EE STATED THAT HE WAS A BRAKEMAN ON A LOCOMOTIVE BEING OPERATED BY COWORKER. THE LOCOMOTIVE HAD COUPLED TO A TRACK MOUNTED ROCK DUSTER. BOTH MEN FAILED TO REMOVE THE SAFETY CHAIN FROM THE DUST ER. WHEN THE SLACK RAN OUT OF THE CHAIN, THE LOCOMOTIVE CAME TO A SUDDEN STOP. THE EE WAS IN THE PROCESS OF DISMOUNTING BEFORE THE LOCOMOTIVE STOPPED. HE STRUCK HIS ARM AGAINST THE LOCOMOTIVE