Residential energy storage systems (ESS) using lithium-ion batteries can present safety challenges for homeowners and firefighters. While the failure of residential ESS lithium-ion batteries is a rare event, fire and explosion hazards have already occurred. This guide provides steps homeowners and ESS installers can take to minimize these hazards.
ESS are electrical devices that can pose shock hazards when in unsafe conditions, such as when wet or damaged. Like laptops, cellular phones, e-bikes, electric vehicles and power tools, residential ESS contain lithium ion batteries which can fail and experience thermal runaway. Thermal runaway failures result in rapid heating, ejection of hot material and the release of flammable and toxic gas, which can create fire and toxic gas/smoke hazards. Thermal runaway of all the lithium ion cells within a residential ESS unit can release a volume of flammable gas similar to a 20 lb propane tank, commonly used in backyard grilling. Thermal runaway also presents an explosion hazard if the resulting flammable gas accumulates in an enclosed space, and then ignites. The force from an explosion could cause bodily injury or death and property damage, including broken windows, structural compromise and the spread of debris. Fortunately, thermal runaway failures are unlikely. Homeowners and ESS installers can take simple actions to reduce both the likelihood and consequences of ESS failures.
Safety Guidelines
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Install ESS systems from reputable manufacturers whose equipment is listed as certified to UL 9540¹ and UL 1741²
What to Install:
Installers should be licensed electricians
Who to install:
Installers should be certified by the ESS manufacturer
Make sure that ESS battery, inverter, controller and photovoltaic system components are compatible as recommended by all associated manufacturers
How to Install:
Installation should follow manufacturer’s instructions
Installation should be performed according to locally adopted building codes and standards. The most up-to-date common requirements are usually based on:
2021 International Residential Code:
Section R328 Energy Storage Systems³
2023 NFPA 855: Standard for the Installation of Energy Storage Systems - Chapter 15⁴
Where to install:
What you can do:
Register your ESS with the manufacturer and connect it to WiFi to allow monitoring. Stay up to date on any firmware updates and safety recalls.
Have working smoke detectors. Check regularly and change the batteries as needed.
Check regularly to make sure that the manufacturer recommended clearance or 3’ feet of clearance is maintained. Remove objects and debris, especially flammable material.
Trim vegetation that may be growing near the ESS, especially close to the clearance zone.
Keep a fire extinguisher handy in your house. You will not be able to stop thermal runaway of your ESS. But if you can extinguish a non-ESS fire while it is small you can prevent the ESS and the rest of your house from becoming involved. DO NOT attempt to stop an ESS fire with a fire extinguisher.
In case of fire, smoke, gas, or chemical odor evacuate and call 911.
In case of abnormal behavior, damage or swelling of ESS equipment call technical support or qualified technicians.
[1] https://www.shopulstandards.com/ProductDetail.aspx?productId=UL9540_2_S_20200227
[2] https://www.shopulstandards.com/ProductDetail.aspx?productId=UL1741_3_S_20210928
[3] “Section R328 Energy Storage Systems,” in 2021 International Residential Code (IRC) | ICC Digital Codes, ICC,
2021. Accessed: Jan. 31, 2023. [Online]. Available: https://codes.iccsafe.org/content/IRC2021P2/chapter-
3-building-planning#IRC2021P2_Pt03_Ch03_SecR328
[4] “NFPA 855: Standard for the Installation of Stationary Energy Storage Systems.” https://www.nfpa.org/codes-
and-standards/all-codes-and-standards/list-of-codes-and-standards/detail?code=855 (accessed Jan. 31, 2023)
[5] “About the NEC” https://www.nfpa.org/nec/ (accessed May 9, 2023)
References:
Prepared by:
Lakshmi Srinivasan
Senior Technical Leader
Erik Archibald, PhD, PE
Partner / Senior Engineer
2023 NFPA 705: National Electrical Code⁵
Where to AVOID:
Install in a safe location
Outdoors (most preferred)
Indoor in a detached garage
Indoor in an attached garage
Mount ESS on non-flammable material, such as masonry, metal, gypsum, etc.
Follow manufacturer’s clearance recommendation or provide a minimum 3’ clearance around the ESS to allow for adequate cooling and prevent the spread of fire
These simple actions can reduce the likelihood and consequences of ESS hazards.
Avoid areas subject to flooding or water leaks from above
Avoid areas subject to snow accumulation. Place outdoor ESS above typical maximum snow level
Avoid areas subject to interference from children,
pets and wildlife
Avoid areas subject to falling items
Avoid areas subject to accidental vehicle impact. If in a space with vehicles, put bottom of ESS above hood level or install barriers to prevent impact.
Avoid areas subject to temperature extremes, such as south-facing walls in hot climates. Do not place near heating equipment
Avoid proximity to flammable vegetation or other flammable materials
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Technical Executive
EPRI
3420 Hillview Avenue, Palo Alto, California 94304-1338 USA • 800.313.3774 • 650.855.2121 • askepri@epri.com • www.epri.com
© 2023 Electric Power Research Institute (EPRI), Inc. All rights reserved. Electric Power Research Institute, EPRI, and TOGETHER…SHAPING THE FUTURE OF ENERGY are registered marks of the Electric Power Research Institute, Inc. in the U.S. and worldwide.
Stephanie Shaw, PhD
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Electrical and shock hazards can be avoided through careful design and protection against water and dust intrusion.
Battery failures can result in fire and explosion hazards. They can be avoided by taking proper precautions.
Physical impact from a vehicle or by dropping can cause battery failure and potentially lead to a fire. Use qualified installers and maintain a clearance zone around the battery.
Stored energy of any kind is a hazard. In the case of abnormal operation, damage, or swelling, immediately contact a qualified technician or the manufacturer.
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