International Organization for Standardization (ISO)

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ISO adds Class L fire rating for lithium-ion as New York enforces 1 kWh storage rule

Published ISO 3941 third edition adding Class L in January 2026; no later revision reported

Lithium-ion battery fires now have their own fire class, after ISO published the third edition of ISO 3941 in January 2026 adding Class L for cells and batteries that contain no metallic lithium. New York City had already set a lower regulatory bar: its amended NFPA 855 requires FDNY approval for lithium-ion storage above 1 kilowatt-hour, against 70 kilowatt-hours for lead-acid.

Updated Oct 21