Following the 26 May 2010 hospitalization of seven fishermen that were working in the cleanup crew, BP requested that the National Institute for Occupational Safety and Health perform a Health Hazard Evaluation. This was to cover all offshore cleanup activities, BP later requested a second NIOSH investigation of onshore cleanup operations. Tests for chemical exposure in the seven fishermen were negative; NIOSH concluded that the hospitalizations were most likely a result of heat, fatigue, and terpenes that were being used to clean the decks.