Satisfying Explosion Prevention for NFPA 855

As an expert within the Energy Storage Systems (ESS) space, Hiller is uniquely positioned to help you understand and meet the NFPA 855 Requirements. One of our fire protection experts, Paul Hayes, has been featured in the Journal of Loss Prevention in the Process Industries on this topic, learn more, below.

Paul and the rest of the Hiller / American Fire Technologies team will be exhibiting and speaking about Energy Storage Systems and NFPA 855 at PowerGen 2023. Visit us at Booth 319 Feb 21-23 in Orlando, FL.

Abstract of the Paper Related to Requirements for NFPA 855

This work developed and analyzed a design methodology for Powin Stack™ 360 enclosures to satisfy the requirements for explosion prevention per NFPA 855. Powin Stack™ 360 enclosures are lithium-ion-based stationary energy storage systems (ESS). The design methodology consists of identifying the hazard, developing failure scenarios, and providing mitigation measures to detect the battery gas and maintain its global concentration lower than 25% of the lower flammability limit (LFL) to meet the prescriptive performance criterion of NFPA 69 – Standard on Explosion Prevention Systems. The UL 9540A test data is used to define the battery gas composition, release rate, and release duration to describe the failure scenario involving thermal runaway propagation. The ESS enclosure consists of individual stacks (compartments) with targeted airflow to ensure the cooling of batteries during normal operational conditions. This arrangement makes it difficult to use a standard exhaust ventilation methodology to design an explosion prevention system. An innovative approach is used to purge the battery gas from individual Powin Stacks™ and from the main enclosure during a thermal runaway event. The designed method is analyzed using a computational fluid dynamics (CFD) model to ensure it meets the intent of NFPA 69. The explosion prevention system functionality presented in this work is limited to removing flammable battery gas generated due to the non-flaring decomposition of batteries and does not consider its interactions with other fire protection features.

Introduction of the Paper Related to Requirements of NFPA 855

Energy storage is playing a pivotal role in empowering the decarbonization of transportation and enabling power grids to function with more resilience. Lithium-ion-based batteries have come a long way from their usage in consumer electronics with tens of Wh (watt-hour) capacity to approximately 100 kWh capacity battery systems in modern electric vehicles (Bisschop et al., 2020). Decarbonizing the electricity generation process is a big issue and critical to supporting the changing landscape in the automotive industry. Addressing this issue ensures we do not deal with greenhouse gases at the electricity generation source. Lithium-ion-based energy storage is one of the leading technologies for sustainable and emission-free energy. The advantage of storing green energy, such as solar or wind, during off-peak hours and using it during peak hours is gaining traction as various governments in the world look toward renewable energy sources. The growth in the energy capacity is tremendous, with the United States having less than 1 GW of large energy storage installations in 2019 to adding a capacity of 6 GW in 2021 and forecasted to achieve an additional 9 GW in 2022 (Blunt and Hiller, 2021).

Like many other energy sources, Lithium-ion-based batteries present some hazards related to fire, explosion, and toxic exposure risks (Gully et al., 2019). Although the battery technology can be operated safely and is continuously improving, the battery cells can undergo thermal runaway when they experience an exothermic reaction (Balakrishnan et al., 2006) of the internal cell components leading to a sudden release of thermal and electrochemical energy to the surroundings. These reactions cause thermal runaway occur when the internal separator of the anode and cathode is compromised due to some abuse of the cell (Ghiji et al., 2021; Roth et al., 2007) Cyclical thermal/electrical loading and unloading, manufacturing defects, and thermal, mechanical, or electrical abuse are many reasons that can cause cell degradation leading to thermal runaway (Bravo Diaz et al., 2020).

As the ESS enclosures are installed at an accelerating rate, a few incidents related to fires and explosions (Zalosh et al., 2021) have occurred. A detailed publicly available database on ESS failure events is maintained by the Electric Power Research Institute (EPRI) that provides a good overview of system capacity, age, event date, and its state during the accident (Long, 2022). The ESS community continues to learn from these incidents, and a lot of progress has been made to ensure the safety of these systems. NFPA 855 (NFPA, 2020) standard now requires ESS installation shall be provided with either an explosion control system, i.e., deflagration vents according to NFPA 68 (NFPA, 2018), or an explosion prevention system, i.e., a mechanical ventilation system according to NFPA 69 (NFPA, 2019). Essentially all ESS installations in the U.S. are required to have some form of explosion control unless the omission is demonstrated by large-scale testing. This paper focuses on developing a procedure to design an explosion prevention system for the Powin Stack™ 360 enclosure.

While the scope of NFPA 69 is extensive and applies to the design, installation, operation, maintenance, and testing of systems to prevent explosions using a variety of methods, this work is limited to the conceptual design of an explosion prevention system by pursuing the performance-based design option that aims at controlling the released battery gas combustible concentration. The system is designed using computational fluid dynamics (CFD) that helps in understanding the dispersion of battery gas within the enclosure. The usage of CFD for simulating an accidental release of flammable gas is well established. The CFD simulations can help demonstrate the evolution of gas release as a function of space and time.

Various metrics can be used to quantify the global parameters, such as volume fraction and mass within an enclosure. In addition, displaying the gas cloud between the lower flammability limit (LFL) and upper flammability limit (UFL) can help quantify the size of the flammable cloud. This detailed information is very useful in understanding the consequence of a scenario and designing the mitigation measures such as gas detection and explosion prevention systems.

The usage of CFD for designing explosion prevention systems is prevalent in process safety industries dealing with flammable fluids (Shen et al., 2020) and explosible dust (Eckhoff, 2009). Different scenarios involving spills, buoyancy-driven leaks, momentum-driven leaks, and a sudden loss of containment can be prescribed using a source term in the CFD model. These different leak scenarios require a deep understanding of the flammable fluid, storage and operating conditions, and the associated hazards. The critical challenge in designing an explosion prevention system for a ESS is to quantify the source term that can describe the release of battery gas during a thermal runaway event. The highly non-linear and stochastic behavior of battery cells requires a different approach from other failure scenarios commonly seen in the process safety industry, with greater emphasis on the availability of UL 9540A test (ANSI/CAN/UL, 2019) data to describe a battery gas release rate. In addition, the released battery gas is a mixture of hydrogen, carbon dioxide, carbon monoxide, and several hydrocarbons (Fernandes et al., 2018), requiring an approach to quantify mixture properties and flammability limits. Furthermore, the HVAC system used to cool the batteries can impact airflows with the formation of hot and cold aisles that can impact the placement of gas detectors as well as supply and exhaust locations for the explosion prevention system.

Performance-Based Assessment of an Explosion Prevention System for Lithium-Ion Based Energy Storage System By: Anil Kapahi , Alberto AlvarezRodriguez , Sunil Lakshmipathy , Stefan Kraft , Jens Conzen , Angelica Pivarunas , Rody Hardy , Paul Hayes Journal of Loss Prevention in the Process Industries

Be sure to visit the ELSEVIER site to read more about this research.

Some keywords for this specific research conducted include:

  • BESS – Battery Energy Storage Systems
  • CFD – Computational Fluid Dynamics
  • Explosions
  • Explosion prevention

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