Abstract: Four employees were working for a chemical company. Employee #2 was inserting a brass wedge between a flange and the dryer of a vessel. As he was using a brass mallet to drive the wedge into place in the gap of the flange, the solid sodium sulfide layer broke and released 1 to 6 psig of nitrogen. The rapid depressurization of the vessel also blew sodium sulfide particles into the face and upper torso of Employee #2. He received first-degree chemical burns and corneal abrasions. Employees #3 and #4 were also exposed to the sodium sulfide particles. Employee #1 was struck in the head and received a laceration above his left ear and a skull fracture. All four employees were hospitalized for their injuries. None of the employees were wearing appropriate PPE.