The present invention is directed to an oxygen lance crane assembly that includes a measuring device positioned to take measurements to a target area within a BOF vessel. The measuring device includes an optical head for receiving and directing an energy beam to the target area within an associated metallurgical vessel, and for receiving and directing a reflected energy beam to a processor that converts the reflected energy beam into a distance measurement. A drive means, provided within a housing fastened to the lance crane assembly, is attached to the optical head so that when the drive means is operated the optical head is either extended through an opening in the housing to a remote measuring position at a line of sight to the target area within the metallurgical vessel, or retracted back through the opening to a stored position within the housing. The drive is also attached to a cover that is removed from the opening when the optical head is extended and placed over the opening when the optical head is retracted. An air purge is injected into the interior of the housing to cool the housing space and maintain a positive pressure within the housing.