THE MECHANIC WAS SENT TO THE MINE TO CHANGE TWO FLAT TIRES ON TWO EXPLOSIVE TRUCKS. WHILE CHANGING THE FLAT TIRE ON THE FIRST TRUCK, THE MECHANIC HAD TO STAND THE REPLACEMENT UP (IT WAS LAYING FLAT ON THE GROUND). HE FEELS THAT HE HURT HIS BACK WHILE LIFTING THE TIRE UP. AFTER HE HAD PUT THE REPLACEMENT ON, HE NOTICED A PAIN IN HIS BACK.