Commercial battery fire safety: PAS 63100 vs the IET Code

Fire safety is the concern most likely to stall a commercial battery project, and rightly so. A poorly specified lithium system is a genuine hazard, and insurers and fire and rescue services look closely at battery installations. It is also the area where the most confused advice circulates, starting with which standard applies. This post deals with the most common confusion, PAS 63100. For the full list of documents and what each one covers, see the fire safety standards map.

What PAS 63100 is, and what it is not

PAS 63100:2024 was published by BSI on 20 March 2024. Its full title is Electrical installations. Protection against fire of battery energy storage systems for use in dwellings. Specification, and it is aimed at the designers and installers of battery systems in homes.

Its scope is narrow, and BSI’s own summary lists what it leaves out. The exclusions include:

• dwellings with more than 200 m² of floor area;
• systems that use second-life batteries;
• battery systems in high-risk residential buildings;
• battery systems connected before the distributor’s cut-out or the consumer’s meter;
• batteries built into other products, such as pluggable UPS units.

Because it is written for dwellings, it is not the standard a commercial or industrial battery is designed to, even though you will see it quoted on commercial battery websites (this one included, until it was corrected in September 2026). If a proposal for a commercial site cites PAS 63100 as its fire standard, ask which commercial references the design actually follows.

What changed in 2026: BS 7671 Chapter 57

The biggest change since PAS 63100 was published is in the Wiring Regulations. BS 7671:2018+A4:2026 was published on 15 April 2026. It adds a new Chapter 57, “Stationary secondary battery installations”, which replaces the old regulation group 551.8 and is the first chapter of BS 7671 written for battery storage. The previous version of BS 7671 is withdrawn on 15 October 2026.

According to the IET’s guidance on the amendment, Chapter 57 applies where a battery’s designed purpose is to store and supply electricity to the installation. It is also where PAS 63100 gains formal standing: regulation 570.6.7.203 requires batteries in dwellings to be installed in accordance with PAS 63100. That is a change from 2024, when MCS noted that PAS 63100 had no standing in UK regulations. The reference to PAS 63100 is for dwellings; on a commercial site, the battery’s location and fire protection are decided through the fire risk assessment, the IET Code of Practice and the insurer.

For a buyer, the practical point is simple: a commercial battery designed from now on should be designed to BS 7671 as amended by A4:2026, and an installer should be able to confirm that in writing.

The references that apply to commercial systems

• BS 7671, including Chapter 57 (A4:2026), for the electrical installation.
• The IET Code of Practice for Electrical Energy Storage Systems (3rd edition, 2024): the main UK design reference, covering dwellings, commercial and industrial systems from specification through to maintenance.
• BS EN IEC 62933-5-2: safety requirements for grid-integrated energy storage systems that use electrochemical storage, covering the system as a whole.
• IEC 62619: safety requirements for lithium cells and batteries used in industrial applications.
• NFCC guidance for fire and rescue services, approved in December 2025, for open-air lithium systems of 1 MWh or more. It proposes an initial minimum distance of 30 m between battery cabinets and occupied buildings before mitigation is considered, and it shapes how battery storage planning permission applications are judged.
• Fire safety law: the premises’ fire risk assessment must be reviewed to cover the battery.
• Your insurer’s requirements, which are often the deciding factor in practice and may add their own expectations on separation, detection and suppression.

“No standards, trust us” is not an answer. A credible installer can show you which references the design follows and how each one is met.

What about MCS?

MCS certification is often mentioned in battery marketing, but its battery installation standard (MIS 3012) covers installations up to 50 kW. Most commercial batteries are larger than that, so MCS is not the test for them. For a commercial project, look for competent-person registration for the electrical work, a track record of G99 connections, and design evidence against the documents above. The installer checklist sets out what to check.

LFP chemistry is a big part of the answer

Most commercial stationary storage now uses lithium iron phosphate (LFP) cells rather than nickel-manganese-cobalt (NMC). LFP is generally regarded as more thermally stable, with a lower risk of thermal runaway, and it contains no cobalt; the trade-off is lower energy density, which rarely matters for a stationary system. Ask which chemistry is proposed and why.

Siting and separation

Chemistry is necessary but not sufficient; siting is where the design earns its keep. For a containerised outdoor system, that means separation distances from buildings, boundaries and escape routes, bunding, firefighting access and, where required, deflagration venting, with NFCC guidance on sites of 1 MWh or more. The great advantage of an outdoor container is that a thermal event stays outside the occupied building.

For an indoor cabinet, the room itself is the fire barrier: compartmentation to the building fire strategy, ventilation for cooling and any off-gassing, and dedicated detection tied into the building alarm. The room needs designing, not just filling with cabinets.

Engage the insurer before installation, not after

The most common avoidable mistake is treating fire and insurance as a formality after installation. Ask for the fire risk assessment early and share it with your insurer and, where needed, the fire and rescue service before the plant is on site. Problems tend to come from poorly specified kit or poor siting, and both are decided at design stage.

Questions to ask an installer

• Is the installation designed to BS 7671 as amended by A4:2026, including Chapter 57?
• Which references does the fire design follow, and is PAS 63100 being cited for a commercial site?
• What chemistry is proposed, and what detection, ventilation and separation does the design include?
• Has the insurer seen the fire risk assessment, and what did they ask for?
• On a containerised site of 1 MWh or more, has the fire and rescue service been consulted?

The bottom line

Commercial battery fire safety is not a reason to avoid storage; it is a reason to ask the right questions. If you have heard that batteries are “too risky”, read the myths vs facts page. If you want quotes, request them here: your enquiry is passed to installers who cover your area, and this site is not one of them.