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Building Regulations Approved Document B (Part B) is concerned with fire spread in buildings. Voltimum UK Managing Editor James Hunt looks at Part B in terms of potential risk of fire spread through use of recessed lighting luminaires in buildings other than dwellinghouses:
Building Regulations Approved Document B (Part B) is concerned with fire safety, and it requires adequate protection for people in such buildings through the provision of fire barriers. A fire-rated ceiling is one such barrier, and these provide protection to the floor above if a fire occurs. In particular, Part B comprises:
- B1 - To provide appropriate means of warning and escape.
- B2 - To adequately resist internal fire spread (linings).
- B3 - To adequately resist internal fire spread (structure).
- B4 - To adequately resist external fire spread.
- B5 - To provide reasonable access and facilities for the fire service.
B1 has implications for the electrical, lighting and fire alarm sectors. Electric cable (and other electrical equipment), if faulty, is clearly a fire risk and electric cables also have to pass through walls - potentially helping a fire to spread. There is also a risk from recessed lighting luminaires. Part B regarding recessed lighting luminaires and fire spread in buildings other than dwellinghouses was written with two constraints in terms of luminaires and lighting diffusers that are part of the ceiling (ie: recessed).
It states:
6.13 (page 65): The following provisions apply to lighting diffusers which form part of a ceiling and are not concerned with diffusers of light fittings which are attached to the soffit of, or suspended beneath, a ceiling (see diagram 26).
Lighting diffusers are translucent or open structured elements that allow light to pass through. They may be part of a luminaire or used beneath rooflights or other sources of light.
6.14 (page 65): Thermoplastic lighting diffusers should not be used in fire protecting or 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.
6.15 (page 65): Subject to the above paragraphs, ceilings to rooms and circulation spaces (but not protected stairways) may incorporate thermoplastic lighting diffusers if the following provisions are observed:
a) Wall and ceiling surfaces exposed within the space above the suspended ceiling (other than the upper surfaces of the thermoplastic panels) should comply with the general provisions of paragraph 6.1 and Table 10, according to the type of space below the suspended ceiling.
b) If the diffusers are of classification TP(a) (rigid), there are no restrictions on their extent.
c) If the diffusers are of classification TP(b), they should be limited in extent as indicated in Table 11 and Diagram 27.
These regulations have been designed to reduce the risk of fire spread. Noting that such lighting diffusers' thermoplastics are designed to pass the 850oC glow wire test, this will not easily catch alight, but will burn if the fire is hotter than 850oC, which many are.
The size issue:
When Part B was originally drawn up (Building Regulations Part B 2000), recessed luminaires were relatively large, representing big sheets of thermoplastic material, albeit separated by the then normal 3m grid spacing. However, modern luminaires have become significantly smaller and lighting designers, architects and installers have been tending to fit a greater number of the latest smaller recessed luminaires closer than 3m, because this provides better and more uniform lighting for office tasks. One result of this trend has been a possibly greater risk of fire spread.
However, note paragraph 6.13, which (in part) states that (the provisions): 'are not concerned with diffusers of light fittings, which are attached to the soffit of, or suspended beneath, a ceiling'. This means, in essence, that Part B's lighting guidance recommends that lighting diffusers that form part of a ceiling have to comply, while suspended luminaires do not - even if they are fitted with thermoplastic diffusers. This, on the face of it, seems to be a logical inconsistency - even though with recessed luminaires, there are other aspects, such as the voids they are recessed into. There is, therefore, a move towards providing an amendment that will remove this inconsistency.
As Miles Pinniger has noted in his column in the latest issue of Lux Magazine (he was writing about the latest high-tech low-energy lighting systems seen at this year's LightFair in Philadelphia):
"Back in the UK, those selling and specifying lighting to save energy are faced with more wishy-washy, out of date legislation that, because of its age, actually prevents manufacturers from using new generation super-efficient optical materials.
"Yes, it's the UK Building Regulations again, but this time Part B. Necessary of course, but don't be fooled by the date of 2000 on the front cover - Approved Document B is based on legislation made after the Summerland disaster in the Isle of Man in 1973, where large amounts of Oroglas flammable plastic cladding caused a deadly result.
"Part B contains a specific section on lighting diffusers (recessed only) and rooflights that was introduced in the 1970s to limit the area of flammable material used in suspended ceilings. It also applies to any recessed lighting diffusers - for example the 1,800 x 600 mm troffers that were popular at the time. It differentiates between the categories of flammable materials TP (a) and TP (b), TP (b) being the more flammable but the better optically and the more stable. For TP (b) materials, Part B limits the maximum surface area to 50% of the relevant floor area - but the real problem is that it limits the spacing between such luminous areas to a minimum of 3m, which exceeds the typical 2.4m or 1.8m luminaire spacings found in most suspended ceilings.
"Now here's the conundrum: smaller, more efficient luminaires need to use newer, super-efficient optical plastics to meet the ever-tightening requirements of the much more up-to-date Part L, which is rightly focused on saving energy. But according to the 30-year-old Part B, you can't use them more closely than three metres apart.
"We've already got LED recessed downlighters that use acrylic - TP (b)- lenses, and more are coming onto the market every day. Their foreign manufacturers know nothing of the archaic Part B that restricts their use. And how ironic is it that most current LED downlighters have so little output that you're forced to space them much more closely than three metres.
"In an attempt to clarify a way forward, I spoke to the Department for Communities and Local Government (Eric Pickles' lot) to find out when Part B might get modernised. Ah well you see, there are other priorities, like making Part L even tougher, so Part B won't even get considered till 2013 -with the possibility of a new draft by 2016. How ridiculous is that?
"So which part of the Building Regulations would you like your scheme to comply with - Part B or Part L? Soon you won't be able to have both." (published by kind permission of Lux Magazine).
This is the conundrum!
UK lighting organisations are currently lobbying for an ammendment to the Regulations that will overcome this contradiction.