Abstract: On August 27, 2008, an employee was removing the blow-off cap assembly from the north end of the pipe system. The employee climbed down into the six foot excavation and removed the 4 by 4 bracing that was securing the blow-off cap. After removing the bracing, the employee was handing the 4 by 4 wooden braces to a coworker on the top of the trench when the blow-off cap blew off and struck the metal shoring that was up against the wall of the excavation. This force broke off the 2-in. pipe connected to the valve which struck the employee in the right leg. The employee received a compound fracture of the right leg, broken fibia and tibia. He climbed out of the excavation and his coworker contacted emergency personnel. The employee was taken to Mercy San Juan and was hospitalized. The failure to depressurize a closed piping system before relieving internal pressure resulted in the sudden release of pressure and caused the serious injury of the employee.