The investigation into the fire started a few days later and was announced recently. Experts at Fisher Engineering and Energy Safety Response Group (SERB) wrote the technical report, noting that the fire was caused by a coolant leak. This caused a dent inside the Megapack battery modules.
The report stated:
“The source of the fire was the MP-1 and the possible root cause of the fire was a leak inside the liquid cooling system From the MP-1 caused a bend in the power electronics of Megapack battery modules.
“This heated up the lithium-ion cells in the battery unit causing thermal escape and a fire to break out.
“Other potential fire causes were considered during the investigation of the cause of the fire; however, the above sequence events were the only fire cause scenario that fits all of the evidence collected and analyzed to date.”
Teslarati He noted 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 firmware and hardware mitigations to avoid similar incidents in the future, which include improved cooling system checks during Megapack assembly.
Tesla also included additional cooling system telemetry data alerts to identify and respond to potential coolant leaks. Furthermore, Tesla has installed newly designed thermally insulated steel ventilation shields inside the thermal roof of all Megapacks.
5 Lessons Learned from the Business of Fire and Tesla
The report detailed several lessons learned from the Victoria Big Battery (VBB) fire. According to the report:
“The VBB fire revealed a number of unlikely factors that, when combined, contributed to the initiation of the fire as well as its spread to an adjacent unit. This combination of factors had not previously been encountered during previous Megapack installations, commissioning and/or organizational product testing” .
These five lessons are:
Lessons learned related to commissioning procedures.
Limited supervision and monitoring of telemetry data within the first 24 hours of commissioning and switch-off use during commissioning and testing.
The report said these two factors prevented the MP-1 from sending telemetry data such as indoor temperatures and fault alerts to the Tesla control facility. These factors have put critical electrical failure safety devices such as kinematic separation into a state of limited functionality and reduced Megapack’s ability to effectively monitor and interrupt electrical failures before they escalate into a fire.
Since this fire, Tesla has modified its commissioning procedures to reduce the telemetry setup connection time for new Megapacks from 24 hours to 1 hour and to avoid using the Megapack’s key lock switch unless the unit is actively maintained.
Lessons learned related to electrical fault protection devices.
There are three lessons learned related to this section. Coolant leak alarms, where the pyro disconnect is unable to interrupt fault currents when the Megapack is switched off via a key lock switch, and the pyro disconnect is likely to be disabled due to loss of power in the circuit operating it.
These factors prevented the MP-1 from actively monitoring and interrupting electrical failure conditions before escalating into a fire, the report said.
Tesla has implemented several firmware mitigations that keep all electrical safety protection devices active regardless of the position of the kill switch or system status while actively monitoring and controlling the power cut-off power supply circuit.
Additionally, Tesla has added more alarms that will better identify and respond either manually or automatically to coolant leaks.
The report indicated that although this fire was started due to a coolant leak, the unexpected failure of the other internal components of the Megapack could cause similar damage to the battery units. Tesla’s new firmware mitigations address the damage caused by coolant leaks while also allowing Megapack to identify, respond, and better contain and isolate issues within the battery modules caused by failures of other internal components if they occur in the future.
Lessons learned related to the spread of fires.
The lessons learned here are the important role that external and environmental conditions such as wind can play in a megapack fire. Also identifying weaknesses in the design of the thermal roof allowed fire to spread from Megapack to Megapack.
This resulted in direct flames hitting the plastic overpressure vents that seal the battery compartment off the thermal ceiling, according to the report.
“With a direct path for the flames and hot gases to enter the battery slots, the cells inside the MP-2 battery units failed and became involved in the fire.”
Tesla created pressure relief devices to protect overpressure vents. Tesla has tested this and mitigations will protect the vents from direct contact with flames or hot gas leakage with new, heat-insulated steel vent shields installed.
They are placed over overpressure vents and are now standard on all new Megapack formulas.
Steel vent shields can easily be installed on field-based Megapacks. The report noted that the vent shields are nearing production and Tesla plans to modify them to advanced Megapack positions soon.
Lessons learned regarding spacing between megapacks.
The lessons here reflect that there is no need to make changes to the installation practices of the Megapack with the Ventilation Shield mitigation application. Analysis of the telemetry data inside the MP-2 during fire showed that the thermal insulation of the Megapack is able to provide significant thermal protection in the event of a fire inside the adjacent Megapack installed only six inches away.
The report added that the MP-2’s internal cell temperatures increased by 1.8 degrees Fahrenheit from 104 degrees Fahrenheit to 105.8 degrees Fahrenheit before communications to the unit were lost at 11:57 a.m., presumably due to the fire itself. This was two hours after the fire.
The report added that the spread of the fire was caused by a weakening of the thermal ceiling and not by heat transfer through the 6-inch gap between the Megapacks. Venting Shield addresses vulnerability and has been validated by unit level fire testing, which includes tests that include ignition of Megapacks.
Tests confirmed that overpressure vents would not ignite even if the thermal ceiling was fully involved in a fire. Tests have also confirmed that battery modules remain relatively unaffected by elevated internal cell temperatures below 1°C.
Lessons learned about emergency response.
These are many lessons learned here.
1. Effective planning before an accident occurs is not only invaluable but can reduce the possibility of injuries.
2. Coordination with Specialized Experts (SMEs) either on-site or remotely provides critical expertise and system information for emergency responders to benefit from.
3. The efficacy of applying water directly to adjacent Megapacks appears to have limited benefits although applying water to other electrical equipment with less fire protection built into their designs (think transformers) can be beneficial in protecting that equipment.
4. Megapack’s fire protection design approach has advantages over other BESS designs in terms of emergency responder safety.
5. The report indicated that the Environmental Protection Agency said that the air quality was good two hours after the fire which indicates that there were no long-term air quality concerns due to the fire.
6. The water samples showed that the possibility of a physical fire effect on firefighting was small.
7. Advance community participation during project planning stages is invaluable. It has enabled Neoen to quickly update the local community while addressing immediate questions and concerns.
8. Face-to-face engagement with the local community as soon as possible is essential when fires occur.
9. The report noted that the Steering Committee of Executive Stakeholders from key organizations involved in emergency response can help ensure timeliness, efficiency, ease of coordination and accuracy of any public communications.
10. The final lesson learned is that effective coordination between stakeholders on the site allowed for a rapid and comprehensive post-fire delivery process. It also allowed for a quick and safe shutdown of the damaged units and a quick return of the site to service.
You can read the full report here.
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