Fire Hazard and Risk Assessment Battery Energy Storage System (BESS)

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Fisher Engineering, Inc. Energy Safety Response Group Investigation
A multi-entity fire investigation commenced on August 3, 2021. The VBB fire investigation process involved analyzing both the root cause of the initial fire in MP-1 as well as the root cause of the fire propagation into MP-2. The investigations included on-site inspections of MP-1 and MP-2 by the CFA, Energy Safe Victoria4 (ESV), Work Safety Victoria5 (WSV), local Tesla engineering/service teams and a local third-party independent engineering firm. In addition to the on-site work immediately after the incident, the root cause investigations also included data analysis, thermal modeling and physical testing (electrical and fire) performed by Tesla at their headquarters in California, USA and their fire test facility in Nevada, USA.
Fire Cause Investigation
Fire Origin and Cause Determination
The origin of the fire was MP-1 and the most likely root cause of the fire was a leak within the liquid cooling system of MP-1 causing arcing in the power electronics of the Megapack’s battery modules. This resulted in heating of the battery module’s lithium-ion cells that led to a propagating thermal runaway event and the fire.
Other possible fire causes were considered during the fire cause investigation; however, the above sequence of events was the only fire cause scenario that fits all the evidence collected and analyzed to date.
Contributory Factors
A number of factors contributed to this incident. Had these contributory factors not been present, the initial fault condition would likely have been identified and interrupted (either manually or automatically) before it escalated into a fire event. These contributory factors include:
1. The supervisory control and data acquisition (SCADA) system for a Megapack required 24 hours to setup a connection for new equipment (i.e., a new Megapack) to provide full telemetry data functionality and remote monitoring by Tesla operators. Since VBB was still in the installation and commissioning phase of the project (i.e., not in operation), MP-1 had only been in service for 13 hours prior to being switched off via the keylock switch on the morning of the fire. As such, MP-1 had not been on-line for the required 24 hours, which prevented this unit from transmitting telemetry data (internal temperatures, fault alarms, etc.) to Tesla’s off-site control facility on the morning of the fire.
2. The keylock switch for MP-1 was operated correctly on the morning of the fire to turn MP-1 off as the unit was not required for commissioning and testing that morning; however, this action caused telemetry systems, fault monitoring, and electrical fault safety devices6 to be disabled or operate with
Victoria’s energy safety regulator
Victoria’s health and safety regulator
These elements include, among other devices, fuses at the cell and module level for localized fault current interruption and a battery module pyro disconnect that severs the electrical connection of the battery module when a fault current is passing through the battery module.
Report of Technical Findings: Page 3 Victorian Big Battery Fire 1/25/2022
On-site inspections commenced on August 3, 2021 and concluded on August 12, 2021. MP-1 and MP-2 were
documented, inspected and preserved for future examinations, if necessary. Concurrently, all available
telemetry data (such as internal temperatures and fault alarms) from MP-1 and MP-2 were analyzed and a
series of electrical fault and fire tests were performed. The on-site investigation findings, the telemetry data
analysis, electrical fault tests and fire tests, when combined, identified a very specific series of fault conditions
present on July 30, 2021 that could lead to a fire event.
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