Abstract: An employee of Eastern Propane Corporation was filling lag cylinders at a private residence. While shutting off the gas flow, he attempted to remove the fill nozzle. On doing so, he realized that the internal check valve was not working properly, and that it was leaking gas. He obtained another check lock valve from his truck, removed the fill nozzle, and attempted to install a backup check valve. While doing this, gas under pressure leaked into the house through an open window located 24 in above the cylinders. An ignition source in the kitchen caused an explosion and fire that flashed back, engulfing the employee and killing him.