7 Battery Electric Bus Fire Mitigation Strategies

Lithium-ion battery fires occur through a process called thermal runaway. This happens when a battery cell short circuits and heats uncontrollably, which then causes surrounding cells to heat up. As the adjacent cells heat up, they create a chain reaction throughout the system, which can lead to the release of flammable gasses and the ignition of battery cells, potentially the entire battery housing. Unfortunately, current facility suppressants do not penetrate the battery housing, making it impossible to reach the cells before they combust.

The initial short circuit can happen as a result of many different situations. Defects in battery construction, such as manufacturing errors, can create an unstable environment for the chemical reactions to take place within the cell. Poor handling, improper charging equipment, and user error resulting in physical damage can lead to battery failure as well.

While BEB fire risk is low, facilities must be prepared to handle battery fire emergencies.

To effectively address the risk of BEB fires, it is essential to implement comprehensive mitigation strategies. These strategies enhance safety and provide a framework for emergency response and risk management. Here are seven key strategies for mitigating BEB fire risks:

BEB compartmentalization is crucial in facility design. Barrier systems typically include a divider lane and concrete walls. At first glance, they may seem exaggerated, but barrier systems restrict fire spread and isolate fire risks, allowing for emergency response to be able to focus their efforts to mitigate the fire.

Emergency isolation procedures involve moving a bus showing signs of thermal runaway to an isolated area to prevent personal injury and facility damage. This is most effective when bus facilities with concrete walls or fire-safe curtains can separate buses to prevent fire spread. This strategy isn’t commonly implemented due to the increased danger and special equipment needed to move a bus on fire. However, if maintenance or operations staff identify a vehicle as not properly functioning, they should isolate it.

Battery suppression and early warning systems are becoming standard equipment. These systems, found directly outside or within the battery itself, divide the BEB into four zones and customize the suppression system to each zone. These sophisticated systems use onboard telematics, providing real-time data and alerts to operators and maintenance personnel. They can either automatically activate suppression mechanisms or allow operators to trigger them manually.

Fire modeling is an innovative fire scenario approach, using facility dimensions and structural elements to design optimal sprinkler and heat detection locations. Fire modeling software visualizes the fire heat release rate over time, evaluates the effectiveness and performance of sprinkler systems, and provides actionable results for the building and BEBs. This aids planners in developing facility layouts and bus placements.

Infrared and thermal imaging have shown significant progress in addressing challenges by detecting hotspots and anomalies in battery temperature. When connected to building automation systems, imaging can analyze thermal data and detect potential fire risks with real-time monitoring. These cameras must have a direct line of sight to critical areas where battery heat build-up might occur.

Deluge sprinkler systems are currently the most effective and recommended fire control and BEB suppression method. They are designed for high-hazard and large-scale fire areas and are zoned with heat detectors. The deluge sprinkler system activates and applies a continuous amount of water in the overheating zone. These systems require regular testing and maintenance to ensure they are fully functional in an emergency.

The most impactful technology is solid-state batteries, which will eventually replace lithium-ion (LI) batteries. These batteries use solid electrolytes instead of liquid ones, significantly reducing the risk of leaks and fires. They can store more energy and charge faster than conventional lithium-ion batteries, leading to safer and more efficient travel for users. However, solid-state batteries are still largely in the prototype stage of development and are not expected to be widely available until the 2030s.

Lithium-iron phosphate (LFP) batteries are another currently available alternative. LFP batteries are safer than traditional lithium-ion batteries because they do not produce their own oxygen, which helps prevent thermal runaway and battery fires. While they have a lower energy density, meaning they store less energy, their stability and safety benefits are significant.

New design considerations for current battery types, such as implementing non-flammable electrolytes and enhanced battery enclosures, are also in progress. Research is being conducted into less volatile and non-flammable electrolytes, reducing fire risk and enhancing overall battery stability and safety. Developers are also interested in battery enclosures designed to withstand high impacts and contain internal fires. Multiple layers of safety features, including thermal barriers and pressure relief mechanisms, suppress fires and reduce the risk of thermal runaway in the battery pack.

As the adoption of BEBs continues to rise, ensuring their safety becomes paramount. By understanding the causes of BEB fires and implementing comprehensive mitigation strategies, transit authorities can better protect their fleets, facilities, and passengers. Ongoing advancements in battery technology and fire suppression systems offer promising solutions to these challenges, paving the way for a safer and more sustainable future in public transportation. Continued research, innovation, and collaboration with first responders and industry experts will be key to addressing the risks and maximizing the benefits of this transformative technology.