New details have come out surrounding the Arizona Public Service (APS) battery failure and corresponding explosion that left eight firefighters and one police officer hospitalized in Surprise, Arizona in April of 2019.
All of the new details regarding the incident are put forth in two reports, one released by APS, the other by the Underwriters Laboratory Firefighter Safety Research Institute.
According to the APS report, developed by DNV GL Energy Insights, “The suspected fire was actually an extensive cascading thermal runaway event, initiated by an internal cell failure within one battery cell in the BESS: cell pair 7, module 2, rack 15.” The cascading thermal runaway is believed to have been caused by an internal cell defect, specifically abnormal Lithium metal deposition and dendritic growth within the cell.
And while the system’s clean agent fire suppression system began operating to contain the event, the system is designed to extinguish developing fires in ordinary combustibles, rendering it entirely ineffective against cascading thermal runaway. From there, the event spread through every cell and module in rack 15 of the system, via heat transfer, as the system did not have adequate thermal barrier protections between battery cells. These thermal barriers could have significantly deterred the spread.
This expansive thermal runaway led to the production of a large quantity of gases, which created a flammable atmosphere within the system. Three hours after the event began, firefighters opened the system’s door, agitating the gasses and allowing them to make contact with a heat source or spark, triggering the explosion.
In short, the two reports find five root causes of the explosion:
- Internal failure in a battery cell initiated thermal runaway
- The fire suppression system was incapable of stopping thermal runaway
- Lack of thermal barriers between cells led to cascading thermal runaway
- Flammable off-gases concentrated without a means to ventilate
- Emergency response plan did not have an extinguishing, ventilation, and entry procedure
According to APS, existing battery storage system safety standards and procedures only acknowledge cascading thermal runaway as a risk. These standards do little to prohibit thermal runaway, and fail entirely to address the risk of non-flaming heat transfer to neighboring cells, modules and racking. According to the utility, those same standards focus on the means to manage a fire, but provide no solutions to restrict or slow cell-to-cell and module-to-module thermal runaway.
And while the Firefighter Safety Research Institute report came to the same conclusions regarding what led to the event, it also outlines steps that can be taken in order to mitigate the likelihood of a failure to this degree in the future.
- Basic Firefighter, Officer, and HAZMAT training should emphasize ESS safety
- Research and full-scale testing should be conducted to understand the most effective and safest tactics for response to lithium-ion battery incidents
- Fire service personnel should define a conservative potential blast radius and remain outside of it while treating the event, until definitive tactics and guidance can be established
- Lithium-ion battery systems should incorporate gas monitoring that can be accessed remotely
- Additional plans for increased monitoring, safety standard development and communication between the battery system, operators and first responders
While these standards will take some time to develop, there is a pressing need for them sooner rather than later. APS has plans in place to install at least 850 MW of nearly-identical batteries across Arizona in the near future, not to mention that the United States is on track install as much as 2,500 MW of battery storage by 2023, according to data from the U.S. Department of Energy’s Energy Information Administration.
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Lead Acid batteries do not do this and cost less. There are other battery chemistries that also do not burn or have runaway thermal problems. For stationary power storage, why use light weight lithium when weight is not a problem as in vehicles? Now, do you want one of these mounted to the side of your home? Lithium batteries need to be mounted 10 feet from the home in a steel rain tight enclosure with fan forced venting to stop build up of gasses just like lead acid batteries are required to have when enclosed in a confined space. .
All the information in the report appears to be a no-brainer. Why in the world haven’t the battery designers learned these things already? I’ve seen this ‘crisis management’ vs. ‘responsible planning’ play out in my industry over & over throughout my career and I’ve seen it play out in many industries. Maybe the engineers did try to design it correctly but maybe this was a another case of engineers vs. bean counters. There’s way too much of that going on everywhere. A great example is the Challenger SRB o-ring disaster. The engineers knew exactly what would eventually happen but management and bean counters and politicians got their way instead.
This is very similar to what occurred with “Sparky,” The Boeing 787 that caught on fire due to lithium batteries being employed for that aircraft. There are some wonderful NASA videos that depict the failures of lithium batteries that were tested for the international space station.
So what causes these batteries to fail? Some of the most common failure modes occur during manufacturing. Just a small speck of copper, that is introduced during the manufacturing process, can introduce a micro fault. It’s this micro fault that eventually causes a short circuit in the battery. Other causes of microfaults include dropping the battery during installation Which results in a small crack in the battery which results in a micro fault and a short circuit. which results in a small crack in the battery which results in a micro fault and a short circuit. So why doesn’t the battery management system shut this particular cell down?
Each small cell in the big battery needs to be monitored by a battery management system that manages each cell for correct voltage, correct temperature, and or outgassing of hydrogen gas when the battery becomes overheated. In addition, for fire protection, the power should be turned off to that cell as soon as anyone of those conditions becomes apparent. Ever notice how there are millions of teslas on the road but very very few catch fire because of a battery malfunction. Usually if a Tesla catches on fire, it’s because some type of road hazard penetrated the battery in the base of the vehicle. Now I have heard that Tesla considered this a significant issue along time ago. To put this in perspective if Tesla’s were catching on fire as often as computer batteries it was thought that no one would buy them. So Tesla had to come up with a solution that would render this possibility extremely remote. Their solution was to keep the batteries in a solution or a fluid to prevent them from catching on fire. Now back to Sparky. Boeing 787 had a problem, their battery management system was not working as hoped. They had to come up a solution or nobody would buy their jets. Can you imagine the battery run away in flight say over the north pole where you’ve got four more hours to go before you could land someplace. So Boeing chose the Chernobyl option. They decided to build a sarcophagus around their battery. I guess they thought that weight was an issue and didn’t want to add a fluid to the batteries that were already fairly heavy. If you can find the NASA videos they talk about all the failure modes that can occur with certain chemistries that use lithium for batteries. Not all lithium batteries are as dangerous That’s because the chemistry in lithium batteries varies with the manufactures.. But that’s enough for now.