The standards are not crystal clear and have left some with the impression that it is acceptable just to let a BESS fire burn itself out—the “let-it-burn” method—without providing any fire suppression measures.

“Let-It-Burn” is not an Effective Fire Suppression Solution for Battery Energy Storage Systems
“Let-It-Burn” is not an Effective Fire Suppression Solution for Battery Energy Storage Systems

Article from | Stat-X® Condensed Aerosol Fire Suppression


A large part of the quest to conquer climate change is centered around the use of renewable energy in some form or fashion. Solar panels and wind turbines are becoming standard features of our landscapes, and with them comes the need to store the excess energy they produce. In the U.S., the Energy Information Administration estimates that by the end of 2023, battery energy storage systems (BESS) will supply over 10,000 megawatts (MW) of power to national electrical grids (that’s approximately enough to power 7.5M average homes). This represents a tenfold increase in BESS installations from 2019 levels.

Most BESS utilize lithium-ion batteries. Lithium-ion batteries are relatively inexpensive, possess a high energy density, and can recharge quickly. BESS are being installed faster than they can be adequately tested, leaving many authorities having jurisdiction (AHJ) with more questions than answers about how to address the fire safety side of BESS use.

What’s more, the fire safety risk of BESS is very real with many incidents to prove it. South Korea in particular has suffered over twenty-three BESS fire incidents since August of 2017.2 The U.S. has had its share of BESS fires as well. One of the more prominent incidents occurred in Arizona in 2019 where a number of firefighters were injured. A thermal runaway in a lithium-ion BESS created an explosive gas mixture that deflagrated when firefighters opened the container door—this despite the fact that the BESS’ fixed clean-agent fire suppression system activated properly.

The Arizona incident is proof positive that the safety for both responders, and citizens around the growing number of BESS installations, is a challenging topic.. The National Fire Protection Association (NFPA) has thankfully gotten involved and released standards regarding BESS operation and fire protection. But the standards are not crystal clear and have left some with the impression that it is acceptable just to let a BESS fire burn itself out—the “let-it-burn” method—without providing any fire suppression measures. This is seriously flawed thinking which may not in fact coincide with the standards. Adopting a “let-it-burn” policy for BESS fires is an absolute last resort and certainly should never be the primary strategy with regards to protecting your BESS assets.


The Standards

There are three NFPA standards related to BESS: NFPA 855 Standard for the Installation of Stationary Energy Storage Systems®, NFPA 1 Fire Code®, and NFPA 70 National Electrical Code®. NFPA 855 is the most BESS-centric of the three and was adopted in 2020 to provide AHJs with the additional guidance necessary to evaluate BESS applications. Comprehensive as it is, it has not yet experienced widespread adoption by AHJs. But many AHJs enforce NFPA 1 which heavily references NFPA 855. So, if your AHJ observes NFPA 1, you are bound in large part by the stipulations of NFPA 855. 



NFPA 1—and thus NFPA 855—apply when the threshold quantity of BESS exceeds 20 kWh of lithium-ion battery power. As a point of reference, an electric vehicle (EV) uses approximately 30 kWh to travel 100 miles, so all but the smallest BESS fall under NFPA 1 and 855. Prominently required in both standards is the provision of an emergency operating plan which is to be available to both facility operations personnel and emergency responders. In NFPA 1, the emergency operations plan refers to NFPA 855 as to its required contents which shall include:

  • Operating procedures for emergency conditions 

  • Procedures for inspecting and testing alarms, interlocks, and controls

  • Procedures to be followed—e.g., notifying the local fire department—when the BESS is operating in a potentially dangerous condition

  • Procedures to be followed in the event of a fire, explosion, or other emergency including safety considerations for responders

  • Management / safe operation of the BESS after it has been damaged or upset

  • Procedures and schedules of drills when the above procedures are exercised

NOTE: The requirement for the emergency operation plan is waived for electric utilities where the BESS is under their complete control.

Any decision to not provide fire suppression for a BESS must be outlined in this plan. But, as we will demonstrate, the BESS operator cannot unilaterally decide to omit fire suppression. The AHJ must agree with this position in advance. 

NFPA 1 continues and provides the usual guidance on system commissioning/decommissioning, operation, maintenance, testing, signage, egress, etc. Then it discusses fire suppression. Under 52.1.22 of the standard, Fire Suppression and Control, it reads: “Where fire suppression and control is provided it shall be in accordance with of NFPA 855.” The following sections in the standard regarding ventilation, smoke and fire detection, and water supply also read with basically the same verbiage. 

It is the inclusion of the phrase “where fire suppression and control is provided” that leads some to believe they have the option not to provide fire suppression. First, NFPA 1 does not reflect any intent to make fire suppression optional. (It does refer the reader to NFPA 855 which we will discuss next.) Furthermore, NFPA 1 allows the AHJ to require BESS operators to establish a fire watch that can “respond to possible ignition or reignition of a damaged or decommissioned [B]ESS…” The response required includes “remediation of hazards and extinguishment of fires that occur.” 

Herein lies the critical takeaway: it is up to the AHJ—not the operator of the BESS—to determine if fire suppression is to be provided or not. As we will see, NFPA 855 makes this abundantly clear.


NFPA 855

Fire suppression is mentioned voluminously throughout NFPA 855. However, there are some limited instances where the AHJ may choose to allow the BESS operator to forgo fire protection, but, this is only allowed in very specific circumstances. And even then, it is a bad idea that can easily and inexpensively be avoided by the options discussed herein.

It is important to note that NFPA 855 covers all manner of BESS as well as electrochemical ESS, capacitor ESS, fuel-cell ESS, and has chapters reserved for flywheel and superconducting magnet ESS. 

But it is easy to see that BESS—and particularly lithium-ion BESS—is at the heart of the standard. NFPA 855 quickly goes into greater detail about the emergency operations plan described in NFPA 1. It also introduces the concept of large-scale fire testing. This is because in some instances in the standard, the mandates can be avoided if large-scale fire testing is conducted on the BESS or its components and its design is proven safe under fire conditions. With the recent surge in BESS manufacturing, many fire-testing facilities are faced with substantial backlogs. Until fire-testing results prove otherwise to an AHJ, the standard must be followed as written.

The requirement for fire suppression is tied to the location of the BESS. For indoor installations, NFPA differentiates between dedicated-use buildings and non-dedicated-use buildings. Dedicated-use buildings are built according to local building codes and their sole purpose is to house the BESS and its associated equipment. Non-dedicated-use buildings are pretty much every other building that contains a BESS.

Table 4.4.2 in NFPA 855 clearly mandates the provision of fire detection and suppression services. However, there is a variance in the footnotes which explains that an AHJ may allow the omission of many of the requirements in Table 4.4.2 (which also includes size and separation requirements, along with fire suppression) in dedicated-use buildings. This provision is only applicable, though, in regard to dedicated-use buildings that are located more than 100 feet from any existing exposure or where an exposure could conceivably be built. There is no such variance for non-dedicated-use buildings. 

Many people think of a shipping container or structures built to resemble a shipping container when they picture a BESS. Outdoor BESS are categorized by NFPA as remote or locations near exposures. Remote locations are those more than 100 feet from any existing exposure or where an exposure could conceivably be built. Locations near exposures include everything else.

In Table 4.4.3, fire detection and suppression services are mandated for outdoor BESS. However, again in a footnote is a provision wherein if both the BESS operator and AHJ agree, the mandate for fire suppression can be omitted. Also within the section is a provision allowing the reduction of required separation distances as long as large-scale fire testing proves the concept safe. 

When a BESS is installed on a rooftop or parking garage, the requirement for fire suppression is less negotiable. Walk-in enclosures must have automatic fire suppression and a Class 1 standpipe outlet. Non-walk-in units on rooftops or parking garages that do not open to the sky must also have the same fire suppression package. The provision for fire suppression in open parking garages can be waived if large-scale fire testing proves that the BESS does not present an exposure hazard to vehicles nor impede egress. 

When it comes to providing fire suppression, automatic sprinkler systems are mentioned, along with the requisite water supply requirements to support the sprinkler system. Additionally, the standard  provides a list of “alternate automatic fire control and suppression systems.” These include the following:

  • Carbon dioxide systems

  • Water spray

  • Water mist

  • Clean agents

  • Aerosol agents

Also contained within the fire suppression section is the criteria for obtaining waivers for fire suppression when large-scale fire testing is performed, confirming the installation safe.


Why “Let-It-Burn” is a Bad Idea

As we will demonstrate, there is no truly sound argument that favors a let-it-burn policy. First, you cannot unilaterally decide to pick this option—the AHJ has to agree. This presents a bad public image of the organization when one approaches an AHJ and says that we want to put a potentially dangerous and possibly explosive BESS in your jurisdiction and we do not plan to provide any fire protection. Instead, we are willing to just let it burn. That is a difficult position in most circumstances and likely a no-go if the fire department has any say.

Regrettably, many communities will bend the rules just to have a viable business in their district. So, with enough pressure and misplaced incentives, it is entirely possible that the concept can be approved by the authorities. But what happens when one of your BESS catches on fire and burns for hours?

First, this creates a very dangerous situation for the responders. They may not know of the let-it-burn policy. Being firefighters, they may choose to attack the fire anyway. By not providing any means to mitigate the fire, the firefighters may easily find themselves in a position where they can be injured such as were the firefighters in Arizona (and remember that BESS had gaseous fire suppression).

Next, you are responsible for all of the runoff from the site as well as the smoke cloud that may pass over occupied areas.Your organization’s image takes a hit because of the fire and the resulting pollution. Also, there could be elevated legal liability associated with these forms of pollution.

Thirdly, a let-it-burn policy is diametrically opposed to the current green movement that is sweeping the world. Few things pollute worse than a fire. With a BESS fire, the smoke effluent is a toxic soup of chemicals that is wafting out into the public. Add to that the resources and manpower required to remediate the problem, and one can see that a BESS fire causes considerable consumption and pollution.

Finally, the financial and operational loss of the BESS itself must be considered. Time and again, the downtime of equipment due to a fire is far more costly than the direct fire damage. When you willingly sacrifice one of your BESS, you are assuring yourself a significant cost in terms of the power it was unable to store and distribute. And likely, it will take a significant amount of time to source and commission a replacement BESS.


The Easy Solution

It is possible that the rationale behind the concept of let-it-burn is simply lack of education. If you give the standard a cursory glance, it appears that the NFPA requires you to install a costly sprinkler system. 

However, there is a readily available, inexpensive solution out there to provide excellent fire suppression service to BESS, and one which is noted and approved in NFPA 855. That solution is condensed aerosol fire suppression units. 

Condensed aerosol is an excellent choice for several reasons. First and foremost, it is proven effective at suppressing BESS fires and mitigating thermal runaways. But the ease of installation is of tremendous benefit as well. Condensed aerosol is supplied in individual units that are mounted in out-of-the-way spots in the BESS. The units can operate as stand-alone units that are heat activated, or, they can be mounted in multiples that are connected together to create a total-flooding effect when activated by a fire detection device.

Once activated, the condensed aerosol quickly fills the unit, interferes with the chemical chain reaction, and quickly suppresses the fire. Condensed aerosol has been proven effective on rack BESS fires through extensive testing by the prestigious DNV organization. Once the units discharge, the agent remains suspended for several minutes providing reflash protection. 

In addition to its effectiveness, condensed aerosol is safe for personnel and the environment. This is a real plus today, where more and more fire suppression agents are being identified as the source of public health and environmental challenges. Condensed aerosol has zero global warming or ozone-depletion effects. It also has zero atmospheric life which means it will not persist in your body. Furthermore, it is safe to use in normally occupied areas.

A condensed aerosol fire suppression system can be easy retrofitted to any BESS. The compact units mount out of the way and require no piping. Once installed, the units are virtually maintenance free and have a 15-year service life. 

“Let-it-burn” is a bad idea that hopefully will not gain much traction. Leaving a fire to burn unabated is never a good plan and can lead to unanticipated consequences, some of which may be tragic such as a first responder being injured or killed.  The consequences of failing to protect your BESS can be severe and can extend far beyond just replacing a burned-out BESS. These tragic scenarios are especially unfortunate when you consider that resources such as condensed aerosol units can be easily and inexpensively installed in each of your BESS enclosures.

The content & opinions in this article are the author’s and do not necessarily represent the views of AltEnergyMag

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