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

Published guidance interpreting ISO Class L for US stakeholders

Lithium-ion battery fires now have their own fire class. In January 2026, the International Organization for Standardization (ISO) published a revised classification, ISO 3941, adding Class L for lithium-ion cell and battery fires that contain no metallic lithium. In late September, ISO finished a further revision that reworked the Class L appendix and added referenced testing frames.

Updated Sep 30

San Francisco went dark—and the same substation has burned before

Built World

Conducting independent investigation of Mission substation fire for PG&E

San Francisco is the kind of city that feels unstoppable—until the lights go out. On Saturday, a substation fire near 8th and Mission helped trigger a blackout that spread across neighborhoods and knocked out traffic signals. Restoration took more than two days and sparked political backlash and raised questions about whether a modern city can tolerate single-point failures in critical infrastructure.

Updated May 16