Fire protection for lithium-ion batteries
Fires in power generation and energy storage can be very costly and quickly lead to a total loss of the system. Lithium-ion batteries are a real fire hazard and require active fire protection.
Renewable energy technologies such as solar and wind energy are at the mercy of the prevailing weather conditions and can only be operated intermittently. This results in the central challenge of the energy revolution to create a spatial and temporal balance between the supply and demand of volatile generated electricity.
Lithium-ion batteries are the means of choice here, as they can store enormous amounts of energy in a small volume. It is estimated that lithium-ion energy storage systems have a market share of over 90% of all energy storage systems worldwide – and the trend is rising.
However, storing large amounts of energy in a small space comes with its own risks. Lithium fires are considered one of the greatest challenges of modern fire protection.
Whether during production, charging processes, damage or external thermal conditions – lithium energy storage systems require the utmost care and special measures to ensure safe processes.
As recently as 2014, the private safety company Underwriter’s Laboratory (UL) published the first safety standard for energy storage systems: UL 9540.
UL is the underlying standard on which many international and national organisations base their regulations and fire safety requirements. In addition, the UL 9540A standard was created in November 2017, which deals specifically with “Thermal Runaway Fire Propagation in Battery Energy Storage Systems”. In the meantime, three further iterations of the standard have been published, which shows that the regulatory environment is evolving rapidly.
Furthermore, the National Fire Protection Association of the USA has recently published its own standard for the installation of stationary energy storage systems, NFPA 855, which explicitly refers to UL 9540A. The International Fire Code (IFC) has published its most stringent safety requirements for energy storage systems in the latest 2021 edition.
Due to the high energy density of lithium-ion batteries, they pose an increased risk of fire. Just think of spontaneously exploding mobile phones and laptops in aeroplanes, which have repeatedly made the headlines in recent years. But what exactly are the fire risks?
The term “thermal runaway” describes a self-reinforcing process of overheating in a battery that leads to an uncontrolled rise in temperature. Due to their chemical properties and design, lithium-ion batteries are particularly at risk.
Oxygen is generated during thermal runaway due to cathode consumption. As a result, lithium-ion fires cannot be reliably extinguished by removing oxygen (e.g. using CO² fire suppression systems).
As the materials involved in igniting and spreading the fire are closely integrated into a cell and the cell itself is often well insulated for protection, fighting the fire becomes a challenge. Most extinguishing agents cannot even reach the fire.
Multiple fuel sources
Lithium-ion batteries have several substances that can be potential fire fuel sources, which makes the spread and development of a lithium-ion fire difficult to predict and further limits the choice of extinguishing agents because not all extinguishing agents are suitable for every type of fire.
Fires involving lithium-ion batteries are always at risk of reigniting hours or even days after they appear to have been extinguished.
Toxicity & risk of explosion
The gases released both during outgassing and upon ignition are both toxic and flammable, so enclosed environments where lithium-ion batteries are in use can be potentially explosive areas.
Localised temperature increase in one or more cells.
The increased temperature leads to an accelerated reaction within the battery cells. Small amounts of gas and cell vapours are released
the released heat further intensifies the process. This can lead to an accelerated release of the electrolyte or even decomposition of the electrode material. Smoke and additional heat are released
The process accelerates exponentially and temperatures in the battery rise rapidly, affecting more and more battery cells. Ignition becomes more likely the higher the temperature rises and the longer the process continues uncontrolled.
There are two crucial time windows for fire protection measures in the event of a thermal runaway:
The results of independent tests have shown that an average of 11-12 minutes elapse between the detection of gases and the thermal runaway or detection of smoke. This results in an initial time window to take preventive measures.
If preventive measures are not successful and the lithium-ion battery ignites, measures must be taken to contain and extinguish the resulting fire as early as possible.
The Li-Ion Tamer is the leading system for the early detection of outgassing events in lithium-ion batteries of all chemistry types, making it the No.1 preventive solution in fire protection for lithium-ion batteries.
With a reaction time of five seconds, even the smallest amounts of gas are detected so that an early warning can be issued to operators. The primary measure is to trigger the battery management systems so that the power supply to the batteries can be switched off. This can prevent a further rise in temperature in the battery cells at an early stage and keep it below the thermal runaway point. In addition, a ventilation system can be activated to extract toxic and flammable gases that have already accumulated in the storage system due to outgassing.
UL9549A quantifies outgassing as a precursor to thermal runaway, while independent testing by DNV-GL concluded after two years of testing that Li-Ion Tamer can prevent thermal runaway of battery storage systems.
In the US, Li-Ion Tamer is now mandatory in many utilities and critical infrastructure as part of the fire protection solutions for battery energy storage systems.
In the event of outgassing, there is no guarantee that the battery management systems will interrupt the power supply in time or that the temperature in the battery cells will not continue to rise due to mechanical damage, for example. In this case, the second stage of our fire protection concept comes into play: containment.
Aerosol fire suppression systems have proven to be the most effective extinguishing system for lithium-ion fires.
Stat-X is the most efficient aerosol fire suppression system on the market and the tool of choice for many lithium-ion battery manufacturers.
The aerosol primarily interrupts the chain reaction of the fire and thus suppresses fires and flames. Secondarily, a cooling effect is achieved as the energy is extracted from the fire. No dangerous and uncontrollable by-products are created, nor are large quantities of extinguishing agent required to bring a lithium fire under control. The Stat-X extinguishing agent has a service life of up to two hours in closed rooms, which guarantees a high level of post-fire safety.
Tragic examples in recent years show just how important post-fire safety is in lithium-ion fires. In 2019, four firefighters in Arizona were injured when they opened a still-smoking battery storage container. A subsequent investigation report by DNV-GL revealed that the fluoroketone extinguishing agent used was unsuitable. 30 minutes after extinguishing, there was no extinguishing agent left in the container, leaving the entire room vulnerable to explosion and fire.
The failure in the selection of the extinguishing agent was identified as the main contributing factor to the severity of the incident.
DNV-GL tests have shown that Stat-X can effectively extinguish a fire in a lithium-ion battery and prevent re-ignition as long as the aerosol remains in the danger zone. It has also successfully undergone rigorous UL and NFPA testing.
The combination of Li-Ion Tamer and Stat-X is arguably the best fire protection solution for lithium-ion battery storage systems, providing comprehensive protection and early warning.
However, the unpredictable nature of a lithium-ion fire means that not every event can be accurately predicted. We therefore recommend installing a backup cooling option.
We consider this to be an important measure, especially for large battery storage systems with several containers, for example, so that if heat develops in one, the surrounding containers are not affected and flashover to the entire system is prevented.
High-pressure water mist systems are ideal here due to their ability to contain heat radiation. Alternatively, a filler neck for extinguishing water from the fire brigade can be installed.