Technical Corner - Fire Rating of LED Panels TPa/TPb
We have seen a shift in office lighting from traditional 4-tube lay-in panels with louvres to 600x600 LED Panels with thermoplastic diffusers. A thermoplastic material is one that can be remoulded and becomes liquid when heated, as opposed to a thermosetting plastic that degrades when heated. A good example of a thermosetting resin is Bakelite. LED Panels use thermoplastic diffusers to direct light from an LED Panel.
600x600mm LED Panels are designed to fit into a grid ceiling and offer a 50% saving in electricity compared to a fluorescent tube and louvre setup.
Fire Safety Part B mentions the use of thermoplastic materials and states that ceilings of rooms and circulation spaces may incorporate thermoplastic lighting diffusers, but there are conditions.
When it is a requirement to comply with Fire Safety Part B of the Building Regulations, two types of diffusers have been developed: TPa and TPb, to ensure the installation is compliant.
TPa rated LED Panels
Thermoplastic materials undergo specific tests to certify their ability to withstand the application of heat and fire. The requirements are established by Building Regulations Approved Document B, which sets out the fire safety of buildings. Section B2 covers internal fire spread.
TPa usually relates to polycarbonate diffusers with a thickness of at least 3mm. The testing procedure requires that the material self-extinguishes and any flaming or afterglow must not exceed five seconds once the source of flame is removed.
There is no restriction on the use of TPa-rated diffuser material.
TPb rated LED Panels
TPb materials tend to be acrylic or polystyrene. It is a more problematic material because its use is limited by the extent of the installation. The testing for TPb requires a flame to be presented to the material. If the material combusts, the spread of flame must be no more than 50mm per minute—that’s 12 minutes to completely blanket a 600mm wide panel.
How the restrictions work in practice is as follows: In circulation spaces, the total area of diffuser panels must not exceed 15% of the total floor area. The maximum area of one diffuser or group of diffusers must not exceed 5m x 5m. There must be a 3m spacing between each 5m x 5m diffuser grouping.
In offices and other rooms, the total area of diffuser panels must not exceed 50% of the total floor space. The maximum permissible area of a single diffuser panel must not exceed 5m2 (this is a big luminaire and is most likely to occur as a rooflight detail).
Where a conventional arrangement of luminaires is used, either the arrangement for circulation spaces should be employed, or else spacing between all luminaires should be no less than twice the diagonal distance (or diameter) of the luminaires in use.
