Employee #1, a welder, was inside a double-walled, approximately 5.5 ft in diameter steel tank to perform leak tests. A contractor had installed new stainless steel piping to the 1,000-gal blending tank, and initial use of the tank revealed some leakage where the new pipe entered the bottom of the tank. To perform the leak tests, the contractor applied air at 120 psi to the shell space and used a soap solution to check welds from inside the tank. When air pressure was applied to the shell space, the inner shell of the tank failed where it was welded to the top rim of the outer shell. Approximately half of the inner shell tore away from the outer shell and fell on Employee #1, who died as a result of blunt force trauma to the head. The job was not supervised in any way by the host employer, and the contractor did not have a confined space entry program. The host employer did not have any documented records or history relating to the tank.
Source: https://www.osha.gov/ords/imis/establishment.inspection_detail?id=300385366