Pressure build-up and release from within the cooler. Sheeting on the south wall of area 500 building was pushed free of screws where sheets were secured together. NOTE: THIS DOES NOT CONSTITUTE AN ADMISSION THAT AN IGNITION OCCURRED. THIS REPORT IS FILED OUT OF AN ABUNDANCE OF PRECAUTION. A CONTRACT EMPLOYEE WAS INJURED; A 7000-1 WAS FILED BY THE CONTRACT COMPANY.