Advancing Fire Safety in Energy Storage: Understanding the 2026 Update to UL 9540A

23 Mar 2026

6th Edition Focuses on Increasing Test Rigor, Improving Hazard Characterization, and Addressing Large-scale Deployment Risks

As energy storage systems (ESS) continue to scale in size, complexity, and deployment environments, safety standards must evolve in parallel. The publication of UL 9540A 6th Edition on March 13, 2026, marks a significant advancement in how the industry evaluates thermal runaway, fire propagation, and explosion risk in battery energy storage systems (BESS).

For manufacturers, integrators, and developers, this update is more than an incremental revision – it reflects a continued shift toward real-world fire scenario validation, large-scale testing, and deeper alignment with modern fire codes.

The Role of UL 9540A in Energy Storage Safety

UL 9540A remains the industry’s primary test method for evaluating thermal runaway fire propagation in battery systems. It is not a certification standard, but a data-driven methodology used to support:

• Compliance with installation codes such as NFPA 855 and the International Fire Code (IFC)
• Certification pathways tied to UL 9540
• Approval by Authorities Having Jurisdiction (AHJs)

Testing is conducted across four levels – cell, module, unit, and installation – providing a comprehensive view of failure behavior and mitigation effectiveness. Depending on how the unit is constructed the unit level is required or not required.

What’s New in the 6th Edition (2026)

The 6th Edition, published March 13, 2026, builds upon the foundation of the 5th Edition, with a clear focus on increasing test rigor, improving hazard characterization, and addressing large-scale deployment risks.

1. Continued Evolution of Large-Scale Fire Testing (LSFT)

A major focus of the 6th Edition is further defining expectations for installation-level and large-scale fire testing:

• More representative ignition scenarios, including open-flame conditions
• Enhanced evaluation of fire spread between units and enclosures
• Increased emphasis on worst-case, real-world conditions

Impact: Aligns testing more closely with how ESS failures occur in the field – particularly in utility-scale and high-density installations.

2. Expanded Explosion and Gas Hazard Evaluation

Building on prior editions, the 6th Edition strengthens requirements around:

• Flammable gas generation and accumulation
• Deflagration and overpressure risk characterization
• Interpretation and ignition of off-gassing behavior

Impact: Addresses a critical and growing area of concern for AHJs and first responders – particularly for indoor and enclosed ESS installations.

3. Greater Clarity and Repeatability in Test Methods

The update continues to refine and added:

• Thermal runaway initiation and propagation criteria
• Developed fire condition initiation and criteria
• Instrumentation requirements and sensor placement
• Test setup consistency across laboratories

Impact: Improves reproducibility of results and confidence in data used for compliance and permitting.

4. Alignment with Evolving Codes and Regulatory Expectations

The 6th Edition further aligns UL 9540A with:

• NFPA 855 (including the 2026 edition)
• International Fire Code (IFC)
• Increasingly stringent local AHJ requirements

Impact: UL 9540A test data is now more directly tied to installation approvals, spacing requirements, and mitigation strategies.

5. Continued Support for Emerging Technologies

The standard maintains and expands its applicability to:

• Alternative battery chemistries (e.g., sodium-ion)
• New system architectures and enclosure designs
• High-capacity and grid-scale ESS deployments

Impact: Ensures the test method remains relevant as energy storage technology continues to evolve.

Why This Update Matters

UL 9540A Is Now Central to ESS Deployment

With the publication of the 6th Edition, UL 9540A continues to solidify its role as a gatekeeper for ESS project approval. AHJs increasingly rely on this data to determine acceptable installation configurations, required fire protection measures, and systems spacing and siting.

Increased Expectations for Real-World Validation

The shift toward large-scale and installation-level testing means component-level compliance is no longer sufficient, full system behavior under fire conditions must be understood, and mitigation strategies must be validated-not assumed.

Greater Pressure on Early Design and Testing Strategy

Manufacturers are now facing increased pressure to integrate UL 9540A considerations much earlier in the product development lifecycle. This shift requires a more proactive approach to system design, with a clear focus on large-scale fire behavior and real-world failure scenarios. At the same time, organizations must be prepared for more rigorous, data-intensive testing programs that demand deeper validation of system performance, mitigation strategies, and overall safety under increasingly complex conditions.

Implications for Manufacturers and Integrators

The 6th Edition reinforces several critical priorities:

• Early engagement with testing partners to align with updated methodologies
• System-level design validation, including enclosure, suppression, and ventilation strategies
• Comprehensive documentation to support AHJ approvals and code compliance

Looking Ahead

The publication of UL 9540A 6th Edition is more than a routine standards update – it reflects a fundamental shift in how energy storage safety is defined, evaluated, and ultimately trusted. The industry is moving beyond controlled, component-level validation toward holistic, system-level understanding of failure, where real-world fire behavior, gas hazards, and installation conditions are central to compliance.

In this new landscape, success will not be determined solely by meeting minimum requirements, but by how effectively manufacturers can anticipate risk, validate performance at scale, and demonstrate safety with confidence. Those who adapt early – embedding these expectations into design and testing strategies – will be better positioned to accelerate approvals, reduce costly redesigns, and lead in an increasingly scrutinized market.

Partnering with an experienced testing and certification organization is critical. Intertek supports manufacturers across the full ESS lifecycle – from early design evaluation and pre-testing to full-scale UL 9540A testing, certification, and AHJ engagement.

Connect with Intertek today to align your energy storage systems with the latest UL 9540A requirements and ensure your products are ready for compliant and successful deployment in a rapidly evolving regulatory environment.