Battery energy storage systems (BESS) are no longer an emerging technology. They are now a central pillar of Europe’s clean energy transition. By 2024, the continent had surpassed 35GW of installed electrochemical storage capacity, with lithium-ion batteries accounting for more than 90% (EMMES 9.0).
Growth is accelerating, and with it, the responsibility to keep systems safe.
Recent incidents, though infrequent, show how a single fire can undermine public trust, delay projects, and expose first responders to significant risks.
This is why the Energy Storage Europe association has developed Guidelines on Safety Best Practices for Battery Energy Storage Systems . These Guidelines provide a comprehensive, performance- based ‘blueprint’ for embedding safety into every stage of BESS projects – from design to deployment, operation and emergency response. At the centre of this blueprint is one key recommendation: Large-Scale Fire Testing (LSFT).
LSFT: What it is, why it matters
LSFT is distinct from the more familiar UL 9540A unit-level testing:
- UL 9540A examines how a single unit or module behaves when forced into thermal runaway. It provides valuable insights into cell and module behaviour but does not replicate a real project environment.
- LSFT simulates actual grid- scale conditions. Multiple fully-charged containers are arranged as they would be in practice. Safety systems are deliberately disabled. A module is forced into runaway, testing whether a fire in one container propagates to others.
The outcome is crucial. If LSFT demonstrates non-propagation, operators can adopt the ‘let-it- burn’ strategy: a fire in one container can be contained without endangering adjacent systems, infrastructure or communities. This approach also significantly reduces risk for firefighters, who no longer need to force open enclosures or directly engage the flames – another Energy Storage Europe recommendation.
For this reason, LSFT is not a minor certification step. It is a critical safeguard for public safety, firefighter protection, and industry credibility.
From innovation to baseline
While LSFT is now widely discussed, it is not new. As early as 2021–2022, pioneering developers carried out full- container fire tests without any regulatory obligation. Their efforts effectively laid the groundwork for the frameworks the industry relies on today.
What has changed is the status of LSFT. Once seen as an advanced, forward-looking measure, it has become an industry baseline. Its importance has grown as insurers, regulators and local communities increasingly demand tangible evidence of non-propagation before approving or accepting projects. The resurgence in LSFT announcements reflects this shift – but also the pressure of time. Regulatory milestones are approaching, such as the UK’s recent Parliamentary debate on BESS safety, and companies are eager to show that they are not just compliant, but ahead of the curve.
Policy milestones
Two developments explain why LSFT has moved from niche to mainstream:
- NFPA 855 (2026 edition) will make LSFT mandatory for grid- scale projects in the United States. From 2026 onwards, all deployments will have to demonstrate non-propagation. This will close the gap between voluntary early adopters and the broader market, while giving insurers and permitting authorities a clear reference point. As US standards often shape international practice, this update is likely to influence Europe as well.
- CENELEC harmonisation is Europe’s path forward. The Batteries Regulation (EU) 2023/1542 sets overarching requirements, but harmonised technical standards are needed to translate them into practice. CENELEC is expected to finalise EU-wide BESS safety standards by late 2026. These will align national practices, reduce fragmentation, and provide clarity for developers.
Until then, the Energy Storage Europe Guidelines act as a bridge. They prescribe LSFT as best practice and offer detailed recommendations for developers, manufacturers and first responders.
Off-gassing and deflagration
While LSFT addresses the risk of container-to-container propagation, it does not capture all hazards. A growing concern is the explosion risk during the early stages of thermal runaway.
As pressure builds inside an enclosure, doors or panels can burst open violently, creating severe health and safety risks for people in the vicinity.
Future safety standards must therefore integrate NFPA 68/69 deflagration testing. This represents the next step in safety assurance – addressing the dangers that occur before a visible fire even begins.
Safety as a system
While LSFT is vital, it cannot be the sole focus of safety strategies. The Energy Storage Europe Guidelines emphasise a holistic approach built on three dimensions:
- Product safety: Robust cell design, advanced BMS, thermal management, validated enclosures.
- Site safety: Proper spacing, ventilation, access routes, and fire mitigation measures.
- Personnel safety: Clear emergency protocols, firefighter training, and real- time system data.
Safety must be designed into every layer. Only then can resilience extend beyond catastrophic failures to cover smaller-scale incidents that also erode public trust.
Transparency
Another challenge is the lack of transparent data on incidents. EPRI reports a 98% decline in failure rates between 2018 and 2024. Yet publicly available root cause analyses exist for less than one-third of known events. Without greater transparency, the sector cannot fully learn from mistakes or build lasting trust.
The solution is clear: a centralised reporting system for incidents and near misses. Transparency is not about assigning liability. It is about building a culture of collective safety learning, and continuous improvement.
From compliance to credibility
The rapid growth of BESS is a success story for Europe’s energy transition. But capacity alone does not equal credibility. Communities, regulators and investors will only fully embrace storage if it is demonstrably safe.
The Energy Storage Europe Guidelines send a clear message: safety is not a barrier to innovation but its enabler. Performance-based standards ensure that new technologies can be adopted, as long as they are validated through testing. LSFT, predictive monitoring, and transparent reporting are the tools to prove that safety is embedded at every stage.
A future built on safety
So, is LSFT a thing of the past or the future? It is both. It was pioneered years ago, and it is now becoming a global standard. Its role is not to close the debate, but to set the baseline from which safety innovation must continue.
The Energy Storage Europe Guidelines prescribe LSFT as part of a broader framework. They make clear that true resilience requires attention not only to product design, but also to sites, people and transparency.
BESS are indispensable for Europe’s clean energy future. Their credibility will depend not only on how quickly we scale them, but on how safely we do so. LSFT proves that the industry can withstand worst-case scenarios. The next challenge is to go further – embracing transparency and building a culture where safety is as integral to storage as capacity itself.
Because in the end, a safer energy future depends on smarter storage.
