EMPLOYEE WAS PREPARING A NEW HARD HAT TO WEAR. HE STEPPED BACK TO TOSS THE OLD HARD HAT IN THE GARBAGE AND STEPPED ON A FLOOR JACK CAUSING HIM TO FALL. EMPLOYEE REQUESTED TO SEE A DOCTOR ON 9- 19-03, DIAGNOSED WITH CONTUSION LEFT KNEE, LEFT SHOULDER. PLACED ON MODIFIED DUTY. THE JACK WAS NOT STORED PROPERLY.