A SHEAR PIN NEEDED TO BE REPLACED IN THE GRATE DRIVE AND EE WAS USING A 2 POUND HAMMER AND PUNCH TO DO THIS. THE HAMMER WAS A COMMUNITY TOOL USED BY EACH OF THE PRODUCTION CREWS IN THEIR JOBS. EE IS FILLING IN ON THE SHIFT FROM THE UTILITY CREW AND DOESN'T HAVE HIS OWN TOOLS. THE HEAD ON THE HAMMER WAS NOT SECURED AND WHEN HE BROUGHT IT BACK THE HEAD CAME OFF STRIKING HIM IN MOUTH