In 2024, an explosion at an Arizona energy storage facility exposed a hidden vulnerability in clean energy infrastructure — the silent risk of hydrogen buildup.

As renewable adoption accelerates, Battery Energy Storage Systems (BESS) have become essential to modern grids, yet they also generate flammable hydrogen gas during normal or fault conditions. Even a small concentration in an enclosed container can reach explosive levels within minutes, making continuous hydrogen monitoring a critical safety requirement.

At the core of this protection are fixed hydrogen detectors for BESS — silent, always-on sensors that identify gas leaks long before ignition can occur. 

Today, fixed hydrogen detection systems are becoming standard in large-scale battery storage facilities—from grid-scale energy containers and telecommunications backup stations to data center microgrids—where early detection of gas leaks can mean the difference between routine maintenance and catastrophic loss.

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Why Hydrogen is the Ultimate BESS Hazard

Under certain fault scenarios, hydrogen (H2) gas is produced from battery operations. The risk associated with hydrogen comes from its physical and chemical nature:

• Highly Flammable: Hydrogen ignites at just 4% concentration in air, so even minor leaks in enclosed BESS units can create flammable atmospheres.
• Invisible and Odorless: Undetectable without sensors, hydrogen buildup can reach ignition levels unnoticed.
• Lighter Than Air: It accumulates near ceilings and vents, making high-mounted detectors essential for safety compliance.

Among all battery safety risks, thermal runaway poses the greatest threat. It occurs when cell temperatures rise uncontrollably and release flammable gases such as hydrogen, carbon monoxide (CO), and hydrogen fluoride (HF).

These gases are emitted minutes before smoke or flames appear, creating a brief but crucial window for early detection. Identifying this off-gassing phase early is key to preventing a small fault from escalating into a catastrophic fire or explosion.

The Role of Fixed Hydrogen Detectors

Fixed gas detection systems provide the unmatched, 24/7, real-time surveillance that mitigates the unique hazards of BESS. 

1. The Early Warning System for Thermal Runaway

The number one job of fixed hydrogen detectors is to give you a warning of a potential battery failure before the battery failure occurs. Fire suppression systems, like smoke and heat detectors, are critical, but ultimately designed to react to an event after it has already begun. The hydrogen detector will detect actual gas that is the byproduct of a battery that is in the process of failing.

When a lithium-ion cell starts to experience internal heating associated with the condition known as thermal runaway, its chemical components will start to degrade and produce hydrogen and other volatile organic compounds (VOCs). 

The fixed gas detector can recognize these gases at ppm levels, long before the temperature becomes high enough to reach ignition, allowing the Battery Management System (BMS) to implement a controlled response. Advanced models — such as GasDog’s fixed hydrogen detectors — include remote monitoring functions that let operators track gas levels and activate safety responses in real time, even when off-site.

This could occur by:

• Activating Enhanced Ventilation – Initiating high-capacity exhaust fans to discharge and highly dilute the gas concentrations immediately.
• Decoupling the System – Canceling or isolating the array or modules to shut it off from the power grid and stop the charging/discharging cycle.
• Notifying Personnel – Alerting operators associated with the site, or site teams, that there is some threat developing that allows time for safe intervention processes to initiate before the fire suppression system is even needed.

In a 2 MWh containerized BESS facility, fixed hydrogen sensors activated the ventilation system 6 minutes before thermal sensors reached their alarm threshold. This early alert prevented a cascading thermal runaway and avoided over $100,000 in equipment downtime — demonstrating how hydrogen detection provides measurable ROI, not just compliance.

2. Compliance and Layered Safety 

Safety codes for BESS installations, such as the codes created and considered by NFPA (National Fire Protection Association), are ever-increasingly requiring gas detection to monitor H₂ accumulations.

Typically, these standards require flammable gas concentration to be restricted to 25% of the LFL, which in the case of hydrogen, is about 1% volume in air.

Fixed detectors allow the operator to implement a critical two-level alarm system:

• Low Alarm (Action Point) – This is set at a much lower concentration (for example, 10% LFL or 0.4% H2) and is the basis for automatically starting or increasing the mechanical ventilation in the room. This will allow the atmosphere to be maintained at a safe level without personnel intervention.
• High Alarm (Critical Point) – This alarm is set closer to that legal limit (for example, 25% LFL or 1% H2), which will initiate audible/visual alarms, notify the BMS, and notify the complex for procedures to shut it down. This point may also initiate expensive off-site emergency service.

With this layered approach, the routine out-gassing of hydrogen is managed quietly and the ventilation system reacts to a fault effectively.

3. Strategic Location and Sensing Technology

The success of a fixed detection system is entirely dependent on its design and its location. Because hydrogen is lighter than air, the sensors must be placed at the highest locations that can be feasibly deployed. In addition, that means at or near the ceiling and within the more chimney-like structure of the rack-tops or the battery cabinets, or at least, locations where localized pockets of gas formation can occur.

Current fixed hydrogen detectors utilize a variety of sensor technologies to pursue accuracy and reliability: 

Sensor Type	Sensitivity Range	Best For	Typical Use in BESS
Electrochemical	ppm level (very low concentrations)	Early off-gassing detection before thermal runaway	Recommended for lithium-ion systems where detecting small leaks early is critical.
Catalytic Bead (Pellistor)	%LEL range	Monitoring higher gas levels or verifying ventilation performance	Common in lead-acid rooms or outdoor enclosures.
Thermal Conductivity	% volume	High-concentration environments or backup verification	Used mainly in large containerized BESS with integrated exhaust channels.

Most modern fixed hydrogen detection systems for BESS use a hybrid dual-sensor architecture, combining electrochemical sensors for early-stage hydrogen monitoring with catalytic bead sensors for redundancy and verification. This configuration provides ppm-level precision, LFL-level protection, and meets the NFPA 855 sensitivity and reliability requirements for enclosed energy storage environments.

In 2–5 MWh containerized systems, engineers typically deploy 2–4 electrochemical sensors near the ceiling or vent channels and one catalytic detector near the exhaust or maintenance access area, ensuring full gas coverage and rapid fault localization.

Built for long-term reliability, industrial fixed hydrogen detectors — such as those developed by GasDog — combine this dual-sensor design within a single enclosure, using die-cast aluminum housings for corrosion resistance and anti-contaminant coatings to prevent SO₂ poisoning.

Together, these design measures ensure hydrogen monitoring NFPA 855 compliance and deliver extended service life in demanding BESS environments.

The Foundation of BESS Safety

As BESS installations continue to grow in size and energy density, the risk of a single cell fault cascading into a larger event increases. Installing rugged, continuously monitored fixed hydrogen detectors remains the most effective non-invasive safeguard against this threat.

These systems provide real-time off-gassing detection and serve as the first line of defense protecting both infrastructure and personnel. Across grid-scale renewables, telecom backup systems, and data center microgrids, early hydrogen detection has become a standard design feature — ensuring compliance, reliability, and long-term operational resilience.

Summing Up

The continued expansion of Battery Energy Storage Systems (BESS) is necessary to deliver a resilient, decarbonized energy future. Yet with this expansion comes an equally serious safety concern — hydrogen gas, an invisible but highly flammable byproduct that must be continuously managed. 

Fixed hydrogen detection systems for BESS are now mandatory components in modern BESS safety systems. With NFPA 855 and UL 9540A requiring hydrogen monitoring, certified fixed detection is no longer optional but essential.

As hydrogen detection becomes standard across BESS design, it’s reshaping the definition of “smart safety” in the clean energy era — protecting assets, uptime, and public trust.