Utility-scale lithium-ion energy storage batteries are being installed at an accelerating rate in many parts of the world. Some of these batteries have experienced troubling fires and explosions. There have been two types of explosions; flammable gas explosions due to gases generated in battery thermal runaways, and electrical arc explosions leading to structural failure of battery electrical enclosures. The thermal runaway gas explosion sce. Utility-scale lithium-ion energy storage batteries are being installed at an accelerating rate in many parts of the world. Some of these batteries have experienced troubling fires and explosions. There have been two types of explosions; flammable gas explosions due to gases generated in battery thermal runaways, and electrical arc explosions leading to structural failure of battery electrical enclosures. The thermal runaway gas explosion scenarios, which can be initiated by various electrical faults, can be either prompt ignitions soon after a large flammable gas mixture is formed, or delayed ignitions associated with late entry of air and/or loss of gaseous fire suppression agent. The electrical explosions have entailed inadequate electrical protection to prevent high energy arcs within electrical boxes vulnerable to arc induced high pressures and thermal loads. Estimates of both deflagration pressures and arc explosion pressures are described along with their incident implications.••••Accounts of energy storage battery fires and explosions.••Lithium-ion battery thermal runaway gas explosion scenarios.••Deflagration pressure and gas burning velocity in one important incident.••High-voltage arc induced explosion pressures.Battery explosionsThermal runawaysArc flashDeflagration protectionAccording to the International Energy Agency (2020), worldwide energy storage system capacity nearly doubled from 2017 to 2018, to reach over 8 GWh. The total installed storage power in 2018 was about 1.7 GW. About 85% of the storage capacity is from lithium-ion batteries.U.S. Energy Information Administration (2019) projections are that megawatt-scale battery capacity will approximately triple from 2018 to 2021. Based on current utility plans, EIA projects most of the additional capacity to come from increasingly large lithium-ion energy batteries. Many such installations are now in the range 2 MW–20 MW, but several planned installations have capacities greater than 100 MW. A major reason for these expansions is that the cost for lithium-ion batteries lowered from approximately $1200 per kWh in 2010 to less than $200 per kWh in 2018 (Bloomberg, 2019).Fig. 1 shows a simplified layout of a utility-scale lithium-ion Energy Storage Battery (ESB) installation unit. Lithium-ion cells, the basic building blocks of the system, are installed in a module. These cells usually have vents to prevent internal over-pressurization. Modules are equipped with electrical protection (fuses) and sensors for monitoring of voltages and (sometimes) temperatures, and either passive or active ventilation provisions.Various recent papers, for example Guo et al. (2018) and Li et al. (2019), describe how any one of several fault conditions, including electrical faults, overcharging, and particulate/moisture contamination, can lead to an escalated temperature in one lithium-ion cell, causing deterioration and eventual failure of the cell separator, with subsequent electrolyte decomposition and elevated vapor pressure. This leads to a thermochemical runaway venting in the cell that can then propagate to many other cells in an energy storage battery module. The vented thermal runaway causes flammable gas to be emitted into the battery enclosure, where the resulting flammable mixture can be ignited by hot module casings, electrical connectors, or ejected sparks from the involved module. This generic explosion hazard has been discussed previously by Marr et al. (2013) and Baird et al. (2020), among others.Three different runaway gas explosion hazard scenarios can occur. In one scenario, the flammable gas mixture is ignited soon after it is formed near the initiating module, such that there is only a minor deflagration and a subsequent fire. In the second scenario, batteries in thermal runaway release flammable gases without igniting initially, and a delayed explosion associated with the accumulation of additional flammable atmosphere then occurs. In the third scenario there is an initial fire with accumulation of incomplete combustion pro.
