We have a somewhat tense relationship with light and fire. After all, for millenia, light and fire meant much the same thing; you set fire to something and it gave off comforting heat and light . . . but it might also burn the house down. Nothing has really changed. We’ve perhaps become a bit less cautious; a bit more blasé – and surprised when the house still, occasionally, burns down.
And it’s that combination of heat and light that causes the problem. It doesn’t matter whether it’s a candle flame blowing against a curtain, a high-temperature light beam setting fire to a cuddly toy (done that!) or a poor electrical connection in the back of a light fixture that sets fire to the ceiling joists, the results can always become catastrophic.
This article sets out to look at luminaires in respect to their potential combustion risks. And we’ll stay with electricity for the duration of this piece. Burning a fossil fuel will always be a fire risk, not to mention a possible planetary disaster for those of us living on it.
Luminaires offering no fire risk
Every electrical light fixture, regardless of its intended function, is a fire risk; not because of the way that the fixture has been constructed necessarily but because, most of the time, it will require an electrical connection. Let’s never forget the risk that comes from poor installation work.
The other thing that can happen with very well-built fixtures is they can be abused. There is a reason why fabric lampshades still show a ‘60W max‘ label – and we’ve probably all seen the scorching effect of a 100W GLS on an old tassled shade. This often arises when elderly relatives complain that the light isn’t what it used to be and decide to put in ‘a bigger bulb’. Regardless of what the EU says about tungsten filament lamps, they are still out there and the shades are still scorching.
And there are many, many, fixtures – usually for domestic use – that use flammable materials, from Ikea’s £1.75 Regolit paper shade to the Akari shade, hand-made using the bark of the mulberry tree and available from Heals at only £2210.00. It doesn’t make them dangerous, provided that they are used correctly and those ‘bigger bulbs’ are avoided.
Flammable or non-Flammable mounting
It’s not always the fixture that is the problem. Many years ago I was asked to intervene in a row between a supplier and an architect; a wall-mounted (300W) tungsten halogen uplight had melted the plastic coating on the wallpaper . . . w-e-e-e-l-l, something had to give there, didn’t it.
There are luminaires that are not suitable for mounting on (or into) a flammable surface. These usually have a high surface temperature that could cause the mounting surface – a wooden panel, for example (or plastic wallpaper), to combust over time. There used to be the ‘F’ Mark; an ‘F’ in a triangle with a cross over the entire label to indicate that the fixture wasn’t to be installed on a flammable surface. This has been replaced by warning labels indicating that fixtures should not be mounted on or within a flammable surface. (see symbols)
One other situation is worth mentioning here and that is installing recessed fixtures into a ceiling void when there is a layer of insulation laid above the ceiling membrane. All light fittings produce heat, even the coolest-running LEDs, so it’s not a good idea to cover them with an insulating blanket. The least worst case is that the internal electronics over-heat and fail and the fixture has to be replaced; worst case – that’ll be a fire in the ceiling void space, then. (see symbol)
Minimum distance between source and object
This is no longer the problem that it used to be. Tungsten halogen lamps had the knack of regularly scorching shop displays (or burning cuddly toys); the LED has more or less removed that problem but we still have some LED lamps that can be replaced with filament lamps, so there is still the potential for damage if careless retrofitting takes place. (see symbol)
And now we come to the most contentious of classifications, because this is about the most commonly used light fixture in the most commonly experienced situation. What happens when you make a hole in a ceiling and fit a recessed downlight?
Firstly, luminaires are not fire-rated per se. What is referred to in the ‘fire-rated’ shorthand is that the luminaire is capable of being fitted into a structure (these are typically recessed and semi-recessed fixtures) without compromising the fire barrier established by that structure.
Where UK Building Regulations (Fire Safety: Approved Document B) require a fire barrier, a minimum period of fire resistance will have been established for each space within a building. There are four periods, dependent on the circumstances: 30 minutes; 60 minutes; 90 minutes, and 120 minutes, generally with suspended ceiling installations.
When a product is placed in a fire-rated structure (typically, a ceiling), that product must not compromise the integrity of the structure. Manufacturers install their fixtures in particular test conditions to confirm the likelihood that the fixture will perform adequately, but this does not mean that the fixture is suitable in other situations. It only means that it probably will be – further testing may be required. Its important to check what test criteria was applied on any fixture that is sold as ‘fire-rated’ because it may not apply to the specific installation that you’re working on.
Its important to mention here that the testing method for luminaire ‘fire-rating’ is a contentious topic as there are different ways of interpreting the data that is produced. The LIA is currently lobbying for a change in the way that these tests are done.
Fire rated materials
Another common question relates to materials used in ‘fire-rated’ luminaires, and to thermoplastic translucent panels, in particular. This has led to a general misunderstanding; the ratings that are applied to thermoplastic materials relate to fire-spread on that material, not ‘fire rating’ of the luminaire.
There are three categories related to thermoplastic materials:
No rating: there are some thermoplastics that are flammable. Luminaires fitted with these diffusers are not suitable for any kind of ‘fire-rated condition’ and there should be NO ‘fire-rated’ luminaires available in the UK that use such materials.
TP(a) thermoplastics tend to be rigid panels that can be used in all circumstances. TP(a) plastics are typically polycarbonate with a thickness of at least 3mm. Be aware, though, that the testing is done to find the limits of the spread of flame; it is not a test to ‘prove’ any self-extinguishing properties of the material.
The usual issue around TP(a) is its transmittance value. Because it is thicker than other types of panel, more light is lost in transmission, making the luminaire less energy-efficient. And that situation tempts some manufacturers to explore the benefits of TP(b) materials.
TP(b) thermoplastics are typically acrylic or polystyrene. These plastics are used because their transmittance qualities are better than TP(a) – and the material itself is cheaper.
Surprisingly, to satisfy a TP(b) rating, the material is allowed to combust but fire spread shouldn’t be greater than 50mm per minute. I make that just 12 minutes to cover an entire 600×600 panel from one side to the other – but perhaps only 6 minutes if the cause of the fire is in the centre of the panel. Not a long time, whichever way you look at it.
Because of the heightened risk, the amount of TP(b) material in a ceiling is limited. In circulation areas, the total area of TP(b) panels must not exceed 15% of the total floor/ceiling area. In working spaces, the maximum permissible area is 50% of the total floor/ceiling area. No grouping of fixtures can have an overall surface area exceeding 25m2. Groups of fixtures should have a minimum 3m separation between them. This is described in detail in Part B of the Building Regulations.
A ceiling constructed from TP(a) Flexible Panels must be no larger than 5m2 in area and must be physically supported on all sides.
Part B of the UK Building Regulations do not mention the use of TP(b) material for rooflights or luminous ceilings.
Ceilings formed by stretch PVC materials are of particular concern at the moment. Such materials need to conform to UK standards in the same way as any other material that forms a fire barrier.
The issue of fire safety is of vital importance to all of us. In this article I’ve tried to raise awareness of the different aspects that apply when light and heat are brought together.
For detailed information about luminaire design, testing and fire safety I suggest that you contact the Lighting Industry Association (LIA) and attend one (or more!) of their informative courses on this and other relevant topics.