EE TRIED TO FREE A STUCK TIPPER VALVE. HE FIRST TRIED TAPPING ON THE HANDLE WITH A ROD BUT THAT DID NOT WORK. HE THEN GRABBED THE HANDLE AND PULLED UPWARD. HE FELT A PAIN IN HIS BACK. THE EE W AS SENT FOR MEDICAL EVALUATION & TREATMENT. THE DOCTOR DIAGNOSED A BACK STRAIN (THORACIC).