The Impact of Thermal Runaway on Sprinkler Protection Recommendations for Warehouse Storage of Cartoned Lithium-Ion Batteries

This study investigates the appropriateness of applying the standard large-scale fire test protocol developed for ordinary combustibles for energetic batteries. A large-scale fire test was recently conducted to determine sprinkler protection guidance for warehouse storage of lithium-ion batteries. The specific battery tested had a 20 Ah capacity, polymer pouch format, lithium iron phosphate chemistry and was at a typical state-of-charge (50%) for long-term storage. The batteries were packaged in single-wall corrugated containerboard cartons on hardwood pallets, as received from the supplier. Each carton contained 20 batteries separated by nested polystyrene plastic dividers. Acceptable ceiling-level sprinkler protection was achieved for 4.6 m (15 ft) tall rack storage under a 12.2 m (40 ft) ceiling using K-Factor of 320 L/min/bar(A 1/2) (22.4 gpm/psi(A 1/2)), quick-response, sprinklers at a discharge pressure of 2.4 bar (35 psig). The effect that thermal runaway of the Li-ion batteries had on the design and outcome of the large-scale fire was evaluated. A focus was placed on the role of thermal runaway during three stages of the fire; ignition leading to sprinkler operation, active sprinkler protection, and conditions after the sprinkler system was turned off. An external ignition source was used in cases where induced thermal runaway, which refers to rapid self-heating of a battery under abuse conditions, did not lead to combustion of the battery contents. Through a combination of experiments and review of literature data, it was found that thermal runaway within a pallet load of cartoned batteries would result in a similar fire hazard as that associated with external ignition scenarios typically used in large-scale fire testing. Regardless of chemistry, evidence shows that fire propagation beyond the battery or carton of origin occurs external to the carton due to limited available air within the carton to support combustion. In addition, intermediate-scale testing showed that sprinkler water would be effective at suppressing a fire at a later stage of battery involvement than was achieved in the large-scale test. This work reinforces the sprinkler protection guidance resulting from the successful large-scale fire test.