Read the sentence.
When disaster struck something was wrong with the aircraft he kept a cool head.
Which is the best way to revise the sentence using dashes?
When disaster struck, something was wrong with the aircraft—he kept a cool head.
When disaster struck—something was wrong with the aircraft—he kept a cool head.
When disaster struck—something was wrong with the aircraft, he kept a cool head.
When disaster—struck—something was wrong with the aircraft—he kept a cool head.