As lithium-ion Battery Energy Storage System (BESS) deployments accelerate worldwide, Honeywell explains how evolving Li-ion BESS fire safety standards and off-gas detection technologies are transforming thermal runaway prevention and regulatory compliance
The global stationary lithium-ion (Li-ion) Battery Energy Storage System (BESS) market is entering a period of rapid expansion. Driven by net-zero commitments, grid modernisation and surging energy demand linked to AI infrastructure and data centres, the sector is expected to grow at more than 18.5% annually through 2034, according to Global Market Insights.
But as deployment accelerates, so too does scrutiny of one of the sector’s biggest risks: thermal runaway.
Until recently, the stationary BESS industry operated in a relatively underdeveloped regulatory environment, despite the growing use of large-scale lithium-ion battery systems in utilities, data centres, telecoms and commercial infrastructure.
That began to change in 2020 with the introduction of new off-gas detection technologies capable of identifying electrolyte solvent vapours released before thermal runaway begins.
These systems represented a significant shift in fire safety strategy. Rather than relying solely on conventional fire suppression, ventilation or flammable gas detection, the industry began focusing on earlier intervention.
This technological development has since influenced a wave of new fire safety standards, product certifications and building codes aimed specifically at Li-ion BESS risks.
For fire safety engineers, OEMs, system integrators and BESS operators, understanding this evolving regulatory landscape is now critical to ensuring compliance and future-proofing installations.
Why Li-ion BESS thermal runaway demands a new fire safety approach
Thermal runaway remains the defining fire hazard in lithium-ion battery systems. Before thermal runaway, lithium-ion cells typically vent trace amounts of electrolyte vapours and volatile organic compounds (VOCs). Detecting these early warning signs can provide a critical intervention window (in some cases up to 30 minutes) to isolate affected batteries, stop charging and activate ventilation.
This shift from reaction to prevention is now being embedded into standards worldwide.
How NFPA and UL standards are reshaping Li-ion BESS fire safety
The US-based National Fire Protection Association (NFPA), whose standards are widely referenced globally, has been central to this regulatory evolution.
NFPA 855 has become the cornerstone standard for stationary energy storage installations. The updated edition introduced stronger requirements. Notably, Annex G of NFPA 855 explicitly recognises the limitations of Lower Explosion Limit (LEL) sensors and battery voltage monitoring as thermal runaway safeguards.
Instead, the guidance highlights off-gas monitoring as one of the most effective methods for early detection, stating that cell-level detection close to or inside battery modules provides the most reliable pre-thermal-runaway warning.
The standard also notes that early detection can enable electrical isolation of affected cells, potentially stopping overheating before escalation.
NFPA 75 addresses lithium-ion battery fire risks in data centres
The rapid growth of AI and hyperscale data centres has increased reliance on lithium-ion Uninterruptible Power Supplies (UPSs), bringing new fire risks into critical digital infrastructure.
Reflecting this, the 2024 edition of NFPA 75, covering fire protection of information technology equipment, introduced off-gas detection requirements for Li-ion UPS systems for the first time.
The standard specifies that approved systems must monitor for electrolyte vapour released prior to thermal runaway and be installed according to manufacturer instructions.
Importantly, NFPA 75 also clarifies that conventional flammable gas sensors are not suitable substitutes. At early off-gas stages, released vapours occur only in trace concentrations – often at ppm or ppb levels – far below thresholds designed for explosion prevention.This means specialised off-gas detection is necessary.
NFPA 76 strengthens Li-ion battery fire safety for telecom facilities
Similar revisions were made to NFPA 76, which governs telecommunications facilities.
The 2024 update requires approved systems to monitor electrolyte vapour release in battery installations above 20kWh where batteries are grouped within close proximity.
Upon detection, systems must automatically stop charging affected batteries and disconnect them from load.
Again, the standard reinforces that traditional flammable gas sensors are insufficient for thermal runaway detection.
NFPA 400 ventilation requirements for Li-ion BESS fire safety
The NFPA 400 Hazardous Materials Code (2025) adds another important dimension, requiring exhaust ventilation systems to account for the density of potential vapours released from hazardous materials.
Off-gas detection systems can support compliance by automatically
triggering ventilation when electrolyte vapours are detected.
Li-ion BESS product certification evolves with fire safety standards
Alongside installation standards, product certification requirements are becoming more rigorous. The recently revised UL 2075 Gas and Vapor Detectors and Sensors standard introduces updated requirements covering detector design, construction and performance.
For off-gas detection manufacturers, this creates a clearer pathway for third-party validation of systems designed to detect lithium-ion electrolyte vapours, hydrogen and carbon monoxide.
How insurers are driving higher Li-ion BESS fire safety standards
Insurance providers have also emerged as influential drivers of BESS safety best practice.FM Global’s Property Loss Prevention Data Sheets 5-33, widely referenced by industrial operators and insurers, provide guidance for the design, operation and protection of stationary Li-ion BESSs.
The 2023 revision introduced new recommendations for thermal runaway prevention. Section 2.5.3.3 calls for early intervention systems capable of automatically and electrically isolating affected batteries when cell temperatures exceed thresholds and VOCs indicate pre-thermal[1]runaway venting.
The guidance requires FM approved VOC detectors which the new FM Approvals Standard 6540 fulfils with the establishment of dedicated testing and verification criteria for off-gas detectors certification.
This reflects growing insurer demand for independently verified detection performance in high-risk energy installations.
Why early off-gas detection is becoming central to BESS fire safety
Europe has also been active in formalising guidance around lithium-ion battery fire risks.The UK’s Fire Industry Association (FIA) was among the earliest organisations to formally endorse off-gas detection.
Its 2020 guidance on Li-ion battery fires concluded that systems capable of detecting low-concentration off-gases can provide early warning of impending thermal runaway and trigger shutdown systems to electrically isolate battery racks before escalation.
It also emphasises strategic sensor positioning to account for cooling airflow and the use of reference sensors to reduce false alarms.Meanwhile, the UK Fire Protection Association’s Need to Know Guide RE1 recommends early detection of off-gases or electrolyte vapours for critical and significant BESS installations, linked directly to shutdown and disconnection systems.
Together, these documents signal a broader European shift toward integrating early gas detection into battery fire protection strategies.
How local fire codes are strengthening Li-ion BESS safety requirements
Beyond standards bodies, regional building and fire codes are increasingly codifying these requirements. Among the earliest examples was the 2022 Connecticut State Fire Safety Code, which introduced provisions requiring systems capable of detecting electrolyte vapours at the start of battery venting, automatically shutting down affected BESS racks, transmitting fire alarm signals and activating mechanical ventilation.
Austin City Council’s 2024 Technical Building Codes, effective from July 2025, include similar requirements. For lithium-ion BESS installations above 20kWh, systems must include off-gas detection that both operates independently from the Battery
Management System (BMS) and identifies the affected rack. These provisions suggest local codes may act as regulatory accelerators, particularly in jurisdictions with fast-growing battery deployment.
New research supports off-gas detection for Li-ion BESS safety
Academic and industry research is also reinforcing the importance of early detection. A DNV study found that off-gas detection combined with automated shutdown protocols can prevent thermal runaway progression.
“Importantly, NFPA 75 also clarifies that conventional flammable gas sensors are not suitable substitutes.”
Separately, a 2024 study showed that commercial VOC sensors consistently triggered during cell venting events, even in large battery packs.
Research supported by UL Research Institutes and ESRI is also exploring improved off-gas monitoring in BESS applications, suggesting standards may become more prescriptive.
So, the stationary lithium-ion BESS sector is no longer operating in a regulatory vacuum Across North America and Europe, fire safety standards, insurer requirements and local building codes are converging around a common conclusion: early detection of electrolyte vapours is essential for mitigating thermal runaway risk.
For developers, operators and manufacturers, this means compliance is no longer simply about installing suppression systems or meeting baseline fire codes. It increasingly requires a proactive safety architecture built around prevention, early warning and automated intervention.
Supporting Li-ion BESS compliance through early off-gas detection
Honeywell’s Li-ion Tamer has emerged as one of the best-known systems designed specifically to address the early detection requirements now referenced across multiple standards and guidance documents.
Unlike conventional flammable gas detection, Li-ion Tamer is engineered to identify trace levels of electrolyte vapours released during the earliest stages of battery cell failure, before thermal runaway occurs.
This enables operators to respond earlier through shutdown, electrical isolation and ventilation strategies, helping reduce the risk of escalation. The system has been referenced throughout the industry’s regulatory evolution because it addresses a critical gap in traditional battery fire protection approaches: detecting battery distress before smoke, heat or explosive gas concentrations are present.
As BESS deployments expand into utilities, data centres, telecoms and commercial buildings, early intervention is becoming central to fire safety design. Solutions such as Li-ion Tamer can help operators and system integrators align installations with increasingly specific requirements around off-gas detection, rack-level monitoring and automated response protocols.
With regulatory scrutiny increasing, technologies that support earlier warning and actionable intervention are likely to play a growing role in helping the industry build safer, more resilient energy storage infrastructure
