A contractor was injured and evacuated after a gas release incident on an offshore facility in the Gulf of America. The incident occurred while a contract employee was performing maintenance on an E-body control valve on a six-inch gas line. BSEE’s investigation found that residual pressure estimated at 128 psi inside the six-inch gas line was released during disassembly and replacement of the valve’s trim and seat. The sudden release caused the valve’s bonnet flange, weighing approximately 50 pounds, to be forcefully ejected. The flange struck the worker in the chest and abdomen, knocking the worker backward onto the elevated scaffold platform. The worker was evacuated for treatment and evaluation. Injuries included bruising and abrasions to the left abdomen wall and chest, a laceration behind the left ear, and abrasions to the left knee.