On 28th March 2022, amendment 2 of BS 7671 IET Wiring Regulations was published and there was a lot of the work was done around Chapter 42 fire safety, especially with the recent significant concerns over fire safety and escape from fire therefore these have been amended for clearer requirements.
In Appendix 5 of BS 7671 There is a classification system which deals with various classifications in buildings, and section BD deals with escape specifically, which in the IEC documents, Appendix 5, it is quite general and doesn’t go into great detail. It is not something which is relatively well understood in Europe where we have our own fire regulations, we where we have BD1, low density, easiest exit (Table 1). Therefore, this was reviewed and decided that it is not in accordance with the way the building regulations in England, Scotland, Wales and Northern Ireland present things.
Table 1 extract from informative Appendix 5 BS 7671:2018+A2:2022
The Building Regulations require clarification of a design and also provision of adequate means of escape as part of those building regulations. Each of the four devolved nations has its own requirements, but we don't have a handle on the BD. Therefore, it was decided that to identify building types and specify escape requirements by IEC code was not really helpful. It doesn't fit in with the way that the UK generally looks at things and so reference to BD classifications was removed from the regulations and it's only necessary for BS 7671 for electrical designers to specify and detail the building's electrical requirements for installations and for amendments and modifications during installation.
Fire safety design of a building is a joint process that starts with the architect and the building designer possibly even a buyer engineers in larger buildings, and the electrical engineer gets an installation layout based on the building layer but they don't identify escape routes, they are identified by the design team of which the electrical designer and the installer are apart.
Records of prior safety designs must be provided as part of the Building Regulations requirements. Regulations 38 specifically says that what is designed as details and what is design has to be provided.
Escape routes, generally in buildings are reasonably well understood people. If you consider a hotel corridor escape route where there will be multiple doors down both sides of a long corridor. BS 9999 for commercial and industrial installations and BS 9991 for domestic installation, detail requirements for escape routes. Generally escape routes have no specific requirements for fire protection, but they have maximum travel distances. Once you get past those travel distances, you have a problem and that you may be unable to escape because of fire.
What has been provided in the UK for many years is that those travel distances are maximized to a protected escape route. The term protected escape route has been brought into the wiring regulations for a clarification and alignment with the Building Regulations.
A protected escape route is effectively a sterile, fire protected route. Figure 1 shows a set of stairs which if you were on a hotel floor would be a protected escape route. You would go through the normal corridor, and you come out of a stairwell, which usually unfinished concrete and stairs and rails made of steel, because that is all extremely high fire resistance, and this would allow people to escape with protected provisions.
Anything electrical required in these stairwells to be minimized, and there are provisions required for electrical. So the regulations have based more on the requirements for electrical installations, and it should be considered that electrical designers or installers are not fire experts. They're not expected to identify or specify fire provisions in buildings, however, they must in association with the members of the design team identify protected escape routes within a building and ensure that the electrical installation in protected escape routes meets the requirements of section 422 of BS 7671 and doesn't undermine the safety of these routes. Effectively, cables have certain specifications, there's only a certain amount of outlets allowed, only things to do with the fire safety are allowed in protected escape routes. You cannot use them as a cable riser unless the cables are to do with the fire escape system and fire alarms only. That is the new requirements as they were taken out the references to BD’s in BS 7671 Chapter 42 and provided this new layout and hopefully, it will make things clearer for the electrical designer.
Fire safety with AFDDs
Changes for arc fault detection devices (AFDDs) have also been made in this amendment. They were recommended for certain installations in BS 7671: 2018, but now the requirements to mandate them has increased. The second amendment has now made it a requirement to install AFDDs on socket outlet circuits not exceeding 32 amps in certain premises. Those premises are listed in regulation 421.1.7 as
High risk residential buildings (HRRB). This is effectively blocks of flats.
Houses in multiple occupation (HMO).They are mostly occupied buildings with common facilities such as kitchens, bathrooms but have separate bedrooms,
Purpose built student accommodation
Care homes for the aged and for vulnerable and disabled people.
Regarding high-risk residential buildings, the terminology of HRRB was used in Grenfell in the early days, but that terminology has changed. The wording in the regulations has been left in this edition but there is a note that this legislation may change over the course of time and the final requirements of the Building Safety Act regulations having been issued at this moment in time. The designer must always comply with the current legislation wherever that may be during the course of the of the installations.
Regulation 421.1.1 does not require AFDDs at all locations, but recommends their use in most locations, and is considered useful for socket outlet circuits to be provided with AFDDs. This leaves a choice to use them to design an installation with input from other parties such as the architect, specialist fire engineer, and of course, the client.
Although these are considered to be expensive the cost alone should not be the overriding factor as BS 7671 requirements are for safety, and fire safety is a part of the complete safety. The costs of AFDDs are expected to reduce over time, as with most technology it becomes more and more widely used, and quantities increase bringing manufacturing costs down and more competition from manufacturers.
Some other changes that have been made on thermal effects are
Chapter 52 has relocated the table 52.2 cables in insulation, to Appendix 4 so that it then aligns with all the other tables for cable rating. It hasn't been changed, it's just been moved.
Table 52.3 has been simplified by removing some requirements and adjusting some other requirements where it's simpler to understand.
In section 714, which is outside lighting installations. There is no requirement to provide additional protection on lighting systems in public spaces e.g. gardens.
Section 753 Heating cables and embedded heating systems. The regulations haven't been amended, they've just been relocated. Changes include the addition of new regulations that was in chapter 53 covering the impact and installation of heating cables has now been moved to Section 753.
A new appendix 13 has been provided to give some guidance on escape routes and fire protection for escape routes.
For more information regarding this subject you may find the IET Guidance 4 Protection Against Fire useful.