Introduction
In October 2025, a fire erupted at a utility-scale battery energy storage facility operated by Salt River Project (SRP) near the Glendale-Peoria border in Arizona. The event drew swift attention. Within minutes, multiple fire departments were on-site. Roads were shut down, and the system was taken offline.
This was a high-visibility disruption at a time when grid-scale energy storage is expanding rapidly. As batteries continue to anchor the clean energy transition, safety incidents like this force an urgent question: How can we prevent the next one?
This blog breaks down what happened at SRP’s Bolster Substation, explores why lithium-ion battery fires escalate so quickly, and demonstrates how advanced technologies, like LiquidShield and HazGuard, can create a safer path forward.
Inside the Incident: What Happened at Bolster Substation
Site and System Overview
The incident took place at SRP’s Bolster Substation, located on the Glendale-Peoria border in Arizona. The site hosted a 25 MW battery energy storage system (BESS), built using Tesla Megapack containers. These systems are common across the United States and are used for:
- Grid reserve capacity
Each container holds high-density lithium-ion battery modules, designed for fast deployment and modular scalability.
The Fire Event
During system operation, a thermal event occurred within one or more of the battery containers. Flames became visible outside the enclosure, prompting an immediate response from fire departments across Glendale, Peoria, and Phoenix.
Firefighters remained on site for several hours, working to control the situation and prevent further escalation. Adjacent battery containers were cooled with water as a defensive measure, while the affected unit was allowed to burn out under controlled conditions. As a precaution, the battery system was taken offline, and nearby roads were closed to ensure public safety.
Fortunately, no injuries or major service interruptions were reported, but the disruption was still significant. The event highlighted a critical vulnerability in system design with broader implications for the energy storage industry as a whole.
Post-Incident Status
In the months following the fire, public disclosures have remained limited. As of early 2026, there has been no confirmed announcement that the 25 MW system at Bolster Substation has been returned to service, and no public timeline for re-energization has been shared. To date, no official cause of the thermal event has been publicly identified.
Additionally, officials noted that conditions were monitored during the response, but no detailed findings on gas exposure, air monitoring results, or hazard evaluations have been made public.
Why Lithium-Ion Battery Fires Escalate So Quickly
The Thermal Chain Reaction
Lithium-ion batteries are energy-dense, but they’re also thermally sensitive. When a cell fails, due to a defect, overcharging, or physical damage, it can heat rapidly. If it reaches a critical threshold, the cell enters thermal runaway, a self-sustaining reaction that:
- Generates extreme heat
- Releases toxic and flammable gases
- Can ignite surrounding cells or components
Once triggered, thermal runaway is extremely difficult to stop. And because the heat continues to propagate, one small failure can cascade across an entire module, rack, or system.
Limitations of Liquid Cooling
Liquid cooling is the standard thermal management strategy in most containerized lithium-ion battery systems. Coolant circulates through channels or plates adjacent to battery modules, removing heat during normal operation.
While effective for steady-state conditions, liquid cooling has limitations during failure events:
- Heat must conduct through multiple layers before it can be removed
- Localized hotspots can develop faster than heat can be dissipated
- Thermal runaway cannot be stopped once it begins
When a cell enters thermal runaway, heat generation can exceed the cooling system’s response capability. At that point, cooling becomes reactive rather than preventive, allowing propagation between cells or modules despite active circulation.
Firefighting and Gas Hazards
Lithium-ion battery fires release more than just heat. They emit hydrogen fluoride (HF), carbon monoxide (CO), and hydrogen (H₂). These gases are toxic, flammable, and invisible. They reduce visibility, delay entry, and increase risk to first responders.
In parallel, water-based suppression introduces electrical hazards, especially if energized equipment is involved or insulation has degraded inside the container.
Preventable by Design: What Could Have Been Done Differently
The Glendale-Peoria fire wasn’t caused by a lack of response. It was a consequence of system design choices made long before the first cell heated up.
Liquid cooling and passive fire barriers are commonly used in many BESS. However, these measures alone may not provide sufficient protection, particularly when thermal events unfold in a matter of seconds.
Fires and gas buildup are risks that can be designed out before they escalate. And that’s where advanced prevention-first architectures come in.
How Immersion Cooling Could Have Prevented Escalation
Direct Cell-Level Heat Management
EticaAG’s LiquidShield immersion cooling technology submerges battery cells in a non-flammable, dielectric fluid.
This fluid performs three essential thermal functions:
- Absorbs heat directly from the surface of each individual cell
- Maintains a uniform temperature throughout the battery pack
- Prevents localized overheating and eliminates thermal hotspots
The result is improved safety, extended battery life, and greater thermal stability, even under aggressive cycling or high-load operating conditions.
Containment of Faults Before They Spread
If a single cell begins to fail thermally, immersion fluid absorbs and disperses the heat, preventing it from reaching nearby cells. This immediate thermal buffering isolates the failure before it can propagate, containing the issue at the source.
Instead of escalating into a runaway fire, the event becomes a localized maintenance issue. It does not require a system shutdown, emergency response, or the loss of an entire container.
Applicability to Utility-Scale Deployments
LiquidShield, EticaAG’s immersion cooling technology, is engineered for utility-grade battery systems and is fully compatible with lithium-ion chemistries and modular container formats like those used at facilities such as Bolster Substation.
For deployments of that scale, LiquidShield provides a clear upgrade path for safety and performance. It delivers superior thermal control, reduces failure risk, and extends system lifespan without requiring a major redesign of the electrical architecture.
The Role of HazGuard in Gas Risk Mitigation
What HazGuard Does
HazGuard is EticaAG’s toxic gas neutralization system, engineered specifically for battery storage environments. The technology:
- Contains off gasses within the battery module and routes them to the HazGuard system.
- Neutralizes HF, CO, and other flammable gases into inert compounds.
- Releases neutralized gases safely into the surrounding area.
Impact on Emergency Response
By containing and neutralizing toxic gases, HazGuard plays a critical role in protecting personnel and minimizing emergency response risks.
It significantly reduces exposure for firefighters and site operators, helping to maintain safer working conditions during and after a thermal event. This early intervention also lowers the likelihood of re-ignition by actively managing internal gas concentrations.
As a result, post-event monitoring becomes simpler, and site recovery timelines can be dramatically shortened. Emergency teams spend less time on-site and face fewer unknowns during containment.
Because HazGuard acts before gases escape or reach dangerous levels inside the container, responders can work with greater confidence, reduced health risk, and better overall control of the situation.
Complementary to Immersion Cooling
Immersion cooling controls heat, while HazGuard manages toxic gas. Together, they address the two primary risk pathways in BESS failure: thermal propagation and hazardous gas.
This dual-layer safety architecture works at the source, preventing escalation before it begins. It gives operators more time to respond, greater situational control, and a dramatically safer operating environment.
A Reimagined Outcome with EticaAG Safety Architecture
Had the Bolster Substation been equipped with LiquidShield and HazGuard, the outcome could have looked very different.
- The failing cell would have been isolated by the immersion fluid, preventing heat from spreading to neighboring cells.
- Gas emissions would have been contained and neutralized.
- Flames would never have breached the container.
- Emergency response would have been minimal.
- The system could have been restored after inspection, not replaced.
What became a regional fire response could have remained a routine fault isolation event.
Moving Forward: A Safer Path for Grid Storage
The Glendale-Peoria battery fire served as a meaningful reminder of the risks associated with high-energy storage systems. While the incident did not result in injuries or outages, it underscored the need for prevention-based system design that addresses both thermal and gas-related failure modes in utility-scale deployments.
As energy storage becomes increasingly critical to grid operations, safety strategies must focus on preventing escalation rather than reacting after failure, and on providing safer infrastructure and clearer conditions for emergency responders and AHJs.
Technologies like LiquidShield for direct, cell-level heat management and HazGuard for toxic gas mitigation offer practical, system-level improvements that align with utility, regulatory, and operational priorities.
EticaAG remains focused on delivering battery storage solutions that prioritize reliability, safety, and long-term performance. These technologies are available today and built to scale with the grid. With the right design choices, grid storage can be both powerful and safe.
