In Compliance | NFPA 13
NFPA 855 and sprinkler protection for energy storage systems
BY BRIAN O'CONNOR
An important set of questions right now among sprinkler designers revolves around ways to protect energy storage systems (ESS)—but a new NFPA standard can help them answer those questions.
An ESS in its simplest sense is any system that stores electrical energy for use at a later time. ESS is a technology that is here to stay because of its wide range of beneficial applications, its increasing efficiency, and its ability to help users decrease energy-related costs. Some of these applications include supplementing renewable energy sources, such as solar panels and wind turbines, or storing and discharging energy when electrical prices fluctuate. There are many different applications and types of ESS, but battery ESS—in particular, lithium-ion battery ESS—has become the most common.
Lithium-ion battery technology, while highly beneficial, also comes with some unique hazards when considering fire protection, including a tendency to generate a lot of heat and emit toxic/flammable gasses when damaged. This can have a cascading effect throughout the battery cells, a process referred to as thermal runaway, potentially causing a fire or explosion. This is very difficult to control once an ESS is fully involved in a fire. ESS can also store large amounts of energy and burn for long periods of time, often many hours, and can reignite after being extinguished.
A new standard, NFPA 855, Standard for the Installation of Stationary Energy Storage Systems, provides requirements for protection of all ESS, but currently focuses on battery installations, which are typically an arrangement of tightly packed cells placed in modules that are stacked vertically in racks. Since these systems often consist of multiple racks, a main objective of the standard is to make sure, if a fire occurs, that it is contained to a single rack. If the fire is able to propagate from one rack to the next, it could last for a considerable length of time, potentially overwhelming the sprinkler system or taxing the water supply.
To mitigate this risk, one of the objectives of an ESS fire protection system should be to contain the fire to the rack of fire origin through the installation of a sprinkler system and the spacing of ESS groups. NFPA 855 addresses this by requiring that ESS be protected by a sprinkler system installed per NFPA 13, Standard for the Installation of Sprinkler Systems, and provides a specific design density and design area. NFPA 855 also requires ESS to be grouped into small segments and spaced apart to prevent large and lengthy fire events. One exemption to the sprinkler and spacing requirements in NFPA 855 is to allow for the use of alternate means of fire protection and spacing as long as it is proven to be effective based on fire testing done in accordance UL 9540A, Test Method for Evaluating Thermal Runaway Fire Propagation in Battery Energy Storage Systems. This is allowed because there is currently a lack of large-scale fire test data; encouraging additional testing can help us understand the hazard better and protect installations more appropriately.
An example of determining protection requirements through testing is illustrated in a recent Fire Protection Research Foundation report, available at nfpa.org/esssprinkler, which looks at large-scale fire and sprinkler testing for two different chemistries of lithium- ion batteries in an ESS arrangement. The main takeaways from the testing are that the two chemistries had vastly different heat release rates, and as a result require different recommended protection schemes. This highlights the need for individual testing since the chemistry and battery layout can alter the amount of water and spacing that would prevent an ESS fire from spreading to adjacent modules.
Ultimately, while NFPA 855 addresses questions of how to protect ESS installations, the technology is evolving rapidly, and additional testing will be necessary to ensure that codes and standards provide the optimal level of safety for all stakeholders.
Brian O’Connor is a fire protection engineer at NFPA. NFPA members and AHJs can use the Technical Questions tab to post queries on NFPA 13 at nfpa.org/13. Top photograph: Getty Images