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CROSS Safety Report

Fire safety risks with lithium-ion batteries

Report ID: 1058 Published: 10 March 2022 Region: CROSS-UK

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A reporter has raised concerns regarding the increase in the use of lithium-ion batteries, along with their related hazards which currently remain unregulated.

Key Learning Outcomes

For designers:

  • Ensure that a competent fire safety engineer is consulted in projects that involve battery systems

For fire engineers:

  • Stay up to date with the latest research developments in the field of battery systems
  • Inform other members of the design team and clients about the potential risks arising when employing novel, unregulated technologies

For Authorities Having Jurisdiction:

  • Carefully review proposals that employ novel, unregulated technologies, so that any potential risks are acknowledged and addressed with the appropriate justification

Full Report

Find out more about the Full Report

This section contains the Full Report submitted to CROSS and describes the reporter’s concerns or experiences. However, the text has been edited for clarity, and identifiable details have been removed to ensure anonymity and confidentiality. If you would like to know more about our secure reporting process, or submit a report yourself, please visit the reporting to CROSS-UK page.


Of the currently available technologies, lithium-ion batteries have the highest energy density and are the first to employ an organic solvent in the electrolyte. Their failure probability is calculated to be extremely low when stored and operated within the recommended limits, but their normal operation can be disrupted if there is electrical (e.g. short-circuit, overcharging) or mechanical abuse (e.g. mechanical crash, self-heating, external heating source). If the heat losses (usually convective) cannot offset the amount of heat increase within the battery system (either by internal exothermic reactions or external heat fluxes), then a phenomenon called ‘thermal runaway’ occurs. During thermal runaway, the temperature increase leads to an exponential increase in the reaction rate within the battery, leading to a cascading effect that can evolve into a very serious fire or explosion.

The ‘thermal runaway’ phenomenon

The reporter explains some of the mechanisms involved, namely that once thermal runaway occurs then “hydrogen (c.a. 30%), carbon monoxide, carbon dioxide, hydrogen fluoride, hydrogen chloride, hydrogen cyanide, small organic molecules such as methane and ethane as well as nitrogen oxides are produced. When the gaseous mixture vents outside the battery, it takes with it fine droplets of the organic solvent, rendering it a dense white vapour”. Depending on the environmental conditions around the battery, there are two hazardous outcomes:

  1. The vapour ignites immediately, and long flare-like flames are produced, as shown in Figure 1.
  2. The vapour does not immediately ignite and forms a cloud instead. An example of such a case is shown in Figure 2.
Figure 1. Flare-like flame, approximately 3m long, resulting from nail penetration of a lithium-ion battery electric vehicle module (8 cells each ca. 54Ah, 1.7 KWh).
Figure 2(a). An identical module to that in Figure 1, at 40 seconds after nail penetration.
Figure 2(b). An identical module to that in Figure 1, at 86 seconds after nail penetration.

For the second case, if or once the cloud is adequately mixed, it can potentially ignite, developing into a deflagration (subsonic speed of the flame front propagation, also known as a flash-fire). Increases in pressure can occur, depending on the surrounding confinement or any turbulence inducing obstructions. When the overpressure generated is enough to damage the surrounding elements and structures, the incident is considered to be a vapour-cloud explosion. Any of these scenarios can be extremely dangerous and it should also be noted that the vapour cloud is highly toxic.

Increasing domestic use of lithium-ion batteries

In the UK, there are some current drivers behind the increased use of domestic lithium-ion battery storage systems (DLiBESS). One of them is the “behind the meter” storage (storing charge when supply is cheap and using this stored energy when supply is expensive i.e. for optimising the time of use (TOU) billing), and storing renewable energy from photovoltaic (PV) arrays for domestic or commercial use (Virtual Power Plants to support the National Grid). However, the reporter considers that when it comes to the use of lithium-ion technology on DLiBESS’s, the risks and hazards remain unregulated. Some indicative numbers for commercial systems are their range from 2 kWh to 130 kWh or more (the modules in the Figures provided are 1.7 kWh).

The reporter goes on to explain how lithium-ion batteries start to go unstable at temperatures as low as 60 – 70˚C, although thermal runaway occurs at temperatures > 120˚C. This could be attributed to possible abuse, e.g. by cycling at temperatures < 5 ºC or > 60 ºC, or by charging at high currents. The latter case causes the deposition of lithium metal on one of the electrodes and this, in turn, facilitates thermal runaway at much lower temperatures; even ambient.

The worry is exacerbated by the rise in the second-hand market of these batteries, which are routinely sold on the internet for the conduction of Do-It-Yourself projects by members of the public. In such cases, there is no guaranteed record of previous operational conditions. There have also been many recalls in recent years and “over thirty five fires and explosions involving industrial LiBESS across the world in the last 3 years, at least four of which involved vapour cloud explosions. The most recent was in April 2021 in a Beijing shopping mall which killed two people and badly injured a third. The testing of a DLiBESS in Australia by the Commonwealth Scientific and Industrial Research Organisation (CSIRO) in 2019 resulted in a vapour cloud explosion and, in the same year, a vapour cloud explosion and fire destroyed a pleasure boat in Sneek harbour in the Netherlands”. In February 2022, a DLiBESS fire badly damaged a home in Adelaide, Australia. Some other accidents have been presented in a review by Wang et al. until 2019.

The reporter considers that these hazards will be present in any facility that has such a storage system installed.

Expert Panel Comments

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Expert Panels comment on the reports we receive. They use their experience to help you understand what can be learned from the reports. If you would like to know more, please visit the CROSS-UK Expert Panels page.

The expert panel agrees with the concerns raised by the reporter. This genuine worry is likely to become more prominent over time as batteries get increased use. The forthcoming Part S of the Building Regulations (on infrastructure for the charging of electric vehicles) is part of a trend that will increase the use of electric charging in car parks. This exponential rise in the use of LiB (and other alternative energy sources with their own respective risks) is being driven by the reduction of emissions and the agenda for achieving ‘net-zero’. This drive has led to the use of LiB in all environments and scales, from small portable devices to scooters and electric vehicles (EVs), and to domestic, mid-scale (shipping containers) and grid-scale (Solar Farms) Battery Energy Storage Systems.

how these alternative fuels and systems interact with the built environment is of particular interest in this case

How these alternative fuels and systems interact with the built environment is of particular interest in this case, because the hazards and risks identified in the report are real to not only the attending emergency services, but also to occupants and those in the vicinity of buildings, as well as to the environment. There is a certain level of uncertainty involved due to the potentially limited extent of research conducted so far, and that is a cause for concern. Specific issues that will be of concern in relation to buildings can vary drastically depending on the particular situation. For example, dealing with the fire risks of electric scooters on underground trains is very different from dealing with the fire risks of electric car charging in underground car parks, both of these could potentially be hazardous, but the methods for dealing with these fire scenarios would be very different.

One of the particular problems that could also be mentioned is the topic of suppressing such fires. It is often impractical or impossible for the fire brigade to extinguish such battery fires, so dealing with them can often simply involve waiting for them to burn out or just immersing them in a tank of water for a day or more. The panel is aware of examples and incidents of multiple vehicle fires in car parks in Merseyside, Cork, and Norway (amongst others) which highlight the risk of structural damage and subsequent collapse from such a large fire.

Regulatory or statutory guidance

Comments and insights are welcome from Building Control Bodies (BCBs) on the process involved in ensuring that the functional requirements of the Building Regulations have been met. Similarly, the approach followed by the Fire and Rescue Service (FRS) in order to enforce the provisions of the Fire Safety (Regulatory Reform) Order 2005 and provide advice on request can also take an interesting turn when LiBs are utilised in a project. This is not only an issue with new buildings, but it should be acknowledged that such systems may be installed retrospectively and be found present in any kind of structure.

The panel is aware that these issues are currently being assessed further, through ongoing work, but until now there is no statutory advice or other (British Standard tec.) guidance available. In the face of this uncertainty, and lack of technical guidance, there is an argument to be made about the approach employed to support any proposal to install any such systems in buildings, and whether that should only be done through an evidence-based first principles approach by competent professionals. One suggestion could be to treat these systems like it is already done with other potential sources of hazards to health (and the environment), which could lead to additional safety provisions being placed alongside these systems.

Given the motivation and the increasing need to use batteries, along with their potential role in a more sustainable future, this is not only an isolated sector issue but one that society must address together in good time. Developers of such technologies, insurers, and government are key stakeholders in this, because if these concerns are left unaddressed then it is highly probable for battery fires to become the next 'legacy' fire issue, with a high cost to society and expensive remediation in the years to come.

left unaddressed it is highly probable for battery fires to become the next 'legacy' fire issue, with a high cost to society and expensive remediation

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