Abstract: At approximately 3:15 p.m. on April 17, 2002, Employees #1 and #2 were modifying a vacuum tank that had been removed from a vacuum truck. The employees were pressure testing the vessel when some of the "dogs" holding the rear hatch in place broke. The rear hatch released and injured the two employees working on the vessel and Employee #3 who was walking by the vessel. All three employees were taken to area hospitals for treatment. The employer was modifying two vacuum tanks to be used in pressure service without any information relating to the design and construction of the tanks. At the time of the incident, the tank had been fitted with a pressure release valve (PRV) that would release at 125 psi. The yard pressure was approximately 60 psi and could vary from as low as 50 psi to as high as 75 psi since no regulators were installed on the pressure lines, except at the main storage tank. The maximum working pressure of the tank was 25 psi with a test pressure of 37.5 psi, which could only be hydro tested and not pressure tested. The employer was not aware of the tank's working pressure because no documentation was provided from the friend that gave the tanks to the employer nor did the employer request the information. The tanks had been de-certified by DOT.