TL;DR: Battery energy storage systems can release hot flammable toxic gas, explode, and burn in ways firefighters have no standard procedure to control.

Why FEMA funded fire research before the Arizona explosion

A Fire Prevention and Safety Research and Development grant set this story in motion more than a year before a high-profile failure. According to FEMA's case study titled Emerging Hazards of Battery Energy Storage System Fires, the agency awarded Grant Number EMW-2016-FP-00833 to the University of Texas at Austin to address firefighter concerns about response safety around battery energy storage systems of all sizes.

The principal investigator is Ofodike Ezekoye, Ph.D., P.E. Professor O.A. "DK" Ezekoye is working with engineers, firefighters and industry partners to develop a better understanding of the magnitude of the fire hazards.

In April 2019, batteries burning inside an Arizona energy storage facility exploded unexpectedly and injured eight firefighters. That incident became a central example of why the research was needed.

The study objective described by Professor Ezekoye was wider awareness of the hazards, greater understanding of underlying fire behavior, and eventual development of safe standard operating guidelines and procedures for firefighters. The project maintains public information at www.UTFireResearch.com, and application information for Fire Prevention & Safety Grants is posted at https://www.fema.gov/fire-prevention-safety-grants.

How home and grid-scale systems grew across the United States

There has been a dramatic increase in use of battery energy storage systems in the United States. According to the FEMA case study, these systems are used in residential, commercial and utility-scale applications.

Most systems consist of multiple lithium-ion battery cells. A single battery cell measuring 7 x 5 x 2 inches can store 350 Whr of energy.

From 2014 to 2018, residential installations increased by 200% annually. The case study states that further research into residential hazards is essential because those hazards could eventually become a regular part of dwelling fires.

Broader federal guidance describes the same growth in grid support roles. According to the U.S. Environmental Protection Agency page titled Battery Energy Storage Systems: Main Considerations for Safe Installation and Incident Response, battery energy storage systems stabilize the electrical grid by providing steady power flow despite fluctuations from inconsistent generation and other disruptions.

The EPA notes that improvements in quality and design have led to a decrease in the number of failure incidents per gigawatt-hour deployed. Communities are advised to consult safety experts when considering and designing installations.

What thermal runaway does inside lithium-ion cells

Lithium cells can experience thermal runaway which causes them to release very hot flammable, toxic gases. In large storage systems, failure of one lithium cell can cascade to include hundreds of individual cells.

The hot flammable gases can result in an explosion or a very difficult to extinguish fire. Lithium-ion batteries contain volatile electrolytes, and exposure to high temperatures or physical damage can release flammable gases, according to the U.S. Fire Administration risks page and the FEMA case study.

The Fire Prevention & Safety study started with a laboratory test in which a single cell failed in one commercial storage module containing a total of 14 cells. In one of the early tests, when a single cell failed, smoke and gases were released that ignited and burned intensely for 12 seconds. Toxic smoke and gases filled the test space.

The research team subsequently connected small-scale battery failure test results to large-scale fire and explosion consequences. Investigators found that utilities and commercial entities that own large battery systems are equally unfamiliar with the potential fire hazards. Many questions remain about the toxicity of the battery vent gas.

Why crews have no shutoff option like natural gas

Although the fire service routinely responds to explosive scenarios such as those associated with natural gas leaks, standard operating procedures do not exist for a battery energy storage system scenario for which there is no way to cut off the gas supply.

The fire service is unaware and inexperienced with the fire and explosion hazards of these systems, according to the FEMA case study. That gap applies even though explosive gas response is routine work in other contexts.

Federal fire guidance emphasizes continued training, accurate incident reporting, emergency shutdown familiarity for vehicles, and coordination with manufacturers and industry experts. The U.S. Fire Administration states that accurate reporting can enable added investigation and clarification that facilitates strategies to reduce incidence.

Communities planning a facility are advised to comply with state and local siting, zoning, marking and permitting requirements, consider battery chemistry, manufacturing quality assurance and quality checks, unit design, battery management system analytic capabilities and system integration, and consult the most recent industry safety standards. Planned sites are also advised to include remote sensors and monitoring such as infrared, thermal and fire detection, and to communicate with local first responders to develop emergency response plans.

What four garage tests revealed about residential fires

A December 21, 2023, U.S. Fire Administration blog post titled Responding to fires that include energy storage systems (ESS) are a new and evolving hazard summarized residential test findings for firefighters and residents living near stored energy.

The International Association of Fire Fighters, in partnership with UL Solutions and the Underwriters Laboratory's Fire Safety Research Institute, released Considerations for Fire Service Response to Residential Battery Energy Storage System Incidents. The report was based on four large-scale tests sponsored by the U.S. Department of Energy and includes considerations for response to fires that include energy storage systems using lithium-ion battery technology.

The report captures results from a baseline test and three tests using a mock-up of a residential lithium-ion battery energy storage system installed in a representative two-car garage. It discusses several critical size-up and tactical considerations developed from the findings.

On fire growth rate, the findings suggest rapid fire growth, explosion hazards, and the potential for unburned battery gas in a ventilation-limited fire to increase smoke flammability, which can increase backdraft risk.

On thermal runaway, lithium-ion batteries may enter thermal runaway without active fire. It can be recognized as distinct white or gray battery gas leaking from the structure and forming low-hanging clouds. If batteries are suspected to be in thermal runaway with no concurrent fire indicators, the structure should not be approached or entered to take gas meter measurements. In all suspected thermal runaway cases, hose lines should be pre-deployed, charged and ready before ventilation or entry.

Where explosion and detection risks concentrate

The explosion hazard begins the instant batteries undergo thermal runaway and release gas without burning. Timing and severity of a battery gas explosion is unpredictable.

Firefighters face greatest explosion risk in the driveway and at doors, windows and other vent points. Fire apparatus should not be parked in front of the garage door.

There are no reliable visual, thermal imaging or portable gas meter indicators to confirm battery involvement in a room-and-contents fire. That limitation complicates size-up because crews cannot rely on a meter or camera to rule storage-system involvement in or out.

Full structural personal protective equipment, described as Level D ensemble, with full self-contained breathing apparatus should be donned before performing size-up. The International Association of Fire Fighters, UL Solutions and the Fire Safety Research Institute will continue work on the project to develop training materials, and the full report PDF is available through the Association's website.

Chemical exposure caution is repeated across federal materials. Firefighters are advised to be cautious of potential chemical exposure and to don proper protective equipment during operations.

What Gateway and Moss Landing showed about large failures

Federal environmental guidance points to two California events to explain community impact. According to the EPA, on May 15, 2024, the Gateway Energy Storage Facility in San Diego, California, experienced a fire with continued flare-ups for seven days following the fire.

The facility held about 15,000 nickel manganese cobalt lithium-ion batteries. Following the incident, EPA required the facility to conduct extensive environmental monitoring during battery handling and disposal operations and to submit detailed work plans and progress reports.

On January 16, 2025, a fire broke out at the Moss Landing site in Monterey County, California, resulting in a 24-hour evacuation of about 1,200 residents. A joint effort among company personnel and the North County Fire Department kept the fire contained to one building, though with one notable flare-up.

Air quality monitoring and sampling occurred during and after the Moss Landing fire and found no risks to public health. Following the incident, EPA continues to work with other regulators to ensure safe storage, handling and transportation of undamaged batteries remaining at the site.

The EPA lists three community challenges from such incidents: lithium battery fires are extremely difficult to extinguish and may reignite hours or days later, battery fires can release harmful gases that pose health risks to nearby residents and first responders, and proper cleanup and disposal of damaged batteries requires specialized procedures.

What isolation, protective equipment and cleanup require

Incident planning guidance calls for self-contained breathing apparatuses to protect against hazardous air emissions. For large commercial systems, planners are advised to set an isolation zone of at least 330 feet, depending on the site.

Responders are advised to position away from vent points, establish safe zones, use cooling techniques to manage heat, implement thorough post-fire assessment and continued monitoring to prevent rekindling, including during post-incident transport and placement, and obtain Emergency Response Guides from original equipment manufacturers for battery and vehicle designs.

Battery ejection is another documented mechanism: batteries can be ejected from a pack or casing during an incident, spreading fire or creating cascading secondary ignitions and fire origins. Overcharging beyond designed capacity can lead to overheating, while cycling and aging degrade cells through charge and discharge cycles.

Signs of damage or thermal runaway include mechanical damage such as cracking, bulging, popping or hissing, visible gases venting, and rising temperature. Even after extinguishing a lithium-ion battery fire, there is a risk of reignition requiring strategic cooling and monitoring.

Sources referenced