Is it a battery fire, or just a fire? This is the first question that should be asked when addressing the fire protection challenges presented by lithium-ion batteries (LIBs).
In a world where we are always technologically connected, the use of LIBs continues to grow significantly. In fact, global battery demand is expected to increase annually by 25% to reach 2,600 GWh in 2030. LIBs or modules (a group of LIB cells electrically connected) in manufacturing and storage have similar inherent hazards as energy storage systems (ESS), that being fire and explosion. However, there is one major difference. In storage, LIBs are not being actively charged and discharged but are holding a state-of-charge (SOC), typically less than 60%.
Even though the LIBs are not in use, they can still act as an ignition source if they suffer any abuse (electrical, thermal, or physical) and enter thermal runaway. Thermal runaway of a LIB can lead to venting of flammable gases and fire as well as thermal abuse to surrounding cells. Testing and continued research efforts provide a good understanding of the hazard and a basis for fire protection of LIBs and modules in manufacturing and storage areas.
FM Global strives to keep pace with emerging LIB technologies hitting the market, evaluating the challenges they create to fire protection and developing protection solutions. The commitment is highlighted by the upcoming release of FM Global Property Loss Prevention Data Sheet 7-112 (DS 7 112), Lithium-ion Battery Manufacturing and Storage.
The LIB assembly process can be broken down into three high-level process steps; electrode manufacturing, cell assembly and cell finishing. During electrode manufacturing and cell assembly, the introduction of the raw materials and manufacturing processes constitute the real hazards as the battery does not become electrically active until the formation process. These hazards will include ignitable liquids due to the electrolyte and potential use of heat transfer fluids as well as process and ignition source hazards.
FM Global recommends manufacturing areas of LIBs be protected as an HC-3 occupancy due to the lack of continuity of combustibles, limited use of ignitable liquids and expected use of plastics. The cell-finishing process steps of formation and aging are going to present the greatest hazard from a fire perspective due to the cells being chemically active at this stage and the number of cells in close proximity.
In manufacturing areas, some amount of storage is usually present and in DS 3-26, it is classified as either incidental or low-piled based on the storage height and area. It is important to note that LIBs (cells or modules) have their own requirements for incidental storage and should never be stored in low-pile arrangements.
The protection of LIBs in non-storage occupancies is based upon maintaining a known fire area and promoting cooling of the batteries and packaging from the sprinkler protection. This is accomplished by limiting the footprint and height of the allowable storage area and maintaining separation from other combustibles.
The incidental storage of LIBs with a SOC less than or equal to 60% should be limited to a 200 ft2 (20 m2) storage area that is no greater than 6 ft (1.8 m) high. Multiple storage areas are acceptable, provided they are separated by 10 ft (3.0 m) wide aisles. Low-piled storage of LIBs is not recommended since the fire may continue to spread throughout the storage as the sprinkler protection cannot stop the fire.
The storage of LIBs can be broken down into three main categories which include; new or refurbished cells or modules, defective or damaged cells or modules and finished products (cells or modules within consumer goods.)
The extent of protection changes with the category as it relates to the expected exposure and involvement of the batteries in a fire. Ceiling-only protection options are available for three tiers of rack or three high palettized cell/module storage under ceilings up to 40 ft (12 m) when the SOC is less than 60%. These restrictions to the storage arrangement enable the water from the sprinklers to provide the needed cooling to limit overall battery involvement.
If the SOC is greater than 60% or any other storage arrangement is used, in-rack sprinkler protection with horizontal barriers is recommended. This robust protection scheme is recommended based on the many unknowns that can negatively impact the protection.
Finished products that contain LIBs or modules such as power tool packs, cell phones or laptop computers can be protected based on the product they are part of and the packaging provided they are at a SOC of less than 60% and stored under a ceiling no greater than 40 ft (12 m) with no storage located above. In the case of a power tool pack that is packaged in a plastic blister pack with multiple units then placed into a cardboard box, a classification of cartoned unexpanded plastic (CUP) would provide adequate protection.
For the cell phone or laptop, CUP may be sufficient however if large amounts of expanded plastics are used to protect the devices, then the classification should be increased to cartoned expanded plastic (CEP). If the SOC or ceiling height limitations cannot be met, in-rack sprinkler protection with horizontal barriers is recommended.
Many factors contribute to the fire risk associated with storage of LIBs. Thermal runaway (TR) is the major hazard of LIBs and refers to the irreversible failure of a LIB that leads to the production of flammable gases. However, fully assembled LIB products are complex, including many combustible and non-combustible components beyond just the batteries. It is therefore helpful to separate the contributions to the fire hazard from the individual components before addressing the corresponding fire hazards of the full storage scenario.
A multi-phase project was completed in 2016 in conjunction with the Property Insurance Research Group and in partnership with the Fire Protection Research Foundation.
A reduced-commodity test evaluated the flammability characteristics of large-format, 20 Ah Li-ion polymer batteries, compared to FM Global’s standard commodities and previously tested LIBs. The performance of ceiling-level sprinkler protection was then assessed with a large-scale sprinklered fire test of large-format 20 Ah polymer pouch batteries. These tests showed that bulk storage of small-format LIBs (i.e., 2.6 Ah) exhibits similar fire growth leading to first sprinkler operation as cartoned commodities. Further, it was determined that the time required for significant involvement of LIBs was slower than the typical sprinkler response.
Ongoing research now seeks to further extend these types of large-scale results by quantifying the battery component of the fire hazard all the way down to the individual cell level. When applied to a warehouse storage scenario, this strategy consists of four main parts to establish the overall fire hazard.
Single-cell overheating tests to observe the effects of thermal abuse on thermal runaway in an open environment. This is a convenient way to determine the impact of variables, such as state-of-charge, electrical capacity, chemistry and form factor.
Multi-cell overheating tests to measure the thermal runaway propagation rate (TRP), as well as the impact of materials used between cells for thermal management both in an open environment and where the cells are located within a battery case. TRP occurs when a cell undergoing thermal runaway heats adjacent cells and causes cascading failure of a cell array.
Fully assembled battery product tests to establish the potential for the fire event to spread from one fully assembled battery to the next, as well as capturing the impact of the non-battery components on the overall fire hazard. This is often a critical step in determining if the dominant hazard is a battery fire, or just a fire.
While optimization of Li-ion cells and storage arrangements will continue to develop and change, one thing is certain: this hazard is here to stay.
This article was originally published in the May 2025 Edition of Fire & Safety Journal Americas. To read your FREE copy, click here.
