Elecsa offer their technical advice on the selection and installation of recessed luminaires.
Installers and designers do not always appreciate that recessed luminaires (including downlighters) need to be appropriately selected and installed to protect against the spread of fire.
The guidance in this article is based on Section 7 of Best Practice Guide 5 – Electrical installations and their impact on the fire performance of domestic premises used as single family houses, produced by the Electrical Safety First in association with leading industry bodies. The guidance relates specifically to domestic premises, but the general principles also apply in non-domestic premises.
Where downlighters are installed into a ceiling or suspended floor, the installer and designer of the installation must ensure that the fire performance provisions mandatorily required under the relevant building regulations are not compromised.
Fire safety in buildings generally requires, among other things, that in the event of a fire:
• certain walls, floors and ceilings provide fire separation for the purposes of constructing fire compartments* and/or protected escape routes, and
• the structure resists collapse.
* In Scotland, compartment walls/floors are known as separating walls/floors.
Fire separation requirements for the purposes of constructing fire compartments and/or protected escape routes may apply depending upon the type of building construction, the number of floors and other factors, including building structural features such as basements, garages and loft conversions. Where an electrical installer is uncertain, advice should be sought from a building control specialist.
Even where downlighters/luminaires are being recessed into building linings that are not considered to be fire compartments, the issues relating to the possibility of structural collapse must still be considered.
In most domestic premises it is the loadbearing capacity of the floor that is threatened by early failure of ceiling linings, not the fire separating function.
Many modern forms of engineered construction, such as suspended floors using joists such as those shown in Fig 1, provide a lower level of fire resistance than given by traditional forms of construction, such as floors using solid structural grade timber joists. Due to this reduced fire resistance, these forms of construction rely on the plasterboard or similar linings for achieving the requisite level of fire separation.
The fire resistance of the resulting construction can easily be compromised by inadequate fire sealing and ‘making good’ after any penetration to accommodate electrical equipment, such as recessed luminaires, including downlighters.
Where exposed to fire from below, downlighters may provide far less protection to a ceiling cavity and to the structural elements within it than given the plasterboard they are replacing, unless suitable precautions are taken.
Selection of downlighters
It is recommended that wherever possible downlighters having integral fire protection are selected for use in all ceilings where the lining that is to be penetrated is the sole means of keeping fire and heat out of the cavity.
A number of types of downlighter are available and it is important that the type selected for a particular application has test evidence to support its fire performance when incorporated in a ceiling of the type into which it is to be installed.
Generally, the tests should have been carried out in accordance with BS 476: Part 21: 1987 or BS EN 1365-2: 2014. The nature of the test evidence can be critical, and is discussed in Annex B of Best Practice Guide 5.
Not all designs and styles of downlighter may be available with integral fire protection, especially where higher levels and/or larger coverage is required.
In these situations, additional fire protection may be fitted at the time of installation in the form of a ‘fire hood’ (see Fig 2), an insulated fire-protective box, or similar. Such separate forms of protection must be fit for purpose, not easily dislodged or compromised after installation by subsequent work, and meet the fire test requirements of BS 476: 21: 1987.
Any cables installed inside a fire hood must be of a type that is suitable to withstand the high temperature conditions there.
Luminaire control gear should not be installed inside a fire hood.
Table 1, shown in Best Practice Guide 5 (www.electricalsafetyfirst.org.uk), gives guidance on the selection of suitable types of downlighter for particular applications.
To avoid the risk of fire caused by overheating, downlighters and any associated transformers must not be covered by thermal insulation.
Building Regulations do not prohibit the leaving of a small area around downlighters free from thermal insulation where this is necessary to permit the dissipation of heat they generate. However, due allowance for this should be made in the overall thermal performance of the premises. In all cases, manufacturers’ installation instructions must be followed to avoid downlighters becoming a source of fire.