Abstract: Employees #1-4 were attempting to clean out a heater treater used to separate water and oil from a pumping operation. The line leading to the saltwater dump valve was opened and attached to a vacuum truck to remove material from the bottom of the tank. The saltwater dump valve was manually held open to allow air into the tank to prevent the tank from collapsing. Employees #1 and #2 were standing next to the dump valve. Employees #3 and #4 were within a three meter radius of the valve. Gas from the tank escaped when the dump valve was opened. The gas found an ignition source and ignited burning all four employees. They were hospitalized for their burns.