By TOM KRISHER and MIKE BAKERWhen debris on a Seattle-area freeway pierced the battery of a $70,000-plus Tesla Model S and touched off a raging fire, it raised new safety concerns for electric-vehicle owners. It also caused rare jitters among investors, who of late have viewed Tesla as nearly invincible. Electric vehicles have scored well in government tests of front and side crashes â¿¿ the Model S earned the highest score possible. But Tuesday's incident demonstrates that real-world driving could reveal some vulnerabilities that don't show up in laboratory testing. "The safety challenges related to electric cars are still in the early stages of being tested and addressed," said Karl Brauer, senior analyst at Kelley Blue Book. Tesla said the Seattle-area driver hit a large metal object in the road, which damaged a battery cell and caused a fire. The company said the car acted as designed by containing the blaze in the front of the car. Still, experts said Thursday that while incidents like this will happen again, they are rare. And electric cars still are safer than those with gasoline engines that haul around a tank full of flammable petroleum. The Tesla fire also shows that automakers need to bolster the shields around batteries, and that firefighters need more training to deal with electric car blazes. Of the estimated 194,000 vehicle fires in the U.S. each year, the vast majority are in cars and trucks with gasoline or diesel engines. Electric vehicles make up less than 1 percent of the cars sold in the U.S. Tesla says this is the only fire ever to happen in one of its batteries. Although a Chevrolet Volt made by General Motors caught fire two years ago after a government crash test, neither GM nor Nissan, which make the top-selling electric cars in the nation, know of any real-world blazes in their vehicles.