调查人员调查了2019年4月的大火，该大火摧毁了由公用事业亚利桑那公共服务公司拥有的2毫W网格连接的锂离子电池存储阵列，发现这是一场广泛的“级联热逃亡”，而不是导致该单元爆炸的大火。

当内部电池电池失败时，由于缺陷，热失控始于细胞中的锂金属沉积物和树突状晶体生长。内部火灾抑制系统按设计运行，但该系统无法防止或停止热逃亡。

根据DNV GL Energy Insights USA在APS的报告中进行的分析，“结果，热失控通过每个细胞和模块传播在每个细胞和模块中。”该公用事业公司于7月27日向州监管机构提交了报告，并将其发布给公众。

APS运营主管描述了这一事件，该事件受伤了9个第一响应者，“显然是悲惨的设备故障。”

当锂离子电池的温度超过150时，导致热失控°C and causes a reaction between the cathode and the electrolyte that releases heat that makes the reaction go faster, said George W. Crabtree, director of Argonne National Laboratory’s Joint Center for Energy Storage Research. The reaction is well known, he said.

The battery storage unit charges with solar energy during the day and discharges power into the grid at night. It is the size of a standard shipping container and had 36 vertical racks, 27 of which had 14 battery modules containing 28 lithium ion battery cells. The absence of adequate thermal barriers between cells at the Arizona battery storage unit in Surprise, Ariz., allowed the thermal runaway to move from module to module in the array, the investigators said.

报告说，热失控的不受控制的级联导致电池能量存储系统中的大量易燃气体产生。它指出，紧急响应计划没有熄灭，通风和进入程序，因此，当消防员打开系统门时，易燃气体爆炸了。

调查人员说：“虽然今天的储能安全法规和标准承认将热失控视为一种风险，但他们停止了禁止它的风险，并且无法应对非固定热传热到相邻细胞，模块和机架的风险。”相反，他们专注于管理火灾的方法，但没有规定限制或慢慢单元间和模块对模块的热失控传播的解决方案。

但是，调查人员指出，有一些可商购的技术来解决热失去传播。报告说：“如今，现在已经存在更好的通风，灭火和冷却热失控方案的实践，应该在未来的储能系统中实施。”

The utility also hired Wood Environment & Infrastructure Solutions and AECOM Technical Services to assess any environmental hazards such as release of particulate matter or heavy metals. Their assessment said impacts were "confined to onsite locations near the structure", with further offsite probes "not recommended."

Calls to Arlington, Va.-based AES Corp., which designed and built the battery energy storage system for APS, were not responded to by ENR press time on July 29. The energy company also built a second unit for the utility.

但在July 30 commentsto Arizona regulators, battery manufacturer LG Chem Lid.,与DNV的分析步骤和conclu需要问题sions, contending that its own outside analysis pointed to an external heat source, such as external electrical arcing, as the potential cause。

APS's plan to install an estimated $1 billion in energy-storage batteries in its service areas were put on hold after the explosion, says one local report. The storage buildup is part of its announced intention to obtain 45% of its energy from renewable sources such as solar and wind by the end of the decade.