Adrian Butler explains fire safety good practice for domestic lithium-ion Battery Energy Storage System (BESS) installations.
Battery energy storage systems (BESS), also known as Electrical Energy (Battery) Storage systems or solar batteries, are becoming increasingly popular for residential units with PV solar installations, and (although much less frequently) small wind-turbines¹.
These enable energy to be stored during times of sunlight or wind, if power use is low, and then released when consumers need power.
The following good practice guidance relates to lithium-ion battery BESS installations and is intended primarily for detached, semi-detached, and terraced dwellings, and also where appropriate and proportionate, small blocks of flats². It should be noted that in multi-tenant accommodation units, there will likely be greater exposure for theft or vandalism and BESS installations should be protected from intrusion to at least the same standard as other utility plant-room areas.
For fire safety of commercial lithium-ion battery BESS installations (including medium/large scale apartment blocks), which will be much larger than domestic BESS installations, proportionately more stringent fire protection standards are needed; refer to RISCAuthority Need to Know Guide RE1 Battery energy storage systems: commercial lithium-ion battery installations.
BESS are typically formed of lithium-ion battery cells, and although there have been few reported fire incidents with domestic BESS, the use of sizeable lithium-ion batteries in residential environments presents an enhanced fire safety hazard, as this type of battery can overheat in adverse circumstances, resulting in a rapid uncontrolled release of heat energy, known as ‘thermal runaway,’ that can result in a fire or explosion.
Details of how lithium-ion batteries can fail are discussed in detail in RISCAuthority Need to Know Guide RE2 Lithium-ion Battery Use and Storage.
Locating domestic BESS units in an outdoor/outbuilding location is the best choice for fire safety. If this is impractical, indoor locations need to be suitably selected and arranged. However, there are currently no UK standards providing definitive guidance on suitable locations and fire-safety arrangements for BESS in residential buildings.
A report for the Office for Product Safety and Standards for domestic BESS3 considers potential failure mechanisms for domestic BESS, the hazards related to a failure, risk mitigation, and both existing safety standards and standards currently under development. This report finds that if manufacturers and installers follow best industry practices and standards, they can significantly mitigate risks in the residential application of BESS.
Consideration should be given to keeping BESS separate from combustible construction and storage, and away from living spaces (bedrooms, living rooms). Garages (with good separation/protection from vehicles) or similar unoccupied utility spaces with suitable fire-separation are the best choice for indoor residential BESS installations.
NFPA guidelines4 for one and two-family dwelling and townhouse units recommend5 that where BESS are installed in unfinished rooms and spaces, walls and ceilings are protected with 15mm Type X gypsum board (e.g. fire rated plasterboard).
Loft spaces are typically unsatisfactory for BESS for a number of reasons, including limited accessibility for maintenance, ambient temperature extremes, exposed timbers, combustible roof coverings, and storage of
combustible items/items in combustible packaging.
Key good practice recommendations
All BESS installations should be subject to a suitable fire risk assessment. Based on available guidance (as referenced) and industry good practice, the FPA offers the following fire risk management guidance for domestic lithium-ion BESS installations:
- System design, installation, and maintenance to be undertaken in accordance with MCS requirements6, the IET Code of Practice for Electrical Energy Storage Systems, and industry good practice guidelines, using designers, suppliers, and electrical technicians holding relevant qualifications and certifications.
- Ensure that BESS are installed in accordance with manufacturers guidelines.
- Preferably locate the BESS in a detached building that does not expose the main dwelling or other important structures. Otherwise, the BESS should be installed outside on exterior walls/floors a minimum of 1m from doors and windows and secure from potential tampering.
- If installing the BESS in an attached garage (or inside unoccupied utility space) cannot be avoided, it should be ensured that this forms a separate fire compartment to occupied areas of the dwelling. UK building codes require a 30-minute fire separation for attached garages. Internal doors between the garage and main dwelling must have smoke seals and self-closing devices.
- Protect BESS from mechanical damage, e.g. a suitable barrier where there is a risk of vehicle impact.
- Ensure that BESS are located in compartments/locations where temperatures will not exceed the safe operating temperature specified by the BESS manufacturer.
- Install interconnected smoke alarms (ideally combined smoke and CO alarms) throughout the dwelling(s), including in the BESS room/compartment.
- Avoid installation of BESS in loft spaces (especially combustible lost spaces), unless they are specifically designed fire compartments.
- Ensure that building owners have all original BESS documentation, including installation and operating instructions, and that they are familiar with correct BESS operation and servicing requirements.
References
- RISCAuthority Need to Know Guide RE3 Rooftopmounted PV Solar systems, 2023
- A guide to making your small block of flats safe from fire, Home Office, 2023
- Domestic Battery Energy Storage Systems, A review of safety risks, BEIS Research Paper Number 2020/037, Department for Business Energy & Industrial Strategy/Office for Product Safety and Standards
- NFPA 855 Standard for the Installation of Stationary Energy Storage Systems, 2023
- Residential Energy Storage System Regulations (online article), NFPA TODAY, 10/2021
- MCS MIS 3012 ISSUE 0.1 The Battery Standard (Installation), 2019
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Adrian Butler is a Principal Consultant at the FPA.