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Hurricane Ian highlights danger of submerged hybrid or electric vehicles

Submerged vehicles can experience thermal runaway if water leaks into the battery box


Hurricane Ian brought significant flooding to the southeastern United States.

AP Photo/John Raoux

Electric vehicles (EVs) are becoming increasingly popular for consumers. EV sales are growing exponentially, and experts expect approximately 6 million EVs on the road by 2024. While EVs offer many benefits in terms of pollution-reduction, they do pose some unique challenges for firefighters.

Hurricane Ian highlighted one of these unique challenges as it relates to submerged hybrid or electric vehicles. Specifically, after the floodwaters receded, Florida firefighters – among many others who traveled to the area to help with recovery efforts – faced several vehicle fires involving electric vehicles. Such incidents strain fire department resources already dealing with countless rescue and recovery efforts in the aftermath of a hurricane.

Let’s consider how this occurs, what firefighters can do to prepare and how to respond in the safest, most efficient manner.

Thermal runaway

The high-voltage lithium-ion batteries are located in a watertight, fire-resistant box that can be made out of steel, aluminum or composite materials. While this box is designed to be watertight under normal operation of the vehicle, natural disasters and floods are far from normal operation. Water may leak into the battery box if the vehicle is partially or fully submerged in floodwaters. Water intrusion into the box can cause corrosion on the battery cells, which can cause a cell to fail, leading to a thermal runaway event.

Delayed fire

Corrosion or damage to the batteries cells in an EV can cause a thermal runaway; however, it isn’t necessarily instantaneous. The cells can fail days, weeks or even months after experiencing an issue. This is often the case with issues caused by corrosion. Delayed fires are just one issue with EVs, and I would expect Florida firefighters to face several additional fires in the coming weeks and months.

Fire attack

Unfortunately, there is not an effective method of extinguishing an EV fire. Typically, it takes multiple hours on scene flowing tens of thousands of gallons of water. If crews are fortunate enough to stop the thermal runaway event, the vehicle has a risk of catching fire again while at the salvage yard.

While not ideal, the best strategy is to move the vehicle away from exposures and allow it to burn itself out, which should take about an hour. Note: DO NOT pry/cut/remove any part of the battery case to gain access to the fire! This presents a significant safety hazard to firefighters.

Hurricane cleanup

When cleaning up after a flood, hybrid and electric vehicles should be transported on a flatbed. If an EV is towed with the drive wheels on the ground, it is possible for the motors to backfeed power into the batteries. If the vehicle has been partially or fully submerged, it’s best to assume that the vehicle’s batteries are compromised and there could be a risk of a delayed fire. Ask the tow operator to store the vehicle outside at least 50 feet from a structure. Also, request the tow operator contact the dealer or manufacturer. They may have different methods of rendering the vehicle safe.

Read the NFPA Bulletin: Submerged Hybrid/Electric Vehicles for emergency response safety guidance and tips for safe response to submerged hybrid or electric vehicles.

Patrick Durham is the captain and training officer at Station 4 on the Troy (Michigan) Fire Department. He is Instructor 2 and Officer 2 certified. Durham is also a mechanical engineer, currently working on advanced development projects in the automotive industry, including, most recently, designing a multi-material battery structure for electric vehicles. Using knowledge gained while working for 15 years as a firefighter and as an engineer, Durham created classes to educate firefighters on a variety of technical topics, including the unique aspects of responding to electric vehicle incidents. Learn more at StacheD Training or reach Durham via e-mail.

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