Battery Energy Storage Systems in Residential Garages

BY CHRIS G. GREENE AND PAUL ROGERS | Energy Hazards

I LOVE MY GARAGE. I couldn’t imagine my home without it. When I was a kid, the garage was where my father and I would work on cars and listen to the Marshall Tucker Band through an old eight-track stereo system.

For most of us, the garage serves as a kind of relief valve for everything we can’t fit into our house. That includes plenty of items that shouldn’t be in the living area of our home.

• Lithium-Ion Battery Disposal: What You Need to Know
• Lithium-Ion Batteries, Fire Investigations, and Keeping Pace with Emerging Technologies
• Batteries Under the Tree Are Not What They Used to Be

The garage becomes home to tools, toys, cars, and boxes of long-forgotten memories that we dare not part with. This cluttered mess helps ensure that the actual living area of the home appears orderly and inviting to our family and to guests.

The garage has the potential to be spacious and orderly—with plenty of room for two cars. But let’s be honest. In reality, the garage is often a crowded, tight, oversized junk drawer. Take a moment and think about all the combustibles, fuels, chemicals, and tools in your garage. And then imagine a fire in that same space. We’ve all been there.

On average, the American fire service responds to more than 6,000 residential garage fires each year. Most of these are the result of electrical failures and malfunctions. But that electrical fire needs some help to really get going. And the fuel supplied by all of the typical garage amenities provides more than enough energy to amplify that electrical failure into a fast-growing and perilous fire for residents and our emergency responders.

Garage fires have and will always be challenging, if for no other reason than the fact that a garage’s contents are so dangerously diverse. They can include anything from cardboard boxes to gasoline, bags of fertilizer, pesticides, and more. Sounds like hazmat to me, and yet that is not the resource tasked with addressing these fires. Instead, handling garage fires is up to our operational companies. That means a couple of engines and, if you’re lucky, a truck company.

Garage fires are often described as “bread and butter” fires; they are anything but that. And now we have added lithium-ion batteries to this labyrinth of fuel. Before we get started, I want to set up the guardrails for this very complicated subject. This article will focus on the challenges created by lithium-ion battery energy storage in residential garages.

However, I would be remiss if I failed to acknowledge that the most common sources for lithium ion in our garages are often those portable tools, e-mobility devices (sometimes called EMD), and vehicles. Both electric vehicles (EVs) and post-2018 hybrid-electric vehicles (HEVs) will likely contain the largest volume of lithium-ion energy sources in a residential garage. And any of the platforms can potentially cause or be involved in exacerbating a garage fire. This article will talk about battery energy storage systems (BESS) in the residential garage spaces.

Historically, residential battery energy storage has been supported using lead-acid batteries, with power generation via photovoltaic (PV) arrays. With these systems, fires were extremely rare—almost unheard of. Today, while the PV systems remain the primary green energy power generators for the residential environment, storage of this energy is accomplished using lithium-ion chemistry batteries (Figure 1).

The driving force behind this transition away from lead acid and toward lithium ion is rooted in increased energy density, shorter charge times, and longer lifespan. All these changes have resulted in a more cost-effective storage platform over time. But new concerns have developed as we install these systems in our private homes.

Today, more than 13% of residential structures that have PVs also have BESS. Typically, you’ll find these systems in garages—but not always. Technically, they can be anywhere in the home where people are not expected to sleep. But they can be located in any room as long as the space is large enough for the BESS rating. This means they can be in small utility rooms and even basements.

Because these systems use lithium-ion chemistry cells, we understand that a system failure can result in a fair amount of hydrogen and carbon monoxide gas discharged into the environment. Failures of lithium-ion supported devices inside of structures have resulted in deflagration events. For our emergency responders, this represents an extremely dangerous situation.

Understanding the signs and response expectations of a BESS failure in a residential home can be challenging. And this is where we really need help from our academic partners.

A Meaningful Partnership

In 2020, the International Association of Fire Fighters (IAFF) established a working agreement with the U.S. Department of Energy (DOE) to better understand the failures of BESS in the residential space. The IAFF partnered with FSRI to execute and evaluate the project. Working with the IAFF and FSRI, and studying the research document, emergency responders have several concerns to consider, including the following:

• Garage fires that involve BESS are difficult to identify at the onset of an incident. The value of having our dispatchers inquire about the presence of BESS may be the easiest way to ascertain this information. Additionally, if the occupants are present, they may be able to offer information. At the least, it is worth asking.
• A PV system may be another indicator of the presence of BESS. If you are uncertain if the home has a PV system and you can’t get a good look at the rooftop, where they are most likely mounted, give the electrical meter a quick read. If there is a PV system, that electrical meter may be the quickest way to tell.

Thermal Imaging Camera Limitations

Using a thermal imaging camera (TIC) from outside a garage is not an effective tool for evaluating a BESS failure. You simply will not have enough heat for the TIC to sense it through the garage door.

Garage fires that are not caused by a failure of the BESS but that involve these systems represent an elevated hazard profile. When the BESS fails, it will introduce hydrogen and carbon monoxideto the environment. In this situation, the confined hydrogen and carbon monoxide can act as an accelerant, making an already flammable, gas-filled environment even more formidable (Figures 2 and 3).

 

Gas-Monitoring Device Limitations

Deflagration events are a real possibility, even with no obvious signs of gas. If crews are investigating an alarm where an odor may be present but with very little visible smoke/gas, they will likely reach for their five-gas monitor. If the BESS has failed and vented gas, crews can expect to find low levels of CO and may feel safe because the 10% LFL indicator has not triggered (Figure 4).

However, this can be a false read of the hazard. This project reflected multiple partial-volume deflagration events within the garage even when the LFL was below 5%. A closer look shows that the gas in proximity to the BESS device can be within the explosive range and trigger a partial deflagration, even when your five-gas meter does not indicate an LFL hazard.

It doesn’t take a complete failure of the BESS to generate the quantity of gas you need to create a partial-volume deflagration event that’s capable of launching the garage door (photo 1). As little as 320 liters of gas from a BESS that is outfitted with lithium iron phosphate (LFP) cells can fail and result in more than enough pressure to damage the garage door (Figure 5).

Ventilation’s Role

While ventilation of the gas-filled garage is the obvious solution, getting there isn’t without risk. Remember, if there is no fire but you believe the BESS has failed and vented the electrolyte vapor, the garage is likely filled with invisible or partially visible “cloudy white” hydrogen and carbon monoxide.

These two gases have unusually large explosive ranges and low minimum ignition energy (MIE) values, which means it takes but the smallest spark to ignite them in air. Any spark-creating switch or tool may trigger a deflagration event. And the weak point will likely be that roll-up garage door. However, garage windows and man doors should be considered potential failure points. Crews should limit time spent directly in front of any of these potential failure points. This also includes where the rigs are parked.

The post-fire conversation will likely include talk of removing the BESS from the inside of the garage. Do not do this. Removal of these systems must remain the responsibility of a trained professional.

Isolating the BESS

If you believe that the BESS has failed or was impacted by a fire event in the garage, isolate it from the home. And if it is connected to a PV system, then isolate that system from the BESS. For the BESS, this can be done via isolation switches near the BESS itself (photo 2).

Per the 2023 National Electric Code (NEC), a residential BESS will be required to have an emergency shutdown device located on the outside of the structure: “2023 NEC 706.15(B) For one- and two-family dwellings, an ESS shall include an emergency shutdown function to cease the export of power from the ESS to premises wiring of other systems. An initiation device(s) shall be located at a readily accessible location outside the building and shall plainly indicate whether in the ‘off’ or ‘on’ position. The ‘off’ position of the device(s) shall perform the ESS emergency shutdown function.”¹–²

Homeowners and occupants should not reenter the structure. Recognize that while the thermal hazards for the BESS may be reduced- this is not a static event. You can consider the BESS stable once it is cool and no longer smoking or off-gassing. However- this so-called stability represents a mere moment in time. The propensity for a thermally damaged BESS to reignite is well established. Occupants should not reenter the structure until a licensed- experi- enced-in-BESS professional has evaluated the system in question.

Supportive Codes and Standards

All eyes are on this. The modernization of our national energy grid will depend- at least in part- on the successful installation of BESS at the residential level. This is where our codes and standard communities play a pivotal role. The good news on this front is that we are ahead of the game and the weight of our academic partners has never been more apparent. Despite the increase in the amount of energy created by BESS- failures have taken a sharp decline since 2018. This is in direct correlation with the development and adoption of National Fire Protection Association (NFPA) 855, Standard for the Installation of Stationary Energy Storage Systems, and UL 9540, Energy Storage System (ESS) Requirements—Evolving to Meet Industry and Regulatory Needs (Figure 3).³, ⁴

Understanding What You’re Up Against

This job is dangerous. It’s a contract with risk. Understanding the tradeoffs associated with the daily deployment of our resources is the decision-making process our responders undertake. Forging relationships between the academic communities and our emergency responders will be critical to the future of the fire service. And the successful implementation of a decentralized energy grid will reflect this relationship.

Our emergency responders will be the ones to carry out the application of information gathered through studies, tests, and trials. They shoulder the load of risk, hazard, and physical injury when plans go awry. And when they roll out the door, we all have a stake in their safety.

Author’s note: Thanks to Adam Barowy and Nathaniel Sauer of UL Fire Safety Research Institute (part of the UL Research Institutes) and Sean DeCrane of IAFF Health and Safety for their help with this article. Additional thanks to Pete Jackson, chief electrical inspector for the city of Bakersfield, CA.

ENDNOTES

PAUL ROGERS is a lieutenant (ret.) from the Fire Department of New York (FDNY), where he worked in the hazardous material field, FEMA USAR NY TF-1, IAFF SME, and more. During his time with FDNY, he led a group of fire service experts in developing and writing codes and standards for BESS installation in New York City. Currently, Rogers represents the fire service on numerous safety codes related to BESS (NFPA 855, UL 9540, UL 9540 A, and more). After retirement, he helped create Energy Safety Response Group (ESRG), which advocates for firefighter safety. ESRG has been used in numerous high-profile utility scale BESS failures/fires, where it coordinated with local fire departments through safe operations.