A little immediately after 8:00 p.m. on April 19, 2019, a captain with the Peoria, Arizona, fireplace department’s Hazmat unit, opened the doorway of a container loaded with extra than ten,000 energized lithium-ion battery cells, part of a utility-scale storage procedure that experienced been deployed two yrs before by the area utility, Arizona Public Support.

Previously that night, at all-around five:forty one p.m., dispatchers experienced obtained a call alerting them to smoke and a “bad smell” in the spot all-around the McMicken Battery Energy Storage System (BESS) web-site in suburban Phoenix.

Sirens blaring, a few fireplace engines arrived at the scene inside ten minutes. Soon immediately after their arrival, 1st responders recognized that energized batteries ended up associated and elevated the call to a Hazmat response. Right after consulting with utility staff and deciding on a system of action, a fireplace captain and a few firefighters approached the container doorway soon before 8:00 p.m., making ready to open it. The captain, recognized in a afterwards investigation as “Captain E193,” opened the doorway and stepped inside. The other a few stood nearby.

The BESS was housed in a container arranged to maintain 36 vertical racks separated into two rows on both aspect of a three-ft-broad hallway. 20-seven racks held fourteen battery modules produced by LG Chem, an 80 kW inverter produced by Parker, an AES Advancion node controller employed for facts selection and communication, and a Battery Security Unit (BPU) produced by LG Chem.

The battery modules in change contained 28 lithium-ion battery cells of Nickel Manganese Cobalt (NMC) chemistry. These modules ended up related in sequence, supplying a per-rack nominal voltage of 721 V. The complete procedure experienced a nameplate ability to offer two MW of electric power around one particular hour for a life time strength score of two MWh. With 27 whole racks, there ended up ten,584 cells in the container. Right after a whole day of charging, the batteries ended up all-around ninety % of ability.

With the doorway to the BESS container open and Captain E193 at its threshold, combustible gases that experienced developed up inside due to the fact the incident commenced various hours before obtained a breath of oxygen and identified an ignition supply.

The gases erupted in what was described as a “deflagration occasion.” Firefighters just outdoors of the incident incredibly hot zone reported they heard a loud noise and observed 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 ended up thrown from and under a chain-url fence encompassing the facility. The captain landed extra than 70 ft from the open doorway the firefighter landed 30 ft absent.

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

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

The timeline and sequence of functions is not commonly disputed. However, a dispute has erupted in latest weeks around what just transpired inside the BESS container at all-around 4:54 p.m. that initiated a thermal runaway that cascaded across a number of battery cells.

In a report unveiled in late July, the utility and its 3rd-get together investigator, DNV-GL, reported that their critique of the proof pointed to the failure of a solitary lithium-ion mobile as triggering the functions.

In a separate, preliminary report submitted times afterwards with state officers, LG Chem, which provided the li-ion batteries, challenged that obtaining. The South Korea-primarily based battery supplier reported the APS report missed a quantity of details about the incident. People details, LG Chem instructed regulators, indicated that the mobile thermal runaway commenced because of to “intense heating” induced by a heat supply “such as exterior electrical arcing” on one particular of the battery racks.

Scott Bordenkircher, who served as APS’ Director of Know-how Innovation & Integration at the time of the incident, reported in an interview that the utility accepts the results of its 3rd-get together incident investigation, which was completed by Davion Hill, Ph.D., the U.S. Energy Storage Chief for DNV GL. “We have self esteem in our 3rd-get together investigator,” Bordenkircher reported.

In its seventy eight-webpage report [PDF], DNV GL reported that what was 1st thought to be a fireplace was in reality an in depth cascading thermal runaway occasion inside the BESS. That occasion was initiated by an inner mobile failure inside one particular battery mobile, recognized as mobile 7-two on Rack 15. The failure was induced by “abnormal lithium steel deposition and dendritic growth” inside the mobile, the report reported.

After the failure happened, thermal runaway cascaded from mobile 7-two by means of every single other mobile and module in Rack 15 through heat transfer. The runaway was aided by the “absence of sufficient thermal barrier protections” amongst battery cells, which otherwise could have stopped or slowed the thermal runaway.

As the occasion progressed, a large sum of flammable gas was made inside the BESS. Lacking ventilation to the outdoors, the gases designed a flammable environment inside the container. Close to a few hours immediately after thermal runaway commenced, when firefighters opened the BESS doorway, flammable gases made contact with a heat supply or spark and exploded.

It was a “tragic incident,” Bordenkircher reported.

It also was not the 1st time that a lithium-ion battery experienced failed.

The APS report outlined functions achieving back to 2006 that associated thermal runaway functions in lithium-ion batteries. In one particular extensively report incident in January 2013, a Boeing 787-8 skilled smoke and heat coming from its lithium-ion battery-primarily based auxiliary electric power unit. It was afterwards established 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 market is that inner problems in battery cells is a identified situation,” reported Hill. Even so, challenges with the engineering have not been very well communicated amongst, say, the private electronics sector and the automotive sector or the aerospace market and the strength market.

“Overall, across the market there was a gap in know-how,” Bordenkircher reported. The engineering moved forward so immediately, he reported, that expectations and know-how sharing experienced not retained up.

The McMicken BESS incident also was not the 1st for APS. In November 2012, a fireplace ruined the Scale Energy Storage Program (ESS) at an electrical substation in Flagstaff in northern Arizona. The ESS was produced by Electrovaya and consisted of a container housing sixteen cabinets that contains 24 lithium-ion cells.

An investigation into that incident established that a seriously discharged mobile degraded and influenced a neighboring mobile, touching off a fireplace. The root result in of the 2012 incident was identified to be faulty logic employed to regulate the procedure.

The regulate logic experienced been up to date extra than two dozen instances all through the eleven months that the BESS operated. But various missed alternatives could have prevented the fireplace that ruined the unit, the incident report reported. It pointed in particular to an occasion the former Might in which a mobile was “severely discharged” even as the logic was “continuously charging the mobile from the supposed structure.” Right after the Might occasion, the logic was not improved to deal with that poor actions.

An APS spokesperson reported that classes discovered from this 2012 incident ended up incorporated into the structure and procedure of the McMicken BESS.

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

The battery supplier reported that primarily based on readily available proof, “metallic lithium plating did not result in an inner mobile failure leading to the original thermal runaway event” at the McMicken BESS facility. As a substitute, mobile thermal runaway commenced by means of powerful heating of the influenced cells induced by an exterior heat supply, these as exterior electrical arcing on Rack 15.

LG Chem reported that its own 3rd-get together investigator, Exponent Inc., tested the inner mobile failure concept. It did so by forcing a parallel mobile configuration into thermal runaway. It then compared the ensuing voltage profile to the voltage profile recorded all through the incident. It identified that the two did not match, leading to the conclusion that the explosion’s result in was not likely to have been “an inner quick inside a solitary mobile.”

The battery maker also reported that facts recorded all through the incident confirmed a discharging present of 4.9A (amps) current all through the voltage excursion. It reported that even though the APS report acknowledged that the present flipped from -27.9A charging to 4.nine A discharging,“it presented no clarification for the occasion.” To LG Chem, on the other hand, the reality that the discharging present was at 4.9A, as an alternative of zero, “means the present certainly flowed to someplace else,” supporting what it reported was a probably double-stage electrical isolation failure and not an inner mobile quick.

(Complicating the submit-incident investigation was the reality that the fireplace ruined procedure regulate electronics inside the container. That left dozens of battery modules energized with no way to discharge them. It took seven weeks for the utility to figure out a system to take away the modules one particular by one particular and bleed off their saved strength.)

The studies and their divergent conclusions signal the begin of competing interpretations of readily available facts as the utility and its battery supplier operate to come across a solitary result in for the incident.

“We really do not want a public argument about it,” reported DNV GL’s Davion Hill. For him, the key stage is that “we experienced a cascading thermal runaway that led to an explosive atmosphere” at the APS McMicken BESS. The target now really should be to make storage units safer by means of expectations growth and info sharing.

Right after the incident, APS put a maintain on BESS deployment across its support territory. The engineering is witnessed as essential to conference the utility’s introduced targets to deliver 100 % “clean energy” by 2050. Two other BESS units that experienced been running at the time of the April 2019 incident ended up taken offline they will remain idle until retrofits can be designed and installed.