Abstract: At 4:45 p.m. on October 23, 2023, Employee #1, a construction inspector, and Employee #2, a pipefitter supervisor, were working for an oil and gas pipeline construction company. Employee #1 was working for the contractor installing a pipeline. Employee #2 was working with a contractor that was hydrostatic testing the pipeline. Employee #1 was conducting pressure testing of a natural gas distribution pipeline that was under construction. The two employees were working with coworkers from the contractor installing the pipeline and coworkers working for the owner of the pipeline. The crew was attempting to use two Boar Foam Disc Pigs to clean/clear the pipeline under the Mississippi River between Illinois and Missouri. The pigs were 36-inch wide by 54-inch long. Part of the crew was working on the other side of the river. The pipeline section being tested was approximately 4,800 feet long and had at least two 45-degree angles. The work was conducted outside in dry and sunny weather conditions. The crew had been conducting a dewatering process when a decision was made to open the Illinois side of the pipeline to install a Sypris Technologies Pig Launcher. The crew had experience with the operation. The crew had removed the header section of the pipe and were installing the pig launcher. They used a forklift to lift the pipeline out of a trench to attach the pig launcher. They then used a crane to hoist the pig launcher into position. They were moving the launcher into position when one of two pigs ejected from the open end of the pipeline striking Employee #1 and Employee #2. Approximately 10 minutes had passed between the removal of the header on the pipeline and ejection of the pig. Both Employee #1 and Employee #2 died from injuries caused by blunt force trauma.