Gefahren bei Batterie-Energiespeichersystemen

Juli 2024 – Ein Gastartikel in Englisch von Tomaž Ažbe, B.A.Sc, Ljubljana Fire Brigade, Ljubljana, Slovenia
Tomaž schreibt einleitend dazu: „I would like to share with you my article on the topic: Battery energy storage systems hazards, which I wrote in the proceedings of the 18th Professional Assembly of Firefighters in Opatija, Croatia, in 2024.
Since this is or will be quite a problematic issue in Europe, especially for firefighters when intervening in the event of incidents at BESS, it is right that things should be improved in the area of legislation, prevention, and above all in response during these events.“

BATTERY ENERGY STORAGE SYSTEMS HAZARDS
Tomaž Ažbe, B.A.Sc, environmental protection
Ljubljana Fire Brigade, Ljubljana, Slovenia, tomaz.azbe@siol.net

Abstract

The storage of electricity is very important due to the increasing production of electricity from renewable sources and, consequently, the efficiency of the operation of the electricity system and thus also energy security. The stored electricity can be used when we need it. The storage of electricity is increasingly common with the help of lithium-ion batteries, which make it possible to store large capacities of electricity in a smaller space. Lithium-ion battery storage systems also carry the risk of thermal runaway of the battery and thermal propagation, which can lead to a fire or an explosion or deflagration of a vapor cloud due to the release of flammable gases in a closed space. Extinguishing the fire itself can be challenging, as it requires firefighters to be cautious when approaching due to explosion or deflagration and hazards from high-voltage electricity. Extinguishing will take a long time, as it may take several hours or days, and large amounts of water will be required for extinguishing. When burning, large quantities of toxic smoke are also produced, which can have a major impact on the environment and the population. Contaminated fire water can also endanger the environment and areas with drinking water.

Keywords: battery energy storage systems, lithium-ion batteries, deflagration, thermal runaway, risk

1. INTRODUCTION

Due to the reduction in the use of fossil fuels and the provision of sustainable energy in the form of renewable energy sources such as solar and wind energy, storage becomes a key factor in providing reliable energy. Especially since sustainable energy sources depend on external factors, which are influenced by weather conditions. This led to the use of energy storage systems (ESS). As a result, the energy grid should also be more efficient and flexible, and at the same time, the ESS also helps to ensure energy needs during peak times, and can also provide backup power during natural disasters and other emergency events [1].

The storage of electrical energy is increasingly common with the help of batteries, especially lithium-ion batteries (LiB), in the form of battery energy storage systems (BESS). LiBs, compared to lead batteries that were used in the past, enable the storage of large capacities of electrical energy in a smaller space. However, the increase in the number of BESS, as a result of the spread of sustainable energy sources, also increases the need for a better understanding of hazards and risks and measures to reduce risks. At the same time, residential BESS installations are also increasing. This, however, is likely to increase the frequency of fires involving these products.

Lithium-ion BESSs also bring risks (e.g. due to malfunction) of thermal runway of the battery and thermal propagation and thus fire, or due to the release of flammable gases in a closed space (mainly hydrogen and carbon monoxide) to explosion or deflagration of a vapor cloud. Extinguishing itself can be challenging, as it requires on the one hand the caution of firefighters when approaching due to explosion or deflagration (e.g. the case of the 2 MWh battery storage explosion in Arizona in 2019, which resulted in four severely injured firefighters) and on the other hand the danger of high-voltage electricity and long-lasting, as extinguishing can last several hours or days (e.g. active extinguishing in 2020 in Liverpool on a 20 MW/10 MWh battery storage lasted 11 hours, while the entire intervention lasted 59 hours), and in addition, they will large quantities of water are required for extinguishing. When burning, large amounts of toxic smoke are also produced, which can also have a major impact on the environment or on the population if the system is in or near populated areas. Extinguishing water, which can be highly contaminated, can also endanger the environment and drinking water areas.

In response to this danger and risk for fire departments, several publications and documents (e.g. from NFPA, CFA Victoria …), research papers and tests have been issued, among which I want to highlight the residential BESS test carried out by the International Association of Fire Fighters, in collaboration with UL Solutions and the UL Fire Safety Research Institute and LiB Vapor Cloud Explosion Test, Newcastle University.

2. WHAT ARE BESS

BESS are systems for the storage of electrical energy produced, for example, by wind or solar power plants, and the subsequent distribution of this energy [1]. Renewable energy sources only produce electricity when the sun is out or the wind is blowing. By storing electricity in BESS, users can take advantage of electricity when renewable energy technologies are not producing electricity. In addition, BESS is also increasingly used in residential, commercial, industrial applications for peak reduction or grid support [2]. Because of its fast response time, BESS can also be used to stabilize the power supply, modulate the grid frequency, provide emergency power supply or load-shedding in industry, thereby reducing electricity costs [3].

BESS consists of one or more batteries, which are divided according to use into: residential with a capacity of 5 to 15 kWh (so-called Powerwall batteries), commercial with a capacity of 30 kWh to 2 MWh and large-scale, which can store several megawatts of electricity. BESS can be installed inside buildings (e.g. warehouse-type buildings) or in external locations (e.g. container systems) or in the form of modular systems [4].

3. NUMBER OF BESS IN EUROPE

According to SolarPower Europe, it is estimated that in 2022, approximately half a million residential BESSs were installed in Europe. With nearly two million homes installing residential PV systems this year, more than one million home batteries are expected to be installed in 2023. Residential BESS capacities in Europe vary between 1 kWh and 6.3 kWh. The most common cell chemicals are lithium nickel manganese cobalt oxide (NMC) or lithium iron phosphate (LiFePO4) [5].

Almost fifty thousand solar power plants are expected to operate in Slovenia at the end of 2023, and as a result, it is also expected that many BESS will be installed in the future. There is no data on the number of BESS in Slovenia. In addition, the legislation or the guidelines regarding the placement are not adequate, as well as the notification of fire brigades regarding the placement of BESS in buildings and space, which means a great risk in case of emergency events [6].

4. BESS HAZARDS

Advances in LiB technology have led to higher energy densities, safer materials such as lithium iron phosphate cathodes, and longer lifetimes. Despite their high energy density, LiBs pose a risk of thermal instability, where thermal runaway caused by defects on the BESS is a serious threat, causing battery operating temperatures to reach 800–1000 °C. When a cell inside a module goes into thermal runaway, it can lead to thermal propagation, release of hazardous substances, fire or explosion [7].

Thermal runaway is the rapid, uncontrolled release of thermal energy from a battery cell when the battery generates more heat than it can efficiently dissipate. An increase in temperature and pressure leads to the release of the flammable electrolyte contained in LiB cells, which usually consists of volatile organic solvents and lithium salt – lithium hexafluorophosphate (LiPF6), and possible flames or cell rupture, which can cause the cell contents to be ejected. Thermal runaway in a single cell causes a chain reaction that heats neighboring cells. The process itself usually continues into a fire or explosion of the battery [8].

The emitted gases may contain volatile organic compounds (e.g. alkyl carbonates, methane, ethylene, ethane), hydrogen, carbon monoxide, carbon dioxide, soot and hydrogen fluoride – HF and other fluorinated compounds, which are particularly problematic due to their toxicity. Hydrogen chloride and hydrogen cyanide were also found in the fire gases of the batteries. Particles containing nickel, cobalt, lithium, aluminum, copper were also found in the emitted gases [8].

These flammable gases, if not ignited before the lower explosive limit is reached, may result in the formation of an explosive atmosphere in the BESS room or container. LiB thermal runaway without an active fire can be identified by a distinct two-layer accumulation of whitish-gray lighter gases near the ceiling and heavier gases and vapors near the floor. However, these are not reliable visual and thermal imaging indications that it is a LiB fire. Also, gas meters or detectors are not a reliable confirmation that it is LiB thermal runaway. Indeed, the explosion itself cannot be predicted, as the risk of explosion can start as soon as the LiBs thermally runaway and release gas without burning, and the explosion can develop before any external indicators appear [9].

Therefore, the consequences of a BESS fire or explosion pose a serious safety risk for firefighters. The release of toxic vapors and hazardous materials during a fire increases the risks to the health and safety of firefighters. Fires and the release of toxic pollutants can also have a negative impact on the environment, as soil, air and water are polluted [10].

Fires in closed BESS are very difficult to extinguish, as it is usually impossible to access the source of the fire with water, since the layers of protection help to prevent damage to the system, but at the same time they also block the access of water to the source of the fire. In addition, large BESSs burn much longer and can reignite hours, days, or even weeks after the initial fire. A big problem is also residual electricity [11].

Residual energy and thus the risk of electric shock are often present in BESS even after LiBs are already involved in a fire, and in addition, damaged systems pose a risk even after a fire [12].

The causes of LiB thermal runaways in BESS, in addition to the usual causes, can also be: improper installation (e.g. mechanical damage to components and cells, incorrect wiring), improper ventilation, improper maintenance (e.g. programming and testing of BMS and thermal management systems) and external fires [7].

It is also worth noting the used LiBs. When electric vehicle packs reach about 80% of the capacity of a new pack, they are no longer suitable for use in electric vehicles, but still have considerable capacity and are now freely available for consumers to purchase online. Such home systems are installed in homes, with questionable BMS and represent a potential danger to firefighters in a fire intervention [11].

5. BESS INCIDENTS

BESS incidents occur despite evolving codes, standards and protection systems, showing that these alone are insufficient and unable to keep up with technological advances and increased energy density of BESS.

Among the incidents in the larger BESS, I would like to point out the explosion that happened in 2019 in the BESS unit, in Arizona and in 2020, in Liverpool.

On April 19, 2019, a fire occurred at the 2 MW BESS at the McMicken site in Surprise, Arizona, USA. Firefighters who responded to the incident did not take immediate action due to a lack of information. However, as the Hazmat team attempted to enter the BESS to survey the extent of the incident, an explosion occurred, seriously injuring four firefighters. Two firefighters who were seriously injured were found approximately 16 and 22 m away from the building. Both required multiple surgeries for broken bones [11] [3].

Although the BESS was equipped with a fire extinguishing system, it was not equipped with deflagration venting or explosion prevention systems. The findings of the BESS incident in Arizona were [7]:

• thermal runaway was triggered by an internal defect in the battery cell,
• the NOVEC 1230 fire extinguishing system did not stop the thermal runaway,
• in the BESS there were no thermal barriers between the battery cells, so this spread to neighboring cells,
• there was no ventilation, so the flammable gases from the batteries were concentrated,
• the emergency response plan did not include extinguishing, ventilation or entry procedures.

On 15 September 2020, an explosion occurred at one of the BESSs in Old Swan, Liverpool, UK. The explosion was followed by a fire that spread to other BESS modules. Firefighters did not directly extinguish the fire due to the fact that they would use excessive amounts of water, and thus the risk of environmental pollution with contaminated water. Therefore, they let the BESS burn in a controlled manner, while cooling the surroundings. Large amounts of water were used for cooling. Active extinguishing alone lasted eleven hours, while the entire intervention lasted fifty-nine hours. A big problem due to the fire was also that the BESS was near a residential area. After the fire was over, they found [13]:

• the fire extinguishing system did not stop the thermal runaway,
• debris from the explosion was found 22 m from the source and that the firefighters could have been injured if they had not been aware of the risk,
• there was a risk of electric shock inside the unit even after the fire,
• hydrogen fluoride and hydrochloric acid were found in waste water,
• the emergency response plan was deficient.

Below are some more incidents at residential BESSs in Germany that resulted in an explosion [9]:

• July 18, 2018 in Theilheim, there was a strong explosion in the basement. The explosion was followed by a fire, and the cause is believed to be the recently installed BESS for the solar power plant.
• On September 3, 2020, a woman reported a fire in the basement of a house in Grub am Forst. Firefighters managed to control the fire, but it exploded in the process. The cause of the fire was a technical error at the BESS of the solar power plant.
• On March 3, 2022, the BESS of the solar power plant exploded in the basement of a house in Bodneggo. The cause is said to be a technical error in the system. The explosion was powerful enough to dislodge several doors and windows and raise the entire roof structure.
• On May 9, 2022, in Althengstett, firemen were informed of white smoke coming from the basement of the house where the BESS for the solar power plant was located. Shortly before the firemen arrived, an explosion rang out. The explosion blew out the basement windows and doors and the doors in the house.

In the context of incidents, I should also mention the residential BESS fire in Ljubljana, on February 15, 2023, which did not explode, but there were quite a few problems in extinguishing LiB, and in addition, the firefighters were heavily contaminated with LiB combustion products during the intervention.

6. PREVENTIVE MEASURES AT BESS

The Country Fire Authority Victoria (CFA Victoria) recommends that the following should be taken into account when managing the risk of fire on BESS in the open [14]:

• effective identification and management of hazards and risks specific to the installation environment,
• setting up infrastructure in such a way as to eliminate or reduce hazards for firefighters,
• safe access for firefighters in and around the facility, including infrastructure and for firefighting,
• provision of adequate fire-fighting infrastructure for safe and effective action in the event of emergencies,
• vegetation arranged in such a way as to prevent an increased risk of forest and grass fires,
• prevention of fire starting on the location and spreading to neighboring buildings,
• prevention of an external fire that would affect the infrastructure of the location,
• provision of accurate and up-to-date information for firefighters during emergencies.

In addition, CFA Victoria recommends that BESS must [14]:

• be equipped with built-in fire and gas detection systems,
• have guaranteed prevention of explosions through detection and venting or mitigation of explosions through deflagration plates,
• adequately protected against sparks, which prevent the spark from penetrating the BESS,
• adequately accessible by roads for fire engines,
• be installed on a non-combustible surface such as concrete,
• properly ventilated,
• protected against impacts,
• have adequate containment of fire water runoff.

The International Residential Code and International Fire Code – 2021 Editions are codes in the USA and specify for residential BESS that they can only be installed in the following locations [9]:

• detached garages and detached ancillary buildings,
• connected garages, separated from the living space of the residential unit,
• in the open air or on external side walls located at least 1 meter from doors and windows that directly enter the residential unit,
• enclosed storage rooms, basements, storage or utility rooms in units being converted, with finished or non-combustible walls and ceilings.

In addition, the codes specify that they should not be installed in bedrooms, closets or spaces that open directly into bedrooms [9].

In the US, residential BESS systems ranged from 5 to 30 kWh, but UL 9540, the Standard for Energy Storage Systems, in 2021 limited the maximum energy capacity of a residential BESS to 20 kWh [9].

The Metropolitan Fire Service of South Australia (MFS) requires that the certifying authority with BESS installations consider the following items [15]:

• appropriate levels of fire resistance for the structure, taking into account the risk of prolonged exposure to fire and the possibility of a vapor cloud explosion,
• adequate detection of fire and flammable gases (including hydrogen),
• automatic shutdown of BESS installations in the event of a fire alarm or detection of elevated levels of flammable gases,
• adequate ventilation to keep flammable gases below their lower flammability limits,
• monitoring the concentrations of potentially flammable gases in closed spaces,
• providing effective fire protection with the sprinkler system,
• provisions for retention and/or management of water runoff,
• contact details of the battery manufacturer for emergencies,
• signage, information and details to be provided at the main point of entry to the building and at all other relevant locations on the site,
• provision of technical and visual data for status monitoring, e.g. sign flashes at the front door to indicate when any system has been activated.

MFS also has reservations about the effectiveness of gas suppression systems for BESS, as these will not prevent thermal runaway but may increase the risk of deflagration [15].

Due to the risk of deflagration, newer containers with BESS have couplings on the outer sides ready to connect the hoses to extinguish the system in the container. However, the explosion in Liverpool showed that this was risky, so the firefighters there required that stable pipes be laid to the containers, to which water for extinguishing (e.g. from a fire engine) outside the danger zone is connected. They also installed signage, flashing signs and information at the main entry point.

7. PRE-INCIDENT PLANNING

The fire department must develop a response plan for fires, explosions and other emergencies related to BESS. The plan should contain the following elements [1]:

• understanding BESS operating procedures and emergency response,
• recognition of BESS technology, potential dangers and response methods to fires and incidents,
• locations of electrical disconnections in the BESS and procedures for stopping and turning off power or isolating equipment to reduce the risk of fire, electric shock and physical injury,
• procedures for handling damaged BESS equipment after a fire with contact details of personnel trained to safely remove damaged equipment from BESS.

A copy of the emergency response plan must also be forwarded to the fire department.

Operators of buildings with BESS must notify the fire department in advance about the dangers. This information must contain [14]:

• diagrams and technical data of the BESS, with the number of containers and the number of battery racks or modules in each container,
• details of the BESS hazards, including the potential for thermal events/runaway, electrical hazards, explosion hazards and the effects of fire on the BESS (e.g. explosion, release of toxic gases),
• details of items controlled by the battery management system (BMS), including internal temperature, state of charge, voltage, etc., and the locations where this information is available,
• details of all battery safety and protection systems, including description and activation process and associated hazards,
• shutdown and/or isolation procedures if LiBs are involved in a fire, and appropriate personnel contact information to verify that the system has been isolated or shut down and is de-energized.

The possibility of direct alarm control to the fire department for systems for automatic detection of fire incidents in BESS should also be taken into account [14].

8. RESPONSE TO THE INCIDENT

Upon arrival at the scene, the incident commander must assess the situation and notify all firefighters of potential hazards. If possible, obtain information from facility staff as well.

In the event of a fire or explosion, firefighters must use fire protective equipment and self-contained breathing apparatus (SCBA). If a fire is in progress, the flammable gases released will be consumed and an explosion is unlikely. The safest approach is to allow the BESS to burn in a controlled manner so that all the fuel is consumed and the possibility of re-ignition is minimized. However, BMS data from adjacent enclosures should be monitored to verify that module temperatures remain at safe levels (typically up to about 80°C). The use of water must be limited to cooling and protecting adjacent BESS enclosures. Once the fire is out, flammable or toxic gases may still be released, so protective equipment and especially SCBA should still be used until releases such as e.g. CO measured at a safe level. However, if the fire in the room was extinguished by an automatic fire extinguishing system, there is a possibility of further release of flammable gases and the risk of explosion [16].

If sensors (e.g. for temperature, smoke, heat, flammable gas) indicate that thermal runaway has occurred, but there are no signs of fire, it should be assumed that there is a risk of explosion. Intervention units must be located outside the potential explosion radius. The BESS enclosure must be inspected remotely, using BMS data, to determine system status, including module temperatures, gas detection, and exhaust ventilation systems. If the BMS is not working due to damage to the system, the thermal camera may show thermal problems. However, we must be aware that the insulation of the BESS case can make it difficult to accurately estimate the internal temperature. If the room has been ventilated by automatically opening a door or panel and there are no signs of high temperatures, we can approach the enclosure with gas monitoring to alert us to any lingering risk. If the case is sealed when gas venting is done via a magnetic flap or if there is no option for gas venting, data from the BMS and an external visual assessment should be reviewed together with a BESS expert before attempting to open the case [16].

Even when BESSs are disconnected from external circuits, LiBs retain stored energy and should be treated as energized. LiB can partially destroy the fire, but it keeps the residual energy at dangerous levels. All LiBs, regardless of their visible state, should be treated as fully charged, with the risk of arcing and electric shock [16].

Toxic substances such as hydrogen fluoride, hydrogen chloride, hydrogen cyanide and carbon monoxide can also be released during a fire. Spraying water on smoke or fumes released from LiB, whether burning or not, may cause skin or lung irritation. Therefore, firefighters must be properly protected at all times. For contaminated firefighters who have come into contact with toxic substances, decontamination must be carried out after the end of the intervention [16].

Fire department must warn the competent services to measure air pollution and fire water pollution during and after the intervention.

For residential properties, a portable gas detector is unlikely to be effective in determining whether a garage fire involves LiB. Therefore, the facility should not be approached or entered for gas detectors measurements if LiBs are suspected to be in thermal runaway and there are no signs of a concurrent fire. Before carrying out an attack, when lithium-ion thermal runaways are suspected, the pressure fire hoses should be lined, charged and prepared for extinguishing before ventilation or entry [9].

9. RESIDENTIAL BESS TEST AND EXPLOSION DANGER TEST DUE TO LIB

UL Solutions and UL Fire Safety Research Institute, in cooperation with the International Association of Fire Fighters, conducted a series of extensive tests due to the danger of residential BESS. The project was intended to support fire departments in responding to such events. The tests showed the following [9]:

• When LiBs thermally runaway without burning, an explosion hazard occurs. The timing of the gas explosion in the battery is unpredictable. The severity of battery gas explosions depends on the amount of gas.
• A significant explosion hazard may develop before any external indicators (visual or measurable) appear.
• Unburnt battery gas is easily ignited and can increase the flammability of smoke in a fire with limited ventilation.
• Without an active fire, LiB thermal runaways can be identified by white / gray battery gas escaping from the structure and forming low-hanging vapor clouds.
• With or without an active fire, smoke layering on the ceiling and floor indicates LiB thermal runaway.
• In an active fire, there are no reliable visual or thermal imaging indicators that would confirm the involvement of the battery from the outside of the building.
• Portable gas detectors are not effective in determining whether LiBs are involved in a garage fire.
• In addition to the appearance of smoke, additional indicators for the installation of a residential BESS should be taken into account during sizing.
• Firefighters are most at risk due to the danger of explosion in the driveway and on doors, windows and other ventilation points. They don’t leave fire trucks or attack groups outside the garage door.
• Firefighters should not approach the facility with a portable gas detector or enter the facility to take measurements if thermal runaway batteries are suspected and if there are no signs of an active fire.
• As conditions can change quickly, personal protective equipment and SCBA should be protected before the examination. Personal protective equipment should also be worn around batteries that have been exposed to thermal runaway until they are removed from the scene.
• As conditions can change rapidly, fire hoses should be pre-positioned, primed and prepared for extinguishing prior to ventilation or entry when LiB thermal runaways are suspected. Fire hose lines must remain available to handle the re-ignition / thermal runaway of batteries that have been exposed to heat until they are removed from the scene.

Newcastle University carried out tests to determine the possibility of a vapor cloud explosion at LiB. Tests have shown that a low state of charge (SOC) is just as dangerous as a high SOC, which is contrary to the general opinion in the literature. Thus, in all the experiments, the first obvious sign of thermal runaway was the eruption of white steam: if this ignited, there was an obvious danger of fire. However, if the vapor did not ignite, it would present an entirely different hazard in terms of high toxicity and the potential for a violent vapor cloud explosion. However, this was the first mention of such a phenomenon related to LiB in the academic literature [11].

Initially, thermal escape was seen by the development of dense, white vapor by pyrolysis of the electrolyte. This vapor consists of H₂, SO₂, NO₂, HF, HCl, CO, CO₂, organic solvent droplets and a large number of small chain alkanes and alkenes. For SOC, >50%, this vapor inevitably ignites in less than 1 minute. However, at low SOC, ≤50%, the vapor may not ignite without sufficient air. Therefore, this phenomenon could cause a flash fire, the development of fire effects or, in extreme cases, even an explosion of a vapor cloud in an enclosed space [10].

10. CONCLUSION

Authors Close J. et al. note that thermal runaways, fires, and explosions continue to occur in many BESSs involving LiB. In incidents such as the BESS explosion in Arizona, facilities were designed with the latest standards, detectors, alarms and safety management systems. However, due to the lack of a holistic approach to BESS safety, particularly in relation to inadequate ventilation and fire extinguishing systems, the thermal runaway incident nevertheless occurred. According to the authors, these incidents are mainly due to lagging codes and standards, knowledge gaps in the approach to safety, and inadequate monitoring of critical failures and abuses in cells that cause thermal runaway. It should be emphasized here that automatic gas fire extinguishers will not extinguish thermal runaway [7].

The Office for Product Safety and Standards notes that the BESS market is still quite small compared to other LiB devices. Experience with fires involving residential BESSs is limited, but the increasing use of BESSs requires a better understanding of how BESSs behave when misused. In addition, several standards regarding BESS are currently under development [8].

Conzen J. et al. to reduce risk in large BESSs, they require hazard reduction analysis, and CFA Victoria recommends that a comprehensive risk management process be done [3].

NFPA requires that explosion prevention or deflagration venting systems be installed. In addition, the units in the BESS must be grouped into small segments, limited to certain capacities and separated from other elements and walls in order to prevent the spread of fire. BMS is to be used in BESS to monitor, control and optimize the functioning of the modules, especially in case of emergency events. He also notes that water is the most effective medium for cooling a BESS fire, so sprinkler systems should be installed in buildings [1].

Christensen P. et al. have found through tests that the first visible sign of thermal runaway is the development of dense, white vapor by pyrolysis of the electrolyte. And if enough air is present, at high SOC, that vapor inevitably ignites in less than a minute. However, at low SOC, the vapor may not ignite if there is insufficient air present. As a result, there may be a possibility of a flash fire, the development of fire effects or, in extreme cases, even an explosion of a vapor cloud in an enclosed space. This explosion hazard, along with the toxicity of the white vapor, can be faced by firefighters wherever large LiBs are present in an enclosed space and one or more cells are in thermal runaway. As an additional problem they see, white vapor could be mistaken for steam, especially after extinguishing a fire [11].

UL Solution’s tests have proven that additional indicators for LiB involvement in a fire should be considered, as it may happen that visual, thermal imaging or gas detector indicators are not always reliable. Indeed, the danger of explosion may develop before any external indicators appear. However, the time and severity of the gas explosion due to the thermal runaway of LiB cannot be predicted. Therefore, firefighters must ensure adequate access, and they must also be adequately protected. In addition, they must have fire extinguishers ready for extinguishing [9].

The „let it burn“ strategy can be used to prevent environmental pollution with toxic combustion products of LiB BESS, but it is necessary to protect other facilities, which will require the availability of larger quantities of water for extinguishing. Firefighters can also be exposed to toxic products, such as hydrogen fluoride, hydrogen cyanide and hydrogen chloride, so it is recommended that they perform decontamination after the intervention [16].

The rapid spread of this technology is worrisome because of the associated risks and undefined answers and guidelines for safe and effective action. Above all, we must be aware that technology often overtakes us in the field of regulations, prevention and action. Thus, in Slovenia we do not yet have guidelines regarding the installation of BESS in premises, as the existing guidelines are intended for lead batteries. In Slovenia too, we have several extensive BESS, several unidentified business BESS and an increasing number of household BESS. For most of these BESS, the fire departments do not have data or risk assessments and emergency response instructions. Therefore, we need to improve the regulations in this area, act preventively, and above all, we need to prepare for extraordinary incidents that may happen. Because the question is no longer „if“ but „when“.

Sources and literature

[1]    NFPA, (2024). „Energy Storage Systems Safety Fact Sheet“.National Fire Protection Association, 2024.

[2]    Stein Z., (2024). „Battery Energy Storage Systems (BESS)“. Carbon Collective. Available at: https://www.carboncollective.co/sustainable-investing/battery-energy-storage-systems-bess. [15. marec 2024]

[3]    Conzen J., idr.,(2023) „Lithium ion battery energy storage systems (BESS) hazards“. Journal of Loss Prevention in the Process Industries, 2023. Available at: .

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[5]    Murray C., (2023). „Residential battery installations grew 83% in Europe in 2022“. 2023. Available at: https://www.energy-storage.news/residential-battery-installations-grew-83-in-europe-in-2022/.

[6]    Kos D., (2024). „Slovenija lani z eno največjih rasti števila sončnih elektrarn v EU“. siol.net. Available at: https://siol.net/novice/posel-danes/slovenija-lani-z-eno-najvecjih-rasti-stevila-soncnih-elektrarn-v-eu-628018. [28. februar 2024]

[7]    Close J., idr., (2024). „Holistic approach to improving safety for battery energy storage systems“. Journal of Energy Chemistry, 2024. Available at: .

[8]    Department for Business, Energy & Industrial Strategy,(2020). „Domestic Battery Energy Storage Systems, A review of safety risks“, 2020. Available at: https://assets.publishing.service.gov.uk/media/5f761b828fa8f55e33275cfc/domestic-battery-energy-storage-systems.pdf.

[9]    Schraiber A., idr. (2023). „Considerations for Fire Service Response to Residential Battery Energy Storage System Incidents“. UL Solution, 2023. Available at: https://www.iaff.org/wp-content/uploads/IAFF_DOE_ResidentialESSConsiderations_Final.pdf. [Poskus dostopa 2024].

[10] Mrozik W., idr., (2022). „Abuse of Lithium-ion Batteries: emergence, composition, and toxicity of vapour cloud,“ 2022. Available at: https://ri.diva-portal.org/smash/get/diva2:1657152/FULLTEXT01.pdf.

[11] Christensen P.A., idr., (2021). „Thermal and mechanical abuse of electric vehicle pouch cell modules“ Applied Thermal Engineering, 2021. Available at: .

[12] National Fire Protection Association, (2024). „Energy Storage Systems Safety Fact Sheet“. National Fire Protection Association, 2024.

[13] Christensen P. A., (2023). „My path to vapour cloud explosions and lithium-ion batteries“. EU Energy Storage Systems Safety Conference 2023, Arnhem, 2023.

[14] Country Fire Authority, State of Victoria, (2023). „Renewable Energy Facilities v4, Design Guidelines and Model Requirements“. State of Victoria, Country Fire Authority, Victoria, 2023.

[15] South Australian Metropolitan Fire Service, (2022). „Battery Energy Storage Systems (BESS)“, 2022. Available at: https://www.mfs.sa.gov.au/community/building-and-commercial-fire-safety/guidelines-and-information/Fire-Safety-Position-Statement-BESS-1.0.pdf.

[16] American Clean Power, (2023). „First Responders Guide to Lithium-Ion Battery Energy Storage System Incidents“, 2023. Available at: https://cleanpower.org/wp-content/uploads/2023/07/ACP-ES-Product-7-First-Responders-Guide-to-BESS-Incidents-6.28.23.pdf.

Anmerkung der Redaktion: Die im Original enthaltenen Fotos wurden aus Urheberrechstgründen entfernt