique properties make it the ideal insulation product for many buildings, but what about its fire safety credentials?

[edit] Reaction to fire

[edit] Construction Products Directive

CE marking of insulation products is mandatory under the Construction Products Directive and part of this process is the declaration of the reaction to fire classification of the naked product.

Classification of EPS:

However, the classification lacks detail about the fire performance of the building element as a whole in which the insulation product is used.

The CPD requires a performance based approach for the whole building or the building elements i.e. walls, floors or roofs. To meet this requirement manufacturers can declare the reaction to fire classification as part of a full system or building element. This classification can be added to the product label just outside the CE marking box.

The main properties to determine the Euroclass for a specific product is its non-combustibility, ignitability, flame spread, calorific value as well as the development of smoke and burning droplets. Depending on the outcome of the various properties, the product is assigned a fire classification as shown below.

[edit] Example:

External Wall Insulation system designers typically carry out independent fire tests on complete wall elements with EPS insulation and declare the reaction to fire typically as Euroclass B-s1, d0. This certification satisfies current building regulations and is a good rating which is comparable to other similar insulation materials used in whole building elements.

Example Fire Classification.jpg

[edit] Design considerations:

Even though EPS insulation is not the first material affected by fire, specifers should consider fire prevention measures when designing buildings.

[edit] Covering material:

A covering material for EPS should always be specified to protect the insulation from fire. Typically these will be:

These coverings provide the whole building element the required level of fire protection to meet building regulations.

[edit] Detailing

Correct construction details are important in preventing the spread of fire. Suitable fire breaks should be designed into any building at floor levels and at compartment walls. Whilst the design of these details is vital, the quality of installation is equally as important.

[edit] Typical Fire Break:

This type of fire barrier is used in between floors using non combustible insulation materials.

EWI Fixing Diagram.jpg

1 - FRA EPS EWI Board

2 - Typical Fire Rated Fixing

3 - Non-Combustible Fire Barrier

4 - Typical render finish

[edit] Typical flooring covering:

Most floors will be covered with a structural topping which is classed as non combustible.

Typical Flooring Covering.jpg

1 - Non-Combustible Screed

2 - EPS Flooring

3 - Non-Combustible Concrete

[edit] Fire retardant additive:

Stylite Expanded Polystyrene is available in Fire Retardant Grades which contain Poly FR a polymeric compound.

Only specify fire retardant EPS insulation manufactured in accordance with: BS EN 13163 : 2012+A1:2015 Thermal insulation products for buildings - Factory made expanded polystyrene (EPS) products and BS EN 13501-1:2007+A1:2009 Fire classification of construction products and building elements.

Fire retardant EPS when exposed to ignition energy behaves by shrinking away from the heat. When it is ignited by the heat source, it will self-extinguish if the heat source is removed therefore not readily supporting fire.

[edit] Conclusion

When designing a building, fire safety is one of the key requirements but the reaction to fire behaviour of naked EPS insulation is misleading since it is the covering material which determines the building element fire behaviour. The EPS is only affected by fire after this covering material fails by which time the whole building or compartment is unlikely to be saved from total loss.

It is perfectly possible to specify EPS insulation within a building and meet all the required fire safety regulations whilst also gaining the other major benefits that EPS has to offer.

[edit] Find out more

[edit] Related articles on Designing Buildings Wiki

--Styrene Packaging and Insulation Ltd