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

A small soon after eight:00 p.m. on April 19, 2019, a captain with the Peoria, Arizona, hearth department’s Hazmat device, opened the door of a container crammed with additional than ten,000 energized lithium-ion battery cells, portion of a utility-scale storage program that had been deployed two a long time previously by the nearby utility, Arizona Community Service.

Before that evening, at around five:41 p.m., dispatchers had been given a phone alerting them to smoke and a “bad smell” in the spot around the McMicken Battery Power Storage System (BESS) site in suburban Phoenix.

Sirens blaring, three hearth engines arrived at the scene within just ten minutes. Shortly soon after their arrival, 1st responders understood that energized batteries were being associated and elevated the phone to a Hazmat response. After consulting with utility personnel and determining on a system of motion, a hearth captain and three firefighters approached the container door soon right before eight:00 p.m., planning to open up it. The captain, determined in a later investigation as “Captain E193,” opened the door and stepped inside. The other three stood close by.

The BESS was housed in a container organized to keep 36 vertical racks divided into two rows on either facet of a three-ft-vast hallway. 20-seven racks held 14 battery modules made by LG Chem, an 80 kW inverter made by Parker, an AES Advancion node controller utilized for information collection and communication, and a Battery Defense Unit (BPU) made by LG Chem.

The battery modules in change contained 28 lithium-ion battery cells of Nickel Manganese Cobalt (NMC) chemistry. These modules were being linked in series, furnishing a per-rack nominal voltage of 721 V. The total program had a nameplate potential to supply two MW of energy around one hour for a lifetime energy rating of two MWh. With 27 whole racks, there were being ten,584 cells in the container. After a whole working day of charging, the batteries were being around ninety {fb741301fcc9e6a089210a2d6dd4da375f6d1577f4d7524c5633222b81dec1ca} of potential.

With the door to the BESS container open up and Captain E193 at its threshold, combustible gases that had built up inside since the incident commenced quite a few hrs right before been given a breath of oxygen and located an ignition resource.

The gases erupted in what was described as a “deflagration occasion.” Firefighters just exterior of the incident scorching zone mentioned they listened to a loud sounds and observed 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 were being thrown towards and less than a chain-hyperlink fence bordering the facility. The captain landed additional than 70 toes from the open up door the firefighter landed thirty ft away.

The captain’s accidents included a traumatic mind injury, an eye injury, backbone damage, broken ribs, a broken scapula, thermal and chemical burns, inside bleeding, two broken ankles, and a broken foot.

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

The timeline and series of activities is not typically disputed. Having said that, a dispute has erupted in recent weeks around what just transpired inside the BESS container at around 4:54 p.m. that initiated a thermal runaway that cascaded across several battery cells.

In a report unveiled in late July, the utility and its 3rd-party investigator, DNV-GL, mentioned that their critique of the evidence pointed to the failure of a solitary lithium-ion mobile as triggering the activities.

In a different, preliminary report filed times later with state officials, LG Chem, which equipped the li-ion batteries, challenged that finding. The South Korea-based mostly battery provider mentioned the APS report missed a selection of particulars about the incident. Those particulars, LG Chem informed regulators, indicated that the mobile thermal runaway commenced thanks to “intense heating” brought about by a warmth resource “such as exterior electrical arcing” on one of the battery racks.

Scott Bordenkircher, who served as APS’ Director of Technologies Innovation & Integration at the time of the incident, mentioned in an job interview that the utility accepts the conclusions of its 3rd-party incident investigation, which was completed by Davion Hill, Ph.D., the U.S. Power Storage Chief for DNV GL. “We have self-assurance in our 3rd-party investigator,” Bordenkircher mentioned.

In its seventy eight-web page report [PDF], DNV GL mentioned that what was 1st believed to be a hearth was in simple fact an extensive cascading thermal runaway occasion within just the BESS. That occasion was initiated by an inside mobile failure within just one battery mobile, determined as mobile seven-two on Rack fifteen. The failure was brought about by “abnormal lithium metallic deposition and dendritic growth” within just the mobile, the report mentioned.

Once the failure happened, thermal runaway cascaded from mobile seven-two by means of each other mobile and module in Rack fifteen by means of warmth transfer. The runaway was aided by the “absence of enough thermal barrier protections” involving battery cells, which normally could possibly have stopped or slowed the thermal runaway.

As the occasion progressed, a huge sum of flammable gas was created within just the BESS. Lacking air flow to the exterior, the gases created a flammable atmosphere within just the container. All around three hrs soon after thermal runaway commenced, when firefighters opened the BESS door, flammable gases made make contact with with a warmth resource or spark and exploded.

It was a “tragic incident,” Bordenkircher mentioned.

It also was not the 1st time that a lithium-ion battery had unsuccessful.

The APS report detailed activities reaching back again to 2006 that associated thermal runaway activities in lithium-ion batteries. In one commonly report incident in January 2013, a Boeing 787-eight expert smoke and warmth coming from its lithium-ion battery-based mostly auxiliary energy device. It was later determined that the failure was brought about by an inside 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 point out of the business is that inside problems in battery cells is a recognized challenge,” mentioned Hill. Even so, difficulties with the know-how have not been effectively communicated involving, say, the private electronics sector and the automotive sector or the aerospace business and the energy business.

“Overall, across the business there was a hole in expertise,” Bordenkircher mentioned. The know-how moved forward so speedily, he mentioned, that standards and expertise sharing had not retained up.

The McMicken BESS incident also was not the 1st for APS. In November 2012, a hearth wrecked the Scale Power Storage Technique (ESS) at an electrical substation in Flagstaff in northern Arizona. The ESS was made by Electrovaya and consisted of a container housing 16 cupboards made up of 24 lithium-ion cells.

An investigation into that incident determined that a seriously discharged mobile degraded and afflicted a neighboring mobile, touching off a hearth. The root bring about of the 2012 incident was located to be defective logic utilized to command the program.

The command logic had been up to date additional than two dozen situations all through the 11 months that the BESS operated. But quite a few missed chances could have prevented the hearth that wrecked the device, the incident report mentioned. It pointed in particular to an occasion the previous May possibly in which a mobile was “severely discharged” even as the logic was “continuously charging the mobile towards the supposed style.” After the May possibly occasion, the logic was not modified to tackle that inappropriate behavior.

An APS spokesperson mentioned that classes learned from this 2012 incident were being included 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 finding of fault with its battery.

The battery provider mentioned that based mostly on obtainable evidence, “metallic lithium plating did not bring about an inside mobile failure main to the first thermal runaway event” at the McMicken BESS facility. Rather, mobile thermal runaway commenced by means of powerful heating of the afflicted cells brought about by an exterior warmth resource, these as exterior electrical arcing on Rack fifteen.

LG Chem mentioned that its personal 3rd-party investigator, Exponent Inc., examined the inside mobile failure idea. It did so by forcing a parallel mobile configuration into thermal runaway. It then when compared the ensuing voltage profile to the voltage profile recorded all through the incident. It located that the two did not match, main to the conclusion that the explosion’s bring about was not likely to have been “an inside small within just a solitary mobile.”

The battery maker also mentioned that information recorded all through the incident showed a discharging current of 4.9A (amps) current all through the voltage excursion. It mentioned that although the APS report acknowledged that the current flipped from -27.9A charging to 4.9 A discharging,“it available no explanation for the occasion.” To LG Chem, having said that, the simple fact that the discharging current was at 4.9A, as a substitute of zero, “means the current in fact flowed to somewhere else,” supporting what it mentioned was a possible double-point electrical isolation failure and not an inside mobile small.

(Complicating the post-incident investigation was the simple fact that the hearth wrecked program command electronics within just 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 system to get rid of the modules one by one and bleed off their stored energy.)

The reports and their divergent conclusions sign the start out of competing interpretations of obtainable information as the utility and its battery provider function to obtain a solitary bring about for the incident.

“We really do not want a general public argument about it,” mentioned DNV GL’s Davion Hill. For him, the main point is that “we had a cascading thermal runaway that led to an explosive atmosphere” at the APS McMicken BESS. The intention now need to be to make storage methods safer by means of standards progress and data sharing.

After the incident, APS put a keep on BESS deployment across its provider territory. The know-how is witnessed as vital to meeting the utility’s introduced ambitions to make a hundred {fb741301fcc9e6a089210a2d6dd4da375f6d1577f4d7524c5633222b81dec1ca} “clean energy” by 2050. Two other BESS methods that had been functioning at the time of the April 2019 incident were being taken offline they will continue to be idle till retrofits can be intended and installed.