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Explainer: Luminaires can ruin fire rating of ceilings

Lack of proper fire protection within luminaire specifications can be very dangerous and could lead to disaster. (Originally published by John Bullock 9/1/17 –

We have seen yet more lurid headlines in the press, reporting that hospital projects built under Private Finance Initiative (PFI) contracts have been condemned as unsafe following inspections of fire protection measures. The stories are being spun as a stick to beat the PFI programme with, but there is a very real issue here for the lighting specifier, contractor and manufacturer.

These reports raise concerns over a lack of proper fire protection within luminaire specifications. The lighting industry needs to look at luminaire specifications within fire barriers such as ceilings and ensure that only luminaires complying with BS476-22 (the fire tests on building materials and structures standard) are used.

There has long been confusion as to what constitutes a properly fire-rated luminaire, with many people believing that simply using a self-extinguishing thermoplastic diffuser constitutes a satisfactory fire barrier. This is not true; neither TP(a) or TP(b) constitutes a fire barrier.

When fire-rating doesn’t mean fire-rated

Many specifiers and installers believe that a luminaire using a diffuser panel rated as TP(a) or TP(b) (see below) will provide effective protection against fire spread. Unfortunately the rating of the diffuser has little to do with the ability of the luminaire to prevent the spread of fire.

This is discussed in Building Regulations Part B (on fire safety)

B2: Para 6.14: Thermoplastic lighting diffusers should not be used in fire-protecting of fire-resisting ceilings unless they have been satisfactorily tested as part of the ceiling system that is to be used to provide the appropriate fire protection.

This regulation explains that a suspended ceiling that acts as a fire barrier must be capable of resisting fire spread across its entire ceiling surface, and that includes any recessed luminaires set into the ceiling. No luminaire should be used in a fire-rated ceiling unless that luminaire carries a fire certificate that states its ability to resist fire, which should match the fire resistance of the general ceiling system. Where a luminaire doesn’t have a certificate, then a fire hood with an appropriate rating should be provided above each luminaire, as is often the case with recessed downlights. Therefore you need to use a compliant BS476-22 luminaire or you will invalidate your ceilings fire rating.

Two steps to disaster: to TP(a) or TP(b) your LED panel

LED panels distribute their light using thermoplastic diffusers. In the drive to improve luminous efficacy, the lighting industry has lobbied to relax the criteria for the use of TP(b) diffusers, which are generally thinner and have better translucent properties than TP(a) polycarbonate. While this may be justifiable in general use, it raises a problem when the diffuser is intended to act as part of a fire barrier.

Step 1

The first step to disaster comes when the requirement stated above, for a certified fire-rated luminaire, is swapped for a standard luminaire with a TP(a) diffuser, believing that fire standards are being met. While the diffuser will not catch fire, it does not guarantee that there is no fire path between luminaire and ceiling structure, creating the risk of fire entering the ceiling void and spreading through the building.

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Step 2

Cost pressures on a project can lead to a down-grading of materials and the obvious one is to change the luminaire fitted with a TP(a) diffuser with a luminaire of higher efficacy, but that uses a TP(b) diffuser. This is a potentially catastrophic situation.

Screen Shot 2017-02-24 at 00.32.29     NB: This is an extract from Table A2, Building Regulations Part B (Fire Safety)

TP(b) materials do not self-extinguish; they are rated on a slow spread of flame, but that flame is not extinguished by the material itself. If a 600×600 panel catches fire along an edge it meets test requirements if it only takes twelve minutes for the flame to spread across the entire surface.

This means that a source of fire is now part of the fire-proof barrier and the entire structure is dangerously at risk.

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Reported in RIBA Journal – Intelligence: Fire (10 February 2015)

Fire and smoke spread in concealed spaces within buildings can present both a risk to life to occupants and fire-fighters, and cause widespread damage with extensive, difficult, and expensive clean-up and re-instatement. In some cases, smoke deposits (and their odour) cannot be adequately removed and buildings have had to be demolished.

Review of actual fires: 2003 – 2013

Concealed spaces in roof voids, and fire spread within them, is being investigated by BRE Global, which provides independent, third-party certification of fire, security and environmental products. Initial studies show salutary lessons about the effect of poor compartmentation from real fires.

Over the past ten years BRE Global has carried out 106 fire investigations on behalf of the UK Department for Communities and Local Government (DCLG). Of these, 34 had an aspect relevant to concealed fire spread. 11 were solely related to compartmentation in roof voids, ten were solely related to issues with cavity barriers and six featured a combination of these issues.—Fire-compartmentation-in-roof-voids-Feb-15.pdf

If in doubt consult your building’s fire strategy document, which should indicate which areas are fire rated at the time of build. Special care should be taken when retrofitting as these areas may have changed along with increased occupancy resulting in a need for greater protection. Our advice is to identify the type of ceiling you are retrofitting.