EE PARKED THE FUEL TRUCK 50 FT AWAY FROM THE ROCK TRUCK DURING LUNCH BREAK. AFTER BREAK, TRUCK OPERATOR BACK UP NOT KNOWING THE FUEL TRUCK WAS THERE. THE ROCK TRUCK SLAMMED INTO THE BACK OF TH E FUEL TRUCK RIPPING THE BUMPER OFF. JUST AT THAT TIME. THE ROCK TRUCK TURNED HIS WHEELS AND PULLED AWAY.