UL 9540A 2025-03 PDF

Full title and description

St UL 9540A 2025-03 — Test Method for Evaluating Thermal Runaway Fire Propagation in Battery Energy Storage Systems. A 2025 revision that defines laboratory and component-level test procedures, measurement methods and reporting criteria to evaluate thermal runaway initiation, propagation, vent gas composition, heat release and flame spread for battery modules, packs and energy storage systems (BESS).

Abstract

This standard specifies repeatable test methods used to assess thermal runaway behavior and fire propagation potential of electrochemical battery systems and components. It covers cell-, module-, rack- and room-level test configurations, required instrumentation, initiation methods, data collection and pass/fail considerations intended to support product design, comparative assessments, and code/authority having jurisdiction (AHJ) decisions.

General information

• Status: Published
• Publication date: March 2025
• Publisher: Underwriters Laboratories (UL)
• ICS / categories: 13.220 (Fire safety), 29.020 (Electrochemical power sources / batteries)
• Edition / version: 2025-03
• Number of pages: 64 (approximate)

Scope

The scope includes test methods to induce and measure thermal runaway in cells, modules and full energy storage system assemblies, characterization of propagation mechanisms, quantification of heat release rates and vent gas outputs, and evaluation of enclosure and room-level fire effects. The standard is intended for use with lithium-based chemistries and other electrochemical storage technologies where thermal runaway is a credible hazard. It does not set installation requirements but provides objective, measured data to inform safety design, mitigation and regulatory decisions.

Key topics and requirements

• Specified initiation methods to trigger thermal runaway (e.g., thermal, electrical, mechanical abuse) with controlled repeatability.
• Cell, module and system-level test configurations, including instrumented calorimetry, thermocouples, pressure and gas-sampling points.
• Measurement and reporting of heat release rate (HRR), peak temperatures, flame duration, mass loss and propagation timelines.
• Gas sampling and analysis procedures to identify toxic and flammable species (e.g., CO, HF, VOCs, H2) and vent volumes.
• Definition of pass/fail criteria and comparative test metrics for propagation likelihood and severity.
• Requirements for test enclosures, ventilation, sensors, safety interlocks and data acquisition systems.
• Guidance on sample selection, preconditioning, repeatability, and statistical treatment of results.
• Recommendations for documenting test set-up, instrumentation calibration and uncertainty analysis.

Typical use and users

Used by battery and energy storage system manufacturers, independent test laboratories, certification bodies, design engineers, code officials, AHJs, fire safety engineers and insurers. Typical applications include product development risk assessments, verification of mitigations (thermal management, enclosures, suppression), comparison of chemistries or designs, and support for compliance with building and fire codes.

Related standards

Standards commonly referenced alongside UL 9540A include UL 9540 (Energy Storage Systems and Equipment), UL 1973 (batteries for stationary applications), NFPA 855 (Installation of Stationary Energy Storage Systems), NFPA 1 (Fire Code), IEC 62619 and IEC 62133 (safety requirements for secondary cells and batteries), and relevant local building and electrical codes.

Keywords

UL 9540A, thermal runaway, battery energy storage system, BESS, propagation testing, heat release rate, vent gas analysis, fire testing, lithium-ion safety, test method

FAQ

Q: What is this standard?

A: It is a test method standard that specifies how to induce and measure thermal runaway and fire propagation in battery cells, modules and energy storage systems to characterize hazards and compare designs.

Q: What does it cover?

A: It covers initiation methods, test configurations (cell-to-room scale), instrumentation, measurement of heat release and vent gases, reporting requirements, and guidance for repeatable, comparable tests. It provides data to inform design and regulatory decisions rather than installation rules.

Q: Who typically uses it?

A: Manufacturers, independent test labs, certification bodies, fire safety engineers, AHJs, designers and insurers use it to evaluate thermal runaway risk, verify mitigations and support product certification or code compliance discussions.

Q: Is it current or superseded?

A: The version indicated is the 2025-03 published edition. Users should check with the publisher for any amendments or later revisions when preparing compliance evidence or test plans.

Q: Is it part of a series?

A: Yes. UL 9540A is part of a suite of standards addressing energy storage safety, including UL 9540 (system safety requirements) and related battery standards such as UL 1973. It is commonly used together with installation and fire codes like NFPA 855.

Q: What are the key keywords?

A: Thermal runaway, battery energy storage, propagation, heat release rate, vent gas, BESS, test method, UL 9540A.