This incident from October is still missing some pieces in the timeline, but as covered by Jalopnik, there’s consensus on the main points. A couple drives their Tesla Model X to the Polk Street boat ramp in Hollywood, Florida, to unload a jet ski. The wife backs the trailer and jet ski into the water, the husband gets the jet ski into the water. While the husband is on the water on the jet ski, the Tesla begins flashing a warning to the wife to get out of the Model X. The car’s electronically powered doors are closed, and whatever malfunction is occurring won’t permit the doors to open. Apparently, the wife didn’t know about the manual release for the doors, so the husband rocks up and gets her out before the Model X ends up submerged. The Hollywood Professional Firefighters Facebook page said the SUV “lost traction and slid into the inter-coastal,” but it’s not clear if this is what caused the malfunction. In video on that FB page, it doesn’t look like the front doors are open, but the falcon doors are open, and It’s clear at least one rear window is open.
After the SUV slides into the water, its battery catches fire, with toxic gases and flames erupting from the water’s surface. The ocean hates batteries.
Patrick Durham is a fire department captain and training officer, a mechanical engineer who helps in the design of EV battery boxes, and YouTube personality StacheD Training. He looked into this accident, explaining that sealed battery boxes must still be vented to let gases escape. He said that when the box gets submerged, there are “very good odds that that ventilation system is going to fail and allow water into the box.” Anytime it’s a case of the ocean versus, well, anything, the ocean wins.
On top of that, salt water especially hates lithium-ion EV batteries, short-circuiting the electronics and sending the chemistry into thermal runaway. Durham gave two more examples of the same kind of boat ramp mishap, one involving a Model X in Spain, the other a Mitsubishi Outlander PHEV in Vancouver. Both vehicles saw their batteries go into the same thermal runaway, the Mitsubishi pulled from the water too soon and re-igniting in the marina parking lot.
Back in Florida, emergency crews let the fire burn until it went out, loaded the Model X on a carrier, and drove it to the impound lot followed by a fire truck in case the battery turned into a grill again. No one was harmed in the accident.