Abstract: At approximately 2:45 a.m. on February 21, 2013, Employee #1, a 48-year-old cheese supervisor with Leprino Foods Company was sprayed with 180 degree Fahrenheit caustic aqueous solution used in CIP sanitation, which resulted from the failure of a sealing O-ring on a centrifugal processing pump. The system was modified during the preceding shift to provide better flow in CIP mode resulting in the script chart to appear different to Employee #1. Employee #1 called maintenance to trouble shoot the system and in the course of the investigation the airline providing pneumatic pressure to the discharge valve (pressure to open type) became disconnected causing the valve to close. The sudden closing of the discharge valve created a deadheaded condition (blanked) resulting in an impact spike in pressure by the water hammer to cause the sealing O-ring to fail. The water hammer was a fluid dynamics phenomenon where the inertia of fluid flowing in a closed system created impact pressure when the flow of discharge was suddenly stopped. By design safety factors were built into the CIP/Processing system, but were not designed to withstand the extremely high over pressures created by water hammer. Employee #1 was hospitalized, as a result of chemical burns received during the event.