Increasing the importance of effective electrical design

Towards the end of 2024, BS 9991, the national standard for fire safety in residential buildings, was revised. The updated code of practice introduced significant changes to fire safety standards and emphasised enhanced protection for residential building occupants. The changes will therefore heavily impact electrical design, especially when it comes to power supplies and installations for life safety and firefighting equipment. Jamie Mitchell, Associate Director at Whitecode Consulting, discusses the BS 9991 updates and reveals how these changes will increase the importance of close collaboration during the design of a building, especially when it comes to the design of utilities, cabling, and power supplies.

The tragic events at Grenfell Tower in 2017 have had far-reaching impacts on every corner of the construction industry and highlighted the need for significant improvements in residential building fire safety standards. As a result, the New British Standard BS 9991 has seen substantial updates, looking to enhance clarity and improve safety measures to ensure the standard aligns with modern building design and construction methods.

Impacting all types of UK residential properties, the BS 9991: 2024 update is a significant one, with vital changes in fire safety expanding the scope to include residential care homes, updating reaction-to-fire classifications for load-bearing structures, revising height limits for sprinkler installation and recommendations for single stair buildings, introducing European classifications for fire resistance in fire doors, enhancing guidelines on smoke control and evacuation lift recommendations, and updating new fire safety standards.

With that in mind, it’s vital that building designers, property developers, and mechanical, electrical, and plumbing (MEP) design consultants pay close attention to these regulation changes. This is especially the case when you consider mixed-use residential buildings need to independently apply both BS 9991 (focusing on residential standards) and BS 9999 (aimed at non-residential use).

Requirements are applicable dependent upon use

The new BS 9991 standards dictate that any mixed-use residential buildings that are partly residential should wherever practicable be designed such that from the standpoint of fire safety, the residential and non-residential uses are compartmented and independent of each other. For instance, BS 9991 and BS 9999 may be applied independently to the parts of the building within their respective scopes.

MEP design consultants, architects, and property developers must also be aware that the most onerous standard needs to be used on mixed use buildings where the fire safety of the residential parts relies on the performance of the non-residential parts.

Power supplies and cable installation for life safety and firefighting equipment

The BS 9991 updates have also seen significant recommendations for life safety and firefighting systems, with the primary power source to be taken from the public electricity supply. However, the secondary source should come from either a life safety generator, an independent high voltage supply – fed from an independent utility primary network substation to that feeding the primary supply – or an uninterruptible power supply (UPS).

From an electrical design perspective, this is the biggest change coming from the BS 9991 updates, as secondary utility supplies are not permitted unless from a separate HV main – the same procedure as BS 9999 in non-residential properties.

It is becoming more difficult to design UPS systems for secondary utility supplies as they are required to sufficiently power all systems they serve after 72 hours of power loss to a building. In many developments, life safety equipment, such as firefighting lifts and evacuation lifts, operate in normal circumstances and would therefore be constantly drawing power from the UPS systems and thus requiring large battery systems.

UPS is also not suitable to be used to supply wet risers, and if one is to be used to serve sprinklers, a separate UPS must be supplied for any other life safety systems.

Able to power vital equipment, such as fire alarms, sprinkler pumps, and smoke detectors, life safety generators help keep all important equipment connected to a power supply even if the mains fails or there is a grid outage. With just a 15 second operation time, life safety generators not only provide critical power when needed, they also can be useful in complying with stringent regulations.

Firefighter and evacuation lifts

Any buildings that are provided with passenger lift access to an upper or lower level should also be provided with a means of using lifts for escape. Any lift provided for means of escape should be designed and programmed to function as an evacuation lift.

It is therefore pertinent for architects, MEP consultants, and building designers to ensure that any buildings more than 50 metres in height have every lift designed as a fire-fighting lift that can also function as an evacuation lift unless recalled for firefighter function.

The close collaboration between all members of the project would also be required to ensure an adequate interface is provided between the fire detection system and the control panel. Furthermore, guidance would need to be sought from the fire consultant to determine if smoke detectors are required at the top of the lift shaft.

Mechanical smoke and heat ventilation

With smoke and heat ventilation a vital way of reducing toxic fumes in the event of a fire and giving occupants vital extra time to escape, the BS 9991 updates state that all smoke control systems should be designed to operate independently and not adversely affect each other’s performance. Furthermore, all heating, ventilation, and air conditioning (HVAC) systems that might operate alongside a smoke control system must be shut down when that system is operational.

It is therefore the duty of MEP consultants, architects, and building designers to incorporate this into fire strategy and implement fire alarm interfaces to shut down all HVAC systems in the event of a fire.

Close collaboration and increasing awareness are vital

While the BS 9991 updates are extensive, their impacts on property developers, architects, and contractors can be reduced through close working relationships and ensuring all design aspects are properly co-ordinated with other disciplines – enhanced further by the Golden Thread of information.

In addition to helping to identify design flaws and potential conflicts early, this close collaboration can also enable the end users’ requirements to be accounted for while considering any potential firefighting needs.

Regular maintenance is key

Of course, while it’s pertinent to use the most efficient and effective technology, ongoing maintenance and monitoring is as important as the quality of the system itself. Playing a crucial role in firefighting in the event of a fire, standby generators, such as life safety generators, should be started up once a month by simulating failure of the normal power supply and allowed to energise the system for at least 60 minutes. Additionally, the system should be monitored for any malfunctioning caused by the use of the generator. Similarly, emergency lighting and emergency escape lighting systems should also undergo rigorous testing to ensure they are functioning correctly should they lose access to the mains power supply.

The regular monitoring and maintenance of electrical systems and the vitally important secondary generators – along with effective design principles and close working partnerships between all involved in the project – will enable property developers to comply with the necessary regulations and standards.

This enhanced accuracy will also help to reduce the frustrations of delays in getting drafts approved, something that can often hamper electrical design projects across the UK.

Calling on the expertise of specialist consultants

Judith Hackitt’s review of the Grenfell Tower tragedy highlighted the need for not only greater collaboration across the industry but also the importance of early consultation with fire authorities during the building design process.

MEP design consultancy specialists Whitecode Consulting take a proactive approach to fire safety provisions, utilising a team of experienced fire engineering consultants to provide a clear solution to any fire engineering challenge. Offering expert advice throughout the MEP design process, the Kent and Birmingham-based company helps property developers, contractors, and architects conform to best practice and comply with all the latest building regulations, including BS 9991.