Fire Performance

Regulations Approved Documents

The performance and reaction of buildings in situations where fire breaks out is heavily dependent upon the way in which a building is designed, and the materials from which it is constructed. There are some key considerations that have to be taken into account; everything from restricting the way in which fire can propagate and spread, to providing safe access routes so that the occupants of the building can escape to safety. Consequently, the Building Regulations Approved Documents B, Volume 1 (Dwellinghouses) and Volume 2 (Buildings other than dwellinghouses), are very detailed and specific in their requirements.

Combustion of GRP Rooflight Sheeting

GRP (Glass Reinforced Polyester) is a composite material comprising glass reinforcement encapsulated in polyester resin. This polyester resin is a ‘thermoset’ type of plastic and fundamentally different to ‘thermoplastic’ plastics materials that soften and eventually melt when exposed to increasing temperatures. The thermoset material is inherently much more stable than a thermoplastic material and can withstand the application of heat up to around 400°C subject to composition, albeit the material will darken significantly and have a charred surface appearance. Above these temperatures, the material will burn, but only with the continued application of the heat source. When the heat source is removed, the GRP will self-extinguish.

Typical Heat Exposure Behaviour

In tests conducted to identify the reaction of GRP to heat, a sample of translucent GRP sheeting manufactured using Class 1 resin with a high resin to glass ratio of 2.4:1 was supplied. Half the laminate was was placed on a support in a muffle furnace with a temperature of 300°C for five minutes. Within the first few minutes of placing the laminate sample in the furnace, smoke was observed. The smoke emission continued throughout the duration of the five minute exposure period.

The laminate was removed from the furnace and allowed to cool to an ambient temperature and the appearance was compared with the other half of the sample. The tested sample was opaque, charred orange/brown in appearance,
with a rough, gritty texture to the surface. To confirm the effects of this high temperature exposure the
flexural strength, modulus and Barcol hardness properties were determined before and after exposure. Results can be discovered at the link at the bottom of this page.

By Products of Combustion

There are, as with all plastics materials, toxic substances produced as a result of burning. It is not possible to manufacture any rooflight material for this type of application without this occurring. The main by-products of
combustion of the polyester resins used in the manufacture of GRP in-plane rooflights are carbon dioxide, water and
carbon monoxide. In addition to these, there will also be some phosphorous halides given off from the halogens added to the material. These halogens are a necessary part of the composition of the material and are essential to improve the fire resistance. The more halogens the product contains, the better the fire resistance will be.

It is not possible to be precise in stating exactly what substances will be produced and in what proportion as this
will depend on the burning conditions of the material and the levels of oxygen present. In selecting a product
manufactured for high strength such as our Zenon Evolution range, and where the glass to resin ratio is much higher than traditional GRP laminates, there is a reduction in the noxious materials produced.

Zenon Pro and Evolution sheets are available in a range of internal fire grade classifications from Class 3 to Class 0 in accordance with BS476-6 and BS476-7, and external fire grade classifications up to S.AA in accordance with BS476-3 to accommodate all UK Building Regulation requirements for exposure to fire.

For information on fire classifications and requirements for rooflights, and fire rating identifications for Zenon Pro and Evolution sheets, you can download the section from our technical manual here. The next rooflight specification consideration within the technical guide is embodied carbon.


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Long March, Daventry, Northamptonshire, NN11 4NR, UK
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