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B1, B2 and B3-PU foam and fire protection foam

The German DIN norm 4102 Part 1 classifies the building materials according to their flammability. The valid norm is differentiated into two fire protection classes. ‘A’ stands for non-flammable and ‘B’ for flammable materials.

Class B is relevant for PU foam. This is then subdivided into the following levels:

  • B1 = low flammability
  • B2 = normal flammability
  • B3 = high flammability

Construction foams that were developed as low-flammable PU foams for filling and sealing joints are usually simply called fire protection foams.

They need to correspond to the requirements of DIN 4102 Fire Behaviour of Building Materials and Parts of Class B1. If there are any special fire protection requirements, for instance if fire resistance classes according to EN 13501-2 (EI) need to be reached, these special foams are used in combination with other fire-inhibiting materials.

Most construction foam cans sold in Germany correspond to the building material class B2. This means that they are of normal flammability according to the specifications of the DIN 4102-1. They can be used throughout the building apart from in places subject to special fire protection requirements. In rare cases, easily flammable B3-PU foams are sold in retail outlets. These B3-PU foams are not allowed to be used for construction projects.

Classification of PU foam acc. To EN 13501-1

This is the German norm. In 2001 the European norm EN 13501-1 was introduced to examine and regulate the fire behaviour of building materials throughout Europe. It defines the material classes A to F :

  • A: no contribution to the fire (A1, A2)
  • B: very limited contribution to the fire
  • C: limited contribution to the fire
  • D: acceptable limited contribution to the fire
  • E: acceptable fire behaviour
  • F: no effect established

The EN 13501-1 is due to replace the still valid DIN 4102-1 in the future. The B2 classification of the DIN 4102 ‘normal flammability’ corresponds to the European classes D and E. The EN 13501-1 also defines several sub-groups, depending on whether the material smokes or drips. In contrast, the DIN only recognises classification B2. B2 PU foams according to DIN 4102 correspond to Class E according to EN 13501. The highly flammable B3 PU foam is covered by Class F.

There is currently no equivalent for B1 foams in the European norm. Whilst there are formal analogue classes for DIN 4102-B1, these do not apply to PU foams because the corresponding tests are completely different to DIN.