Last year’s Tesla Megapack battery fire at Victoria Big Battery in Australia was a learning moment for Tesla and Neoen. The fire happened in July when a Tesla Megapack was being tested. The fire spread to another battery as well and the two Megapacks were destroyed. The fire lasted for six hours and according to Energy Storage Newsthis was a “safe failure.”
An investigation into the fire was initiated a mere few days later and was recently made public. Experts at Fisher Engineering and the Energy Safety Response Group (SERB) wrote the technical report, stating that the fire was caused by a liquid coolant leak. This caused the arcing within the Megapack’s battery modules.
The report stated:
“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 events were the only fire cause scenario that fits all the evidence collected and analyzed to date.”
Teslarati pointed out that the Megapack that started the fire had been manually disconnected from several monitoring, control, and data collection systems since it was being tested at the time. Another factor that contributed to the spread of the fire was wind speed.
The article also noted that Tesla implemented several procedural, firmware, and hardware mitigations to avoid similar incidents from happening in the future, which include improved coolant system inspections during Megapack assembly.
Tesla also included additional alarms to the coolant system’s telemetry data to identify and respond to possible coolant leaks. Further, Tesla has installed newly designed, thermally insulated steel vent shields within the thermal roof of all Megapacks.
5 Lessons Learned From The Fire & Tesla’s Actions
The report detailed several lessons learned from the Victoria Big Battery (VBB) fire. According to the report:
“The VBB fire exposed a number of unlikely factors that, when combined, contributed to the fire initiation as well as its propagation to a unit. This collection of factors had never before been encountered during previous Megapack installations, operation, and/or regulatory product testing.”
Those five lessons are:
Lessons Learned Related To Commissioning Procedures.
Limited supervision and monitoring of telemetry data during the first 24 hours of commissioning and the use of the keylock switch during commissioning and testing.
The report said that these two factors prevented the MP-1 from transmitting telemetry data such as internal temperatures and fault alarms to Tesla’s control facility. These factors placed critical electrical fault safety devices such as the pyro-disconnect in a state of limited functionality and reduced the Megapack’s ability to actively monitor and interrupt electrical fault prior to them escalating into a fire event.
Since this fire, Tesla modified its commissioning procedures to reduce the telemetry setup connection time for new Megapacks from 24 hours to 1 hour and to avoid utilizing the Megapack’s keylock switch unless the unit is actively being serviced.
Lessons Learned Related To Electrical Fault Protection Devices.
There are three lessons learned related to this section. Coolant leak alarms, the pyro disconnect being unable to interrupt fault currents when the Megapack is off via the keylock switch, and the pyro disconnect likely being disabled due to a power supply lost to the circuit that actuates it.
These factors prevented the pyro disconnect of MP-1 from actively monitoring and interrupting the electrical fault conditions before they escalated into a fire event, the report stated.
Tesla implemented several firmware mitigations that keep all electrical safety protection devices active regardless of the keylock switch position or system state while also actively monitoring and controlling the pyro disconnect’s power supply circuit.
In addition to this, Tesla added more alarms that will better identify and respond either manually or automatically to coolant leaks.
The report noted that even though this particular fire was initiated by a coolant leak, unexpected failure of other internal components of the Megapack could create similar damage to the battery modules. Tesla’s new firmware mitigations address the damage from a coolant leak while also allowing the Megapack to better identify, respond, contained, and isolate within the battery modules caused by failures of other internal components if they happen in the future.
Lessons Learned Related To Fire Propagation.
The lessons learned here are the significant role external, and environmental conditions such as wind can have on a megapack fire. And also the identification of a weakness in the thermal roof design allowed for Megapack-to-Megapack fire propagation.
These led to direct flame impingement on the plastic overpressure vents that seal the battery bay from the thermal roof, according to the report.
“With a direct path for flames and hot gases to enter into the battery bays, the cells within the battery modules of MP-2 failed and became involved in the fire.”
Tesla devised hardware mitigation to protect the overpressure vents. Tesla’s tested this and the mitigations will protect the vents from direct flame impingement or hot gas intrusion with the installation of new thermally insulated steel vent shields.
These are placed on top of the overpressure vents and are now standard on all new Megapack installations.
The steel vent shields can easily be installed on existing Megapacks in the field. The report noted that the vent shields are nearing the production stage and Tesla plans to retrofit them to applicant Megapack sites soon.
Lessons Learned Related To Megapack Spacing.
The lessons here reflect that no changes are needed to the installation practices of the Megapack with the vent shield mitigation in place. An analysis of the telemetry data within the MP-2 during the fire showed that the Megapack’s thermal insulation is able to provide significant thermal protection in the event of a fire within an adjacent Megapack installed only six inches away.
The report added that the internal cell temperatures of MP-2 increased by 1.8°F from 104°F to 105.8°F before communications were lost to the unit at 11:57 AM, which is presumed to be due to the fire itself. This was two hours into the fire event.
The report added that fire propagation was triggered by the weakness in the thermal roof and not due to the heat transfer via the 6-inch gap between the megapacks. The vent shield mitigation addresses the weakness and has been validated through unit-level fire testing, which includes tests involving the ignition of the Megapacks.
The tests confirmed that the overpressure vents will not ignite even if the thermal roof is fully involved in a fire. The tests also confirmed that the battery modules remain relatively unaffected with internal cell temperatures rising less than 1 degree Celsius.
Lessons Learned Related To Emergency response.
These are several lessons learned here.
1. Effective pre-incident planning is not only invaluable but can reduce the likelihood of injuries.
2. Coordination with subject matter experts (SMEs) either on-site or remotely provides critical expertise and system information for emergency responders to draw upon.
3. The effectiveness of applying water directly to adjacent Megapacks seems to have limited benefits even though water application to other electrical equipment with less fire protection built into their designs (think transformers) can be useful at protecting that equipment.
4. The fire protection design approach of the Megapack has advantages over other battery energy storage systems (BESS) designs in terms of safety for emergency responders.
5. The report noted that the Environmental Protection Agency said there was good air quality two hours after the fire which shows that there wasn’t any long-lasting air quality concerns that happened from the fire.
6. Water samples showed that the likelihood of the fire having a material impact on firefighting was minimal.
7. Prior community engagement during the project planning stages is invaluable. It enabled Neoen to quickly update the local community while addressing immediate questions and concerns.
8. Face-t0-face engagement with the local community as early as possible is essential when fire events happen.
9. The report noted that an executive stakeholder steering committee from the key organizations involved in the emergency response can help ensure the timeliness, efficiency, ease of coordination, and thoroughness of any public communications.
10. The final lesson learned is that effective coordination between stakeholders at the site allowed for the rapid and thorough handover process after the fire. It also allowed for the swift and safe decommissioning of the damaged units and the site’s fast return to service.
You can read the full report here.
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