UL 9540A is a testing procedure that evaluates and documents the fire performance of stationary ESS and was introduced as a compulsory requirement for all residential systems intended for installation in indoor locations as part of UL 9540 Ed. 2. The tests performed put the ESS through extreme abuse conditions that evaluate the fire and explosion hazard characteristics of the ESS. The test data is used to demonstrate ESS performance when applying for existing exceptions in the fire code to reduce location setback restrictions. Manufacturers may use cell and module-level results when comparing, and selecting, these components for use in an ESS unit.

UL 9540A Test Method: Summary

• Testing is divided into four levels: cell, module, unit, and installation (in order)
  • If the ESS unit does not meet the performance criteria of the level, it is then evaluated at the next level
  • If performance standards are met at a given level, it meets the criteria of UL 9540A and additional testing is not required
• Testing exposes the ESS to a thermal event to determine its ability to contain and prevent the spread of fire
• Performance evaluation of the ESS does not rely on integral safety features or the battery management system

UL 9540A: Test Levels

The following table and diagram demonstrate the performance criteria of each level and when additional testing is required.

Table 1. UL 9540A Test Levels with the Associated Performance Criteria

UL 9540A Test Level	Performance Criteria
Cell	Thermal runaway cannot be induced in the cell, AND Cell vent gas is not flammable in the air per ASTM E918
Module	Thermal runaway is contained by the module design, AND Cell vent gas is not flammable in air per ASTM E918
Unit	Target unit temperatures are less than the cell surface vent temperature, AND Temperature of target walls do not increase more than 97.0° C/206.6° F, AND Explosion hazards are not exhibited by the ESS, AND Flaming beyond the ESS unit doesn’t occur for units intended for residential installations as evidenced by burning or charring of a cheesecloth draped over the ESS in thermal runaway
Installation (not used for residential ESS)	ESS temperature is less than the cell surface vent temperature, AND Temperature of target walls do not increase more than 97.0° C/206.6° F, AND Flaming exceeding the width of the initiating ESS does not occur, AND Flaming outside the test room doesn’t occur and meets heat flux limits for means of egress