Transportation Troubleshooting: Igniting Change: How EV Battery Blazes Are Revolutionizing Transit Facility Design

It’s encouraging to see U.S. transit agencies accelerating their transition to zero-emission battery electric bus (BEB) fleets. But that shift brings with it a need to rethink how bus garages and transit yards are designed to withstand vehicle fires.

Fortunately, electric vehicles (EVs) are no more at risk of catching fire than their internal-combustion engine counterparts. But when an EV battery does ignite, it burns hotter and longer than a traditional vehicle fire with increased explosion hazards.

“EV fires experience extremely high temperatures and explosive hazards within the battery cells,” notes my colleague José Del Solar, P.E., assistant vice president and supervising tunnel ventilation and fire life-safety engineer at WSP.

Understanding that distinction—and having the infrastructure and protocols in place to act decisively and properly—could mean the difference between the unfortunate but recoverable loss of one bus, the catastrophic loss of an entire fleet and nearby structures, and the threat to the life safety of the occupants.

“When an electric-vehicle battery ignites, the unfortunate reality is that the bus is now a lost asset,” adds William Connell, senior vice president of tunnel systems at WSP. “From that moment, the focus is on preventing further loss of valuable assets and structures by mitigating the ability of the fire to spread and removing that vehicle from an enclosed area as quickly and safely as possible.”

Designing for EVs

Connell is part of a WSP team evaluating and testing solutions that help transit agencies design parking areas and maintenance facilities for BEBs that account for the type of fire conditions they impose.

One challenge is that most municipal fire codes, which guide facility design, only prescribe requirements for protecting against fires caused by diesel-fueled vehicles. To help local officials navigate and modernize existing codes, Connell explains that facility designers such as WSP are using their experience and research to develop enhanced fire-protection requirements with EVs in mind.

“We are helping agencies and owners develop a better understanding of how different risks presented by EV fires might require alternative considerations of certain key aspects of the fire-protection design,” adds Connell.

WSP’s research team uses a performance-based design (PBD) approach that incorporates CFD modeling to determine the consequences of a fully engulfed EV.

“PBD is important to fully understand the consequences of an EV fire in new or existing enclosed infrastructure housing EVs,” says Connell. “It has helped us confidently establish best practices for these scenarios so a response can be swift and successful.”

The models test and evaluate the following:

• Structural thermal exposure

• Appropriate water application rate for sprinklers

• Need for passive fire protection for structures

• Appropriate vehicle spacing to limit fire spread

• Toxicity levels and irritant gas products

• Appropriate ventilation

Better Wetter

The best approach to controlling an EV fire? Nothing fancy: it’s water.

“When fire departments battle EV blazes, they douse the bus with as much water as possible until the vehicle can be safely removed from the building before it reignites,” notes Connell. “To ensure there is enough water available at a moment’s notice, certain locations may require installation of an onsite water tank.”

While fire-suppressing foam can control a blaze, Connell said water has proven to be more effective at cooling and containing EV fires.

The CFD fire-modeling analysis provided recommendations for the most-reliable sprinkler system to use along with an appropriate water application rate to reduce the impact of a fully engulfed BEB.

WSP incorporated its research into the design of a state-of-the-art facility, currently under construction in South Florida, that will charge, service, operate, maintain and house a sustainable fleet of BEBs.

“We designed the fire-protection system to allow people to safely evacuate in the event of a fully engulfed BEB fire, protect adjacent parked BEBs and reduce structural thermal exposure,” explains Connell. They’ve also incorporated a strategy to exhaust the smoke combining natural and mechanical ventilation. “It may be several minutes before the fire department arrives, so every element of fire mitigation is critical.”

The risk for thermal runaway and thereby a BEB fire is greater when vehicles are charging. However, it also can occur during daily operations such as due to an electrical failure, mechanical damage or excessive exposure to heat. In such events, it’s crucial that the battery-management system of the BEB can detect this threat and relay it to the driver or responsible personnel so an evacuation can be initiated.

Transportation professionals are invested in a successful transition to zero-emission fleets, which requires public trust in the safety of BEBs and the supporting infrastructure. With every project, we gain a deeper understanding of EV battery-fire behavior and how to prepare for those rare moments when things go wrong.

Locking that down allows us to focus on the things about zero-emission buses that we love and how they’re trans­forming public transportation.