Lets Get Technical

A blog about codes, standards, and best practices for solar, energy storage, and microgrids

Let's Get Technical

A blog about codes, standards, and best practices for solar, energy storage, and microgrids

Fire Codes and NFPA 855 for Energy Storage Systems

Before diving into the specifics of energy storage system (ESS) fire codes, it is crucial to understand why building and fire codes are so relevant to the success of our industry. The solar industry is experiencing a steady and significant increase in interest in energy storage systems and their deployment. Decreasing lithium-ion battery costs and increasing demand for commercial and residential backup power systems are two key factors driving this growth. Unfortunately, as the solar-plus-storage industry has quickly ramped up to meet the increased demand, some notable events have occurred, including fires caused by battery cell failures and even a high-profile explosion.

In the spring of 2019, a defective battery cell short-circuited and caught fire at a 2 MW ESS installed for Arizona Public Service (APS). The fire spread to hundreds of adjacent cells, resulting in an explosive gas build-up in the ESS storage container. A powerful explosion occurred when first responders arrived on-site and opened the container. Nine of those individuals required hospitalization, four with serious injuries. See NFPA Journal fall 2021 edition for an in-depth article covering this event. 

There have also been issues in the U.S. residential energy storage sector. For example, after five reported fires stemming from its RESU10 battery units, LG Chem issued product recalls in December of 2020 and again in August 2021. According to the Consumer Product Safety Commission, these fires resulted in property damage and one injury.

Unfortunate events like these drive home the importance of prioritizing safety in ESS design, component procurement, and manufacturing as well as the design, deployment, and O&M of fielded systems. New and updated ESS codes and standards result from the evolving effort to safeguard against the hazards posed by manufacturing defects and system design and installation errors. The constant drive for cost reduction across the industry can result in substandard equipment entering the supply chain and design and installation shortcuts.

Fire codes and standards inform ESS design and installation and serve as a backstop to protect homes, families, commercial facilities, and personnel, including our solar-plus-storage businesses. Code-making panels develop these codes and standards with two primary goals in mind: (1) reducing the likelihood of fire stemming from energy storage equipment, and (2) minimizing property damage and personal injury should a fire occur.


Building and fire codes provide minimum requirements for the health and safety of the occupants, and the public, in new and existing buildings and structures. International codes (I-Codes) are developed by the International Code Council and provide a base code standard for local governments to adopt and modify as necessary. Commercial buildings are subject to the International Building Code (IBC) and the International Fire Code (IFC), while one- and two-family dwellings follow the International Residential Code (IRC). An authority having jurisdiction (AHJ), such as city or county government, often adopts these codes in their entirety. However, it is important to note AHJs frequently adjust them to meet the unique needs of their jurisdictions.

Most PV system designers and installers are intimately familiar with local building and fire codes that address the sealing and flashing of rooftop PV array penetrations, structural and seismic loading, wind and fire resistance, firefighter access, and marking and labeling requirements. However, many designers and installers, especially those new to energy storage systems, are unfamiliar with the fire and building codes pertaining to battery installations.

 Another code-making body is the National Fire Protection Association (NFPA). Some states adopt the NFPA 1 Fire Code rather than the IFC. Because the NFPA directs and oversees the National Electrical Code, NFPA 1, and NFPA 855, there is often a close correlation in the language between these documents.

You can download I-Codes, published by the International Code Council for specific locations. The site’s left-hand menu allows you to navigate current codes by state (and, in some instances, city). You can also use the NFPA Codefinder tool for NFPA 1 states.

NFPA 1 and IFC code cycle adoption varies by state. For example, as of April 1, 2021, there are eight states on the 2012 cycle, 23 states (plus the District of Columbia) on the 2015 cycle, 17 states on the 2018 cycle, and two states (California and New York) on the most current 2021 cycle. Additionally, some states may be on different fire code and residential code cycles to further complicate things. Finally, keep in mind that these online resources may not be up-to-date. The best way to determine the codes AHJs are enforcing in a specific location is to contact the local building or fire department.

While the 2015 versions of the IFC and NFPA 1 do contain some requirements for energy storage systems, they are few compared to the 2018 and 2021 versions. The ESS requirements in the 2018 version, while certainly more restrictive than the 2015 version, are relatively modest. On the other hand, the 2021 codes build out ESS requirements considerably. 

Also of interest, there were no specific ESS requirements in the IRC before 2018. IRC 2018 requirements specify that ESS must be:

  • Listed and labeled in accordance with UL 9540
  • Installed per manufacturer’s instructions
  • Not installed within a habitable space of a dwelling unit
  • Protected from impact from vehicles with an approved barrier
  • Ventilated if battery chemistry produces flammable gas during normal operation

NFPA 855 and 2021 IFC, IRC, and NFPA 1

The ESS project that led to the first edition of NFPA 855, the Standard for the Installation of Stationary Energy Storage Systems (released in 2019), originated from a request submitted on behalf of the California Energy Storage Alliance. The first version of NFPA 855 sought to address gaps in regulation identified by participants in workshops presented by the U.S. Department of Energy and the Fire Protection Research Foundation. The 2021 versions of IFC, IRC, and NFPA 1 base their ESS fire code requirements on this document.

Chapter 15 of NFPA 855 provides requirements for residential systems. The following list is not comprehensive but highlights important NFPA 855 requirements for residential energy storage systems. In particular, ESS spacing, unit capacity limitations, and maximum allowable quantities (MAQ) depending on location.

  • ESS must be listed and labeled in accordance with UL 9540 and installed per the manufacturer’s instructions.
  • A minimum spacing of 3 feet is required between ESS units unless 9540A testing allows for closer spacing.
  • ESS location requirements are detailed for areas including garages, accessory structures, utility closets, and outdoors. ESS installed outdoors may not be within 3-feet of doors and windows. Note that ESS units may not be installed in living areas or bedrooms.
  • The maximum energy rating per ESS unit is 20 kWh. The maximum kWh capacity per location is also specified—80 kWh when located in garages, accessory structures, and outdoors and 40 kWh in utility closets or storage spaces. For storage capacities that exceed these limits, non-residential requirements come into play (NFPA 855 Chapters 4-9).
  • Fire detection, including smoke and heat alarms, vehicle impact protection with approved barriers, and ventilation requirements for chemistries that produce flammable gas during normal operation are addressed.
  • Electric vehicles used to temporarily power a dwelling must comply with NEC requirements, the vehicle manufacturer’s instructions, and are not allowed for more than 30 days.

It is important to note that the UL 9540A test method differs from the UL 9540 listing process. UL 9540A is referenced by NFPA 855 in the context of large-scale fire testing. The 2021 IRC also utilizes UL 9540A and allows for closer unit spacing if the ESS’s UL 9540A testing has proven that closer spacing is safe. The ESS manufacturer will provide the required unit spacing based on this 9540A testing in their installation instructions.

While currently only California and New York have adopted the 2021 IRC and IFC, other states and cities are likely to start utilizing this code cycle in the coming years making these enhanced ESS fire code requirements applicable across a broader section of the U.S.

Codes and standards that regulate and guide solar and energy storage systems continue to evolve and be adopted throughout the U.S. as systems scale and manufacturers introduce new products and solutions into the market. Staying up-to-date on the most consequential codes and standards for ESS not only helps ensure system safety and functionality but is also good for business. Systems that are up-to-code lead to happier customers, satisfied inspectors, and smoother installations. 

Ready to learn more about fire codes for energy storage systems? Register here for a live or recorded version of the 3-hour training.

Author Justine Sanchez is the solar-plus-storage director at Mayfield Renewables and an NEC Code-Making Panel 13 member. To start a solar-plus-storage design project or inquire about project consulting, simply fill out this quick form

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