Perhaps nothing illustrates the complexity like the fatal Mountain View crash, one already familiar to NTSB investigators because the board had probed the role Tesla's Autopilot played in the crash.
After arriving, Tesla's engineers attempted to inspect battery components, but popping sounds again emanated from the battery, according to the report. They decided it was too risky to further analyze the vehicle along Highway 101.
Authorities needed a flatbed to avoid further stress on the vehicle structure. But it was metal, so they propped the Model X on wooden blocks. Six hours after the crash occurred, a fire truck escorted the flatbed from the scene and along an hourlong, uneventful ride to an impound lot.
When the Tesla engineers arrived, they underscored the importance of leaving a 50-foot radius around the vehicle. That was impractical, so the workers "did the best they could," according to the report. Twenty minutes later, a California Highway Patrol officer heard popping sounds coming from the Model X, and the San Mateo Fire Department was summoned. Forty-five minutes later, they were called again. The battery had reignited.
Five days after the crash, the battery ignited one last time, and firefighters arrived to find flames 8 to 12 inches high.
"For me, that one was really eye-opening," Barth said. "The fire department had access to the engineers, and there was still confusion about how to handle this vehicle and the attempts to remove the stranded energy; they were not able to do it effectively. That pointed to the fact that, 'Hey, this stranded energy, there's still gaps in the regulatory approach.' "
Despite the presence of two fire departments familiar with electric vehicles and two battery engineers from the vehicle manufacturer, the solution proved vexing, the risks resilient.