By: Nicole Imeson 

Energy storage systems (ESS) store energy in batteries until needed. These systems capture generated energy (often paired with renewable sources such as wind or solar) and supply it to end users during off hours. The battery ESS consists of multiple battery cells, creating a large system with capacities in the hundreds of kilowatt-hours. ESS units are installed in remote or urban areas to provide black start resiliency for generators or meet backup power needs in remote locations and critical facilities. Additionally, they are increasingly being deployed in, adjacent to, or on top of buildings in densely populated areas, including cities.  

Between 2017 to 2021 and beyond, over 30 ESS failures globally have resulted in severe injury, power outages, and loss of property. This yields a worldwide ESS failure rate of 1-2%. In a 2019 Arizona incident, a deflagration event at a 2.16 MWh ESS, comprised of more than 10,000 lithium-ion batteries, injured four firefighters, and led to 75ft flames. In 2020, the automatic fire suppression system failed to extinguish the fire or prevent the subsequent explosion of a 20 MWh ESS in Liverpool.  

Figure 1 – Arizona ESS Incident - (top) Off Gasing, (bottom) After the Explosion Event 
Original Source: UL Incident Report 
Shared by Jensen Hughes – BCxA 2023 Annual Conference 
ESS Risk Characteristics 
FM Global conducted tests on a 12.5 kWh lithium-ion battery rack to enhance the understanding of fire characteristics, hazards, and risk. Within minutes, the rack generated a 10.5 MW fire, surpassing the typical 7.5 MW of a car fire. Each ESS usually incorporates multiple racks in each structure or container, and some include several structures all working together to provide a larger storage system. Each rack poses significant hazards, which increase as more racks are added, requiring stringent mitigation measures. 

Figure 2 – Photos of unsprinklered large-scale free burn test of ESS; near time of ignition (top left), near time of predicted sprinkler operation (top middle), peak heat release rate (top right). 
Original Source: FM Global Technical Report 
Shared by Jensen Hughes – BCxA 2023 Annual Conference 
Fire Commissioning Agent 
“It's not IF it's going to happen, it's when it's going to happen” highlighted David LeBlanc, Vice President at Jensen Hughes, and commissioning agent with over 30 years’ experience in the fire and life safety sector. The term "fire commissioning agent" emphasizes a more extensive review level than a typical commissioning project, encompassing adherence to locally adopted codes and standards for fire and life safety systems. “This is beyond the level you would go to for a more traditional commissioning project. You need to understand the required locally adopted codes and standards that apply to a particular fire protection and life safety system and verify the system conformance to these requirements. There is added responsibility and risk in performing commissioning of fire and life safety systems. The term commissioning agent is used in NFPA 3 instead of commissioning provider due to these increased responsibilities” explained LeBlanc. While the fire and life safety commissioning agent are accountable for ensuring that the systems conform to adopted codes and standards, this does not absolve the engineer of record or the contractor of their responsibilities. 
Energy Density of Lithium-Ion Batteries 
ESS commonly utilizes lithium-ion batteries for their energy density. A household AA battery, for instance, generates 1.5amps. In contrast, a lithium-ion battery of a comparable size can produce 100-200 amps, making it 100 times more energy dense and equivalent to the power source of most houses.  
Figure 3 – Components of Lithium-Ion Batteries 
Source: Jensen Hughes – BCxA 2023 Annual Conference 
Thermal runaway occurs when a battery converts chemical energy to thermal energy, and it can occur under a few conditions such as manufacturing defects, overcharging, overheating, or mechanical abuse. In such a scenario, the battery emits flammable and toxic gases, posing the risk of fire or explosion if not properly managed or protected. Approximately 30% of the released toxic gases from a lithium-ion battery consist of hydrogen, which is highly flammable and has the potential for explosion if allowed to accumulate in an enclosed space. “A lithium-ion battery that's the size of a standard AA battery, if it's in thermal runaway and it's off gassing, that little battery produces 10 liters of flammable gas. A single pouch, similar in size to a pop tart package, produces 200 to 300 liters of flammable gas” described LeBlanc. 

Fire Protection and Life Safety Measures 
Several individual batteries are assembled in a series of racks or banks to form a larger energy storage system. The overall capacity of the system and the requirements for fire and life safety system design depend on the type of battery, quantity, and arrangement. A permanent water supply ensures ESS protection through a comprehensive fire suppression system. Deflagration venting directs off-gas, crucial in urban or adjacent installations. Early gas detection aids operators and first responders in understanding hazards. Mechanical switches allow remote activation of ventilation systems, enhancing overall safety and control. Multiple fire protection methods are required because “unlike other typical fire hazards, lithium ion generates its own oxygen and is difficult to extinguish. If a lithium-ion battery is in thermal runaway, and you dump it in a bucket of water, it won't stop the fire, it'll keep going” explained LeBlanc. 

“For installations over 20 kWh, which is very simple to do, that's an extremely small installation, a commissioning plan, emergency planning, and training for any of those types of energy storage systems is required. For a system configuration of more than 600 kw of lithium-ion batteries, a hazards material analysis is required for NFPA 855. It only takes a few racks, depending on the configuration, to be over 600 kWh” explained LeBlanc. If multiple battery technologies are employed at a single site, the capacity threshold for these requirements is lowered to mitigate hazard risks arising from the unknown interplay of different battery hazards. 

Codes and Standards 
Several codes and standards regulate ESS design, installation, and operation, including NFPA 3 Standard for Commissioning of Fire Protection and Life Safety Systems, NFPA 4 Standard for Integrated Fire Protection and Life Safety System Testing (especially crucial when multiple components integrated into a larger system), NFPA 855 Standard for Installation of Stationary Energy Storage Systems, NFPA 68 Standard on Explosion Protection by Deflagration Venting, NFPA 69 Standard on Explosion Prevention Systems, and various UL standards, certifications, and test procedures. Local jurisdictions determine applicable codes; therefore, adoption of each code and version should be confirmed with them. Some codes, recognizing the evolving nature of ESS materials, arrangements, and designs, incorporate clauses to specify measures for ESS not covered by established regulations (i.e., new battery technology). 

The landscape of energy storage systems (ESS) reveals a complex interplay of technology, hazards, and safety measures. Global incidents underscore the critical need for proactive risk mitigation.    

The Hazardous Mitigation Analysis (HMA) and mandatory UL 9540 and 9540A testing are crucial components of the design and commissioning process for any reasonably sized Energy Storage System (ESS). It is essential for the fire commissioning agent to comprehend their significance. David LeBlanc's insight emphasizes the inevitability of challenges, urging a heightened sense of responsibility in the commissioning process. The multifaceted approach to fire protection in ESS involves a careful balance of active and passive elements, recognizing the evolving nature of ESS, codes and standards continue to adapt, underlining the dynamic nature of this critical technology. 
Commissioning providers and BCxA members recently attended the BCxA Annual Conference in Orlando, networking and participating in education sessions covering various technical and business topics related to the commissioning process. David LeBlanc from Jensen Hughes in Boston, MA hosted the session “Energy Storage System Essentials and Hazards to be Aware of”, providing the content for this article. The full recording of this session is available in our online learning platform.