A little just after eight:00 p.m. on April 19, 2019, a captain with the Peoria, Arizona, fireplace department’s Hazmat device, opened the doorway of a container crammed with far more than ten,000 energized lithium-ion battery cells, element of a utility-scale storage program that had been deployed two decades previously by the neighborhood utility, Arizona Community Provider.
Earlier that night, at all around five:forty one p.m., dispatchers had acquired a connect with alerting them to smoke and a “bad smell” in the place all around the McMicken Battery Strength Storage System (BESS) website in suburban Phoenix.
Sirens blaring, 3 fireplace engines arrived at the scene in just ten minutes. Shortly just after their arrival, to start with responders realized that energized batteries ended up associated and elevated the connect with to a Hazmat reaction. Following consulting with utility staff and determining on a plan of motion, a fireplace captain and 3 firefighters approached the container doorway shortly just before eight:00 p.m., making ready to open it. The captain, determined in a afterwards investigation as “Captain E193,” opened the doorway and stepped inside of. The other 3 stood nearby.
The BESS was housed in a container organized to maintain 36 vertical racks separated into two rows on either side of a three-ft-wide hallway. 20-seven racks held fourteen battery modules manufactured by LG Chem, an eighty kW inverter manufactured by Parker, an AES Advancion node controller used for information selection and conversation, and a Battery Protection Unit (BPU) manufactured 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, furnishing a for each-rack nominal voltage of 721 V. The whole program had a nameplate capability to supply 2 MW of ability in excess of a single hour for a life span strength rating of 2 MWh. With 27 comprehensive racks, there ended up ten,584 cells in the container. Following a comprehensive day of charging, the batteries ended up all around ninety % of capability.
With the doorway to the BESS container open and Captain E193 at its threshold, combustible gases that had developed up inside of considering the fact that the incident started quite a few hrs just before acquired a breath of oxygen and identified an ignition source.
The gases erupted in what was described as a “deflagration party.” Firefighters just outside of the incident scorching zone mentioned they listened to 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-url fence encompassing the facility. The captain landed far more than 70 toes from the open doorway the firefighter landed thirty ft away.
The captain’s accidents involved a traumatic brain injuries, an eye injuries, spine injury, damaged ribs, a damaged scapula, thermal and chemical burns, inner bleeding, two damaged ankles, and a damaged foot.
The firefighter endured a traumatic brain injuries, a collapsed lung, damaged ribs, a damaged leg, a separated shoulder, laceration of the liver, thermal and chemical burns, a lacking tooth, and facial lacerations.
The timeline and series of functions is not typically disputed. Even so, a dispute has erupted in modern months in excess of what accurately transpired inside of the BESS container at all around four:fifty four p.m. that initiated a thermal runaway that cascaded across several battery cells.
In a report produced in late July, the utility and its third-get together investigator, DNV-GL, mentioned that their assessment of the proof pointed to the failure of a single lithium-ion mobile as triggering the functions.
In a independent, preliminary report submitted days afterwards with state officers, LG Chem, which supplied the li-ion batteries, challenged that locating. The South Korea-based mostly battery supplier mentioned the APS report skipped a quantity of information about the accident. All those information, LG Chem instructed regulators, indicated that the mobile thermal runaway started because of to “intense heating” caused by a heat source “such as exterior electrical arcing” on a single of the battery racks.
Scott Bordenkircher, who served as APS’ Director of Engineering Innovation & Integration at the time of the accident, mentioned in an job interview that the utility accepts the conclusions of its third-get together accident investigation, which was concluded by Davion Hill, Ph.D., the U.S. Strength Storage Leader for DNV GL. “We have self-confidence in our third-get together investigator,” Bordenkircher mentioned.
In its seventy eight-webpage report [PDF], DNV GL mentioned that what was to start with thought to be a fireplace was in simple fact an in depth cascading thermal runaway party in just the BESS. That party was initiated by an inner mobile failure in just a single battery mobile, determined as mobile 7-2 on Rack 15. The failure was caused by “abnormal lithium metal deposition and dendritic growth” in just the mobile, the report mentioned.
Once the failure transpired, thermal runaway cascaded from mobile 7-2 as a result of every single other mobile and module in Rack 15 via heat transfer. The runaway was aided by the “absence of adequate thermal barrier protections” concerning battery cells, which or else may possibly have stopped or slowed the thermal runaway.
As the party progressed, a large sum of flammable fuel was created in just the BESS. Lacking ventilation to the outside, the gases created a flammable environment in just the container. All over 3 hrs just after thermal runaway started, when firefighters opened the BESS doorway, flammable gases built get hold of with a heat 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 had unsuccessful.
The APS report listed functions achieving again to 2006 that associated thermal runaway functions in lithium-ion batteries. In a single commonly report incident in January 2013, a Boeing 787-eight skilled smoke and heat coming from its lithium-ion battery-based mostly auxiliary ability device. It was afterwards determined that the failure was caused by an inner mobile defect, which was exacerbated as thermal runaway cascaded as a result of all the cells in the battery pack, releasing flammable electrolyte and gases.
“The point out of the market is that inner problems in battery cells is a acknowledged issue,” mentioned Hill. Even so, troubles with the technological know-how have not been effectively communicated concerning, say, the own electronics sector and the automotive sector or the aerospace market and the strength market.
“Overall, across the market there was a hole in information,” Bordenkircher mentioned. The technological know-how moved forward so immediately, he mentioned, that specifications and information sharing had not saved up.
The McMicken BESS accident also was not the to start with for APS. In November 2012, a fireplace wrecked the Scale Strength Storage System (ESS) at an electrical substation in Flagstaff in northern Arizona. The ESS was manufactured by Electrovaya and consisted of a container housing sixteen cupboards that contains 24 lithium-ion cells.
An investigation into that accident determined that a severely discharged mobile degraded and influenced a neighboring mobile, touching off a fireplace. The root bring about of the 2012 accident was identified to be defective logic used to manage the program.
The manage logic had been current far more than two dozen instances through the eleven months that the BESS operated. But quite a few skipped options could have prevented the fireplace that wrecked the device, the accident report mentioned. It pointed in distinct to an party the prior Could in which a mobile was “severely discharged” even as the logic was “continuously charging the mobile against the supposed style and design.” Following the Could party, the logic was not changed to deal with that poor behavior.
An APS spokesperson mentioned that lessons acquired from this 2012 incident ended up integrated into the style and design and procedure 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 mostly on offered proof, “metallic lithium plating did not bring about an inner mobile failure foremost to the preliminary thermal runaway event” at the McMicken BESS facility. As an alternative, mobile thermal runaway started as a result of powerful heating of the influenced cells caused by an exterior heat source, such as exterior electrical arcing on Rack 15.
LG Chem mentioned that its possess third-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 as opposed the resulting voltage profile to the voltage profile recorded through the incident. It identified that the two did not match, foremost to the summary that the explosion’s bring about was not likely to have been “an inner shorter in just a single mobile.”
The battery maker also mentioned that information recorded through the incident confirmed a discharging recent of four.9A (amps) present through the voltage tour. It mentioned that whilst the APS report acknowledged that the recent flipped from -27.9A charging to four.nine A discharging,“it offered no clarification for the party.” To LG Chem, however, the simple fact that the discharging recent was at four.9A, rather of zero, “means the recent in fact flowed to somewhere else,” supporting what it mentioned was a likely double-stage electrical isolation failure and not an inner mobile shorter.
(Complicating the submit-accident investigation was the simple fact that the fireplace wrecked program manage electronics in just the container. That left dozens of battery modules energized with no way to discharge them. It took seven months for the utility to determine out a plan to get rid of the modules a single by a single and bleed off their stored strength.)
The reviews and their divergent conclusions signal the get started of competing interpretations of offered information as the utility and its battery supplier perform to discover a single bring about for the accident.
“We really don’t want a general public argument about it,” mentioned 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 purpose now should be to make storage units safer as a result of specifications progress and data sharing.
Following the accident, APS put a maintain on BESS deployment across its company territory. The technological know-how is seen as vital to assembly the utility’s announced aims to generate a hundred % “clean energy” by 2050. Two other BESS units that had been operating at the time of the April 2019 accident ended up taken offline they will continue being idle until retrofits can be created and mounted.