Curtain Walling- Reaction To Fire

Categories: Performance : Curtain Walling

Principles

Reaction to fire is the response of a material or component in contributing by its own decomposition to a fire to which it is exposed. It may affect the development or spread of fire in a building due to the spread of flame or the release of heat.

Reaction to fire may currently be assessed in accordance with a National classification system using tests given in BS 476 or a European classification system given in EN 13501-2 which is based on European test standards. When CE marking is introduced the national classification will no longer be valid.

The European classification system has seven main classes A1, A2, B, C, D, E, and F. There are supplementary classifications relating to the production of smoke and burning droplets but these are not currently used within UK Regulations. An approximate relationship between the BS476 and EN13501 classifications is given in the following Table:

National classification (England and Wales)	National classification (Scotland)	European classification
Non-combustible	Non-combustible	A1
Limited combustibility	Non-combustible	A2
Class O	Low risk	B
1	Medium risk	C
2	High risk	D
3	High risk	D
	Very high risk	E or F

The table indicates the broad relationship between the National and European classifications and this relationship is used within the Building Regulations however the relationship is not precise and a particular material or component may have a higher classification in one system or the other.
 

Standards

EN13501-2	Fire classification of construction products and building elements. Classification using data from fire resistance tests, excluding ventilation services
EN ISO 1182	Reaction to fire tests for products. Non-combustibility test
EN ISO 1716	Reaction to fire tests for products. Determination of the gross heat of combustion (calorific value)
EN 13823	Reaction to fire tests for building products. Building products excluding floorings exposed to the thermal attack by a single burning item
EN ISO 11925-2	Reaction to fire tests. Ignitability of products subjected to direct impingement of flame. Single-flame source test

 

Method of test

The reaction to fire classification is based on small scale tests and, in the case of curtain walling, the components of the wall would be tested individually. Tests would be required to be carried out on:

Framing members

Infill panels

Seals to be used between the fixed frame and infill (only required where required by national regulations)

Organic finishes (may be assessed in combination with framing or infill panels to which they are applied)

Seals between opening and fixed frames do not need to be assessed.

There are four test methods that may be applicable depending on the class of performance to be provided as follows:

Test	Standard	Class of performance
Non-combustibility	EN ISO 1182	A1 and A2
Heat of combustion	Non-combustible	A2
Single burning item	EN 13823	A2, B, C and D
Ignitability (Single flame test)	EN ISO 11925-2	B, C, D and E

The draft revision of EN 13830 gives guidance on appropriate test specimens for reaction to fire tests on curtain wall components.

The current EN 13830 gives no clear guidance on how the classification of the components may be used to classify the wall as a whole. The draft revision of EN 13830 states that gaskets are only required to give class E even where the remaining components give a higher class. It would be reasonable to take the class for the wall as the lowest class given by the framing members or infill panels allowing for the effect of any finish on the panels or framing members. Where glazing units are used as infill their reaction to fire performance should be given in the CE marking of the glazing unit.
 

Classification

Classes B to F relate to the performance of a surface and the internal and external faces of the wall may have different classifications. Classes A1 and A2 are based on the inherent properties of the materials used. Where a wall gives a performance B to F some components may give a higher classification and this may be required by building regulations for example the external surface may be required to meet class B but the insulation may be required to meet class A2.
 

CE Marking

In UK Building Regulations reaction to fire may be required in relation to:

The external surface of the wall
The requirement depends on the height of the building, distance from the site boundary and occupancy class. The required reaction to fire class will not generally be greater than Class B

The internal surface of the wall
The requirement depends on the use of the internal space. This requirement only applies to surfaces that will be exposed to the internal environment in the completed building and where the curtain wall will be covered by fit out the performance of the internal surface of the wall is not required. The reaction to fire class will not generally be greater than Class B

The combustibility of some or all components of the wall
The requirement depends on the height of the building , the distance from the boundary and the country the building is in. Some or all components of the wall may be required to achieve class A2

It would be reasonable to expect the CE marking to give a reaction to fire classification for the external surface. Specifiers should be aware that they may need to assess the internal surface classification of some components and the combustibility of the wall in some situations.