There are many occasions when electrical equipment is recessed into a surface to make it less obtrusive and most of the time this is no problem at all. However, if that surface is a fire barrier there is a risk of compromising the fire integrity of the structure. Under these circumstances, specifiers and installers need to take measures to restore the fire protection.
In addition, there are a number of other factors to consider in certain circumstances. These include noise transmission, the potential for dangerous heat build up when recessed downlighters project into a roof space and the possibility of moisture laden air entering a roof space.
Such circumstances are most often encountered when specifying or installing recessed downlighters, which are becoming increasingly popular in both commercial and residential applications.
In the majority of purpose built commercial premises this does not pose a problem because it’s the floor slab that provides the fire protection, not the false ceiling. However, for residential applications and the many domestic properties that have been converted for commercial use this can be a major safety concern.
Such buildings require fire-rated ceilings but as soon as you cut a hole in the ceiling the ability to prevent the spread of fire is totally compromised. Less critical, but also important, is the fact that these holes also allow sound to be transmitted through the ceiling void.
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 full 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. The cap seal also features a seal retainer that provides a physical barrier and prevents the seal expanding downwards into the downlighter body. Instead, the expanding seal is forced upwards into the ventilation holes in the top of the downlighter.
There are similar concerns when an electrical accessory is installed in a fire-rated stud wall but the solution needs to be different. Conventional dry lining boxes are manufactured in urea or PVC and will start to deform and deteriorate at temperatures around 170ºC. As intumescent materials are designed to activate at around 900ºC this would happen long after the box itself had degraded.
A much more effective, and simpler, alternative is to use a galvanised steel back box that will withstand temperatures up to 1,000ºC 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.
Keep the noise down
Returning to the challenges posed by some downlighter installations, a side benefit of the integral fire retardancy design is that it can also do a useful job of solving some other potential issues. As mentioned earlier, these include noise transmission and the risk of moisture laden air entering a roof space in a residential application.
For example, in normal use the fire seals described above should also act as a barrier to sound transmission. In order to do this effectively, they need to limit the spread of sound to the standards laid down in BSEN ISO 140-3 1995 and BSEN ISO 140-6 1998.
Another useful measure is to ensure compliance with the requirements of Robust Designs – a scheme introduced to ensure that acoustic considerations are addressed before construction begins. This provides additional reassurance that the downlighters comply with noise requirements as well as fire control.
Meeting these requirements places additional demands on the design of the luminaire, necessitating a rigid steel downlighter body to eliminate any vibration or resonance of the unit, which will also transmit sound. It should also be clamped securely to the ceiling for enhanced rigidity and security, using heavy duty springs.
Stop the rot
Another concern, which has been voiced by the National House Building Council (NHBC), is the potential for moist air, especially in bathrooms and showers, to pass through the downlighter into the roof space. This can lead to condensation damage and, ultimately, rotting of roof timbers. To prevent this problem, the NHBC has established standards for the air tightness of downlighters, so any products selected should also comply with these. In general, this can be achieved by the use of an optional neoprene moisture seal in areas where migration of moist air is a potential hazard.
When downlighters using incandescent light sources project into a roof space, in residential or converted premises, there is another potential fire issue to be addressed. Unlike putting the fitting into a false ceiling, where it has plenty of air to circulate and dissipate the heat, loft spaces tend to be insulated to prevent heat losses – so the fitting may overheat. Tests have shown that the surface of a halogen downlighter can reach a temperature of 350°C under these conditions, sufficient to ignite loft insulation material within about 30 minutes.
To put this into perspective, research by fire authorities in Australia has led to estimates of one loft fire being started by recessed halogen downlighters every 3-5 days – so it’s a common problem and one that’s getting worse as these fittings become more popular. And there’s no reason to believe the same potential doesn’t exist in the UK when such fittings aren’t fitted properly.
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 solution to the 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.
Given the life safety implications of these issues it’s important to ensure that any products used have been fully tested to the relevant standards. Unfortunately, since our company introduced the original designs there have been many ‘me too’ copies which fail to deliver the necessary protection. So I would urge all specifiers 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 cost-effectively without compromising on safety.