How standards can ensure battery safety


From pv magazine USA

Safely managing energy has been an important human activity since the invention of fire. Our homes and businesses store and use multiple forms of energy on a routine basis. Whether it’s a gas-fueled water heater, an electric oven, or the gallons of gasoline in our car’s fuel tank, we accept the potential for dangerous accidents in exchange for the conveniences energy storage and management technologies provide. In most cases, we don’t even think about the dangers since these technologies are familiar parts of our everyday lives, and the risks are seldom realized.

A recent report from the U.S.Fire Administration indicates that the five leading causes of residential fires are faulty outlets and appliances, light fixtures, extension cords, space heaters, and outdated electrical wiring. But we continue to use lamps, space heaters, and ever bigger appliances. Thanks to building codes and product safety standards continuously updated over the years, the risks are minimal.

Climate change will drive dramatic changes in how we make and use electricity. Increased frequency of power outages from natural disasters and the transition to intermittent renewable energy sources drive an increased need for energy storage systems (ESS) for lower-cost electricity and energy resilience. As a result, ESS deployment is proliferating in homes and businesses around the country. Once ESS devices are familiar, the perceived safety concerns will likely dissipate. In order to get there, the solar + storage industry needs to provide a high level of assurance that safety has been validated to minimize both real and perceived risks.

Fortunately, developers and manufacturers of Energy Storage Systems can leverage the body of product and fire safety standards used for decades to ensure electrical and gas-fueled appliances are safe to operate in homes and businesses in North America.

Safety standards are created by cooperating non-profit organizations and industry associations, such as the American National Standards Institute (ANSI), the National Fire Protection Association (NFPA) and the International Code Council (ICC). These organizations develop standards and codes that are adopted and enforced by state and local government authorities such as city building departments. This system provides a practical, cost-effective way for local policymakers to ensure basic safety requirements fit local conditions and are enforced consistently for all permitted construction or improvement projects – such as installing an ESS in a home or commercial building.

In many cases, these safety codes require that any equipment used meet specified product safety standards. OSHA, The U.S. Department of Labor’s Occupational Safety & Health Administration, operates a Nationally Recognized Testing Laboratory (NRTL) program, which enables recognized private companies to certify that a tested product meets a particular safety standard. Underwriter’s Laboratories (U.L.) is the most familiar of these NRTLs, primarily because they have a non-profit affiliate involved in developing the test standards. The current list of NRTLs includes about 20 organizations – each of which is authorized to certify and “list” products for specific standards. Listed products will bear a distinctive logo, called a “mark,” of the NRTL that certifies the product meets the specified safety standard. Penalties for fraudulently applying an NRTL mark are steep enough to ensure it’s rare. To further minimize fraud, most NRTLs have websites that allow anyone to verify that a marked product meets the required safety standards.

These NRTL’s and industry safety organizations have been working with solar and battery manufacturers, installers, and industry associations to update the Codes and Standards for ESS’s so that solar + storage products can be safely installed and used in buildings where people live and work.

NFPA 855

National Fire Protection Association (NFPA) 855, Standard for the Installation of Stationary Energy Storage Systems, was published in late 2019 after a productive engagement between the Energy Storage Association (ESA) – a battery manufacturer and installer trade group – and the NFPA.

NFPA 855 establishes common language and requirements for safe battery installations for incorporation into the comprehensive building and fire codes developed over the past several decades. This standard helps ensure consistency across the variety of codes that may apply to a project and provides more information for inspectors in need of specific guidance. NFPA 855 addresses a variety of battery designs and installation considerations, including spacing between battery packs, sizing of sprinklers, ventilation, related fire mitigation systems, and overall site clearance requirements.

NFPA 855 and other relevant standards are regularly reviewed and updated based on input from subject matter experts who study these technologies, learn from new and ongoing product safety testing, and from analysis of any accidents that do occur. In one example, the findings from a 2019 battery fire that happened in an Arizona Public Service (APS) facility is informing improved safety standard language regarding thermal barriers between battery cells and modules. Recent and ongoing testing performed under the UL 9540A standard will help specify what kinds of restrictions are most effective.


NFPA 70, commonly known as the National Electrical Code (NEC), or just “the Code,” has long been used to help electrical contractors, solar and battery installers, related tradespeople, and inspectors, to ensure electrical work minimizes the potential for shock or fire. Nearly a thousand pages long, NFPA 70 prescribes safe methods for foundational practices, such as proper grounding of electrical systems, and specific activities like the installation of a P.V. array or battery. A diverse group of several hundred technology and safety experts work together, along with input from various stakeholder organizations, to update the NEC every three years. The most recent update, 2020, is harmonized with NFPA 855 and significantly expands coverage of energy storage systems.

International Building Codes

The International Code Council (ICC) develops and publishes several model codes adopted by the vast majority of state or local building authorities. These include the International Building Code (IBC), International Residential Code (IRC), and the International Fire Code (IFC). In contrast to the NEC, which is typically adopted on an all-or-nothing basis, the “I-Codes” are often selected with exceptions and modified to suit local or regional construction needs.

One of the most significant energy storage developments in building codes and standards is the RB154 proposal, which was approved late last year for the 2021 International Residential Code. RB154 establishes ESS size and siting location limitations for homeowners installing battery systems. This code may take effect as early as next July in California, and other states will likely begin enforcing it before the end of 2021. California has already adopted the 2018 IRC as part of its current state residential building code, and with it, the requirement that any ESS placed in a home be listed to UL 9540. RB154 builds on that with specific guidance for builders, installers and inspectors.

UL 9540

The ANSI/CAN/UL 9540 Standard for Safety, Energy Storage Systems and Equipment – typically referred to as “UL 9540” – is a test standard developed explicitly for ESS products and is increasingly referenced in building and electrical codes. Most recently updated in February 2020, UL 9540 focuses on the ESS as a complete system and includes tests of the interaction between the battery and power electronics. To gain certification to UL 9540, the battery must meet the requirements of U.L. 1973 (or U.L. 1989 for lead-acid batteries), and the inverter and charge controller must meet the requirements of UL 1741.

U.L. 9540A

The ANSI/CAN/UL 9540A Standard for Safety, Test Method for Evaluating Thermal Runaway Fire Propagation in Battery Energy Storage Systems – UL 9540A – focuses specifically on the thresholds for thermal runaway and the behavior of the battery assembly once a thermal runaway event is underway. Any lithium-ion batteries, including iron-phosphate chemistries, can be subject to thermal runaway (where a battery cell overheats and subsequently combusts). The testing prescribed in U.L. 9540A establishes what protections are needed to ensure that a thermal runaway event will not lead to a catastrophic fire.

By ensuring that the products they install have the appropriate listings and are installed according to the latest Codes and Standards, installers and inspectors can minimize the risks and hazards associated with battery systems in the same way that they have successfully reduced the risks and dangers of more familiar appliances like water heaters, furnaces, and laundries. Over time, the improved safety standards for ESS products and their increased use will enable homeowners and business owners to accept these energy storage systems as readily as they accept installing a water heater in a house, or parking a car in an attached garage.


Paul Dailey, Director of Product & Market Strategy at OutBack Power Technologies has spent his 20-year career developing, marketing and deploying distributed generation technologies, from micro-CHP to solar + storage. In the course of that work, Paul has interacted with countless solar installation and O&M professionals across the spectrum and continually translates their input into new products and services as well as improvements that help make local control of energy more accessible for everyone.

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