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As the global energy structure accelerates its transition toward low-carbon and electrified systems, and with the continuous expansion of applications in data centers, grid frequency regulation and distributed energy resources, Energy Storage Systems (ESS) are rapidly becoming an essential part of new power infrastructure.

The continuous scaling of energy storage has significantly enhanced grid flexibility, while also imposing higher requirements on system safety management capabilities. Against this backdrop, thermal runaway risks caused by large-scale applications of lithium-ion batteries have evolved from early equipment-level safety issues into critical safety concerns affecting system reliability, project bankability, and the long-term development of the industry.

Retrospective analyses of multiple global energy storage accidents in recent years have shown that gases released by batteries during thermal runaway appear earlier than visible smoke, flames, or even explosions. This consensus is driving a structural shift in energy storage safety philosophy: the focus of safety protection is gradually moving forward from traditional “fire detection and extinguishing response” to “early gas detection and risk warning.”

The evolution of the energy storage safety system from a “post-incident response model” to a “precursor identification model” is becoming an important trend in the global industry. Against this technical background, the world’s two major energy storage markets—China and the United States—have formed distinct and representative technical pathways regarding gas detection and protection for thermal runaway safety.

Divergent Paths of Safety Risk Management in the Two Major Energy Storage Markets

Currently, the mainstream practice in the Chinese market centers on carbon monoxide (CO) detection or composite detection devices combining CO with heat and smoke detection, achieving early identification of thermal runaway through multi‑parameter fusion. Meanwhile, the relevant standard system also covers requirements for the detection of gases such as hydrogen (H₂) and carbon dioxide (CO₂), and supports multi‑type composite detection schemes to improve the overall early warning capability of the system.

The technical framework represented by the expert system of the National Fire Protection Association (NFPA) of the United States, based on long‑term research into the gas emission mechanism during thermal runaway in LIB‑based energy storage systems and the latest practices in gas sensing technology, focuses more safety protection emphasis on hydrogen (H₂) detection.

Within this framework, carbon monoxide (CO) or carbon dioxide (CO₂) detection usually serves as auxiliary reference information for condition judgment, rather than as the primary explosion‑proof control measure.

Under this technical logic:

- Hydrogen detection is mainly used for combustible and explosion risk control;

- Carbon monoxide (CO) and carbon dioxide (CO₂) detection are more used for condition diagnosis and auxiliary criteria, rather than as primary explosion‑proof control parameters.

The difference between the two technical paths is not essentially an opposition between standard systems, but stems from different emphases in understanding the thermal runaway risk mechanism and different priorities of safety objectives.

Gas Release Mechanism: The Technical Basis for Strategic Differences

From an electrochemical mechanism perspective, different battery systems exhibit significant differences in gas release behavior. Under normal operating conditions, the only flammable gas that aqueous batteries (such as lead‑acid, Ni‑Cd, and Ni‑Zn batteries) may release is hydrogen. In contrast, for non‑aqueous battery technologies (such as lithium‑ion batteries and NaNiCl batteries), the electrolyte undergoes minor decomposition during normal charge and discharge, producing a small amount of gas.

In addition, during long‑term cycling, a Solid Electrolyte Interphase (SEI) layer forms on the surface of electrode materials, and this process also releases small quantities of gases such as carbon dioxide and carbon monoxide.

However, when thermal runaway occurs, batteries release a complex mixture of flammable and toxic gases. During thermal runaway in energy storage systems, although carbon monoxide is the most persistently present gas and is itself flammable, in safety engineering practice it is more commonly classified as a toxic risk indicator gas and can also be generated under normal operating conditions.

Hydrogen, due to its extremely low ignition energy and high deflagration sensitivity, is regarded as the key factor determining flammable risk. Therefore, for flammable gas protection, monitoring hydrogen alone is generally sufficient to meet explosion risk control requirements.

Evolution of Standard Systems: Safety Upgrades Driven by Engineering Experience

In terms of standards, both China and the United States are promoting the systematic improvement of energy storage safety capabilities through regulatory upgrades.

For China, GB/T 46261-2025 General Technical Requirements for Fire Monitoring and Early Warning Systems of Electrochemical Energy Storage Power Stations, issued by the State Administration for Market Regulation and the Standardization Administration of China, provides technical guidelines and testing requirements for ultra-early fire monitoring and gas detection in energy storage systems, offering a standard basis for multi-parameter integrated monitoring.

For the United States, NFPA 855-2026 Standard for the Installation of Stationary Energy Storage Systems issued by the National Fire Protection Association (NFPA) applies to the design, construction, installation, commissioning, operation, maintenance, and end-of-life management of stationary energy storage systems (ESS). It also covers mobile and portable energy storage systems installed in fixed applications, as well as the storage management of lithium metal and lithium-ion batteries.

Based on extensive installation and operation experience of energy storage projects, accident investigation data, and feedback from regulators, insurance companies, and industry stakeholders, NFPA 855 (2026 Edition) has further refined relevant technical content and added new guiding clauses on the selection of gas detectors and sensors, supporting more targeted and implementable engineering applications.