NFPA Journal

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Dean Kamen, the noted engineer and inventor, said that “every once in a while, a new technology, an old problem, and a big idea turn into an innovation.” An innovation that has flourished in the past few years is energy storage systems, or ESS, which use new technologies such as lithium-ion batteries to create systems that store energy to be used as electricity at a later time. In response to those innovations in energy storage and the hazards that come along with them, NFPA has developed a new standard: NFPA 855, Standard for the Installation of Energy Storage Systems.

There are several types of energy storage systems, each with its own characteristics: pumped hydro ESS, battery ESS, flywheel ESS, compressed air ESS, and thermal ESS. The common denominator among these technologies is that they all store energy and include components that convert that energy into electricity. Electro-chemical or battery ESS make up a large majority of new installations around the world, according to the Department of Energy's Global Energy Storage Database, which is why much of the recent ESS focus has been on this particular technology.

ESS has many useful and cost-saving applications, such as supplementing renewable energies, load leveling, and peak shaving. Supplementing renewable energies allows users to store excess power generated by wind turbines or solar cells. Load leveling allows power companies to tap into ESS reserves during peak electrical usage hours, preventing the utility from having to dramatically increase power production. Similarly, peak shaving allows ESS users to draw on reserve power during daytime hours, when the cost of power is higher, and recharge at night when rates are lower. This kind of flexibility has made ESS an increasingly attractive option for a range of stakeholders; according to the DOE Global Energy Storage Database, the number of US energy storage system projects increased 174 percent between 2013 and 2018.

A popular use of energy storage systems is to stockpile electricity generated by renewable energy sources. Here, photovoltaic arrays at right generate electrical energy that is stored in the ESS equipment at left, providing a source of backup power for a train station. Photograph: Newscom

While the technology is attractive, it is not without risks. Recent innovations allow more energy to be stored in less space, increasing the energy density and in turn increasing the fire and life safety hazards associated with certain ESS. Even though there are currently published requirements for ESS in NFPA 1, Fire Code, and NFPA 70®, National Electrical Code®, authorities having jurisdiction (AHJs) are looking for additional guidance when the request for an ESS installation lands on their desks.

That’s where the new NFPA 855 comes in. The 2020 edition of NFPA 855 began in 2016 when the NFPA Standards Council approved a request for NFPA to develop a standard on stationary ESS, and a call for members to the committee was posted. The original request was submitted on behalf of the California Energy Storage Alliance in order to address gaps in regulation identified through workshops held by the US Department of Energy and the Fire Protection Research Foundation. Later in 2016, the Standards Council appointed the first NFPA Technical Committee on Energy Storage Systems. The initial draft of the standard was developed by the committee over three meetings and was released to the public in 2017. Over the next two years the committee met several times to review feedback from the public and to make improvements to the standard. The first edition of NFPA 855 is due to be published in September.

Since the development of NFPA 855 is almost complete, much of its content will most likely stay the same as it makes its way through the standards development process. Several NITMAMs have been submitted to remove utilities from the scope of the standard and increase the capacity of ESS groupings that need to be spaced apart. With those possible changes in mind, here are some of the key aspects of NFPA 855:

Scope, purpose, and application

The importance of the scope, purpose, and application statements in the front of the standard is frequently overlooked. Users often assume they know what the standard applies to simply by reading the title, but that is not always the case. An assumption with NFPA 855 is that it applies only to lithium-ion battery ESS, but that is incorrect—the scope is much broader than that.

The scope of NFPA 855 applies to several technologies and to energy storage systems of a certain size or capacity. The threshold when NFPA 855 applies is different for each technology. For example, the standard applies to lead acid battery ESS with a combined capacity of 70 KWh (kilowatt-hour) or more, while ESS using lithium-ion batteries requires a threshold of 20 KWh for NFPA 855 to apply. For those unfamiliar with the units of KWh, a typical smartphone has a 5 watt-hour (0.005 KWh) battery, a laptop has a 50 watt-hour (0.05 KWh) battery, and an electric vehicle has a 75 KWh battery.

Location of ESS installations

Another key aspect of NFPA 855 is that it takes into consideration the location of the ESS installation when applying requirements—the standard recognizes that there are different hazards for different locations. For example, an ESS system in the middle of an empty field will have fewer, and less-stringent, requirements than an ESS inside a shopping mall.

NFPA 855 initially breaks down locations into categories of indoor and outdoor. Indoor locations consider whether the building is to be used only for the purpose of containing an ESS. The standard uses the terms “dedicated use building” and “non-dedicated use building” to describe these. If you are in a non-dedicated use building, the standard requires fire-rated separation from other occupancies, with either a one- or two-hour-rated wall, based on which occupancies are being separated. Another important requirement that applies to indoor installation is that ESS installations need to be approved by the AHJ if they are installed below the lowest level of exit discharge, above external fire department laddering capabilities, or on noncombustible rooftops.

If an installation is outdoors, then it is either classified as remote or near exposures. If an installation is remote, it needs to be 100 feet or more away from any exposures such as other buildings, walkways, or combustible materials. If the installation is not a remote installation, then it is considered to be near exposures. Other acceptable outdoor installations that have specific requirements are rooftops, open parking garages, and standalone walk-in units such as shipping containers.

Size and separation ESS installations

Another key requirement in NFPA 855 applies to the size and separation of ESS installations. Three feet of clear space is required between every 50 KWh grouping of ESS, as well as between the 50 KWh groupings and the walls of the room.

The intent of this requirement is to prevent horizontal propagation of fire through an ESS installation. Horizontal propagation of a fire can overwhelm a fire suppression system and render it ineffective. This was a controversial topic, because one of the benefits of certain ESS technologies is that a large amount of energy can be concentrated in a small area, and this requirement can expand the footprint for an installation. However, this is not required for remote locations because, in the event of a fire, they are less likely to spread to adjacent exposures.

Fire suppression and control

A sprinkler system is required to be installed in accordance with NFPA 13, Standard on the Installation of Sprinkler Systems, with a 0.3 gallons-per-minute-per-square-foot density over a 2,500-square-foot design area. This information has been extrapolated from existing research, testing, and understanding of suppression system performance for this hazard. Additionally, a Fire Protection Research Foundation project is currently testing this exact discharge density on an ESS and will be available soon at nfpa.org/foundation.

While alternate fire suppression methods are permitted if testing shows they are effective, there isn’t much publicly available test data on extinguishing ESS fires. One of the major concerns in extinguishing an ESS fire is cooling the energy storage system down below the auto ignition temperature of the flammable gasses the ESS may discharge in a thermal runaway event. Water is an effective extinguishing agent for most ESS fires including lithium-ion battery ESS, and that is what the committee settled on for a requirement.

Utility and telecom application

There has been much debate about the application of NFPA 855 to electric power utilities (power plants) and telecommunication installations. Much of the concern about ESS installations focuses on nonremote substations that could be close to commercial or residential areas. Since the committee didn’t feel comfortable having a complete exemption for these applications in the scope, several statements throughout the standard permit utility or telecommunications facilities to not comply with certain requirements. The reasoning is that both serve as critical infrastructure and are already regulated by several bodies, including other NFPA standards and recommended practices. Also, these are often in areas where first responders won’t enter without an escort from the utility company.

These are just a few of the critical requirements in NFPA 855—others address ventilation, detection, signage, listings, emergency plans, and many more. It is also not the first standard to address ESS fire safety—current editions of NFPA 70 and NFPA 1 both contain extensive requirements for ESS and can be adopted today. The information in NFPA 855 closely reflects the information in NFPA 1, Chapter 52, on energy storage systems.

Despite the requirements contained in those codes, NFPA 855 is necessary to address additional ESS safety details as part of today’s complex energy infrastructure. Energy storage systems are a hugely beneficial technology with growing popularity and many applications. While ESS is here to stay, NFPA 855 will make sure they are installed safely so this technology can be embraced in a range of applications around the world.

BRIAN O'CONNOR is a licensed fire protection engineer at NFPA and vice president to the New England chapter of SFPE. Top Photograph: Getty Images