EE WAS OPERATING GRADER DOWN HILL. THE ENGINE SHUT OFF, GRADER PICKED UP SPEED. HE PANICKED AND JUMPED FROM MACHINE. HE DID NOT TRY TO USE THE PARKING BRAKE. CAUSE OF INJURY WAS FAILURE TO USE BACK UP BRAKE. COMPLIANCE WITH RULE/REGS WAS FACTOR, PROTECTIVE EQUIPMENT WAS A FACTOR, MINER PROFICIENCY A FACTOR AND MINING EQUIP/SYSTEMS A FACTOR.