The primary concern with lithium-ion batteries is the hazards generated when you have a thermal runaway appear. - Tech Explorist

The primary concern with lithium-ion batteries is the hazards generated when you have a thermal runaway appear.

Tech Explorist

When lithium batteries began to explode in a burning warehouse in Morris, Illinois, on June 29, it caught firefighters by surprise. They were unaware the building held over 200,000 lithium batteries of all sizes. 

The massive fire prompted city officials to order evacuating nearly 4,000 residents living nearby, a church and small businesses. And as if that wasn’t catastrophic enough, officials also had to figure out how to fight the fire. 

Initially, firefighters started using water the blazing building that held 100 tons of lithium-ion batteries, ranging in size from cellphone batteries to automobile batteries. They had to stop this effort when they realized there were batteries inside.

Because of the lithium batteries within the building, the U.S. Environmental Protection Agency (EPA) reports the Morris Fire Department planned to let the fire burn itself out. But after consulting with experts about lithium-ion battery firefighting techniques, the fire department applied a dry chemical agent called “Purple K,” with a small amount of water to suppress the fire. Purple K, when used as a fire suppressing agent, will produce no toxic effects, the EPA report noted.

However, the Purple K was unsuccessful in extinguishing the fire, the report said. 

Firefighters then applied high flow water to the fire and once they cooled the batteries, firefighters applied Portland cement, which helped extinguish the fire by July 2, according to the report.

The challenges encountered by firefighters at this warehouse fire highlights the dangers lithium-ion batteries can present. IFW caught up with Adam Barowy, research engineer in fire protection engineering at UL, to discuss the hazards lithium-ion batteries pose, what can be done to avoid these fires, and how firefighters can respond when these fires occur. Barowy is also a member of the Society of Fire Protection Engineers (SFPE) and actively involved in the organization's efforts to address fire response to battery fires. 

IFW: Adam, tell me a bit about yourself and your research in battery fires.

Barowy: I’m a member of  in UL’s Fire Research and Development Group and have worked in large-scale fire research for 12 years. I began at the National Institute of Standards and Technology conducting fire tests in the field with fire service partners to enable the advancement of structural firefighting tactics, and to improve the understanding of fire dynamics in structures. At UL, we conduct research to support fire safety and continue to support  fire service. For the last four years, my focus on battery fires has increased because they’re becoming more prevalent as battery products become ubiquitous. I am also the R&D lead for UL 9540A, which is the UL standard for the test method for evaluating the fire and explosion hazard potential of battery energy storage systems. The battery fire safety field is advancing rapidly and UL is now testing battery systems exceeding 20,000 pounds.

IFW: What are the primary risks battery fires pose to firefighters, people nearby, and the environment?

Barowy: There are many battery chemistries found in industrial settings, whether it’s a stored commodity, energy storage systems, e-mobility devices or personal electronic devices. Each chemistry has its own hazard characteristics. Lithium-ion batteries are the most common. The cost of lithium-ion technology is attractive and their energy density is high. So, they are a logical choice for expanding battery applications.

Battery fires and propagation of thermal runaway are not completely described by the fire triangle as compared with typical flammable materials. Oxygen is not necessary, as heat transfer between cells from thermal runaway alone can drive propagation from cell to cell. Most cell designs are susceptible to thermal runaway when heat distorts their internal structure and causes internal short circuiting. Independent of any flaming, thermal runaways rapidly release significant heat.

The primary concern with lithium-ion chemistries are significant generation of heat and venting of flammable gases that typically include a high concentration of CO and CO2. As the flammable gases vent, they may ignite and cause jetting flames. If the gases do not ignite during venting, then an explosion hazard can develop if the gases accumulate in an enclosed space like an equipment cabinet or a battery room. In addition to these potential fire, explosion, and toxicity hazards, product enclosures typically prevent suppression media from reaching the problematic battery cells. Whether automatic or manual, this can make fire suppression a significant challenge. If a fire is suppressed, delayed thermal runaways and reignition may occur hours or days after an initial event if all of the cells are not consumed in the initial incident.

IFW: What can be done to mitigate those risks?

Barowy: In recognition of those hazards, energy storage systems are being sited outdoors to minimize hazards imposed on firefighters, facilities, and building occupants. There are more stringent code requirements to install them indoors. Subsequently, indoor energy storage systems are currently uncommon. Warehouse storage of batteries is being addressed through fire protection requirements from authorities having jurisdiction and property insurers. But even then, you can still have personal electronic device hazards in any industrial setting. E-mobility and personal electronic device hazards may occur wherever they are used and present a more difficult hazard to regulate. This year, FDNY has responded to dozens of e-bike fires with serious consequences to people, firefighters and property.

IFW: Are lithium-ion batteries the primary concern? How do concerns change by battery type?

Barowy:  There are dozens of different chemistries for energy storage systems, but lithium-ion currently presents the greatest safety concern because of their popularity and demonstrated frequency of events. Competing technologies like sodium-nickel systems, nickel-zinc, and flow batteries are being deployed in lesser quantities, and work by different principles. They may have hazards, but not currently on the scale of lithium-ion products.

IFW: With so many chemistries, what can mitigate risk?

Barowy: Standards have been developed for evaluating the safety of any battery technology. For example, UL 9540 is intended to evaluate the compatibility and safety of components integrated into an energy storage system, and UL 9540A is intended to evaluate the characteristics of fire and explosions for at-risk energy storage systems. One of the most significant concerns right now is for lithium-ion chemistries, but with each new chemistry we have under evaluation, we will develop test data to determine if fires or explosions are possible. If they are, we produce test data necessary to determine how to protect buildings and people against those hazards.

IFW: How does UL minimize the risk of battery fires in an industrial setting? 

Barowy: UL looks at fire risks in terms of frequency and severity. The process of a UL evaluation encourages good design practices that reduce the frequency of product safety incidents that result in fires. With newer products and technologies, there may initially be an additional need to address the severity of fires. This is usually addressed by the manufacturer through product design and the installation of supporting fire protection equipment.  As an example, data from UL 9540A is used to demonstrate whether the fire hazards presented by an energy storage system under test require fire protection equipment to meet the safety performance requirements of the fire code.

It is critical that battery products have their safety evaluated using consensus-based battery safety standards. For example, UL 2591 is a safety standard for the components that go into cells. UL 1642 is a safety standard the cells, and UL 1973 is a safety standard for battery packs made up of cells. UL 9540 and UL 9540A address systems made up of battery packs. The standards evaluate the safety design of battery products and their resilience against mechanical and electrical and thermal abuses. The standards also evaluate that batteries operate safely and correctly when connected to other components in the system. Outside of UL product evaluations, it is important to install batteries in accordance with their installation instructions. Batteries must also be operated as designed and must be maintained per the manufacturer’s instructions.

IFW: What do firefighters need to know to fight battery fires? 

Barowy: Fortunately, water is the most effective extinguishing agent. Since oxygen is not necessary for thermal runaway, heat must be removed to control and potentially stop the process of thermal runaway. Due to how batteries tend to be enclosed within products or packaging, getting water to cells in thermal runaway may be a significant challenge. For instance, some containerized energy storage systems have water suppression systems that can be easily and safely supplied via a remote fire department connection. Others do not have this feature.

With electric vehicles, fire departments have a difficult time getting water into the battery pack and have established control by applying water as needed over 24 or more hours. In Europe, electric vehicles have been craned into a container which is then filled up to the battery level with water to establish thermal runaway control. For most end products that are powered by internal battery, the product enclosure will likely impede extinguishing agents from reaching the cells.

In all cases, there is potential for continued thermal runaway and reignition hours or even days after the initial event. These should be considered possibilities until the batteries are fully destroyed, submerged in water, or electrically discharged and disassembled by qualified individuals. Safety is progressing rapidly in new products, but what has made the news is events where thermal runaway propagates through an entire battery pack, system or bulk storage array.

IFW: We saw in the Morris, Illinois, fire that firefighters used water and it was very difficult to control the fire. What is it about a battery fire that makes this so?

Barowy: The Morris fire reinforces that the biggest challenge in battery firefighting is in getting water to the cells involved in the battery fire. The most important means of achieving control is by dissipating the thermal energy that perpetuates ongoing thermal runaways. Batteries can have enough stored energy to perpetuate thermal runaways even in the absence of flaming fires. In UL research, we’ve observed propagation of thermal runaway even inside a chamber under vacuum.

It is possible to protect the exposures, including adjacent batteries, via water flow. We have experimented with dry chemicals and Class D agents, and thermal runaway is outside the scope of what these agents are designed for. Smothering a fire with an inert like dry cement may inhibit flaming combustion, but there is significant danger involved in getting close enough to apply the material and it is unlikely to provide the cooling needed to stop cell to cell thermal runaway propagation. Based on the test data available, it is safer to rely on the long reach of a hose stream and the cooling capabilities of water. There is ongoing debate as to whether a battery fire should be left to burn, but that is not viable when exposures are involved or in urban areas.

IFW: Do these fires burn hotter than a structure fire, or some other type of fire, and thus complicate fire response?

Barowy: When batteries are in thermal runaway, the electrical discharge from short circuiting can cause localized Joule heating which may develop temperatures exceeding flaming combustion. However, in a fire involving the flammable contents of the cell are concerned, the fires do not burn hotter. Through cell tests and gas chromatography we know that flammable lithium-ion battery vent gases consist of hydrogen, carbon monoxide, and hydrocarbons and that other battery materials such as plastics are involved. Combustion of these fuels is not substantially different from typical room-and-contents fires. What complicates the fire response is that flaming fires are not needed to perpetuate thermal runaways. The thermal runaways can continue independent of burning, and continue to produce flammable gases which may pose respiratory and explosion hazards. A specific fire service concern which is not the case for typical room and contents fires is that some lithium-ion batteries may release hydrogen fluoride in a gaseous form due to the breakdown of fluoride compounds in the electrolyte. Exposure to hydrogen fluoride is respiratory concern and firefighters worry about what it could do to their personal protective equipment.

IFW: What training do firefighters need to fight a battery fire?

Barowy: Firefighters should be trained to understand the process of thermal runaway, thermal runaway propagation, and deflagration/explosion hazards. Firefighters should be trained on the basic design, operation, and fire and explosion protection features of any battery systems or bulk battery storage in their response area. There’s a gap right now. In the Surprise, Arizona energy storage system  explosion, firefighters were not yet aware that there was an energy storage system in their jurisdiction. They thought they were responding to a brush fire at first. Firefighters need training to be aware of the hazards, but they also need to be looking out for and informed about battery systems and storage of batteries in their backyard. I’m biasing toward lithium-ion but if it’s other battery chemistries, it may be necessary to research the hazards, if any, of those types of batteries. At UL, we’re working to develop battery fire training for the fire service so they can understand how to identify when batteries are involved in a fire and how that fire might differ from other types of fires they respond to.

For energy storage systems, Firefighters should seek UL 9540A test reports for battery energy storage systems, which define the protection required and can be used to provide insights into the hazards, or lack thereof, for a specific product. For bulk storage of batteries, the FM report “Development of Protection Recommendations for Li-ion Battery Bulk Storage” provides insights. The National Fire Protection Association (NFPA) offers training for the fire service on electric vehicle fires. In all cases, specific information and training should be sought from the battery product manufacturers, if available. And in all cases electrical shocks hazards from stranded energy and reignition should be considered before and during overhaul. As battery fire and explosion hazards are relatively new, there is urgent need for research to support the development of safe and effective means for mitigating battery fires as well as information that first responders can use to support the decision-making process at battery fire incidents.

IFW: What equipment do they need on hand to fight a battery fire?

Barowy: The Level D ensemble (structural firefighting gear) should be worn while doing the size up. Portable gas meters can be used to define an exclusion zone based on the readings of gases released from a battery fire. This is particularly important if the battery fire is confined because there could be an explosion hazard. It may be possible to see characteristic dense white vapors emanating from a battery fire, but that alone is insufficient to determine explosion hazards. Currently there is no silver bullet for identifying or addressing explosion hazards that may be present at a battery fire. However, firefighters should seek to determine if explosion mitigation equipment such as explosion venting panels or flammable gas venting systems have been installed at the battery location. As the awareness and understanding of battery fire hazards improves, an increasing number of energy storage systems and battery storage sites are including explosion mitigation equipment. Information should be sought from the owner-operator, installer and manufacturer of that system.

IFW: How can battery fires affect the environment and what they should think about in those terms?

Barowy: From our measurements thus far, the smoke that comes from lithium-ion battery fires is not appreciably different from other fires as far as the environment is concerned. Suppression water runoff should still be contained and treated by an appropriate wastewater specialist. More publicly available data is needed to determine whether battery fire suppression water runoff is an environmental hazard.