Building Regulations Approved Document B (2006 edition amended 2007) sets out the rules for fire safety of buildings. Section B2 covers internal fire spread, and applies to the linings of both the roof and walls of buildings. In general these are surface spread of flame requirements to BS476 Part 7 (typically Class 1 and Class 3) or to BS EN 13501 Part 1 (typically Class C-s3,d2 or Class D-s3,d2). Section B4 covers external fire spread and applies to external coverings or roofs and walls; in general these are fire resistance requirements to BS476 Part 3 (typically AA and AB) or to BS EN 13501 Part 5 (typically BROOF(t4)).
Thermosetting materials (GRP) can be tested to BS476 Parts 3 and 7, and to BS EN 13823 and BS EN ISO 11925 Part 2 then classified to BS EN 13501 Part 1, and a variety of grades are usually available offering alternative fire ratings to meet the main requirements.
Thermoplastic materials cannot be tested to BS476 Part 3, as the material melts during the test. Building Regulations define an alternative classification method for these materials:
- Polycarbonate at least 3mm thick, PVC (any thickness), and multiwall polycarbonate which is rated Class 1 to BS476 Part 7, are given the rating Tp(a).
- Other thermoplastic materials can be tested to BS2782, and given ratings of Tp(a) or Tp(b).
- Polycarbonate or PVC which achieves Class 1 when tested to BS476 Part 7 or Class C-s3,d2 when tested to BS EN 13501 Part 1, can also be regarded as having AA or BROOF(t4) designation.
For the majority of industrial buildings, the requirements can be summarised as follows:
- The lining of a roof or wall should normally be rated Class 1 to BS476 Part 7, Class C-s3,d2 to BS EN 13501 Part 1 or Tp(a).
- A concession allows the lining to be rated Class 3 to BS476 Part 7, Class D-s3,d2 to BS EN 13501 Part 1 or Tp(b) if the area of each rooflight is less than 5m2, and there is a clear space of 1.8 metres in all directions between each rooflight.
- There are no restrictions on use of roof outer sheets rated at least AC to BS476 Part 3 or BROOF(t4) to BS EN 13501 Part 5. Rooflights with outer skin fire ratings less than this should not be used within 6 metres of a boundary.
- A single skin sheet must meet the requirements for both the inner ceiling and outer roof surfaces.
- The only requirement for greater protection of wall outer sheets is where the building is within 1 metre of a boundary or is over 20 metres tall or is a building to which the public have access, when some areas will require sheets rated Class 0 or Class B-s3,d2 to BS EN 13501 Part 1.
|
