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Fire Rating Standards

The industry standard is for recessed luminaires to be fire rated. The British Standard BS476-22 specifies the exact requirements for diffusor material of panels to be able to keep the integrity of the ceiling for a certain time in case of a fire.

There two types of ratings which allow classifying the thermoplastic materials:

TP(a) rated luminaires usually have polycarbonate diffusers. The main requirement for this material is its ability to self-extinguish and not flaming or glowing for more than 5 seconds after a flame has been removed.

TP(b) rated luminaires usually have acrylic or polystyrene diffusers. The requirement is that the spread of the flame must be no more than 50mm per minute.

Below are specific details extracted from Building Regulations Approved Document B (Fire Safety)

The following provisions apply to light diffuser’s that form part of the ceiling

TP(a) class of diffusers material (rigid)

  • Rigid solid PVC sheet
  • Solid polycarbonate sheet at least 3mm thick
  • Multi-skinned rigid sheet made from unplasticised PVC or polycarbonate which has a Class 1 rating when tested to BS 476-7 Fire Tests standard
  • Any other rigid thermoplastic product which when tested to BS 2782-0:2004 Rate of burning performs, which means that the test flame extinguishes before the first mark and the
  • duration of flaming or afterglow does not exceed 5 seconds following removal of the burner.

TP(a) class of diffusers material (flexible)

  • Not more than 1mm thick which comply with BS5867-2:1980 and when applying the flame to the surface of the specimen for a certain time

TP(b) class of diffusers material

  • Rigid solid polycarbonate sheet products less than 3mm thick, or multiple-skin polycarbonate sheet products which do not qualify as TP(a) by a test.
  • Other products which, when a specimen of the material between 1.5 and 3mm thick is tested in accordance with BS 282-0:2004 Rate of Burning standard, does not exceed 50mm/minute.