The National Transportation Safety Board is sending a technical specialist to observe Tesla Inc.’s examination of a Model S that caught fire in California on Friday, the agency said in a statement.

The action is not a formal probe of how the lithium-ion battery pack caught fire without being involved a crash, NTSB spokesman Peter Knudson said. NTSB’s participation in Tesla’s review “will provide the agency with an opportunity to learn more about fires in all types of battery-powered vehicles,” he said.

The agency is investigating three separate incidents involving post-crash lithium-ion battery fires in Tesla vehicles, including fatal crashes that occurred in California and Florida.

In an emailed statement, a Tesla spokeswoman called the fire an “extraordinarily unusual occurrence” and said the company is investigating to determine the cause. The Model S driver was able safely exit the vehicle, she said.

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