Bright idea for safer lighting
August 1st 2008

When a fire-rated ceiling or wall is compromised by lighting or wiring accessories, special precautions have to be taken, explains Barrie Gilroy of Scolmore International

It is now common practice for many light fittings, switches and sockets to be recessed into a surface to make them less conspicuous. In purpose-built commercial premises this usually won't be a problem but it can have significant fire safety implications in dwellings and the many domestic properties that have been converted to offices.

For example, in a commercial building the floor slab provides the fire protection, so recessing a downlighter in a false ceiling has no impact on fire rating. But in other properties there is generally a fire-rated ceiling and cutting a hole in it for a downlighter will negate the fire protection it affords.

For these reasons, there are now regulations to ensure that the flame retardancy properties of the ceiling are restored. In particular, Part B (Fire Safety) of the Building Regulations says that downlighters need to include measures to prevent the spread of flame in compliance with BS 476.

Traditionally, this has been achieved by using a fire hood fitted over the downlighter inside the ceiling void.

Unfortunately, installing these can be a very fiddly procedure and can add significantly to the installation time, as well as increasing overall costs for equipment.

An increasingly popular alternative is to use a downlighter with integral intumescent fire retardant seals, supplied as a single unit. In the event of a fire, the seals expand to seal the aperture, thus preventing the flow of hot air and flames into the ceiling void to restore a full 90 minute fire rating. One seal is located in the cap of the downlighter so the cap is sealed, while the other seal fits around the circumference of the downlighter to seal the cut-out.

Protecting walls The same concerns arise when an electrical accessory is installed in a fire-rated stud wall. Switches and sockets and other plate accessories are conventionally mounted on a moulded dry lining box which offer little or no protection against the spread of fire. This is because conventional plastic dry lining boxes will start to deform and deteriorate at temperatures around 170C, long before the intumescent materials would be activated at around 900C.

A much more effective, and simpler, alternative is to use a fire rated galvanised steel back box that will withstand temperatures up to 1,000C and continue to maintain an effective fire barrier. This eliminates the need for complicated, costly and frequently ineffectual assemblies of hoods or other 'bolt-on' devices.

Stay cool While many downlighters now use compact fluorescent lamps that generate relatively little heat, there is still extensive use of halogen spotlights in downlighters and these can become very hot without sufficient ventilation.

Again, this is a particular problem in buildings originally built for domestic use, as any halogen downlights that project into the roof space are likely to be covered in loft insulation materials. As a result, air circulation to dissipate the heat will be severely restricted.

In fact, tests have shown that the surface of a halogen downlighter can reach a temperature of 350C under these conditions, sufficient to ignite loft insulation material within about 30 minutes.

This can be a real problem. Research by fire authorities in Australia has led to estimates of one loft fire being started by recessed halogen downlighters every 3-5 days and there's no reason to believe the same potential doesn't exist in the UK when such fittings aren't fitted properly.

Understanding 'F-rated' Quite often, people assume that 'F-rated' luminaires do not present a danger, however this is a misunderstanding of the F-rating scheme. F-rated means a fitting is suitable for mounting on normally flammable surfaces in compliance with BS EN 60598 Part 1.

A quick and simple remedy for this potential problem of downlighters and loft spaces is to install an insulation support box between the fitting and the insulation.

Effectively, the box covers the fitting and provides enough space for air to circulate while providing a rigid skin to lay the installation over.

As with any life-safety products, it is vital that products used to resolve these issues provide full protection in full compliance with legislation and best practice.

Unfortunately, since our company introduced the original designs there have been many 'me too' copies which fail to deliver the necessary protection.

The only way to be safe, therefore, is to seek proof of any claims made by manufacturers, ideally through independent testing. With the right level of vigilance, it is possible to address the design issues simply and costeffectively without compromising on safety.

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