(Bloomberg) -- The National Transportation Safety Board has opened an investigation into a crash of a Tesla Inc. vehicle, the second probe by the agency of a fatal accident involving the electric carmaker’s models in less than six months. 

Two people were killed September 13 when a Tesla crashed into a tree and caught on fire in Coral Gables, Florida. The NTSB, which investigates highway safety issues but has no regulatory authority, is coordinating with the City of Coral Gables Police Department and sending three investigators to the scene, it announced Friday in a tweet.

The new federal inquiry comes as the EV maker has faced increased scrutiny from regulators. Last month, the National Highway Transportation Safety Administration, another agency which is authorized to enact auto-safety rules, initiated a formal defect investigation into Tesla’s Autopilot driver-assistance system after almost a dozen collisions at crash scenes involving first-responder vehicles. 

Read More: Tesla Probe Ushers In Get-Tough Era at Auto-Safety Watchdog

The lithium-ion batteries that power Tesla models and other EVs are highly flammable and difficult to extinguish. Once damaged, they can reignite hours or days after being doused, the safety board has warned. In January, the NTSB issued a special report about the dangers of battery fires from electric cars, saying manufacturers have left emergency responders vulnerable to battery blazes.

The NTSB also is investigating a fatal crash in Texas involving a Model S sedan that hit a tree and caught on fire, killing both occupants in April. The Tesla owner had almost twice his state’s legal limit of alcohol in his system, an autopsy report obtained by Bloomberg News showed.

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