The CEO of electric car company Tesla Motors Inc. says a vehicle that caught fire near Seattle this week was apparently impaled by a metal object.

Elon Musk wrote in a blog post that fires are more common in conventional gas-powered vehicles and that it's safer to power a car with a battery.

Musk says a curved metal object that fell off a tractor-trailer was apparently to blame for the fire Tuesday. He says the object's shape led to a powerful hit on the underside of the Tesla Model S, punching a 3-inch hole through an armor plate that protects the bottom of the vehicle.

The company says the car properly contained the blaze. The driver was able to exit the highway in the Seattle suburb of Kent before flames engulfed the front of the vehicle.