Abstract: At approximately 10:30 a.m. on June 21, 2008, an employee was processing a 5,000 gallon capacity tank containing nonhazardous waste water plus a precipitating agent called Sodium Hydrogen Sulfide. The employee became exposed to a major release of Hydrogen Sulfide gas which caused him to lose consciousness and collapse onto a catwalk located approximately 12 to 15 feet above the floor of the building. Three coworkers who happened to be in this building due to working on a renovation project heard coughing sounds. They made an attempt to ascend the stairs in order to check on the employee, but they encountered a strong rotten egg odor in the air shortly after seeing the employee lying in an apparently unconscious state on his back on the floor of the catwalk. Coworker #1 screamed out: "It's Hydrogen Sulfide! We need to get out of here now!" All coworkers quickly evacuated the building and called the emergency medical services. They alerted the emergency medical services Operator about the presence of Hydrogen Sulfide. Coworker #1 pulled a gas meter out of his vehicle and observed a reading of 24 ppm of Hydrogen Sulfide approximately 10 to 20 feet outside of the back building containing the employee. Several of the responding Middletown Fire Department workers also smelled a rotten eggs odor, some as much as 80 to 100 feet away from the back building. They donned SCBA's before entering this building and transporting the employee toward a waiting ambulance and then on toward Atrium Medical Center in Middletown, Ohio. Two Middletown Fire Department workers were checked out by this medical facility because they had experienced abnormal symptoms such as chest tightness, throat numbness and coughing up of excess sputum. On June 24, 2008, OSHA detected the following lingering levels of Hydrogen Sulfide gas: 0 ppm in the front building, 1 ppm on the ground level of the back building, 2 to 3 ppm on the catwalk level, and 42 ppm approximately 1 foot below the opening in the upper surface of Tank Number 204. The employee died of overexposure to Hydrogen sulfide.