Most searched for brands of measuring and regulation technology
Lithium-ion and lead-acid batteries are now found wherever backup power or energy storage is needed – in data centres, UPS rooms, battery energy storage systems (BESS) and rapid charging stations. However, as their use becomes more widespread, so does a risk that conventional fire detectors cannot adequately address: the release of hydrogen and other gases during charging or cell failure. This article explains why gases are released, why standard fire detection responds too late, and how the issue is addressed by the Evikon E2673 off-gas detector.
Author: Jaromír Bittner, BSc – Evikon Product Specialist
Hydrogen generation has two main mechanisms – and both need to be considered when designing battery room safety:
Lead-acid batteries (lead-acid, AGM, gel, VRLA). During charging, electrolysis splits water in the electrolyte into hydrogen and oxygen. With flooded cells, gas release is entirely normal; with VRLA batteries, leakage typically occurs only during overcharging or valve failure. Hydrogen accumulates beneath the ceiling (it is 14 times lighter than air), and if the room is not adequately ventilated, the concentration around the battery can rise rapidly.
Lithium-ion batteries. Hydrogen is not a product of normal charging – it appears only as part of so-called off-gassing, i.e. the release of gases from a cell when it overheats or degrades. Alongside hydrogen, electrolyte vapours are also released (volatile organic compounds, typically diethyl carbonate DEC and dimethyl carbonate DMC, or DEMC), carbon monoxide and other by-products. Off-gassing is the first physically measurable sign of so-called thermal runaway – a self-accelerating reaction in which the rising cell temperature triggers further exothermic processes inside the cell, which increase the temperature further and may ultimately lead to ignition or explosion.
The common factor in both cases is one fact: hydrogen is colourless, odourless and highly flammable. Its lower explosive limit (LEL) is approximately 4% by volume in air – so it takes very little for a room to become an explosive atmosphere.
A standard fire alarm control panel relies on three types of detector – smoke, heat and flame. In the event of battery failure, all three have a fundamental timing problem:
There is virtually no smoke during the off-gassing phase. Gas release occurs before combustion. At this stage, there may be no visible smoke or flame in the room, and the ambient temperature may rise only minimally. The smoke detector therefore remains silent, even though a reaction is already taking place inside the cell that could still be stopped.
The temperature rises inside the cell, not in the room. By the time the temperature gradient is transferred into the surrounding space where a heat detector responds, several adjacent cells are usually already in thermal runaway. In the meantime, the reaction continues to spread through the module.
A flame detector only responds after ignition. At that point, it is no longer about prevention, but damage limitation.
The only method that detects a fault before an open fire develops is gas detection – specifically hydrogen and electrolyte vapours (VOC). That is why, for battery energy storage systems and UPS rooms, it is recommended to supplement the conventional fire alarm system with gas detection connected to the fire alarm control panel or SCADA.
If only lead-acid batteries were involved, a standalone hydrogen detector would be sufficient. With lithium-ion cells, however, the situation is more complex. Slow cell degradation may first manifest itself through electrolyte vapour release (VOC), without a large amount of hydrogen being released immediately. Rapid faults, on the other hand, may begin with a rise in hydrogen. If you monitor both groups of gases simultaneously, you increase the likelihood of detecting failure at the earliest possible stage – regardless of which path it starts with. That is precisely the strength of a combined detector.
In a battery room, temperature and relative humidity are also usually monitored. The recommended range for data centres and UPS rooms is typically between 40–60% RH and 21–25 °C. Higher humidity leads to contact corrosion, low humidity to electrostatic discharge, and high temperature shortens cell life and increases the risk of thermal runaway.
The Estonian manufacturer Evikon MCI designed the E2673 detector specifically for this type of application. In a single DIN rail enclosure, it combines four functions:
As a result, it covers all key environmental parameters in a battery room with a single device, saving the installation of two to three separate sensors.
For hydrogen, the detector uses the principle of thermal conductivity. The sensor measures how the target gas affects the thermal conductivity of the sample compared with a reference environment. Hydrogen has around 7 times higher thermal conductivity than air, so it can be reliably detected using this method. Unlike electrochemical cells, the sensor is also not susceptible to poisoning. The measuring range is 0–100% LEL H₂ with a resolution of 0.02% LEL, and the alarm threshold can be user-set within the range of 10–40% LEL – i.e. well before the lower explosive limit is reached.
For volatile organic compounds, an MOS sensor (metal-oxide semiconductor) is used with an index of 0–500. It responds to DEC, DMC and other organic electrolyte vapours released during Li-ion cell degradation. Sampling is diffusion-based – gases reach the sensors through natural air circulation via the device housing, so no pump or sampling line is required. Warm-up time after start-up is up to 1 minute, with a response time of up to 20 seconds.
The sensors have an expected service life of approximately 15 years, which is close to or exceeds the service life of lithium-ion storage systems themselves. The detector is designed without the need for regular field calibration – eliminating the typical problem of hydrogen detectors that lose accuracy after a few years and are difficult to keep calibrated across large installations. Detector status can be monitored by self-diagnostics during start-up and operation.
The E2673 offers two ways of connecting to a higher-level system:
The detector status is indicated directly on the device by three LEDs: green (power), yellow (fault), red (alarm).
Technical parameters at a glance:
The E2673 is suitable wherever gases may be released from lithium-ion batteries or where lead-acid batteries are charged on a larger scale:
The compact enclosure allows installation directly in a battery rack or in a control cabinet alongside other DIN rail components. For use in areas with a risk of explosive atmosphere, the detector is certified for ATEX Zone 2 in accordance with Directives 2014/30/EU and 2014/34/EU.
When designing gas detection in a battery room, it is worth following a few rules:
Place the detector close to the ceiling. Hydrogen rises and accumulates at the highest point in the space. A detector installed at rack level will detect a leak more quickly than a sensor mounted 1.5 m above the floor.
Consider ventilation. Detection alone will not extinguish a fire. The alarm should trigger ventilation of the area – ideally in two stages: when the first threshold is reached, ventilation starts; when the second is reached, charging is disconnected and both audible and visual alarms are activated.
Connect the detector to the fire alarm system. Route the detector relay output to an input on the fire alarm control panel so that an alarm triggers the standard fire alarm protocols. Modbus can then be used for visualisation and trending in the BMS.
Do not forget zoning. For large BESS containers or multiple racks in one room, allow for multiple detectors positioned to cover all risk areas.
For modern battery systems, gas detection is what a smoke detector is for standard fire protection – the first line of defence. The difference is that, for lithium-ion storage systems, it is often the only way to detect a fault before it progresses to an irreversible stage. The Evikon E2673 detector combines everything a battery room or UPS room needs in one compact device – hydrogen detection, electrolyte vapour detection, humidity and temperature – and thanks to its 15-year service life without field calibration, it keeps operating costs low throughout the life of the storage system.
If you are deploying the detector only in areas with lead-acid batteries (telecommunications backup systems, conventional UPS rooms with older technology), hydrogen detection alone is usually sufficient – hydrogen is the main hazardous gas in such applications. With lithium-ion batteries, however, electrolyte vapours often appear before hydrogen. For Li-ion storage systems, data centres with modern UPS systems and BESS, we therefore recommend combined H₂ + VOC detection, which the E2673 handles in a single device.
Safety standards recommend an alarm in the range of 10–25% LEL, i.e. approximately 0.4–1% by volume of H₂ in air. The first stage (pre-alarm) is usually set at 10% LEL to start ventilation, and the second stage (main alarm) at 20–25% LEL to disconnect the source and initiate the fire alarm. The E2673 allows the threshold to be set within the range of 10–40% LEL according to project requirements.
Yes, the E2673 is ATEX-certified for Zone 2 in accordance with EN 60079-0, EN 60079-7 and EN 60079-29-0/-3. The detector cannot be used in Zone 1 or Zone 0 – in such cases, a different device with Ex “d” or “ia” protection is required.
Not in the field. The detector is designed for maintenance-free operation throughout the sensor service life (~15 years). Long-term stability is < 3% LEL H₂ over 5 years. This is a major difference compared with electrochemical sensors, which need annual calibration or replacement after 2–3 years of operation.
The 94 × 56 × 32 mm enclosure is normally clipped onto a DIN rail, or alternatively mounted using a wall bracket (supplied in the package). Detection is diffusion-based, so there is no need to run a sampling tube or deal with pump placement. For maximum effectiveness, position the detector as close as possible to the ceiling of the space where hydrogen accumulates.
In addition to two alarm relays, the E2673 also has a separate fault relay. If the detector identifies an internal fault (e.g. sensor failure, supply voltage out of range), it activates the yellow LED and switches the fault relay in NC logic – so operators know that detection is not functioning and can take action. Status can also be monitored via Modbus RTU.
Yes, via two SPST alarm relays (NC, 300 mA / 30 VDC). This is a standard volt-free contact that virtually any fire alarm control panel can accept on a gas detection input.
Off-gassing is the actual release of gases from the cell – the first physically measurable sign of a problem. Thermal runaway is the subsequent self-accelerating reaction in which the cell irreversibly exceeds its critical temperature and may ignite. The aim of gas detection is to identify off-gassing before the reaction progresses to the thermal runaway stage – within this window, you still have a chance to stop the fault by ventilation, disconnection and isolation of the affected module.
Bola.cz
