UK Market Guidance on TPA and TPB Rated Diffusers for LED Panel Lights
UK Market Guidance on TPA and TPB Rated Diffusers for LED Panel Lights
1. Background and Applicability
Under the UK Building Regulations – Approved Document B (Fire Safety), thermoplastic diffusers that form part of a ceiling construction (e.g. recessed luminaires where the diffuser is flush with or replaces part of the ceiling) must comply with TP(a) or TP(b) classifications.
If the diffuser does not form part of the ceiling (e.g. suspended, surface-mounted, or pendant luminaires), the TPA/TPB classification is not mandatory, though luminaires must still comply with standard safety requirements (e.g. BS EN 60598).
2. Definition and Key Differences between TP(a) and TP(b)
TP(a): Materials that are self-extinguishing when the ignition source is removed, with flaming/afterglow not exceeding 5 seconds in the standard test.
Example: Polycarbonate diffusers with thickness ≥ 3 mm are automatically regarded as TP(a).
Usage: No significant area or spacing restrictions (except not permitted in protected stairways).
TP(b): Materials that are permitted to burn, but with a maximum burning rate of 50 mm/min under test conditions.
Example: Thermoplastic diffusers of 1.5-3 mm thickness tested and confirmed within the rate limit.
Usage: Permitted but with strict limitations on area, spacing, and distribution.
3. Usage Restrictions for TP(b) Diffusers
| Location / Application | Restrictions |
|---|---|
| Rooms / Offices | Single diffuser area ≤ 1 m²; total TP(b) diffuser area ≤ 50% of room area; minimum spacing between diffusers ≥ the largest dimension of the diffuser or 3 m. |
| Corridors / Circulation Areas | Total TP(b) diffuser area ≤ 15% of ceiling area; individual panels ≤ 1 m²; spacing ≥ 3 m. |
| Protected Stairways | Use of any thermoplastic diffuser (including TP(a)/TP(b)) as part of the ceiling is strictly prohibited. |
| TP(a) Diffusers | Generally free of restrictions except for the prohibition above. |
4. Test Methods and Certification
The fire behaviour of thermoplastic diffusers is typically tested in accordance with BS 2782-0 Method 508A, measuring flame spread rate and self-extinguishing performance.
TP(a) classification can be given automatically if material/geometry conditions are met (e.g. polycarbonate ≥ 3 mm).
A complete test report should include:
Sample details (material, thickness, orientation)
Flame spread rates / afterflame times
Test photos or raw data
Final classification (TPa or TPb)
Accredited laboratories such as BSI, SGS, Intertek, TÜV, or UL can issue official reports accepted in the UK market.
5. Our Commitment
For the LED panel models supplied, we can provide third-party TP(a) or TP(b) fire test reports where applicable.
Technical datasheets will state diffuser material, thickness, and classification (TPa/TPb).
For TP(b) rated panels, we can assist with layout planning (spacing, percentage coverage) to ensure compliance with UK regulations.
6. Risks and Recommendations
Using non-certified diffusers may lead to project rejections or remedial work during building inspections in the UK.
While TP(b) solutions can be cost-effective, they come with significant design limitations, so TP(a) is generally preferred.
We recommend submitting full third-party certification documents to end clients or building control authorities to demonstrate compliance and build trust.
7. Conclusion
The correct classification and certification of thermoplastic diffusers is essential for compliance with UK Building Regulations. We can provide supporting documentation, testing reports, and design guidance to ensure your projects meet the fire safety requirements in the UK market.
