Two maintenance workers were troubleshooting an actuator. They removed the end covers to check for air leakage around the piston head. When they connected an air hose to the side of the actuator and applied pressure, the piston head blew out of its housing. It struck one of the employees in the chest, causing the employee to fall to the ground. The employee suffered an abdomen contusion, resulting in a laceration to the liver, and was hospitalized.