Arizona ESS Explosion Investigation and Line of Duty Injury Reports Now Available
Two reports from the Surprise, Arizona Energy Storage System (ESS) explosion that occurred in April, 2019 were published this week. One report, titled, “Four Firefighters Injured In Lithium-Ion Battery Energy Storage System Explosion – Arizona” is written by the UL Firefighter Safety Research Institute and is part of a Study of Firefighter Line of Duty Injuries and Near 
The Incident
On April 19th, 2019 an explosion occurred at the McMicken Battery ESS in Surprise, Arizona injuring four firefighters. The battery ESS was placed into service in 2017, which is prior to the publication of NFPA 855. The system was comprised of 10,584 Lithium Nickel Manganese Cobalt (NMC) battery cells organized in modules and racks within an ESS specific walk-in enclosure. The system included a total flooding clean agent fire suppression system, a very early smoke detection apparatus, and an HVAC system. The entire system could supply 2MW over one hour (2MWh) and was used to supplement solar panels at the time of the incident.
While there was some information about the incident already known, these reports provide a great level of detail, insight and recommended paths forward.
Technical Analysis Report
The DNVGL report documents a thorough investigation that was conducted on the incident. It gives a lot of relevant background on the technology, the layout, and associated hazards. After building a foundation of knowledge about how batteries fail, the report analyses the factors that contributed to the failure and how we can prevent this from happening in the future. Some of the major conclusions reached in the report are as follows:
- The cause of the incident was most likely an internal failure in a single battery cell which was caused by a defect in the cell.
- The clean agent fire suppression system that was installed was not designed to prevent or stop thermal runaway.
- The absence of barriers allowed thermal runaway to propagate from cell to cell.
- Flammable off-gases concentrated to create a flammable atmosphere and did not have a means to ventilate.
- The emergency response plan did not address extinguishing, ventilation, or entry procedures.
Some of these items are addressed by NFPA 855, Standard for the Installation of Stationary Energy Storage Systems while others are included in the section of the report, “ Shortcomings that should be addressed in NFPA 855.” NFPA codes and standards are living documents that are constantly looking for ways to improve and keep up with new technology. Recommended improvements are always welcome in the form of Public Inputs or Public Comments.
First Responder Report
This UL report gives an overview of the fire department and the incident. When addressing the responding fire departments, the document talks about their training, experience, equipment, and personnel. Regarding the Arizona incident, the report covers the building construction, the energy storage system, and responder PPE, and it walks through the timeline as well as provides a detailed incident narrative. This report does a great job addressing some of the contributing factors that led to the incident and firefighter injuries. Some of those factors include:
- HAZMAT training curricula does not cover basic ESS hazards.
- There was no way to monitor the conditions of the ESS container from a safe location.
- The emergency response plan didn't address mitigating ESS hazards and the plan was not provided to the responding personnel before the incident.
- Deflagration venting and explosion prevention systems were not provided in the ESS unit.
The issue of training first responders on the basics of ESS hazards can be addressed through an updated NFPA online training course, Energy Storage and Solar Systems Safety Online Training for Fire Service Personnel.
It is encouraging to see that such a collaborative approach was taken in response to this incident to determine what happened and what could be done to prevent this type of equipment failure in the future. In the field of ESS, one of the major needs of the industry is better information like this or other publicly available test data to help guide our codes and standards. A number of related reports, articles, relevant standards, and other content can all be found on NFPA's ESS webpage www.nfpa.org/ESS.
Let us know what your thoughts are on these reports or if you've had any recent experience with ESS installations by commenting below.
