Dispute Erupts Over What Sparked an Explosive Li-ion Energy Storage Accident

A small right 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 far more than 10,000 energized lithium-ion battery cells, portion of a utility-scale storage procedure that had been deployed two many years earlier by the nearby utility, Arizona General public Support.

Previously that evening, at close to five:41 p.m., dispatchers had been given a connect with alerting them to smoke and a “bad smell” in the place close to the McMicken Battery Vitality Storage System (BESS) internet site in suburban Phoenix.

Sirens blaring, three fire engines arrived at the scene within just 10 minutes. Soon right after their arrival, to start with responders recognized that energized batteries ended up involved and elevated the connect with to a Hazmat response. Soon after consulting with utility personnel and deciding on a system of motion, a fire captain and three firefighters approached the container doorway shortly just before 8:00 p.m., getting ready to open it. The captain, discovered in a afterwards investigation as “Captain E193,” opened the doorway and stepped within. The other three stood close by.

The BESS was housed in a container organized to keep 36 vertical racks divided into two rows on possibly aspect of a three-ft-huge hallway. Twenty-7 racks held 14 battery modules created by LG Chem, an eighty kW inverter created by Parker, an AES Advancion node controller applied for information selection and conversation, and a Battery Protection Device (BPU) created by LG Chem.

The battery modules in flip contained 28 lithium-ion battery cells of Nickel Manganese Cobalt (NMC) chemistry. These modules ended up linked in series, offering a for each-rack nominal voltage of 721 V. The complete procedure had a nameplate capacity to supply two MW of power above one hour for a life span power ranking of two MWh. With 27 comprehensive racks, there ended up 10,584 cells in the container. Soon after a comprehensive day of charging, the batteries ended up close to ninety percent of capacity.

With the doorway to the BESS container open and Captain E193 at its threshold, combustible gases that had constructed up within considering the fact that the incident began a number of several hours just before been given a breath of oxygen and uncovered an ignition resource.

The gases erupted in what was described as a “deflagration occasion.” Firefighters just outdoors of the incident warm zone stated they read a loud sound and saw a “jet of flame” prolong some seventy five ft out and twenty ft up from the doorway.

In the explosion, Captain E193 and firefighter E193 ended up thrown against and below a chain-link fence surrounding the facility. The captain landed far more than 70 feet from the open doorway the firefighter landed thirty ft away.

The captain’s accidents integrated a traumatic mind harm, an eye harm, spine injury, damaged ribs, a damaged scapula, thermal and chemical burns, inner bleeding, two damaged ankles, and a damaged foot.

The firefighter experienced a traumatic mind harm, 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 series of activities is not generally disputed. Nonetheless, a dispute has erupted in latest months above what exactly transpired within the BESS container at close to 4:54 p.m. that initiated a thermal runaway that cascaded throughout various battery cells.

In a report introduced in late July, the utility and its third-social gathering investigator, DNV-GL, stated that their evaluate of the evidence pointed to the failure of a single lithium-ion cell as triggering the activities.

In a independent, preliminary report submitted times afterwards with state officials, LG Chem, which equipped the li-ion batteries, challenged that getting. The South Korea-based mostly battery supplier stated the APS report missed a number of facts about the incident. People facts, LG Chem explained to regulators, indicated that the cell thermal runaway began owing to “intense heating” prompted by a warmth resource “such as external electrical arcing” on one of the battery racks.

Scott Bordenkircher, who served as APS’ Director of Technological innovation Innovation & Integration at the time of the incident, stated in an interview that the utility accepts the results of its third-social gathering incident investigation, which was concluded by Davion Hill, Ph.D., the U.S. Vitality Storage Chief for DNV GL. “We have self-confidence in our third-social gathering investigator,” Bordenkircher stated.

In its 78-web page report [PDF], DNV GL stated that what was to start with thought to be a fire was in truth an considerable cascading thermal runaway occasion within just the BESS. That occasion was initiated by an inner cell failure within just one battery cell, discovered as cell 7-two on Rack 15. The failure was prompted by “abnormal lithium metal deposition and dendritic growth” within just the cell, the report stated.

The moment the failure happened, thermal runaway cascaded from cell 7-two by means of each individual other cell and module in Rack 15 via warmth transfer. The runaway was aided by the “absence of sufficient thermal barrier protections” involving battery cells, which normally may possibly have stopped or slowed the thermal runaway.

As the occasion progressed, a significant sum of flammable fuel was made within just the BESS. Lacking air flow to the outdoors, the gases established a flammable ambiance within just the container. Around three several hours right after thermal runaway began, when firefighters opened the BESS doorway, flammable gases designed make contact with with a warmth resource or spark and exploded.

It was a “tragic incident,” Bordenkircher stated.

It also was not the to start with time that a lithium-ion battery had failed.

The APS report detailed activities achieving again to 2006 that involved thermal runaway activities in lithium-ion batteries. In one commonly report incident in January 2013, a Boeing 787-8 expert smoke and warmth coming from its lithium-ion battery-based mostly auxiliary power device. It was afterwards decided that the failure was prompted by an inner cell defect, which was exacerbated as thermal runaway cascaded by means of all the cells in the battery pack, releasing flammable electrolyte and gases.

“The condition of the industry is that inner problems in battery cells is a known issue,” stated Hill. Even so, troubles with the technologies have not been effectively communicated involving, say, the personal electronics sector and the automotive sector or the aerospace industry and the power industry.

“Overall, throughout the industry there was a gap in understanding,” Bordenkircher stated. The technologies moved ahead so immediately, he stated, that requirements and understanding sharing had not stored up.

The McMicken BESS incident also was not the to start with for APS. In November 2012, a fire wrecked the Scale Vitality Storage Process (ESS) at an electrical substation in Flagstaff in northern Arizona. The ESS was created by Electrovaya and consisted of a container housing sixteen cupboards made up of 24 lithium-ion cells.

An investigation into that incident decided that a seriously discharged cell degraded and influenced a neighboring cell, touching off a fire. The root result in of the 2012 incident was uncovered to be faulty logic applied to regulate the procedure.

The regulate logic had been up to date far more than two dozen instances all through the 11 months that the BESS operated. But a number of missed chances could have prevented the fire that wrecked the device, the incident report stated. It pointed in certain to an occasion the prior May well in which a cell was “severely discharged” even as the logic was “continuously charging the cell against the intended style.” Soon after the May well occasion, the logic was not altered to handle that inappropriate habits.

An APS spokesperson stated that lessons learned from this 2012 incident ended up integrated into the style and procedure of the McMicken BESS.

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

The battery supplier stated that based mostly on offered evidence, “metallic lithium plating did not result in an inner cell failure foremost to the first thermal runaway event” at the McMicken BESS facility. As a substitute, cell thermal runaway began by means of rigorous heating of the influenced cells prompted by an external warmth resource, these as external electrical arcing on Rack 15.

LG Chem stated that its possess third-social gathering investigator, Exponent Inc., examined the inner cell failure idea. It did so by forcing a parallel cell configuration into thermal runaway. It then in comparison the ensuing voltage profile to the voltage profile recorded all through the incident. It uncovered that the two did not match, foremost to the conclusion that the explosion’s result in was not likely to have been “an inner short within just a single cell.”

The battery maker also stated that information recorded all through the incident showed a discharging existing of 4.9A (amps) current all through the voltage excursion. It stated that even though the APS report acknowledged that the existing flipped from -27.9A charging to 4.9 A discharging,“it available no clarification for the occasion.” To LG Chem, nevertheless, the truth that the discharging existing was at 4.9A, instead of zero, “means the existing in fact flowed to someplace else,” supporting what it stated was a most likely double-stage electrical isolation failure and not an inner cell short.

(Complicating the article-incident investigation was the truth that the fire wrecked procedure regulate electronics within just the container. That still left dozens of battery modules energized with no way to discharge them. It took 7 months for the utility to figure out a system to take out the modules one by one and bleed off their saved power.)

The reports and their divergent conclusions signal the commence of competing interpretations of offered information as the utility and its battery supplier perform to uncover a single result in for the incident.

“We really do not want a general public argument about it,” stated DNV GL’s Davion Hill. For him, the main stage is that “we had a cascading thermal runaway that led to an explosive atmosphere” at the APS McMicken BESS. The goal now need to be to make storage units safer by means of requirements development and details sharing.

Soon after the incident, APS positioned a keep on BESS deployment throughout its provider territory. The technologies is witnessed as vital to assembly the utility’s introduced objectives to deliver 100 percent “clean energy” by 2050. Two other BESS units that had been working at the time of the April 2019 incident ended up taken offline they will keep on being idle until finally retrofits can be made and set up.

Rosa G. Rose

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