The U.S. Chemical Safety Board issued a subpoena to the owner of the oil and gas platform that exploded last week...The explosion Friday of Black Elk Energy Offshore Operations LLC's platform left one worker dead, four critically injured and one missing. The Board['s]...subpoena [seeks] details on the company's safety and environmental management plans and audits by the U.S. Department of Interior... A Black Elk representative wasn't immediately available for comment...Black Elk Energy hired commercial diving boats to continue the search for the missing worker after the U.S. Coast Guard suspended its search Saturday.