With both pigs assumed to have properly arrived the pressure in the line was checked and the receiver door opened. A minute later one of the pigs blew out of the end of the line landing 50 m away. It was concluded that the second pig had not actually made it all the way down the line but had become stuck near the end. When the operator had thought they had vented the line, enough gas remained behind the pig to eject it once the door was opened. The procedures established for the handling of the two pigs did not adequately cover all the potential hazards of the process.