EMPLOYEE WAS DRIVING HIMSELF TO HIS ASSIGNED ROTARY DRILL WITH A FORD E-350 VAN. AS HE PROCEEDED INTO THE MINE HE TOOK HIS EYES OFF THE ROAD TO ADJUST THE HEATER. THE VAN CAME IN CONTACT WITH THE BERM ON THE RIGHT SIDE OF THE ROAD AND TIPPED ON ITS SIDE. EMPLOYEE IS ON RESTRICTED DUTY.