A minimal just after 8:00 p.m. on April 19, 2019, a captain with the Peoria, Arizona, fire department’s Hazmat device, opened the doorway of a container crammed with a lot more than 10,000 energized lithium-ion battery cells, element of a utility-scale storage process that had been deployed two many years previously by the area utility, Arizona General public Provider.
Earlier that night, at about five:41 p.m., dispatchers had been given a connect with alerting them to smoke and a “bad smell” in the region about the McMicken Battery Power Storage System (BESS) website in suburban Phoenix.
Sirens blaring, 3 fire engines arrived at the scene inside of 10 minutes. Shortly just after their arrival, 1st responders recognized that energized batteries had been concerned and elevated the connect with to a Hazmat reaction. After consulting with utility staff and deciding on a plan of motion, a fire captain and 3 firefighters approached the container doorway shortly right before 8:00 p.m., preparing to open up it. The captain, recognized in a later investigation as “Captain E193,” opened the doorway and stepped within. The other 3 stood close by.
The BESS was housed in a container arranged to keep 36 vertical racks separated into two rows on both aspect of a 3-ft-large hallway. 20-seven racks held fourteen battery modules manufactured by LG Chem, an eighty kW inverter manufactured by Parker, an AES Advancion node controller applied for facts assortment and communication, and a Battery Protection Unit (BPU) manufactured by LG Chem.
The battery modules in transform contained 28 lithium-ion battery cells of Nickel Manganese Cobalt (NMC) chemistry. These modules had been linked in series, offering a for every-rack nominal voltage of 721 V. The full process had a nameplate ability to source 2 MW of electric power above one particular hour for a life span electrical power ranking of 2 MWh. With 27 whole racks, there had been 10,584 cells in the container. After a whole day of charging, the batteries had been about 90 percent of ability.
With the doorway to the BESS container open up and Captain E193 at its threshold, flamable gases that had developed up within since the incident commenced quite a few hours right before been given a breath of oxygen and observed an ignition resource.
The gases erupted in what was described as a “deflagration celebration.” Firefighters just exterior of the incident incredibly hot zone said they read a loud sounds and saw a “jet of flame” lengthen some seventy five ft out and twenty ft up from the doorway.
In the explosion, Captain E193 and firefighter E193 had been thrown from and less than a chain-connection fence surrounding the facility. The captain landed a lot more than 70 feet from the open up doorway the firefighter landed 30 ft away.
The captain’s injuries provided a traumatic brain harm, an eye harm, backbone damage, damaged ribs, a damaged scapula, thermal and chemical burns, internal bleeding, two damaged ankles, and a damaged foot.
The firefighter endured a traumatic brain harm, a collapsed lung, damaged ribs, a damaged leg, a separated shoulder, laceration of the liver, thermal and chemical burns, a missing tooth, and facial lacerations.
The timeline and series of situations is not commonly disputed. On the other hand, a dispute has erupted in new weeks above what specifically happened within the BESS container at about four:54 p.m. that initiated a thermal runaway that cascaded across multiple battery cells.
In a report introduced in late July, the utility and its 3rd-celebration investigator, DNV-GL, said that their evaluate of the evidence pointed to the failure of a one lithium-ion cell as triggering the situations.
In a different, preliminary report filed times later with state officials, LG Chem, which supplied the li-ion batteries, challenged that obtaining. The South Korea-based battery provider said the APS report skipped a quantity of information about the incident. People information, LG Chem advised regulators, indicated that the cell thermal runaway commenced thanks to “intense heating” induced by a warmth resource “such as exterior electrical arcing” on one particular of the battery racks.
Scott Bordenkircher, who served as APS’ Director of Technological innovation Innovation & Integration at the time of the incident, said in an interview that the utility accepts the findings of its 3rd-celebration incident investigation, which was accomplished by Davion Hill, Ph.D., the U.S. Power Storage Leader for DNV GL. “We have assurance in our 3rd-celebration investigator,” Bordenkircher said.
In its 78-website page report [PDF], DNV GL said that what was 1st considered to be a fire was in simple fact an intensive cascading thermal runaway celebration inside of the BESS. That celebration was initiated by an internal cell failure inside of one particular battery cell, recognized as cell 7-2 on Rack fifteen. The failure was induced by “abnormal lithium steel deposition and dendritic growth” inside of the cell, the report said.
As soon as the failure transpired, thermal runaway cascaded from cell 7-2 as a result of each and every other cell and module in Rack fifteen by way of warmth transfer. The runaway was aided by the “absence of satisfactory thermal barrier protections” involving battery cells, which if not may well have stopped or slowed the thermal runaway.
As the celebration progressed, a substantial volume of flammable gas was manufactured inside of the BESS. Lacking ventilation to the exterior, the gases made a flammable environment inside of the container. Around 3 hours just after thermal runaway commenced, when firefighters opened the BESS doorway, flammable gases manufactured make contact with with a warmth resource or spark and exploded.
It was a “tragic incident,” Bordenkircher said.
It also was not the 1st time that a lithium-ion battery had failed.
The APS report stated situations reaching back again to 2006 that concerned thermal runaway situations in lithium-ion batteries. In one particular commonly report incident in January 2013, a Boeing 787-8 skilled smoke and warmth coming from its lithium-ion battery-based auxiliary electric power device. It was later established that the failure was induced by an internal cell defect, which was exacerbated as thermal runaway cascaded as a result of all the cells in the battery pack, releasing flammable electrolyte and gases.
“The point out of the market is that internal problems in battery cells is a acknowledged challenge,” said Hill. Even so, difficulties with the technological know-how have not been very well communicated involving, say, the individual electronics sector and the automotive sector or the aerospace market and the electrical power market.
“Overall, across the market there was a hole in know-how,” Bordenkircher said. The technological know-how moved ahead so rapidly, he said, that criteria and know-how sharing had not held up.
The McMicken BESS incident also was not the 1st for APS. In November 2012, a fire ruined the Scale Power Storage Technique (ESS) at an electrical substation in Flagstaff in northern Arizona. The ESS was manufactured by Electrovaya and consisted of a container housing sixteen cabinets containing 24 lithium-ion cells.
An investigation into that incident established that a severely discharged cell degraded and affected a neighboring cell, touching off a fire. The root induce of the 2012 incident was observed to be defective logic applied to management the process.
The management logic had been updated a lot more than two dozen situations throughout the 11 months that the BESS operated. But quite a few skipped alternatives could have prevented the fire that ruined the device, the incident report said. It pointed in individual to an celebration the preceding Could in which a cell was “severely discharged” even as the logic was “continuously charging the cell from the supposed design.” After the Could celebration, the logic was not improved to address that incorrect conduct.
An APS spokesperson said that classes acquired from this 2012 incident had been included into the design and operation of the McMicken BESS.
In its 162-website page rebuttal [PDF] of the McMicken incident LG Chem refuted the utility’s obtaining of fault with its battery.
The battery provider said that based on obtainable evidence, “metallic lithium plating did not induce an internal cell failure leading to the preliminary thermal runaway event” at the McMicken BESS facility. As a substitute, cell thermal runaway commenced as a result of powerful heating of the affected cells induced by an exterior warmth resource, these as exterior electrical arcing on Rack fifteen.
LG Chem said that its individual 3rd-celebration investigator, Exponent Inc., tested the internal cell failure idea. It did so by forcing a parallel cell configuration into thermal runaway. It then compared the resulting voltage profile to the voltage profile recorded throughout the incident. It observed that the two did not match, leading to the conclusion that the explosion’s induce was not likely to have been “an internal brief inside of a one cell.”
The battery maker also said that facts recorded throughout the incident showed a discharging recent of four.9A (amps) current throughout the voltage excursion. It said that despite the fact that the APS report acknowledged that the recent flipped from -27.9A charging to four.nine A discharging,“it presented no clarification for the celebration.” To LG Chem, nonetheless, the simple fact that the discharging recent was at four.9A, rather of zero, “means the recent certainly flowed to someplace else,” supporting what it said was a most likely double-place electrical isolation failure and not an internal cell brief.
(Complicating the put up-incident investigation was the simple fact that the fire ruined process management electronics inside of the container. That remaining dozens of battery modules energized with no way to discharge them. It took seven weeks for the utility to figure out a plan to eliminate the modules one particular by one particular and bleed off their saved electrical power.)
The experiences and their divergent conclusions sign the commence of competing interpretations of obtainable facts as the utility and its battery provider perform to discover a one induce for the incident.
“We don’t want a community argument about it,” said DNV GL’s Davion Hill. For him, the major place is that “we had a cascading thermal runaway that led to an explosive atmosphere” at the APS McMicken BESS. The intention now should really be to make storage systems safer as a result of criteria improvement and info sharing.
After the incident, APS placed a keep on BESS deployment across its service territory. The technological know-how is observed as essential to assembly the utility’s announced plans to make a hundred percent “clean energy” by 2050. Two other BESS systems that had been running at the time of the April 2019 incident had been taken offline they will continue being idle right until retrofits can be designed and set up.