The legislative timelines governing building and fire code adoption are fundamentally mismatched with the pace of lithium-ion BESS technology development, often leaving enforceable state building and fire codes years behind current standards.

The National Fire Protection Association (NFPA) 855 (2026 edition) Standard for the Installation of Stationary Energy Storage Systems and UL 9540A (6th Edition) Test Method for Evaluating Thermal Runaway Fire Propagation in Battery Energy Storage Systems have both recently been updated to significantly improve fire safety and risk mitigation. These recent updates to the standards reflect lessons learned from lithium-ion BESS incidents and should be incorporated directly into project requirements documents.

The NFPA 855 (2026 edition) represents a major revision to the document’s content and format. Numerous enhancements to critical safety system design were incorporated. The 2026 edition added a requirement for Large-Scale Fire Testing (LSFT) in accordance with UL 9540A (or equivalent), along with a new chapter addressing explosion requirements. The fire suppression requirement was removed, which aligns with AEGIS’s longstanding position first articulated in the original edition of the AEGIS  white paper nearly five years ago. Fire suppression systems do not address thermal runaway conditions and may introduce additional failure modes or increase explosion potential in lithium-ion BESS.

UL 9540A, 6th Edition, was released on March 25, 2026. This edition reflects more than a year of development supported by AEGIS and industry stakeholders through UL’s Standards Technical Committee. The 6th Edition introduces LSFT performance criteria used to evaluate and justify manufacturer-prescribed separation distances for model-specific, containerized BESS. These updates align UL 9540A with LSFT requirements adopted in the 2026 edition of NFPA 855.

AEGIS member utilities should update internal standards, practices, and purchase/bid specifications to incorporate these updated standards and requirements. AEGIS has reviewed several LSFT submissions covering multiple makes and models of containerized BESS. In some cases, test results support adjusting AEGIS Loss Control’s recommended 25-foot separation guidance allowing for increased site energy density. AEGIS anticipates reviewing additional LSFT submissions as manufacturers and member utilities adopt the updated standards.

• Reference NFPA 855 (2026 Edition) as a project requirements document.
• Require Large-Scale Fire Testing (LSFT) to be conducted in accordance with UL 9540A, 6th Edition, without active fire suppression. If active suppression is used during LSFT, the results should not be used to justify separation distances for insurance purposes. If testing is performed to another LSFT standard, provide an equivalency evaluation identifying all variances.
• Require a product-specific Hazard Mitigation Analysis (HMA) as part of initial bid documentation.
• Require the product-specific HMA to be revised based on planned site conditions early in project development (i.e., converted to a project-specific HMA) and maintained as design progresses (e.g., 30%, 60%, 100%).
• Require that product-specific and project HMAs meet NFPA 855 requirements and follow guidance in the AEGIS Li-ion BESS white paper, including, where applicable, the following:
  • Inclusion of all information identified on the Battery Energy Storage Systems Key Loss Control Information Sheet.
  • A summary evaluation of LSFT, including manufacturer-recommended spacing criteria and an assessment of damage to target enclosures (i.e., repairs or replacements needed to return affected containers to service with warranties intact). For each target container, compare worst-case internal temperature and cell vent temperature readings to determine margin and determine whether cells/modules can be returned to service.
  • Inclusion of, or a summary of, Deflagration Hazard Study results and Partial Volume Deflagration Analysis.
  • Provide UL 9540 label/listing documentation and a summary of any exceptions.
• Require a hydrology study where "value at risk" exceeds corporate maximum loss guidance.
• Require both emergency ventilation and deflagration vents.
• Require that all Battery Energy Storage Systems Key Loss Control Information be provided without the need of a nondisclosure agreement (NDA), including LSFT, so it may be shared with insurance stakeholders.

For further information, please contact Chuck Bruce, Sr. Loss Control Professional, Loss Control Property Operations, at 201.994.8267, or by email.