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

A very little immediately after eight:00 p.m. on April 19, 2019, a captain with the Peoria, Arizona, fire department’s Hazmat device, opened the doorway of a container filled with a lot more than 10,000 energized lithium-ion battery cells, aspect of a utility-scale storage system that experienced been deployed two years previously by the local utility, Arizona Community Assistance.

Previously that night, at about five:forty one p.m., dispatchers experienced obtained a connect with alerting them to smoke and a “bad smell” in the location about the McMicken Battery Electricity Storage System (BESS) internet site in suburban Phoenix.

Sirens blaring, 3 fire engines arrived at the scene inside 10 minutes. Soon immediately after their arrival, to start with responders realized that energized batteries had been associated and elevated the connect with to a Hazmat response. Soon after consulting with utility personnel and selecting on a program of action, a fire captain and 3 firefighters approached the container doorway shortly right before eight:00 p.m., getting ready to open it. The captain, discovered in a later investigation as “Captain E193,” opened the doorway and stepped inside. The other 3 stood close by.

The BESS was housed in a container arranged to maintain 36 vertical racks divided into two rows on either aspect of a three-ft-large hallway. 20-7 racks held 14 battery modules created by LG Chem, an 80 kW inverter created by Parker, an AES Advancion node controller used for info selection and interaction, and a Battery Defense Device (BPU) created by LG Chem.

The battery modules in transform contained 28 lithium-ion battery cells of Nickel Manganese Cobalt (NMC) chemistry. These modules had been connected in series, offering a per-rack nominal voltage of 721 V. The overall system experienced a nameplate capability to supply two MW of electricity in excess of one particular hour for a lifetime strength score of two MWh. With 27 whole racks, there had been 10,584 cells in the container. Soon after a whole day of charging, the batteries had been about 90 p.c of capability.

With the doorway to the BESS container open and Captain E193 at its threshold, combustible gases that experienced created up inside due to the fact the incident started a number of hours right before obtained a breath of oxygen and found an ignition source.

The gases erupted in what was described as a “deflagration occasion.” Firefighters just outside of the incident incredibly hot zone mentioned they read a loud noise and noticed a “jet of flame” increase some 75 ft out and 20 ft up from the doorway.

In the explosion, Captain E193 and firefighter E193 had been thrown against and less than a chain-website link fence bordering the facility. The captain landed a lot more than 70 ft from the open doorway the firefighter landed thirty ft away.

The captain’s injuries involved a traumatic brain damage, an eye damage, backbone harm, damaged ribs, a damaged scapula, thermal and chemical burns, inner bleeding, two damaged ankles, and a damaged foot.

The firefighter suffered a traumatic brain 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 series of situations is not usually disputed. On the other hand, a dispute has erupted in new weeks in excess of what specifically happened inside the BESS container at about four:fifty four 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-celebration investigator, DNV-GL, mentioned that their evaluate of the evidence pointed to the failure of a one lithium-ion mobile as triggering the situations.

In a different, preliminary report submitted times later with state officers, LG Chem, which equipped the li-ion batteries, challenged that locating. The South Korea-based battery supplier mentioned the APS report skipped a amount of information about the accident. Those information, LG Chem explained to regulators, indicated that the mobile thermal runaway started due to “intense heating” induced by a warmth source “such as external electrical arcing” on one particular of the battery racks.

Scott Bordenkircher, who served as APS’ Director of Technologies Innovation & Integration at the time of the accident, mentioned in an interview that the utility accepts the results of its third-celebration accident investigation, which was completed by Davion Hill, Ph.D., the U.S. Electricity Storage Chief for DNV GL. “We have self esteem in our third-celebration investigator,” Bordenkircher mentioned.

In its 78-webpage report [PDF], DNV GL mentioned that what was to start with believed to be a fire was in actuality an considerable cascading thermal runaway occasion inside the BESS. That occasion was initiated by an inner mobile failure inside one particular battery mobile, discovered as mobile 7-two on Rack 15. The failure was induced by “abnormal lithium steel deposition and dendritic growth” inside the mobile, the report mentioned.

At the time the failure happened, thermal runaway cascaded from mobile 7-two by means of every single other mobile and module in Rack 15 through warmth transfer. The runaway was aided by the “absence of ample thermal barrier protections” involving battery cells, which in any other case may well have stopped or slowed the thermal runaway.

As the occasion progressed, a substantial volume of flammable gasoline was generated inside the BESS. Lacking ventilation to the outside, the gases produced a flammable ambiance inside the container. About 3 hours immediately after thermal runaway started, when firefighters opened the BESS doorway, flammable gases created get hold of with a warmth source or spark and exploded.

It was a “tragic incident,” Bordenkircher mentioned.

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

The APS report mentioned situations reaching back again to 2006 that associated thermal runaway situations in lithium-ion batteries. In one particular extensively report incident in January 2013, a Boeing 787-eight knowledgeable smoke and warmth coming from its lithium-ion battery-based auxiliary electricity device. It was later identified that the failure was induced by an inner mobile 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 business is that inner flaws in battery cells is a recognized concern,” mentioned Hill. Even so, problems with the technology have not been well communicated involving, say, the particular electronics sector and the automotive sector or the aerospace business and the strength business.

“Overall, throughout the business there was a gap in information,” Bordenkircher mentioned. The technology moved forward so promptly, he mentioned, that requirements and information sharing experienced not saved up.

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

An investigation into that accident identified that a seriously discharged mobile degraded and affected a neighboring mobile, touching off a fire. The root bring about of the 2012 accident was found to be faulty logic used to management the system.

The management logic experienced been up-to-date a lot more than two dozen moments through the eleven months that the BESS operated. But a number of skipped alternatives could have prevented the fire that destroyed the device, the accident report mentioned. It pointed in specific to an occasion the earlier Could in which a mobile was “severely discharged” even as the logic was “continuously charging the mobile against the intended structure.” Soon after the Could occasion, the logic was not altered to address that poor conduct.

An APS spokesperson mentioned that lessons uncovered from this 2012 incident had been included into the structure and operation of the McMicken BESS.

In its 162-webpage rebuttal [PDF] of the McMicken accident LG Chem refuted the utility’s locating of fault with its battery.

The battery supplier mentioned that based on out there evidence, “metallic lithium plating did not bring about an inner mobile failure main to the original thermal runaway event” at the McMicken BESS facility. In its place, mobile thermal runaway started by means of rigorous heating of the affected cells induced by an external warmth source, these types of as external electrical arcing on Rack 15.

LG Chem mentioned that its have third-celebration investigator, Exponent Inc., examined the inner mobile failure concept. It did so by forcing a parallel mobile configuration into thermal runaway. It then as opposed the ensuing voltage profile to the voltage profile recorded through the incident. It found that the two did not match, main to the summary that the explosion’s bring about was not likely to have been “an inner brief inside a one mobile.”

The battery maker also mentioned that info recorded through the incident confirmed a discharging existing of four.9A (amps) existing through the voltage excursion. It mentioned that despite the fact that the APS report acknowledged that the existing flipped from -27.9A charging to four.9 A discharging,“it supplied no explanation for the occasion.” To LG Chem, however, the actuality that the discharging existing was at four.9A, instead of zero, “means the existing in fact flowed to somewhere else,” supporting what it mentioned was a probably double-position electrical isolation failure and not an inner mobile brief.

(Complicating the write-up-accident investigation was the actuality that the fire destroyed system management electronics inside the container. That still left dozens of battery modules energized with no way to discharge them. It took 7 weeks for the utility to determine out a program to clear away the modules one particular by one particular and bleed off their stored strength.)

The experiences and their divergent conclusions signal the start out of competing interpretations of out there info as the utility and its battery supplier operate to uncover a one bring about for the accident.

“We really don’t want a public argument about it,” mentioned DNV GL’s Davion Hill. For him, the major position is that “we experienced a cascading thermal runaway that led to an explosive atmosphere” at the APS McMicken BESS. The purpose now must be to make storage techniques safer by means of requirements growth and information and facts sharing.

Soon after the accident, APS positioned a maintain on BESS deployment throughout its services territory. The technology is viewed as crucial to meeting the utility’s declared ambitions to develop a hundred p.c “clean energy” by 2050. Two other BESS techniques that experienced been operating at the time of the April 2019 accident had been taken offline they will keep on being idle until eventually retrofits can be created and set up.

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