Three (3) Elk Grove Village Fire Department investigators, along with one from the Bureau of Alcohol, Tobacco, Firearms, and Explosives (ATF), established that a faulty 1/4″ drain valve on a vessel level controller system caused the liquid ammonia leak at the food processing plant in Elk Grove Village, IL. The leak led to an explosion at the plant on July 7, 2017, causing nearly $30M in damages to the structure, equipment, and business. The ammonia, which was under pressure at 150 psi, leaked into an 80′ X 40′ X 20′ mechanical room, which from video footage, we can surmise there was either a lack of ventilation or the safety system (detection and interlock) failed. It took over 7 months to build a new mechanical room.