On July 14, 2009, Employees #1 and #2 were performing a pneumatic test to verify leak tightness of a new meter station at the Midcontinent Express Pipeline. The test medium was nitrogen gas, and the system being tested included piping and two pressure vessels. Numerous leaks were found in the system during the test. The system reached the required test pressure of 2225 psig at approximately 3:25 p.m., and Employee #1 observed that the pressure on the system had dropped to 2205 by approximately 3:30p.m. Employee #1 was then replaced at the test table by Employee #2. As Employee #1 walked away from the test table, the door on the PECO separator (a pressure vessel) blew off, releasing pressurized nitrogen gas that sent projectiles flying. Employee #2 was killed, and Employee #1 suffered burns and was hospitalized.
Source: OSHA.gov