Fatal explosion caused by an intermittently used fuel gas piping system

A fatal explosion occurred at a foundry during a routine test of an intermittently used liquid propane standby system. Just before the explosion, maintenance personnel were preparing the propane standby system for a startup test. While preparing for the startup test, the group was alerted that employees in an adjacent building had detected the odor of propane. The test was stopped, and the group conducting the test implemented emergency shutdown procedures. The explosion occurred during the execution of the emergency shutdown. The explosion resulted in three fatalities, numerous injuries, and extensive property damages.