Abstract: At about 3:40 p.m. on April 13, 1994, digester #15, one of 22 digesters operating at the time, ruptured catastrophically during an otherwise normal cook that was processing wood chips into pulp at a pulp and paper mill. The top one-third of the digester tore through a concrete floor and the roof of the digester building, and crashed down through the roof of the paper building. Employees in that building were not injured. The center one-third of the digester split open and exploded outward into the digester room, inverting itself and causing severe damage to the digester building. The base section fell off of the digester rack. Employees #1, #2, and #3 were killed and Employees #4 through #8 were injured. Failure analysis revealed that at the point of initiation of the rupture, the carbon steel wall thickness was .010 inches; the minimum allowable wall thickness was calculated to be .058. This severe breach in minimum wall thickness occurred due to deteriorated stainless steel overlay on the interior of the digester. The area had been reoverlaid a number of times without wall thickness measurements having been taken to ensure maintenance of minimum allowable wall thickness.