A tiny immediately after 8:00 p.m. on April 19, 2019, a captain with the Peoria, Arizona, hearth department’s Hazmat unit, opened the door of a container crammed with a lot more than 10,000 energized lithium-ion battery cells, portion of a utility-scale storage program that had been deployed two several years previously by the area utility, Arizona Community Provider.

Earlier that night, at about 5:41 p.m., dispatchers had acquired a phone alerting them to smoke and a “bad smell” in the place about the McMicken Battery Energy Storage System (BESS) web site in suburban Phoenix.

Sirens blaring, a few hearth engines arrived at the scene within just 10 minutes. Shortly immediately after their arrival, initial responders realized that energized batteries had been involved and elevated the phone to a Hazmat response. Right after consulting with utility personnel and choosing on a prepare of action, a hearth captain and a few firefighters approached the container door shortly in advance of 8:00 p.m., planning to open it. The captain, discovered in a later on investigation as “Captain E193,” opened the door and stepped within. The other a few stood close by.

The BESS was housed in a container organized to maintain 36 vertical racks divided into two rows on both aspect of a 3-ft-large hallway. Twenty-7 racks held fourteen battery modules made by LG Chem, an 80 kW inverter made by Parker, an AES Advancion node controller utilised for data selection and conversation, and a Battery Security Device (BPU) made by LG Chem.

The battery modules in transform contained 28 lithium-ion battery cells of Nickel Manganese Cobalt (NMC) chemistry. These modules had been related in collection, furnishing a for each-rack nominal voltage of 721 V. The complete program had a nameplate capability to source 2 MW of electric power more than a person hour for a lifetime vitality ranking of 2 MWh. With 27 entire racks, there had been 10,584 cells in the container. Right after a entire day of charging, the batteries had been about ninety % of capability.

With the door to the BESS container open and Captain E193 at its threshold, flamable gases that had designed up within given that the incident started many several hours in advance of acquired a breath of oxygen and observed an ignition supply.

The gases erupted in what was described as a “deflagration function.” Firefighters just outside the house of the incident incredibly hot zone claimed they read a loud noise and saw a “jet of flame” extend some seventy five ft out and 20 ft up from the door.

In the explosion, Captain E193 and firefighter E193 had been thrown from and under a chain-connection fence encompassing the facility. The captain landed a lot more than 70 feet from the open door the firefighter landed thirty ft absent.

The captain’s injuries provided a traumatic mind damage, an eye damage, spine hurt, damaged ribs, a damaged scapula, thermal and chemical burns, interior bleeding, two damaged ankles, and a damaged foot.

The firefighter endured a traumatic mind damage, a collapsed lung, damaged ribs, a damaged leg, a divided shoulder, laceration of the liver, thermal and chemical burns, a missing tooth, and facial lacerations.

The timeline and collection of situations is not commonly disputed. Having said that, a dispute has erupted in new weeks more than what precisely occurred within the BESS container at about four:fifty four p.m. that initiated a thermal runaway that cascaded throughout many battery cells.

In a report unveiled in late July, the utility and its third-social gathering investigator, DNV-GL, claimed that their evaluation of the proof pointed to the failure of a single lithium-ion cell as triggering the situations.

In a independent, preliminary report submitted days later on with state officers, LG Chem, which provided the li-ion batteries, challenged that obtaining. The South Korea-dependent battery provider claimed the APS report skipped a selection of aspects about the incident. Those people aspects, LG Chem explained to regulators, indicated that the cell thermal runaway started due to “intense heating” brought on by a heat supply “such as external electrical arcing” on a person of the battery racks.

Scott Bordenkircher, who served as APS’ Director of Technology Innovation & Integration at the time of the incident, claimed in an interview that the utility accepts the results of its third-social gathering incident investigation, which was completed by Davion Hill, Ph.D., the U.S. Energy Storage Leader for DNV GL. “We have self esteem in our third-social gathering investigator,” Bordenkircher claimed.

In its seventy eight-web site report [PDF], DNV GL claimed that what was initial believed to be a hearth was in actuality an intensive cascading thermal runaway function within just the BESS. That function was initiated by an interior cell failure within just a person battery cell, discovered as cell seven-2 on Rack 15. The failure was brought on by “abnormal lithium metallic deposition and dendritic growth” within just the cell, the report claimed.

Once the failure transpired, thermal runaway cascaded from cell seven-2 through every single other cell and module in Rack 15 via heat transfer. The runaway was aided by the “absence of enough thermal barrier protections” amongst battery cells, which or else might have stopped or slowed the thermal runaway.

As the function progressed, a significant sum of flammable fuel was generated within just the BESS. Lacking air flow to the outside the house, the gases designed a flammable environment within just the container. About a few several hours immediately after thermal runaway started, when firefighters opened the BESS door, flammable gases produced get hold of with a heat supply or spark and exploded.

It was a “tragic incident,” Bordenkircher claimed.

It also was not the initial time that a lithium-ion battery had unsuccessful.

The APS report stated situations reaching back to 2006 that involved thermal runaway situations in lithium-ion batteries. In a person broadly report incident in January 2013, a Boeing 787-8 experienced smoke and heat coming from its lithium-ion battery-dependent auxiliary electric power unit. It was later on determined that the failure was brought on by an interior cell defect, which was exacerbated as thermal runaway cascaded through all the cells in the battery pack, releasing flammable electrolyte and gases.

“The condition of the industry is that interior defects in battery cells is a acknowledged situation,” claimed Hill. Even so, complications with the engineering have not been perfectly communicated amongst, say, the personal electronics sector and the automotive sector or the aerospace industry and the vitality industry.

“Overall, throughout the industry there was a hole in know-how,” Bordenkircher claimed. The engineering moved forward so quickly, he claimed, that specifications and know-how sharing had not kept up.

The McMicken BESS incident also was not the initial for APS. In November 2012, a hearth ruined the Scale Energy Storage System (ESS) at an electrical substation in Flagstaff in northern Arizona. The ESS was made by Electrovaya and consisted of a container housing sixteen cupboards that contains 24 lithium-ion cells.

An investigation into that incident determined that a severely discharged cell degraded and afflicted a neighboring cell, touching off a hearth. The root induce of the 2012 incident was observed to be faulty logic utilised to handle the program.

The handle logic had been up-to-date a lot more than two dozen times for the duration of the eleven months that the BESS operated. But many skipped possibilities could have prevented the hearth that ruined the unit, the incident report claimed. It pointed in specific to an function the past May possibly in which a cell was “severely discharged” even as the logic was “continuously charging the cell from the supposed layout.” Right after the May possibly function, the logic was not transformed to address that inappropriate behavior.

An APS spokesperson claimed that lessons discovered from this 2012 incident had been incorporated into the layout and procedure of the McMicken BESS.

In its 162-web site rebuttal [PDF] of the McMicken incident LG Chem refuted the utility’s obtaining of fault with its battery.

The battery provider claimed that dependent on offered proof, “metallic lithium plating did not induce an interior cell failure top to the original thermal runaway event” at the McMicken BESS facility. In its place, cell thermal runaway started through powerful heating of the afflicted cells brought on by an external heat supply, such as external electrical arcing on Rack 15.

LG Chem claimed that its individual third-social gathering investigator, Exponent Inc., tested the interior 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 for the duration of the incident. It observed that the two did not match, top to the summary that the explosion’s induce was unlikely to have been “an interior brief within just a single cell.”

The battery maker also claimed that data recorded for the duration of the incident showed a discharging present of four.9A (amps) current for the duration of the voltage excursion. It claimed that even though the APS report acknowledged that the present flipped from -27.9A charging to four.9 A discharging,“it provided no rationalization for the function.” To LG Chem, having said that, the actuality that the discharging present was at four.9A, instead of zero, “means the present certainly flowed to someplace else,” supporting what it claimed was a possible double-issue electrical isolation failure and not an interior cell brief.

(Complicating the put up-incident investigation was the actuality that the hearth ruined program handle electronics within just the container. That still left dozens of battery modules energized with no way to discharge them. It took 7 weeks for the utility to figure out a prepare to remove the modules a person by a person and bleed off their stored vitality.)

The reports and their divergent conclusions sign the start of competing interpretations of offered data as the utility and its battery provider get the job done to discover a single induce for the incident.

“We really don’t want a general public argument about it,” claimed DNV GL’s Davion Hill. For him, the main issue is that “we had a cascading thermal runaway that led to an explosive atmosphere” at the APS McMicken BESS. The aim now really should be to make storage methods safer through specifications enhancement and info sharing.

Right after the incident, APS put a maintain on BESS deployment throughout its provider territory. The engineering is viewed as crucial to assembly the utility’s announced plans to deliver one hundred % “clean energy” by 2050. Two other BESS methods that had been working at the time of the April 2019 incident had been taken offline they will remain idle until eventually retrofits can be developed and mounted.