THE EE WAS EXITING THE HOT CHANGE BUS AND STEPPED DOWN ONTO A FROZEN TIRE TRACK IN THE MUD AND TWISTED HIS RIGHT ANKLE. HE THOUGHT IT WOULD BE ALRIGHT AND CONTINUED TO WORK. AT APPROX. 0900 HE REPORTED THE ACCIDENT TO HIS SUPERVISOR. WHEN HE REMOVED HIS BOOT, THE ANKLE BECAME EXTREMELY SWOLLEN AND PAINFUL. HE WAS TRANSPORTED TO E.R. FOR EVALUATION AND TREATMENT.