Fire Code Requirements for Indoor vs Outdoor Energy Storage Installations

  Fire code requirements for energy storage systems (ESS) can vary significantly depending on whether a system is installed indoors or outdoors. While both installation types are governed by similar code tables, indoor installations introduce additional challenges that designers, installers, and authorities having jurisdiction (AHJs) must work through before a project can move forward.

The most significant of these challenges involve fire suppression, fire alarm integration, and the unique hazards of lithium ion batteries. Each one plays a role in how energy storage projects are designed, permitted, and integrated into existing buildings.

Indoor and outdoor installations follow similar code tables

The 2024 International Fire Code (IFC) and the 2025 California Fire Code both organize ESS requirements into tables that outline which compliance features apply to a given installation. Table 1207.8 covers outdoor ESS installations and divides them into two categories: remote installations and installations near exposures. Each category lists the features that must be addressed, including clearance to exposures, fire suppression systems, maximum enclosure size, means of egress separation, smoke and automatic fire detection, technology specific protection, and vegetation control.

Remote installations face fewer requirements than installations near exposures. They are not subject to maximum allowable quantities or size and separation requirements, and fire suppression systems may be omitted where approved by the fire code official. Installations near exposures, on the other hand, must comply with every feature listed in the table.

Indoor installations follow a very similar table with two columns of their own, one for dedicated use buildings and one for nondedicated use buildings. The structure is comparable, but indoor projects carry additional considerations once the system has to be integrated into an occupied building.

Why is fire suppression the biggest hurdle for indoor systems?

One of the most difficult parts of an indoor ESS installation is integrating the system with the building’s existing fire protection. This includes fire suppression, fire alarm annunciation, and tying the ESS into the building’s fire control panel, along with all of the testing that comes with it. These requirements can also apply to larger residential systems that end up being treated as commercial installations.

Table 1207.7 requires fire suppression systems in both dedicated use and nondedicated use buildings, although the fire code official may approve omitting suppression in dedicated use buildings located more than 100 feet from buildings, lot lines, public ways, and other exposure hazards.

Chemical suppression systems are a common point of discussion when comparing commercial and residential applications. AHJs are increasingly relying on UL 9540A test results, which evaluate fire propagation and thermal runaway, to determine what level of protection an installation requires. This shift reflects a growing understanding of how lithium-ion batteries behave in a fire and why traditional suppression methods have limits.

Lithium-ion thermal runaway can only be stopped by time

Once a lithium-ion battery cell enters thermal runaway, the only way to stop it is time. The cell needs to consume its fuel before the event can end, and fire suppression cannot reverse that process once it has started.

Suppression systems can be designed to choke out a fire and starve it of oxygen, but lithium-ion batteries carry their own fuel source, and some chemistries release oxygen as the cell materials break down. After the battery reaches a certain temperature, the reaction will continue until it has run its course. Suppression still plays an important role, however, because water cools the surrounding equipment and helps keep thermal runaway from spreading to adjacent cells and units.

This is what makes indoor installations more onerous than outdoor ones. When a system is located inside a building, the consequences of thermal runaway extend to the occupants and the structure itself, which is why integrating the ESS with the building’s fire suppression and alarm systems carries so much weight in the permitting process.

Can other industries offer a model to follow?

The energy storage industry is largely on the cutting edge when it comes to fire code requirements. The most direct comparison is the generator industry, where fossil fuel systems have long been installed for backup power and other uses. Those systems have their own set of hazards, but they don’t parallel the risks presented by batteries.

Without a clear precedent from other industries, energy storage is navigating new territory as codes and standards continue to develop. Designers, installers, and AHJs are working through these challenges together as the industry moves forward.

Conclusion

The energy storage industry is largely on the cutting edge when it comes to fire code requirements. The most direct comparison is the generator industry, where fossil fuel systems have long been installed for backup power and other uses. Those systems have their own set of hazards, but they don’t parallel the risks presented by batteries.

Without a clear precedent from other industries, energy storage is navigating new territory as codes and standards continue to develop. The Mayfield Standard helps fill that gap by giving project teams a consistent development framework to work from, even as codes and requirements continue to evolve.

Indoor and outdoor ESS installations follow similar code tables, but indoor projects carry a heavier burden once the system has to be integrated into an occupied building. Fire suppression, fire alarm annunciation, and tying into the building’s fire control panel are among the most challenging parts of the process, and the nature of lithium ion thermal runaway makes these requirements especially important. Addressing them early in the design process is essential to keeping energy storage projects on track.