The growing increase in lithium-ion battery ESS facilities in recent years presents a new challenge for the fire-protection community. Proactive measures such as appropriate fire-safety provisions and regular inspections are essential to protect employees and firefighters from thermal-runaway fires including cascading thermal-runaway events in larger-capacity battery systems.
According to the US Energy Storage Association, battery storage deployments in the US have grown almost 600% from 2016 to 2019, doubling in 2018 alone. Energy storage is an emerging market in Australia driven by demand for electric vehicles and renewable energy. Australia’s Smart Energy Council (SEC) expects energy storage systems to increase from 52,500 in 2016 to 450,000 by 2020. This growth has accelerated the international need for research to inform design and operational safety.
On 19 April 2019, a cascading thermal-runaway event within a 2.16MWh Public Utility-owned lithium-ion battery ESS in Arizona, USA, led to four firefighters suffering serious injuries. At the invitation of the local fire departments involved, the UL Firefighter Safety Research Institute (FSRI) conducted an incident review and published a report on the findings. UL FSRI, a research-driven organization that is part of UL’s non-profit entity, is dedicated to decreasing firefighter injuries and fatalities through increasing the fire service knowledge. The UL FSRI report ‘Four Firefighters Injured In Lithium-Ion Battery Energy Storage System Explosion – Arizona’1 is publicly available and is intended to educate industry, regulators and the fire service by outlining contributing factors and recommendations that, if implemented, may reduce the risk of a similar occurrence.
The dedicated ESS structure was placed into service in March 2017 and built under the 2012 Edition of the International Fire Code (IFC). It was approximately 15m (50ft) x 4m (13ft) x 3.65m (12ft) housing 27 battery racks each containing 14 modules. This system contained 10,584 cells at a 90% State of Charge. The fire protection system consisted of a VESDA smoke detection system and Total Flooding Clean Agent suppression system utilizing 323kg (713lbs) of Novec 1230. This was designed to deploy, per industry standards, at a 10% concentration 30 seconds after the VESDA system registered an alert status.
Prior to this event the battery system had been operating normally. The first indication of anomalous behaviour occurred when the minimum battery cell voltage in Rack 15 began to decrease. 14 seconds later the air temperatures began to rapidly increase. Within 50 seconds of the initial voltage decrease, the VESDA smoke detector registered an alarm condition with all breakers and contacts open. As designed, the suppression system discharged 30 seconds after the alarm indication.
Forty-seven minutes later the Phoenix Metro Dispatch Center received a call from a passer-by reporting smoke in the area and a bad smell. Fire Dispatch notified the closest firefighting units, who immediately responded. Three minutes after the call, all communication with the ESS system was lost, prior to the arrival of the firefighting units.
Upon arrival, the fire officer from the responding crew initiated a 360° size-up around the exterior of the structure. An operations and maintenance contractor on the scene indicated that the structure served as storage for lithium-ion batteries. The fire officer recognized the potential for a hazardous materials situation, and he requested a Hazardous Materials (HazMat) response.
Upon arrival, the officer of the HazMat crew became aware of a low-lying vapour cloud surrounding the structure. After consulting the fire officers on-scene, the HazMat team donned full firefighter PPE with SCBA and conducted a 360° size-up utilizing several handheld gas meters and thermal imagers. They noted dangerously elevated levels of hydrogen cyanide (HCN) and carbon monoxide (CO) (above 50 ppm HCN and 500 ppm CO). The thermal imager indicated one small spot on the north wall with a temperature of 54.4°C (130°F).
Over the next 33 minutes the HazMat Team continued to monitor the situation and consult with industry representatives and fire department command officers. They noticed the amount of vapour emitting from the structure began to diminish. They also conducted two additional 360-degree size-ups with their gas meters and thermal imagers. Within the vapour cloud, gas readings still indicated dangerously elevated readings of HCN and CO.
The HazMat Team and Fire Command officers discussed potential options to end the situation. They considered life-safety issues, length of time on scene and impact to local major roadways. They also sought additional information from the industry representatives on the scene and off-site. At this time, it was also witnessed that vapours were no longer emanating from the structure.
With the agreement of all officers within the Command Staff it was determined that the HazMat team would approach the structure, continue to conduct readings with their gas meters and thermal imager. If the hot zone was safe, they would open the door and check for live fire. If fire was present, they would retreat and permit the fire to burn. If no fire was present, they would retreat and allow the structure to vent any remaining smoke/vapour.
As the HazMat team executed the response plan and opened the door to the structure, a white vapour fell out of the structure below waist level. The HazMat team stood in the doorway attempting to collect reliable gas meter measurements. The HazMat officer saw no indication of conditions changing and decided to use his thermal imager to assess conditions inside the structure. The officer saw no active fire and a reported a maximum temperature of 40°C (104°F).
Shortly after this series of events, the fire service personnel outside the hot zone heard a loud noise and witnessed a jet flame extending horizontally into the desert approximately 23m (75ft) and vertically 6m (20ft). They immediately issued a Mayday and began searching for injured firefighters. This was the result of the unintended ignition of flammable gases that were released by the batteries during thermal runaway and collected inside the ESS.
All four members of the HazMat team lost consciousness and were found in various locations. The officer of the HazMat team was projected under the surrounding chain-linked fence approximately 23m (75ft) into the desert. A second firefighter was propelled under the fence approximately 9m (30ft) into the desert as well. Each firefighter had pieces of their PPE blown off or removed when they passed under the fence.
The following are identified contributing factors with corresponding recommendations by the FSRI report. They are presented together as the recommendations are in direct correlation to the contributing factors.
Moving forward: contributing factors and recommendations
Education for firefighters and subject matter experts
Simply put, there is a lack of research-based information and educational tools for firefighters and subject matter experts who may need to work cooperatively in response to a lithium-ion based ESS incident.
- Training should emphasize ESS safety, the potential explosion hazard from lithium-ion batteries, vapour-cloud formation and dispersion, and the dynamics of deflagrations.
- Full-scale research testing should be conducted to understand the most effective and safest fire-service response tactics for lithium-ion battery ESS incidents.
- Until definitive tactics can be established, fire-service personnel should define a conservative blast radius to remain outside of, while treating the gas/vapour mixture in the ESS as if it is above the LEL until proven otherwise.
- An online education tool should be developed regarding the relevant hazards and tactical considerations.
- Education and training should be required for all industry representatives who may respond and act in a supportive role. Current and accurate information regarding battery technology and protection systems is critical.
Design and construction considerations – safety systems & signage
Knowing the gas concentrations within the ESS could have made a difference in deciding when or if to open the door. Gas monitoring of conditions is important.
The ESS did not have deflagration venting panels or adequate ventilation to prevent accumulation of flammable gases. These measures may have mitigated the deflagration that resulted in the injuries to the firefighters.
It also appears that the Total Flooding Clean Agent suppression system most likely prevented flaming combustion early in the incident. However, it may have contributed to the accumulation of flammable gases and vapours as well as stratification of the atmosphere that facilitated the deflagration.
The crew that initially responded to the ESS did not know the intended use of the structure or that a lithium-ion battery system was stored inside it. This was due to a lack of outreach between the utility and the fire department as well as a lack of signage on the ESS.
- Lithium-ion ESSs should incorporate gas monitoring that may be accessed remotely.
- Research that includes multi-scale testing should be conducted to evaluate the effectiveness and limitations of stationary gas monitoring systems for lithium-ion battery ESSs.
- Lithium-ion battery ESSs should incorporate adequate explosion protection as required by consensus standards in coordination with the emergency operations plan.
- Research that includes full-scale testing should be conducted to determine the most effective fire-suppression and explosion-prevention systems for lithium-ion battery ESSs.
- Signage that identifies the contents of an ESS should be required on all ESS installations to alert fire responders to the potential hazards associated with the installation.
- It is important, when designing or approving a structure, to consider the location of the ESS and exposures involved, especially in urban settings where other structures, facilities or pedestrians represent increased risk.
Emergency Response Plan
A single-page emergency response plan was provided in electronic form during the incident and contained very little information. It was inadequate for providing guidance on a cascading thermal runaway incident. There was no prior collaboration between relevant stakeholders to develop an appropriate plan.
ν Owners and operators of ESS should develop an emergency operation plan in conjunction with local fire-service personnel and the Authority Having Jurisdiction (AHJ) and hold a comprehensive understanding of the hazards associated with lithium-ion battery technology.
The owner of the structure required almost two months to develop the decommissioning plan and then conducted the operations on-site over several weeks. It was a long and complicated process, that would have been impractical in an urban or occupied building setting.
ν The decommissioning process, including the role of the fire department and what potential hazards may be present must be made clear prior to commissioning ESS installations.
The report into this incident has highlighted the need for ongoing education and vigilance regarding fire-safety hazards underpinned by research that is conducted in controlled manners by reputable agencies and laboratories.
This research needs to be collaborative between industry and the fire service to develop sound fact-based education and then disseminate this to reduce the risk of a similar occurrence happening again.
To learn more about UL FSRI’s work regarding this incident and other contemporary fire-safety research, please visit www.ulfirefightersafety.org
For more information, go to www.ul.com