A string of high-profile battery energy storage system (BESS) fires-from the catastrophic blaze at Vistra's Moss Landing facility to repeated incidents in Warwick, New York-has pushed fire-safety standards into their most consequential revision cycle in years. The 2026 edition of NFPA 855 and the 6th Edition of UL 9540A now mandate large-scale fire testing, thermal runaway propagation prevention systems, and strengthened emergency response coordination. For project developers, operators, and equipment manufacturers, the updated framework carries significant implications for cost, scheduling, and insurability.
The Incident Backdrop Driving Standards Reform
The urgency behind these revisions is not theoretical. On January 16, 2025, a fire at the Vistra Moss Landing Energy Storage Facility in California-the world's largest grid-scale battery installation-burned for several days, forced the evacuation of approximately 1,500 residents, and destroyed roughly 75% of the Phase 1 facility, according to Inside Climate News1Inside Climate News and a study published in Scientific Reports2study published in Scientific Reports. The facility used nickel manganese cobalt (NMC) batteries in an indoor configuration that industry experts have since characterized as uniquely risky compared to newer outdoor, containerized designs.
The Moss Landing fire was not an isolated event. In December 2025, a fire at a Convergent Energy & Power battery storage facility in Warwick, New York, involved a system that local officials said was "unauthorized" and non-compliant, operating without a required Certificate of Compliance, as reported by CTIF3as reported by CTIF. That town had already experienced a BESS fire in June 2023 traced to a manufacturing defect that allowed water infiltration.
These incidents have fueled a wave of local moratoriums. New York state alone accounts for 98 active BESS moratoriums across 37 counties-more than two-thirds of all such moratoriums in the United States, according to Carina Energy4Carina Energy. The pattern is clear: safety incidents erode public trust, generating permitting friction that slows deployment industry-wide.
NFPA 855 (2026): What Has Changed
The 2026 edition of NFPA 85552026 edition of NFPA 855, the primary U.S. installation standard for stationary energy storage systems, represents a substantial tightening of safety expectations. Produced on a three-year revision cycle by a task force of industry players, certification agencies, authorities having jurisdiction (AHJs), and nationally recognized testing laboratories, the updated standard reflects lessons learned from real-world failures.
Large-Scale Fire Testing Becomes Mandatory
The most significant change is the introduction of a large-scale fire testing (LSFT) requirement. NFPA 855 (2026) now explicitly requires LSFT in conjunction with UL 9540A testing, ensuring that entire ESS installations are evaluated under realistic worst-case fire and explosion conditions, according to Telgian6Telgian.
Under previous editions, UL 9540A testing could conclude early if a system passed at the module level-meaning some large installations were never tested as complete units. The 2026 edition closes that gap by requiring full-container fire propagation evaluations that simulate a scenario where fire suppression systems are disabled and a single unit is left to burn.
Hazard Mitigation Analysis as the Default
The standard elevates Hazard Mitigation Analysis (HMA) from an optional exercise to the default requirement for most ESS projects. The 2026 edition requires that HMA be directed by a registered Professional Engineer experienced in fire protection engineering and energy storage risk assessment, as outlined in an analysis by Engineering Fire Protection7an analysis by Engineering Fire Protection. From a project management standpoint, budgets and schedules must now treat HMA as a baseline deliverable rather than a late-stage addition.
Thermal Runaway Propagation Prevention Systems
A new Section 9.7.6.6 introduces requirements for Thermal Runaway Propagation Prevention (TRPP) systems. These are defined as active, automatic systems that detect precursors to thermal runaway-such as off-gassing or abnormal temperature-and actuate targeted suppression or cooling media to stop propagation to adjacent cells, modules, or racks. Passive features like barriers and spacing, while complementary, do not satisfy the TRPP requirement on their own.
Expanded Detection and Chemistry Coverage
Detection requirements have broadened. The 2026 edition now accepts thermal image fire detection systems, listed to UL 2684, alongside existing smoke and radiant-energy detection options, per Telgian's analysis6Telgian. The standard also expands technology-specific chapters to address emerging chemistries beyond lithium-ion, reflecting the growing diversity of ESS deployments.
UL 9540A 6th Edition: Raising the Testing Bar
Running in parallel, UL Standards & Solutions published the 6th Edition of UL 9540A86th Edition of UL 9540A on March 13, 2025. The test method, widely recognized as the benchmark for evaluating thermal runaway fire propagation in BESS, now incorporates several key changes:
- Definition of thermal runaway propagation has been clarified, with refined criteria for establishing cell-to-cell propagation
- Module-level testing now includes a temperature limit for the module casing
- Large-scale fire testing is explicitly incorporated, addressing spacing and fire propagation at the system level
- Test report requirements now mandate inclusion of summaries from all previous testing levels
UL 9540A is the only fire and explosion testing method referenced in the 2026 edition of NFPA 855, according to UL Solutions9according to UL Solutions, cementing its role as the cornerstone of the testing and certification framework.
Key Differences: Previous vs. Updated Standards
| Requirement Area | Previous Standard | Updated Standard (2026) |
|---|---|---|
| Fire Testing Scope | UL 9540A testing could conclude early at module level | LSFT now required alongside UL 9540A; full installations evaluated under worst-case conditions |
| Hazard Mitigation Analysis | Optional for many project types | Default requirement; must be PE-directed |
| Detection Systems | Smoke and radiant-energy detection | Thermal image fire detection (UL 2684) added |
| Thermal Runaway Propagation Prevention | Not specifically addressed | Active, automatic TRPP systems required (Section 9.7.6.6) |
| Qualified Person Definition | Generic electrical equipment focus | ESS-specific skills, training, and hazard recognition required |
| Emergency Response | General requirements | Annual reviews with local AHJs mandated |
| Chemistry Coverage | Primarily lithium-ion | Expanded to emerging chemistries |
Implications for Existing Facilities
The updated standards do not apply only to new construction. NFPA 855 (2026) introduces retroactivity provisions that carry significant weight for operators of older installations.
For existing ESS facilities not originally listed to UL 9540, the standard empowers AHJs to require HMA and corrective action. State and local governments can require an HMA and corrective action for pre-2020 facilities, including the use of fire barriers or engineered solutions to meet large-scale fire testing requirements, as the American Clean Power Association's Blueprint for Safety10American Clean Power Association's Blueprint for Safety outlines.
Retrofit Alert: Operators of pre-2020 installations should evaluate whether a Hazard Mitigation Analysis is now required under the updated framework. AHJs may mandate corrective action, including fire barriers, upgraded detection, or engineered solutions to demonstrate compliance with LSFT requirements.
In practice, developers are pursuing several near-term mitigations:
- Enhanced thermal runaway containment through modular designs that isolate cells to halt cascading failures
- Upgraded battery management systems (BMS) with more granular cell-level temperature monitoring
- On-site water supply improvements for firefighting, including dedicated tanks and hydrant access
- Gas suppression systems in enclosed containerized units
- Standardized fire drill protocols developed in coordination with local fire departments
Insurance Market Response
The evolving standards framework is directly reshaping how insurers price and underwrite BESS projects. New fire safety standards and thermal runaway protocols have become mandatory requirements for most insurers, with enhanced BMS certifications and stricter installation standards directly impacting insurance eligibility and premium calculations, according to Solarif11Solarif.
BESS insurance costs typically range from 0.3% to 1.2% of project value, per Solarif's analysis11Solarif, but the spread within that range increasingly depends on demonstrated compliance with current NFPA and UL standards. As Tom Harries, Partner at NARDAC, has noted, if underwriters do not see a path forward on better management of thermal runaway risks, "insurance capacity will be reduced-lifting premiums-financing will be harder to secure, and battery development costs will remain high," according to TWAICE12according to TWAICE.
Key insurer expectations now include:
- UL 9540 listing and UL 9540A test data as baseline requirements
- Minimum spacing between modules in outdoor containerized systems-often at least 7.6 meters unless full-scale testing verifies alternatives
- Active monitoring and early warning systems to reduce claim frequency and severity
- Documented emergency response plans filed with local fire and emergency authorities
Some insurers have begun offering performance-based models where premiums are tied to ongoing operational health indicators-a trend that rewards operators investing in continuous monitoring and proactive maintenance.
Regional Enforcement Divergence
The market impact of these revisions is likely to be uneven across jurisdictions. Regions with strict enforcement and robust inspection regimes-such as New York, California, and states that have already legislated NFPA 855 compliance-may see higher upfront project costs but lower long-term risk exposure.
In Michigan and Indiana, the energy storage industry helped advance new laws requiring compliance with NFPA 855, while Maryland and New York have supported new regulations enforcing the latest requirements, according to the ACP10American Clean Power Association's Blueprint for Safety. However, many jurisdictions are only now adopting the 2024 International Fire Code, which still references the 2023 edition of NFPA 855, creating a transitional gap.
Markets with slower regulatory adoption risk lagging on safety improvements-a concern regulators stress as standard revisions complement permitting reforms rather than substitute for them. First responders in jurisdictions with less prescriptive enforcement may confront unfamiliar chemistries and containment requirements without adequate training or protocols.
First Responder Training Gap
Regulators and industry groups underscore that updated standards are only as effective as the responders trained to manage incidents under them. The American Clean Power Association's Blueprint for Safety calls for the industry and state and local governments to regularly coordinate on safety planning and continuously provide training to facility operators and the fire service, per ACP10American Clean Power Association's Blueprint for Safety.
The challenges for fire services are distinct. Lithium-ion battery fires behave differently from conventional structure fires: they can reignite after apparent suppression, produce toxic off-gases including hydrogen fluoride and hydrogen cyanide, and may require controlled burn-out strategies rather than active suppression. Annual emergency response plan reviews with local AHJs-now mandated under NFPA 855 (2026)-are designed to close this knowledge gap.
For additional context on how the broader U.S. safety framework is evolving, see the analysis in New U.S. Safety Framework for Long-Duration Storage and US Tightens National BESS Safety Framework After Fire Incidents.
Outlook
The convergence of NFPA 855 (2026) and UL 9540A 6th Edition marks a maturation point for energy storage safety standards. The framework moves decisively toward data-driven, site-specific risk assessment, requiring demonstrated performance under worst-case conditions rather than relying on component-level testing alone.
For the industry, the near-term calculus involves balancing additional compliance costs and schedule impacts against the long-term benefits of reduced incident risk, improved public trust, and more favorable insurance terms. Developers who integrate safety architecture from the design phase-rather than treating compliance as a late-stage checkbox-stand to reduce both project risk and total cost of ownership.
The pace of new deployments and the viability of retrofitting existing sites will hinge on how quickly jurisdictions adopt the updated standards and how effectively the industry demonstrates that the era of high-profile battery fires can be left behind.
Key Takeaways:
- NFPA 855 (2026) introduces mandatory large-scale fire testing, default HMA requirements, and new TRPP system provisions-the most significant revision in the standard's history.
- UL 9540A 6th Edition adds large-scale fire testing and tighter propagation criteria, and remains the sole fire testing method referenced in NFPA 855.
- Existing facilities face retroactivity provisions that may require HMA and corrective action, particularly for pre-2020 installations not listed to UL 9540.
- Insurance markets are tying coverage eligibility and premium pricing to demonstrated compliance with current NFPA and UL standards.
- Local moratoriums-98 in New York alone-underscore the deployment risks created when public trust outpaces safety assurance.
- First responder coordination is now a mandated, ongoing requirement rather than a one-time permitting exercise.
