Fatal Explosion Caused by an Intermittently Used Fuel Gas Piping System

摘要

A fatal explosion occurred at a foundry during a routine test of an intermittently used liquidpropane standby system. Just prior to the explosion, maintenance personnel were preparing thepropane standby system for a startup test. While preparing for the startup test, the group wasalerted that employees in an adjacent building had detected the odor of propane. The test wasstopped and the group conducting the test implemented emergency shutdown procedures. Theexplosion occurred during the execution of the emergency shutdown. The explosion resulted inthree fatalities, numerous injuries, and extensive property damage.The propane standby system was intended to supply synthetic natural gas in the event of aninterruption of the natural gas supply from outside utility company. Synthetic natural gas is amixture of propane and air that has similar combustion properties to natural gas. To ensure thereliability of the propane standby system, it was scheduled for two routine maintenance taskseach year: a preventative maintenance task and a startup task. The liquid propane supply pipingfor the standby system was a buried pipe. When the underground propane piping was placedback into service for the test, flashing liquid propane discharged from an undetected hole in the pipe into loose backfill material in the surrounding soil. The propane vapor migratedunderground and entered a nearby building through a penetration in the building foundation andwas subsequently ignited. Following the incident, the buried liquid propane line was excavatedand the hole in the piping was discovered.This accident was caused by the failure of the mechanical integrity of the liquid propane piping.Within the body of this paper the root causes of the piping failure are discussed along withcorrective actions that could have prevented this accident. The corrective actions includeselecting an alternative material of construction for the piping, implementing proper constructionpractices for buried piping, following appropriate test and maintenance procedures for theexisting cathodic protection system, and verification of piping integrity by leak testing with aninert gas before placing it into service.