As public transit agencies across the United States adopt battery electric buses (BEBs), the unique fire risks associated with these vehicles have prompted a reassessment of facility designs.
According to WSP, BEB fires can reach extreme temperatures and emit gases such as hydrogen fluoride, which poses significant health hazards.
José Del Solar, assistant vice president and supervising engineer at WSP, stated: “Electric vehicle (EV) fires experience extremely high temperatures and explosive hazards within the battery cells.”
Current fire codes, which primarily address diesel-powered vehicles, are lagging behind the needs of electric vehicle infrastructure.
WSP’s William Connell explained: “Most current codes do not yet specifically address facilities wherein an EV fire could occur.”
This gap has led municipalities to explore strategies beyond existing regulations to safeguard their operations.
To address these challenges, WSP employs performance-based design (PBD) methods.
This approach uses computational fluid dynamics (CFD) modeling to simulate BEB fire scenarios and determine necessary safety measures.
Hasan Raza, a fire-life safety and computational fluid dynamics engineer at WSP, highlighted the importance of this approach: “PBD is important to fully understand the consequences of an EV fire in new or existing enclosed infrastructure housing EVs.”
Through CFD modeling, WSP evaluates factors such as water application rates for sprinklers, structural thermal exposure, passive fire protection requirements, and ventilation strategies.
These insights were crucial during a recent project involving the renovation of an urban bus facility, where CFD analysis helped guide fire mitigation strategies.
Research conducted by WSP underscores the importance of using water as the primary method for controlling BEB fires.
The team determined that high water density, as specified in the National Fire Protection Association (NFPA) 13 code for Extra Hazard Group classification, is necessary to manage the intense heat and prevent fire spread.
William Connell emphasized the approach: “The moment a battery ignites, that bus can be considered a lost asset.
“The focus is not on saving it but on containing the fire to protect the facility and adjacent vehicles.”
Proper water application ensures fire control until emergency responders arrive.
Onsite water tanks are often recommended to maintain an adequate supply for such emergencies.
WSP collaborates with transit agencies to develop state-of-the-art maintenance facilities tailored for BEBs.
These designs incorporate fire protection systems that prioritize safe evacuation, minimize structural damage, and contain smoke using a mix of natural and mechanical ventilation.
Hasan Raza noted the design objectives: “We have designed the fire protection system of the facility in such a way that allows people to safely evacuate in the event of a fully engulfed BEB fire.”
These efforts aim to align facilities with the evolving requirements of zero-emission fleets, ensuring the safe transition to electric transportation.
Transit agencies in the United States are transitioning to battery electric buses, which present unique fire risks due to high temperatures and hazardous gases from lithium-ion batteries.
WSP is addressing these risks by using performance-based design methods, including computational fluid dynamics modeling, to guide the design of safer bus depots and maintenance facilities.
Key strategies involve the use of advanced sprinkler systems, structural protections, and adequate ventilation to contain BEB fires.
WSP’s research emphasizes the effectiveness of water in controlling such fires and highlights the importance of updating existing fire codes to accommodate the needs of electric vehicle infrastructure.
The designs aim to protect assets, ensure the safety of individuals, and support the broader transition to zero-emission fleets across the United States.
